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Syllacon

NOTES

SINGAPORE-CAMBRIDGE GCE O-LEVEL

BIOLOGY OUTLINE SYLLABUS 5158

UPDATED 20 JAN 2014

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Overview Themes

Chapters Count

I. Principles of Biology

1-3

3

II. Maintenance and Regulation of Life Processes 4-11

8

III. Continuity of Life

12-15

4

IV. Man and his Environment

16

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1. Cell Structure and Organisation ................................................................................................ 10 2. Movement of Substances .......................................................................................................... 15 3. Biological Molecules.................................................................................................................. 18 4. Nutrition in Humans .................................................................................................................. 24 5. Nutrition in Plants ...................................................................................................................... 30 6. Transport in Flowering Plants.................................................................................................... 35 7. Transport in Humans................................................................................................................. 39 8. Respiration in Humans .............................................................................................................. 45 9. Excretion in Humans ................................................................................................................. 50 10. Homeostasis ........................................................................................................................... 53 11. Co-ordination and Response................................................................................................... 55 12. Reproduction........................................................................................................................... 61 13. Cell Division ............................................................................................................................ 70 14. Molecular Genetics ................................................................................................................. 73 15. Inheritance .............................................................................................................................. 76 16. Organisms and their Environment ........................................................................................... 83

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‘Consylladated’ by Lim Ting Jie

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Contents 1. Cell Structure and Organisation ............................................................................................ 10 (a) identify cell structures (including organelles) of typical plant and animal cells from diagrams, photomicrographs and as seen under the light microscope using prepared slides and fresh material treated with an appropriate temporary staining technique: • chloroplasts • cell membrane • cell wall • cytoplasm • cell vacuoles (large, sap-filled in plant cells, small, temporary in animal cells) • nucleus ........................................................................................................... 10 (b) identify the following membrane systems and organelles from diagrams and electron micrographs: • endoplasmic reticulum • mitochondria • Golgi body • ribosomes ........................ 11 (c) state the functions of the membrane systems and organelles identified above ..................... 12 (d) compare the structure of typical animal and plant cells ........................................................ 12 (e) state, in simple terms, the relationship between cell function and cell structure for the following: • absorption – root hair cells • conduction and support – xylem vessels • transport of oxygen – red blood cells ............................................................................................................ 13 (f) differentiate cell, tissue, organ and organ system .................................................................. 14 2. Movement of Substances ....................................................................................................... 15 (a) define diffusion and discuss its importance in nutrient uptake and gaseous exchange in plants and humans .................................................................................................................... 15 (b) define osmosis and discuss the effects of osmosis on plant and animal tissues ................... 16 (c) define active transport and discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, as in ion uptake by root hairs and uptake of glucose by cells in the villi .......................................................................................... 17 3. Biological Molecules............................................................................................................... 18 (a) state the roles of water in living organisms ........................................................................... 18 (b) list the chemical elements which make up: • carbohydrates • fats • proteins......................... 18 (c) describe and carry out tests for: • starch (iodine in potassium iodide solution) • reducing sugars (Benedict’s solution) • protein (biuret test) • fats (ethanol emulsion) ............................... 19 (d) state that large molecules are synthesised from smaller basic units: • glycogen from glucose • polypeptides and proteins from amino acids • lipids such as fats from glycerol and fatty acids .. 20 (e) explain enzyme action in terms of the ‘lock and key’ hypothesis .......................................... 20 (f) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex, lowering of activation energy and enzyme specificity ................................................................. 21 (g) investigate and explain the effects of temperature and pH on the rate of enzyme catalysed reactions.................................................................................................................................... 22 4. Nutrition in Humans ................................................................................................................ 24 (a) describe the functions of main regions of the alimentary canal and the associated organs: mouth, salivary glands, oesophagus, stomach, duodenum, pancreas, gall bladder, liver, ileum, colon, rectum, anus, in relation to ingestion, digestion, absorption, assimilation and egestion of food, as appropriate .................................................................................................................. 24

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syllacon.weebly.com (b) describe peristalsis in terms of rhythmic wave-like contractions of the muscles to mix and propel the contents of the alimentary canal ............................................................................... 27 (c) describe digestion in the alimentary canal, the functions of a typical amylase, protease and lipase, listing the substrate and end-products ............................................................................ 27 (d) describe the structure of a villus and its role, including the role of capillaries and lacteals in absorption ................................................................................................................................. 28 (e) state the function of the hepatic portal vein as the route taken by most of the food absorbed from the small intestine.............................................................................................................. 28 (f) state the role of the liver in: • carbohydrate metabolism • fat metabolism • breakdown of red blood cells • metabolism of amino acids and the formation of urea • breakdown of alcohol ....... 29 (g) describe the effects of excessive consumption of alcohol: reduced self-control, depressant, effect on reaction times, damage to liver and social implications ............................................... 29 5. Nutrition in Plants ................................................................................................................... 30 (a) identify and label the cellular and tissue structure of a dicotyledonous leaf, as seen in transverse section under the microscope and describe the significance of these features in terms of their functions, such as the: • distribution of chloroplasts in photosynthesis • stomata and mesophyll cells in gaseous exchange • vascular bundles in transport ....................................... 30 (b) state the equation, in words and symbols, for photosynthesis .............................................. 31 (c) describe the intake of carbon dioxide and water by plants .................................................... 31 (d) state that chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage ......................................................................... 32 (e) investigate and discuss the effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis (e.g. in submerged aquatic plant) ............................ 33 (f) discuss light intensity, carbon dioxide concentration and temperature as limiting factors on the rate of photosynthesis ............................................................................................................... 34 6. Transport in Flowering Plants ................................................................................................ 35 (a) identify the positions and explain the functions of xylem vessels, phloem (sieve tube elements and companion cells) in sections of a herbaceous dicotyledonous leaf and stem, under the light microscope .................................................................................................................. 35 (b) relate the structure and functions of root hairs to their surface area, and to water and ion uptake ....................................................................................................................................... 35 (c) explain the movement of water between plant cells, and between them and the environment in terms of water potential (Calculations on water potential are not required). ........................... 36 (d) outline the pathway by which water is transported from the roots to the leaves through the xylem vessels ............................................................................................................................ 37 (e) define the term transpiration and explain that transpiration is a consequence of gaseous exchange in plants .................................................................................................................... 38 (f) describe and explain: • the effects of variation of air movement, temperature, humidity and light intensity on transpiration rate • how wilting occurs ............................................................. 38 (g) define the term translocation as the transport of food in the phloem tissue and illustrate the process through translocation studies ....................................................................................... 38 7. Transport in Humans .............................................................................................................. 39 4


syllacon.weebly.com (a) identify the main blood vessels to and from the heart, lungs, liver and kidney ...................... 39 (b) state the role of blood in transport and defence • red blood cells – haemoglobin and oxygen transport • plasma – transport of blood cells, ions, soluble food substances, hormones, carbon dioxide, urea, vitamins, plasma proteins • white blood cells – phagocytosis, antibody formation and tissue rejection • platelets – fibrinogen to fibrin, causing clotting ......................................... 40 (c) list the different ABO blood groups and all possible combinations for the donor and recipient in blood transfusions ................................................................................................................. 40 (d) relate the structure of arteries, veins and capillaries to their functions .................................. 41 (e) describe the transfer of materials between capillaries and tissue fluid .................................. 41 (f) describe the structure and function of the heart in terms of muscular contraction and the working of valves ....................................................................................................................... 42 (g) outline the cardiac cycle in terms of what happens during systole and diastole. (Histology of the heart muscle, names of nerves and transmitter substances are not required) ..................... 43 (h) describe coronary heart disease in terms of the occlusion of coronary arteries and list the possible causes, such as diet, stress and smoking, stating the possible preventative measures44 8. Respiration in Humans ........................................................................................................... 45 (a) identify on diagrams and name the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries ................................................................................................................ 45 (b) state the characteristics of, and describe the role of, the exchange surface of the alveoli in gaseous exchange .................................................................................................................... 46 (c) describe the removal of carbon dioxide from the lungs, including the role of the carbonic anhydrase enzyme .................................................................................................................... 47 (d) describe the role of cilia, diaphragm, ribs and intercostal muscles in breathing .................... 47 (e) describe the effect of tobacco smoke and its major toxic components – nicotine, tar and carbon monoxide, on health ...................................................................................................... 48 (f) define and state the equation, in words and symbols, for aerobic respiration in humans ....... 48 (g) define and state the equation, in words only, for anaerobic respiration in humans ............... 48 (h) describe the effect of lactic acid in muscles during exercise ................................................. 49 9. Excretion in Humans .............................................................................................................. 50 (a) define excretion and explain the importance of removing nitrogenous and other compounds from the body ............................................................................................................................ 50 (b) outline the function of kidney tubules with reference to ultra-filtration and selective reabsorption in the production of urine ...................................................................................... 51 (c) outline the role of anti-diuretic hormone (ADH) in the regulation of osmotic concentration.... 51 (d) outline the mechanism of dialysis in the case of kidney failure ............................................. 52 10. Homeostasis.......................................................................................................................... 53 (a) define homeostasis as the maintenance of a constant internal environment ........................ 53 (b) explain the basic principles of homeostasis in terms of stimulus resulting from a change in the internal environment, a corrective mechanism and a negative feedback ................................... 53 (c) identify on a diagram of the skin: hairs, sweat glands, temperature receptors, blood vessels and fatty tissue .......................................................................................................................... 53 5


syllacon.weebly.com (d) describe the maintenance of a constant body temperature in humans in terms of insulation and the role of: temperature receptors in the skin, sweating, shivering, blood vessels near the skin surface and the co-ordinating role of the hypothalamus ..................................................... 54 11. Co-ordination and Response ............................................................................................... 55 (a) state the relationship between receptors, the central nervous system and the effectors ....... 55 (b) describe the gross structure of the eye as seen in front view and in horizontal section ........ 55 (c) state the principal functions of component parts of the eye in producing a focused .............. 56 image of near and distant objects on the retina ......................................................................... 56 (d) describe the pupil reflex in response to bright and dim light ................................................. 56 (e) state that the nervous system – brain, spinal cord and nerves, serves to co-ordinate and regulate bodily functions ............................................................................................................ 57 (f) outline the functions of sensory neurones, relay neurones and motor neurones ................... 57 (g) discuss the function of the brain and spinal cord in producing a co-ordinated response as a result of a specific stimulus in a reflex action ............................................................................. 58 (h) define a hormone as a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then broken down by the liver .... 58 (i) explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the pancreas ................................................................................................................................... 58 (j) state the role of the hormone adrenaline in boosting blood glucose levels and give examples of situations in which this may occur.......................................................................................... 59 (k) explain how the blood glucose concentration is regulated by insulin and glucagon as a homeostatic mechanism ............................................................................................................ 59 (l) describe the signs, such as an increased blood glucose level and glucose in urine, and the treatment of diabetes mellitus using insulin ............................................................................... 59 12. Reproduction......................................................................................................................... 61 (a) define asexual reproduction as the process resulting in the production of genetically identical offspring from one parent .......................................................................................................... 61 (b) define sexual reproduction as the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring ........................................................................ 61 (c) identify and draw, using a hand lens if necessary, the sepals, petals, stamens and carpels of one, locally available, named, insect-pollinated, dicotyledonous flower, and examine the pollen grains under a microscope ........................................................................................................ 61 (d) state the functions of the sepals, petals, anthers and carpels ............................................... 62 (e) use a hand lens to identify and describe the stamens and stigmas of one, locally available, named, wind-pollinated flower, and examine the pollen grains under a microscope .................. 62 (f) outline the process of pollination and distinguish between self-pollination and cross-pollination .................................................................................................................................................. 63 (g) compare, using fresh specimens, an insect-pollinated and a wind-pollinated flower ............. 64 (h) describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (Production of endosperm and details of development are not required) ................................... 64

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syllacon.weebly.com (i) identify on diagrams of the male reproductive system and give the functions of: testes, scrotum, sperm ducts, prostate gland, urethra and penis .......................................................... 65 (j) identify on diagrams of the female reproductive system and give the functions of: ovaries, oviducts, uterus, cervix and vagina ............................................................................................ 66 (k) briefly describe the menstrual cycle with reference to the alternation of menstruation and ovulation, the natural variation in its length, and the fertile and infertile phases of the cycle with reference to the effects of progesterone and estrogen only ....................................................... 67 (l) describe fertilisation and early development of the zygote simply in terms of the formation of a ball of cells which becomes implanted in the wall of the uterus.................................................. 68 (m) state the functions of the amniotic sac and the amniotic fluid .............................................. 68 (n) describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (Structural details are not required) ............................. 68 (o) discuss the spread of human immunodeficiency virus (HIV) and methods by which it may be controlled................................................................................................................................... 69 13. Cell Division .......................................................................................................................... 70 (a) state the importance of mitosis in growth, repair and asexual reproduction .......................... 70 (b) explain the need for the production of genetically identical cells and fine control of replication .................................................................................................................................................. 70 (c) identify, with the aid of diagrams, the main stages of mitosis (e) identify, with the aid of diagrams, the main stages of meiosis........................................................................................ 71 (d) state what is meant by homologous pairs of chromosomes.................................................. 72 (f) define the terms haploid and diploid, and explain the need for a reduction division process prior to fertilisation in sexual reproduction.................................................................................. 72 (g) state how meiosis and fertilisation can lead to variation ....................................................... 72 14. Molecular Genetics ............................................................................................................... 73 (a) outline the relationship between DNA, genes and chromosomes ......................................... 73 (b) state the structure of DNA in terms of the bases, sugar and phosphate groups found in each of their nucleotides .................................................................................................................... 73 (c) state the rule of complementary base pairing ....................................................................... 74 (d) state that DNA is used to carry the genetic code, which is used to synthesise specific polypeptides (details of transcription and translation are not required) ...................................... 74 (e) state that each gene is a sequence of nucleotides, as part of a DNA molecule .................... 74 (f) explain that genes may be transferred between cells. Reference should be made to the transfer of genes between organisms of the same or different species – transgenic plants or animals ...................................................................................................................................... 74 (g) briefly explain how a gene that controls the production of human insulin can be inserted into bacterial DNA to produce human insulin in medical biotechnology ............................................ 75 (h) discuss the social and ethical implications of genetic engineering, with reference to a named example .................................................................................................................................... 75 15. Inheritance ............................................................................................................................. 76

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syllacon.weebly.com (a) define a gene as a unit of inheritance and distinguish clearly between the terms gene and allele .......................................................................................................................................... 76 (b) explain the terms dominant, recessive, codominant, homozygous, heterozygous, phenotype and genotype ............................................................................................................................ 76 (c) predict the results of simple crosses with expected ratios of 3:1 and 1:1, using the terms homozygous, heterozygous, F1 generation and F2 generation ................................................. 77 (d) explain why observed ratios often differ from expected ratios, especially when there are small numbers of progeny .................................................................................................................. 77 (e) use genetic diagrams to solve problems involving monohybrid inheritance. (Genetic diagrams involving autosomal linkage or epistasis are not required) ......................................................... 77 (f) explain co-dominance and multiple alleles with reference to the inheritance of the ABO blood group phenotypes – A, B, AB, O, gene alleles IA, IB and IO ........................................................ 78 (g) describe the determination of sex in humans – XX and XY chromosomes ........................... 78 (h) describe mutation as a change in the structure of a gene, such as in sickle cell anaemia, or in the chromosome number, such as the 47 chromosomes in the condition known as Down syndrome .................................................................................................................................. 78 (i) name radiation and chemicals as factors which may increase the rate of mutation ............... 79 (j) describe the difference between continuous and discontinuous variation and give examples of each .......................................................................................................................................... 79 (k) state that competition which arises from variation leads to differential survival of, and reproduction by, those organisms best fitted to the environment ............................................... 79 (l) give examples of environmental factors that act as forces of natural selection ...................... 80 (m) explain the role of natural selection as a possible mechanism for evolution ........................ 81 (n) give examples of artificial selection such as in the production of economically important plants and animals .................................................................................................................... 81 16. Organisms and their Environment ....................................................................................... 83 (a) briefly describe the non-cyclical nature of energy flow .......................................................... 83 (b) explain the terms producer, consumer and trophic level in the context of food chains and food webs.......................................................................................................................................... 83 (c) explain how energy losses occur along food chains, and discuss the efficiency of energy transfer between trophic levels .................................................................................................. 83 (d) describe and interpret pyramids of numbers and biomass.................................................... 84 (e) describe how carbon is cycled within an ecosystem ............................................................. 85 (f) evaluate the effects of: • water pollution by sewage and by inorganic waste • pollution due to insecticides including bioaccumulation up food chains and impact on top carnivores ................ 86 (g) outline the roles of microbes in sewage disposal as an example of environmental biotechnology ............................................................................................................................ 87 (h) discuss reasons for conservation of species with reference to the maintenance of biodiversity, management of fisheries and management of timber production ............................................... 87

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THEME I: PRINCIPLES OF BIOLOGY Overview A basic characteristic of life is the hierarchy of structural order within the organism. Robert Hooke (1635–1703), one of the first scientists to use a microscope to examine pond water, cork and other things, was the first to refer to the cavities he saw in cork as "cells", Latin for chambers. Subsequent scientists developed Hooke‘s discovery of the cell into the Cell Theory on which modern Biology is built upon. The Cell Theory states that all organisms are composed of one or more cells, and that those cells have arisen from pre-existing cells. In this section, we study two key principles of biology. The first principle is the correlation of structure to function. This is illustrated by how each part of the cell is suited for its intended function. The second principle is that specialisation results in the division of labour which enables the cell to effectively carry out a number of vital life processes. A strong foundation in the principles of biology will pave the way for students to master the content in the subsequent topics. Extracted from BIOLOGY GCE ORDINARY LEVEL (2014) Syllabus Document

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1. Cell Structure and Organisation Content • Plant and Animal Cells • Specialised Cells, Tissues and Organs Learning Outcomes: Candidates should be able to: (a) identify cell structures (including organelles) of typical plant and animal cells from diagrams, photomicrographs and as seen under the light microscope using prepared slides and fresh material treated with an appropriate temporary staining technique: • chloroplasts • cell membrane • cell wall • cytoplasm • cell vacuoles (large, sap-filled in plant cells, small, temporary in animal cells) • nucleus Cells  Cells are the simplest units of life  Each cell is made up of structures known as organelles for the cell to function

#

Structures

Description

Diagram

1

Chloroplast

 Ovular structure with a double membrane  Made of grana (stacks of discs) containing chlorophyll linked by thylakoid membranes  Found only in plant cells

2

Cell membrane

Partially permeable membrane that surrounds the cytoplasm of the cell

Refer to ‗Diagram of an entire plant cell‘

3

Cell wall

 Fully permeable wall made of cellulose surrounding the cell membrane  Found only in plant cells


4

Cytoplasm

Jelly-like substance between the cell membrane and the nucleus


5

Cell vacuole

Fluid-filled space enclosed by a membrane


6

Nucleus

 Spherical or ovular structure with a double membrane, usually found at the centre of the cell  Made of a nucleolus (a smaller-sized spherical structure) and DNA in the form of chromatin

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syllacon.weebly.com (b) identify the following membrane systems and organelles from diagrams and electron micrographs: • endoplasmic reticulum • mitochondria • Golgi body • ribosomes #

Structures

Description

Diagram

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Smooth endoplasmic reticulum

 Tubular network of flattened spaces lined by a membrane  Connected to rough endoplasmic reticulum  Does not have ribosomes attached to its outer membrane, unlike the rough endoplasmic reticiulum

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Rough endoplasmic reticulum

 Tubular network of flattened spaces lined by a membrane  Less tubular than smooth endoplasmic reticulum  Connected to smooth endoplasmic reticulum  Ribosomes are attached to its outer membrane, unlike the smooth endoplasmic reticiulum

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Mitochondrion

 Small sausage-shaped structure surrounded by a double membrane  The inner membrane is folded inwards

10

Golgi body

 Shaped like a disc  Consists of a stack of flattened spaces surrounded by membranes  Vesicles may fuse with or pinch off from the body

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Ribosome

 Small round structure  Either found attached to the rough endoplasmic reticulum or lies freely in the cytoplasm

Diagram of an entire plant cell

Note: Only study structures identified in the learning outcomes

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syllacon.weebly.com (c) state the functions of the membrane systems and organelles identified above #

Structures

Functions

1

Chloroplast

Absorbs sunlight to allow for the manufacture of food through photosynthesis

2

Cell membrane

Controls substances that leave and enter the cell

3

Cell wall

Gives the plant cell its fixed shape and protects it from injury

4

Cytoplasm

 Allows cell activities to take place using organelles present  Catalyses biological reactions using enzymes present (e.g. breakdown of proteins into amino acids)

5

Cell vacuole

Stores substances (e.g. water, mineral salts, amino acids) within cell

6

Nucleus

Control all cell activities within the cell (e.g. cell division, repair of worn out parts)

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Smooth endoplasmic reticulum

 Synthesises fats and steriods  Detoxifies harmful substances (e.g. toxins)

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Rough endoplasmic reticulum

Transports proteins made by the cell ribosomes to the Golgi body for packaging

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Mitochondrion

Releases energy for cell activities (e.g. growth and reproduction) through aerobic respiration of food substances

10

Golgi body

Stores, modifies and packages substances made by vesicles of the endoplasmic reticulum to be secreted out of the cell

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Ribosome

Manufactures proteins to be either used within the cell or transported out of the cell

(d) compare the structure of typical animal and plant cells #

Differences

Animal cells

Plant cells

1

Shape of cell

Usually irregularly shaped

Usually regularly shaped

2

Presence of chloroplasts

Absent

Present

3

Presence of cell wall

Absent

Present

4

Presence of centrioles

Present

Absent

5

Presence of vacuole

Temporarily present

Always present

6

Presence of sap

Absent in vacuole

Present in vacuole

7

Number of vacuoles

Several

Single

8

Size of vacuoles

Small

Large

Additional information  Sap contains various dissolved substances (e.g. sugars, mineral salts and amino acids)  Centrioles are small hollow cylinders involved in cell division  The table above only lists differences present. Remember to include some similarities too!

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syllacon.weebly.com (e) state, in simple terms, the relationship between cell function and cell structure for the following: • absorption – root hair cells • conduction and support – xylem vessels • transport of oxygen – red blood cells Cell Root hair cell

Xylem vessel

Red blood cell

Function

Adaptations

Significance

Long and narrow

 Increases surface area to volume ratio  This allows rate of absorption of water and dissolved mineral salts from soil to be increased

Cell sap present

 Cell sap has less water potential than soil  This allows water to diffuse into the cell down a concentration gradient

Cell membrane present

 Prevents sap leakage  This maintains the abovementioned concentration gradient

Mitochondria present

 Respires to release energy for the cell  This allows active transport to occur if the cell has a higher concentration of ions and mineral salts than soil

To conduct water and dissolved mineral salts from the roots to the stem and leaves

Lumen is long and hollow

Conducts water and dissolved mineral salts up the plant effectively

Cross walls and protoplasm absent

 Less obstructions enable water to flow more easily through the lumen  This maintains a continuous flow

To support the plant structure

Walls are made of lignin

 Strengthens the walls of xylem vessels by providing mechanical support to the plant  This prevents the walls from collapsing

To transport oxygen from the lungs to all parts of the body

Circular and biconcave shape

 Increases surface area to volume ratio of the cell  This allows oxygen can diffuse in and out of the entire cell at a faster rate

Nucleus absent

 Allows cell to carry more haemoglobin (since there is more space)  This increases the rate at which oxygen is transported from the lungs to all parts of the body

Able to change into a bell shape

 Decrease in diameter enables them to move through lumens (with small diameters) easily  Also increases surface area to volume ratio to speed up oxygen exchange

To absorb water and dissolved mineral salts from soil

Additional information Protoplasm is made up of the cell membrane, cytoplasm and nucleus

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syllacon.weebly.com (f) differentiate cell, tissue, organ and organ system Level Smallest

Largest

Description

Example

Cells

Cells are the simplest units of life

Muscle cell

Tissues

Cells of the same type group together to form a tissue, which performs a specific function

 A muscle tissue is made of muscle cells  Muscle tissues allow various parts of the body to move by contracting and relaxing

Organs

Different tissues group together to form an organ, which performs an overall function

 The stomach is made of muscular, glandular, connective and nervous tissues  The various types of tissues work together so that the stomach can perform the overall function of storing, digesting and churning food

Organ system

Several organs working together for a common purpose form an organ system

The digestive system is made of various organs (e.g. stomach, intestines)

Organism

Various organ systems work together to make up the entire organism

The human is made of various organ systems (e.g. digestive system, respiratory system)

Use the knowledge gained in this section in new situations or to solve related problems

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2. Movement of Substances Content • Diffusion • Osmosis • Active Transport Learning Outcomes: Candidates should be able to: (a) define diffusion and discuss its importance in nutrient uptake and gaseous exchange in plants and humans Term Definition

Diffusion    

Net movement of particles (i.e. atoms, ions or molecules) from a region where they are of higher concentration to a region where they are of lower concentration (i.e. down a concentration gradient)

Importance In humans

Nutrient uptake N.A.

Gaseous exchange  Oxygen from the air diffuses from the air sacs of lungs, where it is of higher concentration,  into the red blood cells, where it is of lower concentration  Likewise, carbon dioxide from the organism diffuses from the red blood cells, where it is of higher concentration,  into the air sacs of lungs, where it is of lower concentration

In plants

 Water and dissolved mineral salts diffuse via osmosis [will be discussed in the next learning outcome] from the soil, where it is of higher concentration,  into the root hair cells, where it is of lower concentration

 Oxygen from the air diffuses from the soil, where it is of higher concentration,  into the root hair cells, where it is of lower concentration  Likewise, carbon dioxide from the organism diffuses from the root hair cells, where it is of higher concentration,  into the soil, where it is of lower concentration

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syllacon.weebly.com (b) define osmosis and discuss the effects of osmosis on plant and animal tissues Term

Osmosis

Water potential  Relative number of water molecules per unit volume of solution  Measure of the tendency of water to move from one place to another

Definition

   

Movement of water molecules from a solution of higher water potential to a solution of lower water potential through a partially permeable membrane

Scenario

   

If a partially permeable membrane is placed between a more dilute solution (more water molecules and less solute per unit volume) and a more concentrated solution (more solute and less water molecules per unit volume), water will move from the dilute solution to the concentration solution

Effects of

Entry of water

No net movement of water

Exit of water

On animal cells

On plant cells

Effects of

Entry of water (in dilute solution)

Exit of water (in concentrated solution)

On animal tissues

 Cells expand, swell and burst  This is because no cell wall is present to prevent cells from bursting  Tissue experiences loss of cells

 Cells shrink in size and crenate (i.e. little spikes appear on the cell membrane)  Tissue becomes flaccid

On plant tissues

 Cells enlarge and become turgid  This is because the cell wall present prevents the cell from bursting  Tissue experiences increase in turgor pressure

 Vacuole of cells shrink  Cells plasmolyse (i.e. cytoplasm and cell membrane shrinks away from cell wall)  Tissue becomes flaccid

Additional information The verbal form of movement of particles via osmosis is also ‗diffuse‘ (i.e. there is no such thing as ‗osmosises‘!)

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syllacon.weebly.com (c) define active transport and discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, as in ion uptake by root hairs and uptake of glucose by cells in the villi Term Definition

Active transport     

Process in which energy is used to move the particles of a substance from a region where they are of lower concentration to a region where they are of higher concentration (i.e. against a concentration gradient)

Importance

Ion uptake by root hairs

Uptake of glucose by cells in the villi

Case

Only when root hair cells have a higher concentration of dissolved ions in water than soil

Only when villi of the small intestine have a higher concentration of glucose than soil

Description

 Ions dissolved in water move via active transport from the soil, where it is of lower concentration,  into the root hair cells, where it is of higher concentration  Energy is consumed in the process

 Glucose moves via active transport from the chyme of digested material that passes, where it is of lower concentration,  into villi of the small intestine, where it is of higher concentration  Energy is consumed in the process

Use the knowledge gained in this section in new situations or to solve related problems Differences

Diffusion

Osmosis

Particles moved

Particles except water molecules

Water molecules

All particles

Type of gradient

Concentration

Water potential

Concentration

Direction of transport

Down gradient

Down gradient

Against gradient

Energy consumption

Absent

Absent

Present

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Active transport


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3. Biological Molecules Content • Water and Living Organisms • Carbohydrates, Fats and Proteins • Enzymes Learning Outcomes: Candidates should be able to: (a) state the roles of water in living organisms Organism type Animals

Roles Digestive products can be transported from small intestine to body parts Waste products can be transported from tissue cells to excretory organs for removal Hormones can be transported from glands to requiring parts of the body Regulates body temperature (i.e. when water in sweat evaporates, latent heat of vapourisation is removed)

Plants

Photosynthesis Keeps plant upright (i.e. water keeps plant cells turgid and firm) Mineral salts can be transported up the xylem from the roots to the leaves Food substances can be transported from the leaves to other plant parts

(b) list the chemical elements which make up: • carbohydrates • fats • proteins Nutrient

Carbohydrates

Fats

Proteins

Carbon

Present

Present

Present

Hydrogen

Present

Present

Present

Oxygen

Present

Present

Present

Nitrogen

Absent

Absent

Present

Sulfur

Absent

Absent

May be present

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syllacon.weebly.com (c) describe and carry out tests for: • starch (iodine in potassium iodide solution) • reducing sugars (Benedict’s solution) • protein (biuret test) • fats (ethanol emulsion) Biomolecule Carbohydrates

Fats

Test name

Procedure

Benedict‘s test

 Benedict‘s solution is a solution containing blue copper (II) sulfate 3 3  Add 2cm of Benedict‘s solution to 2 cm of the substance in a test tube Shake and leave the test tube in a beaker of boiling water for 5 minutes  A green, yellow or brick-red precipitate (based on amount of reducing sugar) would be formed (i.e. traces, moderate amount and large amount of reducing sugar respectively)

Iodine test

 When a few drops of potassium iodide is added to a substance containing starch, the iodine solution will turn from brown to blue-black

Ethanol emulsion test

 A cloudy white emulsion (i.e. a suspension of small drops of liquid in another liquid) is formed when ethanol and water are added to fats  If tested on solid food, the food has to be cut up into many small pieces 3 and added with 2cm ethanol  After shaking and allowing the solid particles to settle, decant the 3 ethanol into another test tube with 2cm of water, a cloudy white emulsion is formed if the food contains fat

Proteins

Biuret test

 Biuret solution is made up of sodium hydroxide and copper (II) sulfate 3 3  When 2cm of the substance is added and stirred with 2cm of biuret solution, the solution turns from blue to violet if the substance contains protein

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syllacon.weebly.com (d) state that large molecules are synthesised from smaller basic units: • glycogen from glucose • polypeptides and proteins from amino acids • lipids such as fats from glycerol and fatty acids Large molecule Carbohydrates

Synthesis (enzyme not required)

Starch

Many glucose molecules  Maltose Many maltose molecules  Starch

Glycogen

Many glucose molecules  Glycogen Many amino acids  Polypeptides

Protein

Many polypeptides  Proteins Glycerol + 3 Fatty acid  Fat + 3 Water

Fat

Large molecule Starch

Protein

Fat

Breakdown (enzyme required)

Enzyme

Starch  Many maltose molecules

Amylase

Maltose  Many glucose molecules

Maltase

Proteins  Many polypeptides

Pepsin (protease)

Polypeptides  Many amino acids

Erepsin (protease)

Fat + 3 Water  Glycerol + 3 Fatty acid

Lipase

(e) explain enzyme action in terms of the ‘lock and key’ hypothesis Terms

Relation to ‘lock and key’

Definitions

Enzyme

Protein that speeds up the rate of a biological reaction

Lock

Substrates

Substances on which enzymes act

Key (that fits into the lock)

Active site of enzyme

Small portion of the enzyme that comes into direct contact with the substrates

Groove (of the lock)

Diagram

Explanation  The substrates have shapes that are complementary to the active site of the enzyme  Thus the substrates are able to fit into the active site of enzyme  This allows the reaction to take place  This is similar to a key that is inserted into a lock, based on the ‗lock and key‘ hypothesis  The key will only be able to open the lock if it is complementary in shape and fits into the grooves of the lock

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syllacon.weebly.com (f) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex, lowering of activation energy and enzyme specificity Key question

Exam response

What are enzymes?

An enzyme is a protein that speeds up the rate of a specific biological reaction

What is the structure of enzymes that helps them achieve their role?

Each enzyme has an active site, which is a small portion of the enzyme that comes into direct contact with the substrates

How do enzymes achieve their role?

 Collision between substrates and enzyme at the correct orientation  causes the substrate to bind to the enzyme at its active site  to form an enzyme-substrate complex  This increases the likelihood of bond breaking/forming,  which lowers the activation energy of the reaction (the minimum energy needed to start the reaction)  thus speeding up the rate of the reaction

21


syllacon.weebly.com (g) investigate and explain the effects of temperature and pH on the rate of enzyme catalysed reactions Term

Definition

Denaturation

Random unlooping of the 3D structure of a protein or enzyme

Factor

Optimum level

Temperature

 At optimum temperature, the enzyme is most active  as high kinetic energy supplied causes more collisions between enzyme and substrate molecules  and vibrations in protein atoms are not high enough to denature the enzyme

As temperature decreases from optimum,

 the kinetic energy supplied to the reacting molecules decreases  This causes less frequent collisions between the substrate and enzyme molecules,  decreasing the chance of substrates fitting into active sites  Rate of formation of products thus decreases gradually

As temperature increases from optimum,

 vibrations in the atoms of the enzyme become more violent  This breaks the hydrogen bonds of protein within the enzymes  The enzyme loses its specific shape and denatures  Rate of formation of products thus decreases steeply

 Some enzymes work best in slightly acidic solutions  while others require slightly alkaline solutions

 Extreme changes in acidity or alkalinity of the solutions denature the enzymes

pH

Effects of changes from optimum

Diagram

 The first reason is that hydrogen bonds of protein within the enzymes are broken  The second reason is that most substrates and enzymes have opposite electrostatic charges that allow them to bind  The extreme changes alter the charges on the substrate and enzymes such that they bind less well


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THEME II: MAINTENANCE AND REGULATION OF LIFE PROCESSES Overview Life is sustained through the integrated organisation of the whole organism. In humans, the maintenance and regulation of life processes include nutrition, transport, respiration, excretion, homeostasis and co-ordination and response. The key overarching theme in the study of the organ systems is the correlation between form and function. Extracted from BIOLOGY GCE ORDINARY LEVEL (2014) Syllabus Document

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4. Nutrition in Humans Content • Human Alimentary Canal • Chemical Digestion • Absorption and Assimilation Learning Outcomes: Candidates should be able to: (a) describe the functions of main regions of the alimentary canal and the associated organs: mouth, salivary glands, oesophagus, stomach, duodenum, pancreas, gall bladder, liver, ileum, colon, rectum, anus, in relation to ingestion, digestion, absorption, assimilation and egestion of food, as appropriate #

Region

Function

Description of function

1

Mouth

Ingestion

Has teeth which chews to break down large pieces of food into smaller pieces to increase surface area to volume ratio of food lumps

2

Salivary gland

Ingestion

Secretes saliva containing mucin which softens the food so that swallowing the food lumps is easier

Digestion

Secretes saliva containing salivary amylase is secreted by salivary glands through salivary ducts into the mouth, which digests some starch into maltose

3

Oesophagus

Digestion

Induces peristalsis (along with other parts of the alimentary canal) that allows food to be mixed with digestive juices easily and broken down further through churning, increasing rate of collision of enzymes and substrates and rate of digestion

4

Stomach

Digestion

[Initial process] Secretes gastric juice to convert pepsinogen to pepsin, and prorennin to rennin [Eventual process] Secretes gastric juice containing hydrochloric acid which provides a suitable pH for pepsin to digest proteins to polypeptides, and rennin to turn soluble milk proteins insoluble so that it can be fully digested before moving to small intestine [Combination of the above processes] Digestion in the stomach turns the partly digested food into liquified chyme, enabling food to pass into the duodenum in small amounts instead of altogether increasing surface area to volume ratio and giving small intestine more time to digest

5

Duodenum

Digestion

Secretes intestinal juice 1. Carbohydrases: Maltase converts maltose to glucose 2. Proteases: Erepsin digests polypeptides to amino acids

6

Pancreas

Digestion

Secretes pancreatic juice 1. Amylase: Pancreatic amylase digests starch to maltose 2. Lipase: Pancreatic lipase digests fats to fatty acids and glycerol 3. Proteases: Trypsin converts remaining protein to polypeptides

Assimilation

Secretes the hormone glucagon to stimulate the liver to convert glycogen into glucose when blood glucose concentration is low, and transported to the cells and oxidised to produce more energy

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syllacon.weebly.com #

Region

7

Gall bladder

Digestion

Storage and release area of bile from the liver, assisting emulsification

8

Liver

Digestion

Secretes bile released from gall bladder to emulsify fats 1. Lower surface tension of fats 2. Smaller fat droplets 3. Lipase digests fats faster

Assimilation

Carries out deamination of excess amino acids by converting part of it to glucose that can be used to provide more energy

Egestion

 Carries out deamination of excess amino acids by converting part of it to urea  Breaks down haemoglobin from red blood cells to be converted into bile

Absorption

 Blood capillaries transport sugars and amino acids to the hepatic portal vein  Lacteals transport minute fat globules of glycerol and fatty acids to lympatic vessels

Hepatic portal vein

Absorption

Transports sugars and amino acids to the liver to convert excess of them into glycogen and urea, then distributing remaining to the body parts

Lymphatic vessels

Absorption

Transports small fat globules to the bloodstream to be distributed to the rest of the body

Absorption

Water and mineral salts absorbed

Egestion

Controls emptying of the rectum

9

10

Ileum

Colon

Function

Description of function

11

Rectum

Egestion

Intestinal wall secretes mucus that lubricates undigested contents, which stays for 36 hours

12

Anus

Egestion

Stores undigested food as faeces temporarily

#

Process

1

Ingestion

Digestion

Absorption

Assimilation

Egestion

Mouth











2

Salivary gland











3

Oesophagus











4

Stomach











5

Duodenum











6

Pancreas











7

Gall bladder











8

Liver











9

Ileum











10

Colon











11

Rectum











12

Anus











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syllacon.weebly.com Diagram

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syllacon.weebly.com (b) describe peristalsis in terms of rhythmic wave-like contractions of the muscles to mix and propel the contents of the alimentary canal Term

Definition

Peristalsis

Rhythmic wave-like contractions of muscles of the gut

Peristalsic action

Function

Mixes food well with digestive juices easily

Increases rate of collision of enzymes and substrates and rate of digestion

Propel food down the gut

Pushing of food from behind down the gut

By contracting of internal circular muscles and relaxing external longitudinal muscles, which constricts the lumen

Providing space for food in front to move down the gut

By relaxing of internal circular muscles and contracting external longitudinal muscles in front of the food provides space for food to move forward easily

Churning to create chyme

Enables food to pass into the duodenum in small amounts instead of altogether, giving small intestine more time for digestion

Diagram

(c) describe digestion in the alimentary canal, the functions of a typical amylase, protease and lipase, listing the substrate and end-products Large molecule

Enzyme

Carbohydrates

Amylase

Proteins

Proteases

Fats

Lipase

Substrate

End-products

Starch

Maltose

Pepsin

Polypeptides

Proteins

Erepsin

Amino acids

Polypeptides

Glycerol + Fatty acids

Fat + Water

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syllacon.weebly.com (d) describe the structure of a villus and its role, including the role of capillaries and lacteals in absorption Region in small intestine

Role

Villus

Highly folded with microvilli (in-foldings) to increase surface area to volume ratio for faster rates of absorption

Blood capillaries

Transports sugars and amino acids to the hepatic portal vein

Lacteals

Transports minute fat globules of glycerol and fatty acids to lympatic vessels

Adaptation of small intestine

Significance

Highly folded with villi and microvilli of finger-like structures

Increases surface area to volume ratio for faster rates of absorption

Epithelial wall is one cell thin

Decreases time needed for food molecules to travel through the wall, increasing rate of absorption

Long and making up 60% of the small intestine

Ensures sufficient time for complete absorption

Many capillaries in intestinal wall and villi transports food molecules away from intestine

Maintains concentration gradient of digested food substances through epithelial wall

(e) state the function of the hepatic portal vein as the route taken by most of the food absorbed from the small intestine Region Hepatic portal vein

Function Route taken by most of the food absorbed from the small intestine to be distributed to other body parts

Route of food taken from small intestine to other body parts

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syllacon.weebly.com (f) state the role of the liver in: • carbohydrate metabolism • fat metabolism • breakdown of red blood cells • metabolism of amino acids and the formation of urea • breakdown of alcohol #

Roles of liver

Description of roles of liver

1

Carbohydrate metabolism

 Insulin produced by the islets of Langerhans of the pancreas stimulates the liver to convert glycogen to glucose  and converts glucose back to glycogen by glucagon and adrenalin if the concentration ratio of glucose is high to regulate blood glucose concentration

2

Fat metabolism

 Secretes bile containing bile salts and bile pigments that emulsify fats,  enabling it to turn into more, smaller droplets with high surface area to volume ratio and lower surface tension,  increasing the digestion rate between fats and water into fatty acids and glycerol by lipase

3

Breakdown of red blood cells

Haemoglobin in red blood cells is broken down into iron and bile salts to be excreted out of the body through faeces

4

Amino acid metabolism

 Deanimates amino acids and converts part of them into glycogen, to be stored in liver and muscles that can convert it to glucose of blood glucose level is low  The other part will be converted to urea, to be excreted through urine

5

Breakdown of alcohol

Alcohol dehydrogenase from liver breaks down alcohol into acateldahyde compounds that can be broken down during respiration to release energy  However, if alcohol used excessively, acids are secreted in the stomach that might cause gastric ulcers  In worser cases, cirrhosis will destroy liver cells, diminishing its function

(g) describe the effects of excessive consumption of alcohol: reduced self-control, depressant, effect on reaction times, damage to liver and social implications #

Effects

1

Depressant

Description of effects of excessive alcohol consumption Alcohol inhibits the function of the central nervous system by disrupting the brain‘s communication pathways

2

Reduced self-control

As a result, it is more difficult for the person to think clearly and move with coordination

3

Effect on reaction times

 It also takes a longer time for the person to process information  For example, the slower rate of reaction to sudden changes in traffic to makes it easier for drivers to cause an accident

4

Damage to liver

 Liver inflammations may occur  For example, cirrhosis will destroy liver cells, diminishing its function

5

Social implications

Furthermore, excessive alcohol use can effect all areas of a person's life, including family, work and personal relationships 1. Family problems: Arguments over someone's drinking can cause family and relationship problems that may lead to break up 2. Work problems: Drinking alcohol at work and hangovers can lead to poor performance and accidents at work, while illness can result in absenteeism 3. Legal problems: Drink-driving may lead to fines, loss of license and even imprisonment Source: http://www.adf.org.au/policy-advocacy/alcohol-and-its-effects#sthash.dF0kKMzn.dpuf

Use the knowledge gained in this section in new situations or to solve related problems.

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5. Nutrition in Plants Content • Leaf Structure • Photosynthesis Learning Outcomes: Candidates should be able to: (a) identify and label the cellular and tissue structure of a dicotyledonous leaf, as seen in transverse section under the microscope and describe the significance of these features in terms of their functions, such as the: • distribution of chloroplasts in photosynthesis • stomata and mesophyll cells in gaseous exchange • vascular bundles in transport Features

Aspects

Distribution of chloroplasts in photosynthesis

Palisade mesophyll cells

 Contains numerous chloroplasts, located right below the upper epidermis and closely packed together  to absorb maximum sunlight for photosynthesis

Spongy mesophyll cells

 Contains chloroplasts  to maximise photosynthesis of plant

Increase stomatal receival of carbon dioxide

 In sunlight, photosynthesis occurs  Energy is used to pump potassium ions into the guard cells, + increasing K concentration and decreasing water potential of guard cells, causing water to enter these guard cells by osmosis  This turns them turgid and pulls stomata open, resulting in more carbon dioxide received to facilitate higher photosynthesis rates under sunlight

Decrease stomatal loss of water vapour

 At night, K ions accumulated in the day diffuse out of the guard cells, increasing water potential and causing water to leave the guard cells through osmosis  As the cells are more flaccid, the stomatal pore closes

Stomata and mesophyll cells in gaseous exchange

Significance

+

Under high temperature, excess evaporation (transpiration) of water causes the guard cells to be more flaccid, closing the stomatal pore.

Vascular bundles in transport

Epidermal layer

All mesophyll cells (carbon dioxide and oxygen)

 Covered with a thin film of water for gases  to dissolve in to allow rapid diffusion of carbon dioxide and oxygen in and out of the mesophyll cells

Spongy mesophyll cells

Irregular with large intercellular air spaces among them to allow rapid diffusion of gases from stomata to the vascular bundles through the leaf

Xylem (top) for loss of water vapour

Transports water and dissolved mineral salts from the roots to the leaf so that once out of the xylem, the water and mineral salts move from cell to cell right through the mesophyll of the leaf by osmosis

Phloem (bottom) for transport of sugars

When the mesophyll cells receive water from xylem and carbon dioxide from the air through the stomata, they can manufacture food under light by photosynthesis, in which the phloem will transport sugars to other plant parts

Cuticle of the upper and lower epidermis

Closely packed with waxy cuticle that prevents excessive evaporation (transpiration) of water Transparent to allow sunlight to penetrate the leaf easily

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syllacon.weebly.com Diagram

(b) state the equation, in words and symbols, for photosynthesis Equation for photosynthesis In words Carbon dioxide

+

Water

Glucose

+

Oxygen

6 CO2

+

6 H2O

C6H12O6

+

6 O2

In symbols

(c) describe the intake of carbon dioxide and water by plants Processes

Description of processes

Photosynthesis

Photosynthesis occurs whenever there is sunlight

Water potential

Energy is used to pump potassium ions into the guard cells, increasing K concentration and decreasing water potential of guard cells, causing water to enter these guard cells by osmosis

Turgidity of guard cells

This turns them turgid and pulls stomata open, resulting in more carbon dioxide (and water vapour) received to facilitate higher photosynthesis rates under sunlight

+

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syllacon.weebly.com (d) state that chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage Substance Chlorophyll

Function Traps light energy and converts it into chemical energy for the formation of carbohydrates via photosynthesis and their subsequent storage as starch

Components of photosynthesis

Significance

Reactants (raw materials)

Carbon dioxide

Produced by all living organisms during respiration are removed in photosynthesis for plants to produce food

Water

Required to produce glucose as it contains the hydrogen element

Activation energy

Chlorophyll traps light and converts it to chemical energy

Chemical energy would be used to start the photochemical reaction to convert carbon dioxide and water to glucose and oxygen

Endproducts

Glucose

 Transported through the phloem to various parts of the plant by translocation  Used as a reactant of respiration to release energy for cellular activities in the plant

Sucrose

Excess glucose produced in the leaf is converted to sucrose and transported to storage organs (e.g. seeds)

Starch

Excess glucose produced in the leaf is converted to starch to be stored temporarily, converted back mostly at night when photosynthesis stops

Oxygen

Oxygen is produced and used by all organisms in respiration, allowing them to release energy

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syllacon.weebly.com (e) investigate and discuss the effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis (e.g. in submerged aquatic plant) # 1

Factors Light intensity

Effects When light intensity increases, the rate of photosynthesis generally increases When light intensity is at light compensation point

 Rate of photosynthesis is equal rate of respiration (i.e. rate of carbon dioxide intake is equal to that of oxygen)  Any rise in light intensity after this point will cause rate of photosynthesis to be greater than rate of respiration

When light intensity is at light saturation point

 Rate of photosynthesis is maximum  Any rise in light intensity after this point will not affect rate of photosynthesis (i.e. rate of photosynthesis remains constant)

2

Carbon dioxide concentration

 When carbon dioxide concentration increases, the rate of photosynthesis generally increases  This is because carbon dioxide is a key reactant in photosynthesis  Rate of photosynthesis remains constant eventually as carbon dioxide concentration rises further

3

Temperature

 When temperature increases up to 40 C, the rate of photosynthesis increases  This is because enzymes involved in photosynthesis are more active o

 When temperature is increases beyond 40°C, the rate of photosynthesis drops  This is because enzymes involved in photosynthesis are denatured

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syllacon.weebly.com (f) discuss light intensity, carbon dioxide concentration and temperature as limiting factors on the rate of photosynthesis Term

Definition

Clarification

Limiting factor

The factor that  directly increases the rate of a process if its quantity is increases  and is the lowest in concentration among all other factors

While a process can be affected by many factors, only one of the factors can be the limiting factor at any given time (i.e. the one that is lowest in concentration)

#

Factors

When the factor is limiting

1

Light intensity

 When light intensity increases, the rate of photosynthesis generally increases  In this case, light intensity is the limiting factor

Graph

 At light saturation point, rate of photosynthesis is maximum and cannot increase further  In this case, either carbon dioxide or temperature replaces light intensity as the limiting factor 2

Carbon dioxide concentration

 Carbon dioxide is an important limiting factor as it makes up only 0.03% of air  It ceases to be the limiting factor when rate of photosynthesis is maximum

3

Temperature

 When light intensity is low, temperature cannot be a limiting factor  When light intensity is high, temperature is a likely limiting factor  Temperature ceases to be the limiting factor when rate of photosynthesis starts to fall

Relationship between the above-mentioned factors


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6. Transport in Flowering Plants Content • Water and Ion Uptake • Transpiration and Translocation Learning Outcomes: Candidates should be able to: (a) identify the positions and explain the functions of xylem vessels, phloem (sieve tube elements and companion cells) in sections of a herbaceous dicotyledonous leaf and stem, under the light microscope Plant parts

Functions

Xylem

 Transport mineral salts and water  through lignified walls, which provide mechanical strength to the plants

Phloem

 Allows water to move efficiently  by not having cross walls, which maintains a continuous lumen

Sieve tube elements

 Protoplasm of the sieve tube is disintegrated and the sieve plate walls contain holes,  allowing rapid movement of food from the leaves due to less obstructions

Companion cells

 Contain mitochondria to release energy needed  for active transport of food from the leaves to other parts of the plant Diagrams

Xylem and phloem in leaf

Xylem and phloem in stem

Note: Xylem is shaded in the diagrams while phloem is not

(b) relate the structure and functions of root hairs to their surface area, and to water and ion uptake Structure

Function

Long and narrow (surface area)

 Increases surface area to volume ratio  to allow rate of absorption of mineral salts and water to be increased

Contains cell sap (water uptake)

 Cell sap has less water potential than soil  to allow water to diffuse into the cell down a concentration gradient

Mitochondria present (ion uptake)

 Releases energy during respiration for the cell  to allow active transport to occur if the cell has a higher concentration of ions and mineral salts

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syllacon.weebly.com (c) explain the movement of water between plant cells, and between them and the environment in terms of water potential (Calculations on water potential are not required). Direction

Movement

Explanation

Either: Water molecules move from the soil water across the partially permeable cell membrane into the root hair cell by osmosis

This occurs if there is a higher water potential in soil water than the root hair cell

Or: Root hair cell absorbs water molecules from the soil water across the partially permeable cell membrane by active transport

This occurs if there is a lower water potential in soil water than the root hair cell (energy from cell respiration is used for active transport)

From root hair cell to cortex cell beside

Water molecules move from the root hair cell into the cortex cell by osmosis

The root hair cell has higher water potential than the cortex cell beside it

From the series of cortex to xylem vessel

The above movement of water continues from cell to cell through the series of neighbouring cortex cells until the water molecules reach the xylem tissue in the root

Water molecules travel up the xylem through transpiration pull to the leaves

Xylem vessel of leaves to the spongy mesophyll cell

Water molecules move from the xylem tissue to the mesophyll cells by osmosis

There is a higher water potential in xylem tissue in the leaf than the mesophyll cells

Water evaporates from the mesophyll cells

Water forms a thin film of moisture over the mesophyll surfaces and turns into water vapour

Spongy mesophyll cell to atmosphere

Water moves from the thin film of moisture into the intercellular air spaces, accumulating in the air spaces that are near the stomata

Water vapour diffuses through the stomata to the drier air outside the leaf through transpiration

From soil to root hair cell

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syllacon.weebly.com (d) outline the pathway by which water is transported from the roots to the leaves through the xylem vessels Outline

Diagram

37


syllacon.weebly.com (e) define the term transpiration and explain that transpiration is a consequence of gaseous exchange in plants Term

Definition

Transpiration

The loss of water vapour from the aerial parts of a plant, especially through the stomata of the leaves

Explanation  As water vapour evaporates from the film of water on the spongy mesophyll cells, the water potential of the cell sap decreases  The mesophyll cells then absorb water by osmosis from the xylem vessels deep inside the leaf, removing water from the xylem vessels  A suction force results, pulling the whole column of water up the xylem vessels  Thus transpiration is a consequence of gaseous exchange

(f) describe and explain: • the effects of variation of air movement, temperature, humidity and light intensity on transpiration rate • how wilting occurs #

Factor

Effect

Explanation

1

Air movement

As increase in air movement increases transpiration rate

Wind blows away water vapour that accumulates outside the stomata, increasing water vapour concentration gradient

2

Temperature of air

An increase in temperature increases transpiration rate

Rate of evaporation increases as temperature increases

3

Humidity of air

An increase in humidity decreases transpiration rate

 Intercellular air spaces are normally saturated with water vapour  Increase in humidity (water vapour in the air) decreases the water vapour concentration gradient

4

Light intensity

An increase in light intensity increases transpiration rate

As light increases, the size of the stomata on the leaf increases and widens

Term

Description

Explanation

Advantage

Disadvantage

Wilting

Loss of rigidity of non-woody parts of plants due to loss of turgor

 Any of above factors can cause rate of transpiration to be more than that of absorption  Cells lose turgor due to loss of water and therefore wilts

Reduces transpiration  Leaf folds up, reducing surface area exposed to light  Guard cells become flaccid and stomata close

Reduces rate of photosynthesis  When stomata close, amount of carbon dioxide entering plant is reduced, which becomes the limiting factor  When folded, surface area is reduced, causing light received to be limited

(g) define the term translocation as the transport of food in the phloem tissue and illustrate the process through translocation studies Term Translocation

Definition Transport of manufactured food substances such as sugars and amino acids in phloem tissues

Illustration  When the mouthpart of an aphid penetrates a leaf or stem, anaesthetise it with carbon dioxide while it is feeding  Cut off body of aphid and analyse liquid from the cut end of mouth

Use the knowledge gained in this section in new situations or to solve related problems.

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7. Transport in Humans Content • Circulatory System Learning Outcomes: Candidates should be able to: (a) identify the main blood vessels to and from the heart, lungs, liver and kidney Circulatory system

Diagram

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syllacon.weebly.com (b) state the role of blood in transport and defence • red blood cells – haemoglobin and oxygen transport • plasma – transport of blood cells, ions, soluble food substances, hormones, carbon dioxide, urea, vitamins, plasma proteins • white blood cells – phagocytosis, antibody formation and tissue rejection • platelets – fibrinogen to fibrin, causing clotting Components of blood

# 1

Red blood cells

Features

Functions

Haemoglobin

 Oxygen is being transported by haemoglobin in red blood cells  Absence of nucleus allows space for haemoglobin which combines reversibly with oxygen, binding easily with oxygen to carry it in blood and unbinding to release oxygen to requiring parts

Oxygen transport

Circular and biconcave shape increases surface area to volume ratio and thus rate of absorption and release of oxygen

Elasticity

Able to turn into a bell shape, allowing it to squeeze through blood vessels of diameter smaller than itself, easing movement through lumen and increasing surface area to volume ratio to speed up oxygen exchange

2

Plasma

Transport of substances within body

Transports substances like blood cells, soluble food substances, plasma proteins, water, ions, carbon dioxide, vitamins, hormones and urea around the body

3

White blood cells

Phagocytosis

Phagocytes engulf and ingest pathogens and harmful foreign bacteria

Antibody formation

Lymphocytes produce antibodies that clump foreign bacteria together, protecting the body against fatal bacteria and viruses

Tissue rejection

Lymphocytes produce antibodies to destroy foreign organs, as organs from another person are usually treated as a foreign body by his immune system

Blood clotting

When tissues are damaged, enzymes released from platelets convert prothrombin to thrombin so that fibrinogen can be converted to insoluble fibrin, meshing up to trap blood cells, preventing them from flowing out

4

Platelets

(c) list the different ABO blood groups and all possible combinations for the donor and recipient in blood transfusions Components

Combinations for donor and recipient

Blood group

Antigens

Antibodies

Give blood to

Receive blood from

AB

A, B

-

AB

A, B AB, O

A

A

B

A, AB

A, O

B

B

A

B, AB

B, O

O

-

A, B

A , B, AB, O

O

Importance

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Failure to abide by the guidelines of giving and receiving blood will result in agglutination


syllacon.weebly.com (d) relate the structure of arteries, veins and capillaries to their functions Vessels

Structure

Arteries

Veins

Capillaries

Features

Functions

Small lumen size

At higher pressure this allows fast rate of flow of blood to body parts

Elastic

To withstand high pressure from the small lumen size and recoil for blood to travel in spurts under the high pressure

Muscular

Enables artery to dilate and constrict by the relaxation and contraction of muscles of arterial wall

Semi lunar valves present

To prevent the backflow of blood

Parts of vein are found alongside skeletal muscles

Contracting of skeletal muscles during exercise compresses the vein, exerting more pressure and pushing blood flow forward at a faster rate

Small lumen of arteries and large lumen of veins

Higher pressure of the arteries and lower pressure of the veins allow constant flow of blood through the capillaries

Endothelium partially permeable

Enables certain substances to diffuse quickly through the capillary walls

Capillaries branch repeatedly

Increases cross sectional area, lowers blood pressure, slows flow of blood, increases time for exchange of substances

(e) describe the transfer of materials between capillaries and tissue fluid Key question

Exam response

How is tissue fluid is formed?

High pressure at the arterial end of capillaries force out diluted blood plasma and white blood cells, giving rise to tissue fluid

Which substances are transported from the capillaries?

Dissolved food substances and oxygen are transported from the blood in blood capillaries, into the tissue fluid, then to the tissue cells

Which substances are transported into the capillaries?

Excretory waste products diffuse from the tissue cells into the tissue fluid, then to the blood, to be transported to excretory waste organs

Diagram

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syllacon.weebly.com (f) describe the structure and function of the heart in terms of muscular contraction and the working of valves Structure

Function

Median septum

Divides the heart to the left side and the right side, separating both sides so that blood flows in only one direction as oxygenated and deoxygenated blood do not mix together

Chamber valves

Tricuspid, bicuspid and semi lunar valves prevent the blood from flowing backwards, ensuring that blood flows in only one direction

Chordae tendineae

Attached to the wall of ventricles to prevent the flaps of the valves from inverting during ventricular contraction

Ventricles thicker muscular walls than atria

Ventricles would be able to pump blood a longer distance to ease the pumping of blood out of the heart (since blood leaves the heart via the ventricles)

Left ventricle thicker muscular walls than right ventricle

Right ventricle able to pump blood at a lower pressure along a small distance, ensuring that the slow rate of blood flow allows sufficient time for gaseous exchange at the lungs (unlike left ventricle that pumps blood around the body)

Diagram

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syllacon.weebly.com (g) outline the cardiac cycle in terms of what happens during systole and diastole. (Histology of the heart muscle, names of nerves and transmitter substances are not required) Happenings

Atrial Systole

Ventricular Systole

Ventricular Diastole

Atria

Contract [1]

Relax

Relax

Ventricles

Relax

Contract

Relax [3]

Blood Flow

From atria to ventricles

From ventricles to aorta and pulmonary artery

From vena cava and pulmonary veins to atria

Pressure

Ventricular pressure increases

Pressure in ventricle higher than aorta

Ventricular pressure decreases

Tricuspids and Bicuspids

Open

Close (―lub‖ produced)

Open [4]

Semi-Lunar Valves

Closed

Forced open [2]

Close (―dub‖ produced)

Diagram

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syllacon.weebly.com (h) describe coronary heart disease in terms of the occlusion of coronary arteries and list the possible causes, such as diet, stress and smoking, stating the possible preventative measures Coronary arteries

Coronary heart disease (CHD)

Function

Significance

Coronary arteries lie on the outside of the heart and carry blood to muscles in the walls of the heart

Heart muscles must be supplied with oxygen and nutrients via blood in order to pump blood around the body

Causes of CHD

Explanation  Blocked or narrowed coronary arteries reduces blood supply to the walls of the heart greatly  This causes the supply of oxygen and nutrients to the muscles in the walls of the heart to be insufficient  Heart will not be able to pump blood around the body

Description of causes of CHD

Cholesterol metabolism

A diet rich in cholesterol and saturated animal fats causes fatty substances like cholesterol to be deposited on the inner surface of coronary arteries

Size of lumen

Narrowed lumen increases blood pressure from rough inner artery surfaces

Blood clots

Risk of blood clots being trapped in the coronary arteries via thrombosis

Insufficient supply of oxygen

Supply of blood and oxygen may be insufficient, resulting in insufficient energy released to heart muscles

Emotional stress and smoking increases the risk of atherosclerosis

Measures

Description of measures to prevent CHD

Proper diet

Use of polyunsaturated plant fats and dietary fibres will lower cholesterol level in blood

Proper stress management

Reduces risk of a heart attack as people with high stress levels tend to require more oxygen levels

Decrease or stop smoking

 Nicotine increases blood pressure and risk of blood clotting  Carbon monoxide increases risk of fatty deposits

Regular physical exercise

Strengthens the heart and maintains elasticity of arteriole walls, reducing high blood pressure


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8. Respiration in Humans Content • Human Gas Exchange • Aerobic Respiration • Anaerobic Respiration Learning Outcomes: Candidates should be able to: (a) identify on diagrams and name the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries Diagrams Larynx

Bronchiole

Alveoli

Trachea Bronchus Capillaries

Bronchioles

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syllacon.weebly.com (b) state the characteristics of, and describe the role of, the exchange surface of the alveoli in gaseous exchange Characteristics

Adaptation

Relation to role

Rich supply of blood capillaries

Ensures a constant concentration gradient of gas molecules

Helps the lungs ensure continuous uptake of oxygen for respiration in order to release energy...

Thin film of moisture on internal surface of alveoli

Allows oxygen to dissolve and diffuse into the alveoli easily

Large surface area of alveoli

Faster rate of diffusion of gases with high surface area to volume ratio

... by being specially adapted for rapid transfer of gases between the lungs and the blood capillaries

One cell thick wall of alveoli

Shorter distance for gas molecules to diffuse across it increases rate of diffusion and efficiency

Diagrams

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syllacon.weebly.com (c) describe the removal of carbon dioxide from the lungs, including the role of the carbonic anhydrase enzyme Relation Formation of carbon dioxide

Removal of carbon dioxide

Processes

Description

Inspiration

Oxygen is taken in through the nose and diffuses from the alveoli in lungs to blood capillaries heading to the heart

Oxygen leaves alveoli

After leaving the lungs and the heart, oxygen is distributed to tissue cells for respiration

Respiration

Glucose reacts with oxygen to produce carbon dioxide and water

Carbon dioxide leaves the capillaries of tissue cells

Acidification in red blood cell

Water and carbon dioxide react to form carbonic acid with the help of the enzyme carbonic anhydrase

Deassociation, entry to plasma

Carbonic acid is converted to hydrogen and carbonate ions (hydrogencarbonate ions) and leaves the red blood cell and enters blood plasma to be transported

Carbon dioxide enters alveoli

Hydrogencarbonate ions are converted back to carbonic acid then to water and carbon dioxide in red blood cells by carbonic anhydrase, thereafter diffusing out to plasma, then to alveoli

Expiration

Carbon dioxide is expelled when expiration occurs

(d) describe the role of cilia, diaphragm, ribs and intercostal muscles in breathing Part of lungs

Inspiration

Expiration

Diaphragm

Contracts and flattens

Relaxes and arches upwards

Intercostal muscles

Relax internal, contract external (RICE)

External relaxes, internal contracts (ERIC)

Ribs

Upwards and outwards

Downwards and inwards

Sternum

Up and forward

Moves down back to original position

Air pressure to force air in or out

Decreases in lungs, atmospheric pressure is higher

Increases in lungs, atmospheric pressure is lower

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syllacon.weebly.com (e) describe the effect of tobacco smoke and its major toxic components – nicotine, tar and carbon monoxide, on health Components of tobacco smoke

Characteristics

Effects on health

Nicotine

Blood clots more easily

Increases risk of blood clots in blood vessels that might potentially obstruct flow of blood through them

Tar

May induce cancer in the epithelium that paralyses cillia lining air passages

Air sacs are blocked, reducing efficiency of gas exchange

Damages lining of blood vessels

Increases risk of blood clots in blood vessels that might potentially obstruct flow of blood through them

Increases rate of fat deposition on inner arterial wall

Obstructions slow down blood flow, decreasing efficiency of rate of oxygen distribution and carbon dioxide removal, slowing glucose production

Combines more readily than oxygen to form carboxyhaemoglobin

Reduces oxygen transport efficiency of red blood cells as oxygen has to compete with carbon monoxide to bind with haemoglobin

Carbon monoxide

Dust particles trapped in mucus lining the airways cannot be removed

Effects of tobacco smoke on health

Explanation

Chronic Bronchitis due to excessive irritant particles within smoke

   

Emphysema due to persistent violent coughing of chronic brochitis

     

Epithelium lining the airways is inflamed Excessive mucus secreted by the epithelium Mucus lining airways cannot be removed Persistent coughing needed to clear airways and breathe, increasing the risk of lung infections and emphysema  Severe breathlessness as airways become blocked Severe breathlessness as airways become blocked Lungs are inflated with air Lungs lose elasticity Partition walls between air sacs break in violent coughing Surface area for gaseous exchange decreases More severe breathlessness

(f) define and state the equation, in words and symbols, for aerobic respiration in humans Equation for aerobic respiration Oxidation of food substances

to release a large amount of energy (CO2 + H2O as waste)

Glucose

Oxygen

Carbon dioxide

Water

Energy is released

C6H12O6

6 O2

6 CO2

6 H2O

Large amount of energy

(g) define and state the equation, in words only, for anaerobic respiration in humans Equation for anaerobic respiration Breakdown of food substances in the absence of oxygen Glucose

With the absence of oxygen

Less energy released than aerobic Lactic acid

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Little energy


syllacon.weebly.com (h) describe the effect of lactic acid in muscles during exercise Effect of lactic acid Anaerobic respiration During exercise  When the intensity of exercise is raised, muscular contractions become more vigorous  Aerobic respiration is unable to meet the higher energy demand, so anaerobic respiration also occurs  This causes lactic acid to build up slowly in muscles  Glucose  Lactic acid + Small amount of energy

 When lactic acid concentrations become high enough,  the high acidity causes muscular pains and fatigue,  increasing the need for the body to rest and recover through deep breathing

Right after exercise  Oxygen debt is paid off through deep breathing  Lactic acid is quickly oxidised to form carbon dioxide and water  Lactic acid + Oxygen  Carbon dioxide + Water  The oxidation of some of the lactic acid provides energy for the conversion of the remaining lactic acid to glucose


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9. Excretion in Humans Content • Structure and Function of Kidneys • Kidney Dialysis Learning Outcomes: Candidates should be able to: (a) define excretion and explain the importance of removing nitrogenous and other compounds from the body Term

Definition

Importance

Excretion

Process by which metabolic waste products and toxic materials are removed from the body of an organism

 Metabolic waste products and toxic materials can be poisonous and harmful if they accumulate in the body  If they cannot be converted to harmless substances, excretion is the only way to remove them

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syllacon.weebly.com (b) outline the function of kidney tubules with reference to ultra-filtration and selective reabsorption in the production of urine Processes Ultrafiltration

Selective reabsorption

Urine collection

Kidney portions Renal capsule leading to each tubule

Functions Glucose, mineral salts, amino acids, water and nitrogenous waste products is ultrafiltrated from the glomerulous to the renal capsule Afferent arteriole is wider than efferent arteriole

Creates a high hydrostatic blood pressure

Basement membrane covering the capillaries has small pores

Allows only some substances to pass through by being partially permeable

Proximal convoluted tubule

Some mineral salts, all glucose and all amino acids are reabsorbed into blood capillaries

Loop of Henle

Some water reabsorbed into blood capillaries

Distal convoluted tubule

Some water and some salts reabsorbed into blood capillaries

Collecting tubule

Some water reabsorbed into blood capillaries

Renal pelvis, ureter, urinary bladder, urethra

The remaining solution of excess water, excess salt and nitrogenous waste products (e.g. urea, uric acid and creatinine) form urine and is stored in urinary bladder

Diagram

(c) outline the role of anti-diuretic hormone (ADH) in the regulation of osmotic concentration Stimulus

Receptor

Effectors

Corrective mechanism

Water potential in blood plasma rises

Hypothalamus in the brain monitors and senses a rise in water potential

Pituitary gland

 Less anti-diuretic hormone (ADH) released from the pituitary gland into the bloodstream  Kidney tubules reabsorb less water into blood capillaries  Urine turns more dilute and increases in volume

Water potential in blood plasma falls

Hypothalamus in the brain monitors and senses a fall in water potential

Pituitary gland

 More anti-diuretic hormone (ADH) released from pituitary gland into bloodstream  Kidney tubules reabsorb more water into blood capillaries  Urine turns more concentrated and decreases in volume

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syllacon.weebly.com (d) outline the mechanism of dialysis in the case of kidney failure Mechanism

Outline

 Blood is drawn from the artery in patient‘s arm  It is then pumped into a tubing with partially permeable walls bathed in a specially controlled dialysis machine

Ensures that excretion is performed without much disturbance on the body‘s homeostatic system

 Small molecules like urea and other metabolic waste products diffuse in the fluid  Blood cells, platelets and big molecules remain in the tubing

Takes the place of the failed kidney to enable excretion to continue taking place

The filtered blood is then returned to a vein in the patient‘s arm

Ensures that there is no change in rate of flow of blood between the artery and vein

Diagrams

Adaptations

Functions

Same concentration of essential substances like mineral salts

Ensures that they do not diffuse out of the bloodstream, or that minerals can diffuse into the bloodsteam if it lacks minerals

Long, narrow and coiled

Increases surface area to volume ratio to speed up exchange

Does not contain any metabolic waste products, excess water and mineral salts

Concentration gradient allows these products to diffuse out of the tubing, and water potential of blood to be maintained

Direction of flow of dialysis fluid is opposite that of blood flow

Maintains concentration gradient to remove waste products


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10. Homeostasis Content • Principles of Homeostasis • Skin Learning Outcomes: Candidates should be able to: (a) define homeostasis as the maintenance of a constant internal environment Term

Definition

Homeostasis

The maintanence of a constant internal environment

Full definition  The maintanence of a constant internal environment  that occurs whenever a receptor detects a change in condition of the internal environment,  stimulates a self-regulatory corrective mechanism to bring about the reverse effect of the stimulus,  and receives a negative feedback when the condition is restored

(b) explain the basic principles of homeostasis in terms of stimulus resulting from a change in the internal environment, a corrective mechanism and a negative feedback Principles

Explanation

Stimulus

A change in the internal environment that is from the normal condition requires homeostasis to maintain it and bring the condition back to normal

Receptor

Organs or structures that can detect the stimulus to stimulate the effector

Corrective mechanism

Mechanism is stimulated to bring about the reverse effect of the stimulus, usually through regulatory fluids, to correct the condition until it is normal again

Negative feedback

After a system has brought about an opposite effect to changes in the system,  negative feedback is the process of restoring the system to its original state, undisturbed,  through nerve impulses to the receptor

(c) identify on a diagram of the skin: hairs, sweat glands, temperature receptors, blood vessels and fatty tissue Diagram of the skin

temperature receptor

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syllacon.weebly.com (d) describe the maintenance of a constant body temperature in humans in terms of insulation and the role of: temperature receptors in the skin, sweating, shivering, blood vessels near the skin surface and the co-ordinating role of the hypothalamus Maintanence

Parts

Final effect

Mechanism

Insulation

Fatty adipose tissue

Slows down heat production

 Found beneath the dermis to store fat  Slows the loss of heat through insulation

Temperature sensing

Temperature receptors and hypothalamus of the brain

Via receptors and effectors of homeostasis

 Senses temperature changes from surroundings  Sends nerve impulses to hypothalamus of the brain, which receives information to be activated  Sends nerve impulses to target organs

Ventilation

Lungs

Speeds up heat loss

 More carbon dioxide and water vapour is exhaled,  causing heat to be lost through these gases

Metabolic rate

Cells in general

Speeds up heat production

Increase in metabolic rate

Slows down heat production

Decrease in metabolic rate

Sweating

Sweat glands, duct and pores

Speeds up heat loss

Sweat containing latent heat of vapourisation  is produced by the sweat duct  and released from the sweat pores  will evaporate, thus removing heat

Shivering

Skeletal muscles

Speeds up heat production

Contracts spasmodically in a reflex action known as shivering to increase heat production

Blood vessels near the skin surface

Arterioles, capillaries and venules

Speeds up heat loss

 Arterioles vasodilate to allow more blood flow to capillaries,  transferring more heat by conduction and radiation to the skin surface then atmosphere,  bringing less heat back through the venules

Shunt vessels

Speeds up heat loss

 Shunt vessels constrict to allow less blood to be brought back to body parts through the venules  and more blood to flow to capillaries,  thus less heat is brought back to the body parts

Slows down heat loss

 Shunt vessels dilate to allow more blood to be brought back to body parts through the venules  and less blood to flow to capillaries,  thus more heat is brought back to the body parts


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11. Co-ordination and Response Content • Receptors – Eye • Nervous System – Neurones (Reflex Action) • Effectors – Endocrine Glands Learning Outcomes: Candidates should be able to: (a) state the relationship between receptors, the central nervous system and the effectors Part

Relationship in response

Receptors

Gathers information and converts it into electrical signals known as nerve impulses

Central nervous system

Nerve impulses are transmitted through nerves in the peripheral nervous system to the central nervous system of the brain and spinal cord to interpret the nerve impulses and is stimulated to take action

Effectors

Impulses are transmitted by nerve impulses to effectors to carry out intended actions

(b) describe the gross structure of the eye as seen in front view and in horizontal section Diagram choroid cornea fovea iris

suspensory ligaments

ciliary body retina

pupil optic nerve to brain

lens

sclera

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syllacon.weebly.com (c) state the principal functions of component parts of the eye in producing a focused image of near and distant objects on the retina #

Eye part for imagery

1

Retina

Light sensitive area

2

Blind spot

Insensitive area over optic nerve

3

Fovea

Light rays are sharply focused here

4

Optic nerve

Transmits nerve impulses

5

Choroid

Supplies oxygen and nutrients to the eye via blood vessels in it

#

Function

Eye part for accommodation

Far vision

Near vision

6

Ciliary muscles of ciliary body

Relaxes and pulls the suspensory ligaments

Contracts and relaxes pull on suspensory ligaments

7

Suspensory ligaments

Becomes taut and pulls the edge of lens

Slackens and relaxes

8

Lens

Pulled thin

Shrinks and thickens

#

Supporting eye parts

Function

9

Conjunctiva

 Covers the sclera  Secretes mucus for a moist eyeball

10

Sclera

 Shapes the eye  Protects the eye from mechanical injury

11

Cornea

Refracts light into eye

12

Aqueous humor

 Keeps eyeball firm  Refracts light into pupil

13

Iris

Controls intensity of light that enters

14

Pupil

Allows entry of light

15

Vitreous humor

 Keeps eyeball firm  Refracts light onto retina

16

Rectus muscle

Allows the eyeball to move

(d) describe the pupil reflex in response to bright and dim light Focus Light rays from the [nature of object] object are sharply focused on retina Eye parts

Receptors

Impulses

Photoreceptors are stimulated and sends nerve impulses to the brain Dim light

Bright light

Circular muscles of iris

Relaxes

Contracts

Radial muscles of iris

Contracts

Relaxes

Pupil

Dilates

Constricts

Amount of light entering eye

Higher

Lower

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Nerve impulses travel through the optic nerve to the brain for it to interpret the pulses and the person to see the object Answering instructions

Write what contracts first before writing what relaxes Then write the final result: Ensures that the right amount of light enters the eye


syllacon.weebly.com (e) state that the nervous system – brain, spinal cord and nerves, serves to co-ordinate and regulate bodily functions Parts

Roles in coordinating bodily functions

Brain

Consists of cranial nerves in which impulses are received from the receptor, pain is felt, and an intended action is made, passing this information to the effector by neurones in a cranial reflex

Spinal cord

Consists of spinal nerves in which impulses are brought to the brain through relay neurones in a cranial reflex for an action to be undertaken, or are carried from sensory to motor neurone by grey matter in a spinal reflex

Nerves

Allow impulses to be brought to the neurones in spinal cord and brain in a reflex action

(f) outline the functions of sensory neurones, relay neurones and motor neurones Diagram dorsal root ganglion

brain cell in grey matter of brain pin

skin

white matter of spinal cord

relay neurone receptor synapses sensory neurone

cell bodies motor neurone grey matter of spinal cord effector (muscle)

Neurones

Functions

Sensory

Transmits nerve impulses from the receptors to the central nervous system

Relay

Transmits nerve impulses from the sensory neurone  to the motor neurone  to the brain in a cranial reflex

Motor

Transmits the central nervous system to the effectors to produce a response

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syllacon.weebly.com (g) discuss the function of the brain and spinal cord in producing a co-ordinated response as a result of a specific stimulus in a reflex action Stimulus

Reflex

Receptors

Touching a hot object

Cranial reflex (for upper body parts)

 Heat on object  stimulates thermoreceptors in skin

Spinal cord Nerve impulses  are transmitted by a sensory neurone to the grey matter of spinal cord  and then cross a synapse to a relay neurone where they will  be transmitted to the brain  cross another synapse to a motor neurone, then to the biceps muscle effector

Tap on tendon below the knee cap

Spinal reflex (for lower body parts)

 Tap on knee tendon  stimulates stretch receptor

Nerve impulses are  transmitted by a sensory neurone to the grey matter of spinal cord  and then cross a synapse to the motor neurone, then to the knee muscle effector

Effects Person feels the sensation of pain

 Biceps muscle contracts  Hand withdraws  Knee muscle effector contracts  Leg jerk forwards

(h) define a hormone as a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then broken down by the liver Outline

Definition

Substance

Chemical substance...

Production

...produced by an endocrine gland...

Carrier

...carried by the blood...

Effect

...alters the activity of one or more specific target organs...

Destruction

...and is then destroyed by the liver

(i) explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the pancreas Meaning of endocrine gland

Reference to islets of Langerhans in the pancreas

Ductless glands of internal secretion that secretes hormones directly into the bloodstream...

Islets of Langerhans are cells in the pancreas that secrete insulin and glucagon when blood glucose levels are above normal levels and when they are below normal levels respectively

... to be distributed around the body through blood...

These hormones are transported by blood until they reach body parts they require their effects

... to alter the activity of one or more specific target organs

Insulin

Stimulates liver and muscle cells to convert glucose into glycogen for storage

Glucagon

Glycogen, fats, amino acids and lactic acid into glucose

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syllacon.weebly.com (j) state the role of the hormone adrenaline in boosting blood glucose levels and give examples of situations in which this may occur Role of the hormone adrenaline in boosting blood glucose levels

Examples of situations

 Speeds up the breakdown of glycogen and glucose in liver and muscles  Increases metabolic rate, releasing more energy in respiration  Increases rate of heartbeat, resulting in rise in blood pressure, thus oxygen and glucose are carried faster to muscles  Constricts arterioles in skin to cause paleness, resulting in more blood and hence more oxygen and glucose to be channeled to muscles

   

Fear Anger Anxiety Stress

(k) explain how the blood glucose concentration is regulated by insulin and glucagon as a homeostatic mechanism Receptor-effector

Target

Effects

Feedback

Islets of Langerhans of pancreas sense increase of glucose levels and secrete insulin

Liver and muscles

 Increases permeability of cell membranes to glucose (to increase the rate of glucose uptake by cells)  Stimulates liver and glucose (to convert excess glucose to glycogen for storage)  Increase oxidation of glucose during tissue respiration

Negative feedback to the receptor

Islets of Langerhans of pancreas sense decrease of glucose levels and secrete glucagon

Liver and muscles

Stimulates the conversion of glycogen, lactic acid, fats and amino acids to glucose

Negative feedback to the receptor

(l) describe the signs, such as an increased blood glucose level and glucose in urine, and the treatment of diabetes mellitus using insulin Diabetes mellitus Signs

Reasons

Treatment

Persistently high blood glucose levels

Kidney tubules reabsorb the maximum amounts of glucose it is able to reabsorb and cannot be stored and utilised by tissue cells

Presence of glucose in urine

Kidney tubules do not have sufficient time to reabsorb glucose during selective reabsorption, and hence excreted in urine

Healing of wounds is slow and difficult

 As there are no reserves of glycogen, the body is unable to assimilate glycogen and convert it to new protoplasm to heal wounds  Oxidises fats instead to produce energy and poisonous ketones that may cause further harm

Loses weight

Reserves of glycogen are at minimal levels

 Daily injection of insulin (supply sugary foods if too much insulin is used, there‘s too much exercise or too little food, otherwise a coma may result)  Constant, consistent regulation of exercising  Metformin tablets and insulin injections


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THEME III: CONTINUITY OF LIFE Overview The many aspects of form and function that we have examined in this syllabus can be viewed in the widest context as various adaptations aimed at ensuring reproductive success. Reproduction is vital for the survival of species across generations. In 1953, James Watson and Francis Crick developed the model for deoxyribonucleic acid (DNA), a chemical that had then recently been deduced to be the physical carrier of inheritance. In this section, we examine how genes interact to produce hereditary characteristics in the offspring. This section focuses on understanding the processes involved in the continuity of life and how genetic information is passed from one generation to the next. Extracted from BIOLOGY GCE ORDINARY LEVEL (2014) Syllabus Document

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12. Reproduction Content • Asexual Reproduction • Sexual Reproduction in Plants • Sexual Reproduction in Humans • Sexually Transmitted Diseases Learning Outcomes: Candidates should be able to: (a) define asexual reproduction as the process resulting in the production of genetically identical offspring from one parent Term Asexual reproduction

Definition

In other words

The process resulting in the production of genetically identical offspring from one parent with no fusion of gametes

Mitosis (2n to 2n×2)

(b) define sexual reproduction as the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring Term Sexual reproduction

Definition

In other words

The process resulting in the production of a zygote and genetically dissimilar offspring, involving the fusion of nuclei

1. Meiosis (2n to n×4) 2. Fertilisation (n×2 to 2n)

(c) identify and draw, using a hand lens if necessary, the sepals, petals, stamens and carpels of one, locally available, named, insect-pollinated, dicotyledonous flower, and examine the pollen grains under a microscope Typical diagram of a flower

Diagram of insect-pollinated Clitoria

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syllacon.weebly.com (d) state the functions of the sepals, petals, anthers and carpels Part

Functions

Sepal

Encloses and protects the other parts of the flower in the bud stage

Petal

 Attracts insects for pollination, brightly coloured  Provides a platform for insects to land on for insect pollination

Stamen

Carpel

Anther

Produces pollen grains and splits open to release them when mature

Filament

Holds the anther upright

Stigma

 Receives pollen grains from the anther from the surroundings  Secretes sugary fluid to stimulate pollen grains to germinate

Style

 Connects the stigma to the ovary for the male gamete to travel and meet the female gamete  Holds stigma in suitable position to trap pollen grains

Ovary

Encloses one or more ovules containing an ovum

(e) use a hand lens to identify and describe the stamens and stigmas of one, locally available, named, wind-pollinated flower, and examine the pollen grains under a microscope Typical diagram of a flower

Diagram of wind-pollinated Ischaemum muticum

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syllacon.weebly.com (f) outline the process of pollination and distinguish between self-pollination and crosspollination Term

Definition

Pollination

Transfer of pollen grains from the anther of a flower to the stigma of the same or different flower of the same species

Differences

Insect pollination     

Wind pollination

The heavy insect lands on standard petal Follows the nectar guide into flower Squeezes past anther to reach nectar Collects pollen on its body while entering Pollen is dusted onto stigma of the same flower by insect when it leaves, or another flower of the same species (when it enters that other flower to collect nectar again)

 Pendolous filaments hang out of the bracts to expose mature anthers to the wind  Dust-like pollen is shaken free upon swaying of filament in wind  High surface area feathery stigmas that project out then receives the pollen floating in the wind

Self-pollination

Cross-pollination

Definition

Pollen transferred to stigma of same flower or different flower in same plant

Pollen transferred to stigma of a flower in another plant of the same species

Parent plant

Only one is required

Two is required

Probabilty and location

 Stigma situated directly below the anthers  More likely to occur

 Stigma situated some distance away from anthers  Less likely to occur

External factors

Independent from external factors

Dependent on external factors

Wastage

Less pollen and energy is wasted

More pollen and energy is wasted

Qualities

Beneficial qualities are more likely to be passed down to the offspring

Beneficial qualities may be inherited from both parents

Variation

 Offspring‘s genes are similar to parent‘s  Less varieties  Lower adaptability

 Greater genetic variation  More varieties produced  Higher chance of surviving changes in environment

Survival

Offspring may be weaker, smaller and less resistant to diseases

Viable seeds which are capable of surviving longer before germination are produced

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syllacon.weebly.com (g) compare, using fresh specimens, an insect-pollinated and a wind-pollinated flower Differences

By insects

Reason

By wind

Reason

Nectar

Present

Food to attract insects

Absent

To prevent insect pollination

Nectar guides

Present

Guide the insects towards the nectar

Absent


Petals

Present

Large, brightly coloured

Absent

Flowers are small, dull coloured

Pollen

Fairly abundant, large, rough, usually hairy

To cling onto insect bodies easily

More abundant, smooth, tiny and light

More easily blown about by wind

Stigma

Small and compact

To prevent wind pollination

Large and feathery, protrudes out

Large surface area to trap pollen

Stamen

Non-pendulous

To prevent wind pollination

Pendulous filaments, long protruding anthers

Easily shaken out from anthers

Scent

Fragrant or sweetsmelling

Attracts insects

No scent


(h) describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (Production of endosperm and details of development are not required) #

Acroynm

Stages

Description

1

S

Sugary fluid

Mature stigma secretes sugary fluid

 Pollen grains germinate  Pollen tube grows out from each grain

2

E

Enzymes

Pollen tube secretes enzymes

 Surrounding tissues of stigma and style are digested  Tube penetrates through the style

3

M

Micropyle

Pollen tube enters the micropyle

 Generative nucleus divides, forms two male gametes  Pollen tube nucleus disintegrates

4

F

Fertilisation

Tip of pollen tube absorbs sap

 Bursts to release male gametes  One male gamete fuses with ovum to form zygote

5

E

Embryo

Zygote divides

Develops into embryo formed in the seed

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syllacon.weebly.com (i) identify on diagrams of the male reproductive system and give the functions of: testes, scrotum, sperm ducts, prostate gland, urethra and penis Diagrams of male reproductive system

#

Part

Functions

1

Testis

Produces sperms and male sex hormones like testosterone

2

Scrotum

 Contains testes lying outside main body cavity  Provides sperms with a suitable temperature (slightly lower than body temperature) for proper development

3

Sperm duct

Conducts sperms from the testis to seminal vesicle to be stored temporarily before being released to urethra

4

Prostate gland

 Secretes a slippery alkaline fluid with Cowper‘s gland and seminal vesicle  It contains nutrients and enzymes to nourish sperms and allow sperm motility

5

Urethra

Conducts urine and semen out of the body separately, with sphincter muscle to prevent urine from coming out during ejaculation

6

Penis

Deposits semen into the female reproductive system through the vagina after blood fills the erectile tissue, turning it erect

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syllacon.weebly.com (j) identify on diagrams of the female reproductive system and give the functions of: ovaries, oviducts, uterus, cervix and vagina Diagrams of female reproductive system

#

Part

Functions

1

Ovary

 Produces ova and releases them when mature  Produces female sex hormones

2

Oviduct

 Conducts mature egg from the ovary into the uterus through funnel-like opening  Location from egg fertilisation

3

Uterus

 Provides a suitable environment for foetal development during pregnancy  Contains smooth muscles in the uterine wall which contract to expel the foetus during birth

4

Cervix

 Keeps the opening of the uterus closed to maintain pregnancy  Dilates during birth to allow the foetus to pass out of the uterus during birth

5

Vagina

 Allows flow of blood out of the uterus during menstruation  Receives semen during sexual intercourse  Allows passage of foetus out of the uterus during birth

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syllacon.weebly.com (k) briefly describe the menstrual cycle with reference to the alternation of menstruation and ovulation, the natural variation in its length, and the fertile and infertile phases of the cycle with reference to the effects of progesterone and estrogen only #

Stages of menstrual cycle

Description of stage

Duration

1

Menstruation

Uterine lining breaks down and flows from the uterus out of the body by menstrual flow through the vagina

Days 1 to 5

2

Repair and growth of uterine lining

Ovaries secrete oestrogen to ensure that the uterine is vascularised, thickened and well supplied with blood vessels

Days 6 to 13

3

Ovulation

Ova are produced during the fertile period

Day 14

4

Ovulation inhibited

Progesterone and oestrogen maintain the thickness of uterine lining and further supply blood vessels with blood capillaries

Days 15 to 28

Outcome of fertilisation

Egg

Hormones

Uterine lining

Nature of cycle Alternates between menstruation and ovulation

Role of placenta

Not successful

Egg breaks down

Progesterone is not secreted

 Uterine lining breaks down  Cycle repeats

Not applicable

Successful

Zygote develops into embryo

Secretion of progesterone and oestrogen sustained by ovary and then placenta later on

Embryo embeds itself in uterine lining

 Placenta develops from the embryonic villi (embedded in uterine lining)  Secretion of hormones by the ovary stops after placenta is able to start secreting them

Aspect of cycle Natural variation in its length

Average 28 days

Range

Remarks

Anomalies of 21 to 33 days

 May take up to 3 years for periods to be regular  Stress, tiredness, illnesses, and an unbalanced diet or malnutrition, may alter or stop the menstrual cycle

Aspect of cycle

Gamete

Lifespan

High presence in uterus

Fertile and infertile phases of the cycle

Sperms

2 to 3 days

Ejaculation starts on day 11

Uterine lining must have been repaired by then

Ova

1 to 2 days

Days 14 to 16

Ovulation must have occurred on day 14

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Conditions required


syllacon.weebly.com (l) describe fertilisation and early development of the zygote simply in terms of the formation of a ball of cells which becomes implanted in the wall of the uterus #

Acronym

Stages

Description

1

P

Penetration

Acrosome of sperm releases enzymes

Part of the egg membranes are broken down

2

F

Fertilisation

One sperm nucleus enters

 Nucleus fuses with egg to form a diploid zygote  Other sperms eventually die

3

I

Implantation

Cilia and peristaltic movements sweep zygote along oviduct

 Zygote divides by mitosis to form a ball of cells  Embryo reaches uterus after 5 days from fertilisation  Embeds in uterine lining after 2 days

4

P

Placenta

Villi with blood capillaries grow from embryo to uterine

 Placenta forms after villi grows fully  Embryo separates from placenta  Umbilical cord connects the embryo to placenta

5

F

Fetus develops

All major organs are formed, 10 to 12 weeks after fertilisation

(m) state the functions of the amniotic sac and the amniotic fluid Parts

Functions

Amniotic sac

Encloses the fetus in the amniotic cavity containing amniotic fluid

Amniotic fluid

Cushions

Supports and cushions fetus before birth

Shock

Absorbs shock if mother falls

Injury

Protects fetus against physical injury due to its incompressibility

Lubrication

Lubricates and reduces friction in the vagina or birth canal

Movement

Allows fetus to move freely during growth

(n) describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (Structural details are not required) Parts Placenta

Umbilical cord

Functions Oxygen and dissolved substances

Allows oxygen and dissolved substances to diffuse from the mother's blood into the fetus‘ blood

Excretory products

Allows excretory products such as urea and carbon dioxide to diffuse from the fetus‘ blood to mother‘s blood

Antibodies

Allows protective antibodies to diffuse from the mother‘s blood into the fetus' blood which protect the fetus against certain diseases

Progesterone

Produces progesterone which maintains the uterine lning in a healthy state during pregnancy

Carbon dioxide and metabolic waste products by arteries

Transport deoxygenated blood and metabolic waste products from the fetus to the placenta through 2 umbilical arteries

Oxygen and food substances by veins

Transport oxygenated blood and food substances from the placenta to the fetus through 1 umbilical vein

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syllacon.weebly.com (o) discuss the spread of human immunodeficiency virus (HIV) and methods by which it may be controlled Means of spread of HIV Sex

Methods of its control

In general

Sexual intercourse with an infected person

No sex

Keep to one sex partner or do not have sex

Condom

During sex, males should wear a condom to protect themself in case their partner has HIV

Sharing of hypodermic needles, if not sterilised properly, like acupuncture and ear piercing

Drug abuse

Do not abuse drugs, as drug addicts usually share needles and chances of getting HIV is higher

Dispose

Use sterilised or disposable needles always

Blood transfusion

Blood transfusion from an infected person

Contamination

Do not share instruments that can break the skin and may be contaminated with blood

Pregnancy

Infected mothers may transfer the virus to fetus through umbilical cord

N.A.

N.A.

Hypodermic needles

 Transmission can only be through bodily fluids and when infected blood contaminates the new victim's blood  Transmission will not occur by surface level contact or flow as it does not enter the skin


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13. Cell Division Content • Mitosis • Meiosis Learning Outcomes: Candidates should be able to: (a) state the importance of mitosis in growth, repair and asexual reproduction #

Importance

Description of importance of mitosis

Examples

1

Growth

Mitosis allows for the growth and development of a multicellular organism

Development of a fertilised egg into an adult human being

2

Repair

Mitosis allows for the repair or replacement of worn-out parts of the body

 Sealing up of wounds from injuries  Replacement of dead and worn-out cheek cells may be shed during teeth brushing and mouth rinsing

3

Asexual reproduction

Mitosis is also the basis for asexual reproduction

Enable shoots and roots to develop in storage organs (e.g. bulbs)

(b) explain the need for the production of genetically identical cells and fine control of replication #

Reasons for production of genetically identical cells

1

Growth

Mitosis allows for the growth and development of a multicellular organism

2

Repair

Mitosis allows for the repair or replacement of worn-out parts of the body

3

Asexual reproduction

Mitosis is also the basis for asexual reproduction

#

Reasons for fine control of DNA replication

Description of reasons

Related mechanism in control of DNA replication

1

Ensures that cells produced are genetically identical

Chromosomes of parent nucleus are already duplicated before mitosis begins

2

Ensures that 2 sets of identical genetic material is present before cell division

Arrangement of chromosomes at the equator during metaphase ensures that chromosomes are shared equally between the 2 daughter cells

3

Prevents abnormal development of the embryo

 If there are errors in DNA replication, they will be transmitted to the daughter cells  May lead to harmful changes to genes and affect how the cells function  Embryo may not develop normally

4

Prevents cancer

If there are errors in DNA replication, this may cause cells to lose the ability to control the way they divide and their normal functions

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syllacon.weebly.com (c) identify, with the aid of diagrams, the main stages of mitosis (e) identify, with the aid of diagrams, the main stages of meiosis #

Stage

1

I

Interphase

2

P

Prophase

Mitosis

Meiosis I

Meiosis II

centriole microtubules (spindle fibres)

a pair of homologous chromosomes

centromere nuclear envelope

3

M

equator

Metaphase

pole

4

A

Anaphase

5

T

Telophase

separated chromosome

nuclear membranes

chromosome uncoiling

nuclear membranes

nuclear membrane reforms

6

C

Cytokinesis

Differences

Mitosis

Meiosis

Definition

Cell division by which one single diploid parent result in the production of two daughter cells

Cell division by which one single parent diploid cell divides to produce four haploid cells

Daughter cells

All are identical the original parent cell

Gametes with half the diploid chromosomes in parent and may contain variations from parent cell

Pairing

Pairing of homologous chromosomes do not occur

Homologous chromosomes pair up at Prophase I

Crossing over

Does not occur

May occur

Divisions

One nuclear division

Two nuclear divisions for a reduction division

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syllacon.weebly.com (d) state what is meant by homologous pairs of chromosomes Meaning Term Properties Homologous pairs of chromosomes

Two chromosomes that pair along their whole length during synapsis

Similarities Same shape, genes and length with genes found on the same loci

Differences Alleles of each trait may not be the same

(f) define the terms haploid and diploid, and explain the need for a reduction division process prior to fertilisation in sexual reproduction Term

Definition

Diploid

The number of chromosomes present in a normal body cell of a species of an organism

Haploid

The number of chromosomes present in a gamete of a species of organism, containing half the number of chromosomes as the normal body cell

Reduction division

 The process by which one diploid parent nucleus divides to form four haploid daughter nuclei, where each daughter nucleus contains half the number of chromosomes as the original nucleus in the parent cell  (This is because of the separation of homologous chromosomes during Anaphase I)

Fertilisation

The process by which gametes fuse to produce a zygote which restores the diploid number of chromosomes

Need for reduction divison prior to fertilisation  A reduction division prevents doubling of the number of chromosomes in each successive generation  The number of chromosomes after each successive generation will thus remain diploid

(g) state how meiosis and fertilisation can lead to variation Processes Meiosis

Explanation

Crossing over

 Two non-sister chromatids of homologous chromosomes may cross and twist around each other at a chiasma  Coiling causes exchange of chromatids or crossing over  New combinations of genes along chromosome are produced

Independent assortment

 Four chromosomes randomly pair up with one other  Two assorted pairs of chromosomes form, each in every pair face opposite poles of the cell  New combinations of genes are produced after meiosis I

Fertilisation

 Fertilisation involves the fusion of a male gamete and female gamete  These gametes have been produced by meiosis which crossing over may have occurred  As new combinations of genes are produced, the new organism may vary from parents


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14. Molecular Genetics Content • The Structure of DNA • The Role of DNA in Protein Synthesis • Genes • Genetic Engineering and Medical Biotechnology Learning Outcomes: Candidates should be able to: (a) outline the relationship between DNA, genes and chromosomes Structure

Description

Diagram

Gene

A gene is a sequence of nucleotides containing genetic information used to make proteins

DNA

 DNA (deoxyribonucleic acid) consists of two parallel strands of nucleotides twisted around each other in a double helix  Each strand of DNA is made up of many genes

Chromosome

A chromosome is made of condensed chromatin threads, which consists of DNA wrapped with proteins

(b) state the structure of DNA in terms of the bases, sugar and phosphate groups found in each of their nucleotides Components of a nucleotide

Description

Polynucleotide formation

Nitrogenous base

Adenine or Cytosine or Guanine or Thymine

Deoxyribose sugar

Form the sugar-phosphate backbone in a polynucleotide

Phosphate group

Nucleotides can be joined together to form polynucleotides

Diagrams Nucleotide

Polynucleotide (section)

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syllacon.weebly.com (c) state the rule of complementary base pairing Rule

Description of the rule to form pairs of bases

TA rule

Thymine always hydrogen bonds with adenine to form complementary bases

CG rule

Cytosine always hydrogen bonds with guanine to form complementary bases

(d) state that DNA is used to carry the genetic code, which is used to synthesise specific polypeptides (details of transcription and translation are not required) Molecules involved in protein synthesis

Role

DNA

DNA carries a gene that occupies a locus along a chromosome

Gene

 A gene carries a genetic code that is used to synthesise specific polypeptides  It controls exactly how a particular protein is made in the cell through transcription and translation

RNA

 RNA (ribonucleic acid) is a temporary molecule to transfer information from DNA to molecules directly involved in protein synthesis  It contains uracil instead of thymine, which also bonds with adenine only

(e) state that each gene is a sequence of nucleotides, as part of a DNA molecule Term

Description

Gene

 Each gene is a sequence of nucleotides as part of a DNA molecule  The sequence of nucleotides stores a message that determines how a protein should be made

(f) explain that genes may be transferred between cells. Reference should be made to the transfer of genes between organisms of the same or different species – transgenic plants or animals Term

Definiton

Genetic engineering

Technique used to transfer genes from one organism to another

Examples of transfer

Method Genes are extracted (‗cut off‘) from the cells of one organism and inserted into the cells of another organism

Between different species

Between same species

Gene transferred

Soil fungus Myrothecium verrucaria

Healthy gene

Desired function of gene

To produce cyanamide hydratase enzyme that converts cyanamide to urea, a harmless source of nitrogen

To replace genes of lung disease cystic fibrosis when excessive mucus produced blocks the respiratory system, causing breathlessness

Product

This process produces transgenic plants since it is between different species

This process of gene therapy does not produce transgenic animals since it is between the same species

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syllacon.weebly.com (g) briefly explain how a gene that controls the production of human insulin can be inserted into bacterial DNA to produce human insulin in medical biotechnology #

Steps

Procedures

Key molecules

1

Isolate the desirable human gene

Restriction enzyme cuts out the gene for producing human insulin at 2 specific points from the insulin DNA, forming a single strand sequence of bases on each side of the gene

Restriction enzyme

2

Plasmid preparation

Same restriction enzyme cuts open the plasmid DNA (vector from a bacterial cell), forming a single strand sequence of bases complementary to bases on the sides of insulin DNA

Restriction enzyme

3

Join desirable gene to the plasmid

DNA ligase joins the cut ends of the plasmid DNA and insulin DNA by complementary base pairing of both ends to form the plasmid containing the human insulin gene

DNA ligase

4

Insertion of gene into E.coli bacteria

Mix the plasmid with E.coli bacteria and heat shock is carried out temporarily

Electric shock

5

Plasmid multiplication

Transgenic bacteria makes copies of the plasmid when they reproduce when dividing

Division

(h) discuss the social and ethical implications of genetic engineering, with reference to a named example Prior knowledge of named example Example

Bt corn (a plant)

Synthesis

Bt gene from Bacillus thuringiensis bacteria is inserted into corn

Significance

 Bt gene produces a protein that is lethal to pests of the corn, but not lethal to humans and other vetebrates  This reduces agricultural loss due to pests attacks

Knowledge required to respond to question Social implications

Threatens the safety of the environment  Genetically modified crops may be carried by wind to other places and grow quickly, potentially establishing themselves as weeds  Pollen grains from these plants may also fertilise wild relatives to form superweeds and compete with the natural species

Ethical implications

 Making a staple crop more resistant under marginal conditions may be a potential boon for Third World agriculture as richer countries benefit at the expense of poorer countries  World food production may also be dominated by a small number of large companies with the technical know-how in the long run, leading to rising income inequality


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15. Inheritance Content • The Passage of Information from Parent to Offspring • The Nature of Genes and Alleles, and their Role in Determining the Phenotype • Monohybrid Crosses • Variation • Natural and Artificial Selection Learning Outcomes: Candidates should be able to: (a) define a gene as a unit of inheritance and distinguish clearly between the terms gene and allele Terms

Definitions

Gene

[Inheritance, for this chapter] A unit of inheritance and a section of a DNA that codes a particular trait

Allele

Alternative forms of the same gene

Examples  Height of pea plants  Colour of flowers

[Molecular Genetics] A sequence of nucleotides as part of a DNA molecule

Tall/short, Purple/white

(b) explain the terms dominant, recessive, codominant, homozygous, heterozygous, phenotype and genotype Terms

Definitions

Examples

Phenotype

Visible characteristics of an organism

Black fur on rabbits is a phenotype represented by BB and Bb genotypes

Genotype

Genetic makeup of an organism to determine phenotype

BB, Bb, bb are genotypes that determine the phenotype of either black fur or white fur

Homozygous

Two copies of an allele controlling an organism‘s trait are similar

 BB (Homozygous dominant)  bb (Homozygous recessive)

Heterozygous

Two alleles controlling an organism‘s trait are different

Bb (Heterozygous)

Dominant

Allele which gives same phenotype in both homozygous and heterozygous conditions

 B is the dominant allele (capital letter)  BB and Bb represent the same phenotype

Recessive

Allele which expresses itself only in the homozygous condition and does not express itself in the heterozygous condition

 b is the recessive allele (small letter)  bb shows a different phenotype from BB and Bb

Codominance

Condition in which both alleles exert equal effects in the offspring‘s trait

When I is codominant B to I , Blood Group AB is the phenotype

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A

If RR shows red and rr shows white, then Rr represents pink


syllacon.weebly.com (c) predict the results of simple crosses with expected ratios of 3:1 and 1:1, using the terms homozygous, heterozygous, F1 generation and F2 generation Punnett square (gametes bolded) Offspring phenotypic ratio

B B B BB BB B BB BB 1

B b B BB Bb B BB Bb

B b B BB Bb b Bb bb

B b b Bb bb b Bb bb

 1  1:1 (if codominant)

 1:3  1:2:1 (if codominant)

1:1

b b b bb bb b bb bb 1

F1 and F2 generation  The F1 generation of 2 parents are the offsprings of the parents  The F2 generation of 2 parents are the offsprings of the F1 generation above

(d) explain why observed ratios often differ from expected ratios, especially when there are small numbers of progeny Explanation to learning outcome     

Observed ratios often differ from expected ratios as expected ratios are based mainly on chance and probability This is especially when there are small numbers of progeny (offspring) when the actual number of progeny would be more unlikely to match the expected number precisely as chances of the offspring to match its expected characteristic is lower than expected

(e) use genetic diagrams to solve problems involving monohybrid inheritance. (Genetic diagrams involving autosomal linkage or epistasis are not required) Example of genetic diagram (must be based on question asked) Organism

Pink flower

Parental Phenotype

Pink colour

X

Pink colour

Parental Gentoype

Aa

X

Aa

A

Gametes (must be circled)

Pink flower

a

A

a

Offspring Genotype (from punnett square)

AA

Aa

Aa

aa

Offspring Phenotype

Purple colour

Pink colour

Pink colour

White colour

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syllacon.weebly.com (f) explain co-dominance and multiple alleles with reference to the inheritance of the ABO blood group phenotypes – A, B, AB, O, gene alleles IA, IB and IO Phenotype

Genotype

Blood Group A

A A

A O

B B

B O

Allele relationship

I I or I I

Blood Group B

I I or I I

Blood Group AB

I I

Blood Group O

I I

A

O

B

O

I dominant over I

I dominant over I

A B

I is codominant to I

A

O O

Nil

B

Exam response  Explain all sides, e.g. if asked to determine that an allele is dominant,  explain why being dominant would cause the result and  why the result will be different if the allele is recessive

(g) describe the determination of sex in humans – XX and XY chromosomes Chromosome number in humans  Each cell in humans has 23 pairs of chromosomes  It consists of 22 pairs of autosomes and 1 pair of sex chromosomes

Phenotype

Genotype (in sex chromosomes)

Allele relationship

Male

XY

Y dominant over X

Female

XX

(h) describe mutation as a change in the structure of a gene, such as in sickle cell anaemia, or in the chromosome number, such as the 47 chromosomes in the condition known as Down syndrome Mutation

Example of Gene mutation

Example of Chromosome mutation

Example

Sickle cell anaemia

Down Syndrome

Details

Inherited disease

Happens by chance

How it happens

 Someone with sickle cell anaemia produces haemoglobin S instead of haemoglobin A  It is a homozygous recessive disease, aa

 Mutation causes one gamete from either the male or female to have 2 copies of chromosome 21  When it fuses with the normal gamete of the other sex, the zygote will have 3 copies of chromosome 21, resulting in 47 chromosomes instead of the normal 46

Effects

 Stiff and sticky to form clumps in blood vessels which may obstruct blood flow  Lead to serious infections  Organ damage

 Low resistance to disease  Mental retardation  Stunted growth

Special cases

Heterozygous humans, Aa, without the disease:  May pass on to the next generation  Can survive better in a malaria prone area

Older mothers have a higher chance of giving birth to a child with the disease than younger ones

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syllacon.weebly.com (i) name radiation and chemicals as factors which may increase the rate of mutation Mutation catalysts

Examples

Radiation

UV light, Gamma radiation

Chemicals

Mustard gas, Formadehyde, Ferrous and manganous salts

(j) describe the difference between continuous and discontinuous variation and give examples of each Term

Definition

Variation

Differences in traits between individuals of the same species

Differences

Continuous variation

Discontinuous variation

Intermediate characteristics

Yes

No

Distinct phenotype

No

Yes (to the extremes)

Genes

Yes

Yes

Environment

Yes

No

Number of genes

Controlled by a few genes

Controlled by a single gene usually

Additive effect of genes

Yes

No

Causes of variation

(k) state that competition which arises from variation leads to differential survival of, and reproduction by, those organisms best fitted to the environment Term Natural selection

Mechanism  Variation in a population means that some organisms are more well fitted to the environment,  which may result in competition  This leads to those organisms best fitted to the environment to survive better (i.e. differential survival)  which allows more of these organisms to reproduce than those less fitted (i.e. differential reproduction)

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syllacon.weebly.com (l) give examples of environmental factors that act as forces of natural selection Explanation

Predation example

Droughts example

Organism

Rabbits

Finches

Situation

Mutation took place and produced varieties of traits like coat colour and size of rabbit variety

There was a natural variation in the sizes of the beaks of the finches on the Galápagos island Plants on the island produce either big, hard and dry seeds from trees or small, soft and moist seeds from vines and creepers

Change in environment

When a predator species start to thrive, rabbits of different varieties start move away from their dangerous habitat at risk of predation in search of other suitable habitats

When a drought occured for a period of a few years, many vines died due to lack of moisture and supply of small and moist seeds decreased sharply, causing relatively more seeds from trees to be available

Type(s) at selective advantage

Type with light colour of fur coat and is bigger sized moved to an open plain and to escape predation

Finches with bigger beaks survived the drought better as they were able to crack the harder seeds better and therefore better able to source for food

Appearance

Adaptation

Light colour

Camouflages well

Long hind legs

Escape from predators

Long ears

Detect predators

Upright position

See further to source food

Type with dark fur colour and is smaller sized moved to a dense forest and to escape predation Appearance

Adaptation

Dark colour

Camouflages well

Small size and able to crouch

Less detectable as they are able to hide among logs

Type(s) at disadvantage

The type of rabbit with an appearance that makes it easy to spot by predators or rabbits that travel to a habitat that does not favour escape from predation

Finches with smaller, weaker beaks died off during the drought as supply of soft seeds dropped sharply, food was not readily available

One-sided survival

Light coated, bigger sized rabbits in open plains and dark coated, smaller sized rabbits in dense forests had the selective advantage and more of them survived predation to adulthood

Finches with bigger beak size had the selective advantage and more of them survived to adulthood

Time passes

These rabbits reproduced and started to have offsprings at a faster rate than other species

These finches reproduced and started to have offspring at a collectively faster rate than other species

Domination

The big light coated rabbits and small dark coated rabbits dominated the population of their repective habitats in the next generation

Finches with bigger beaks dominated the population in the next generation

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syllacon.weebly.com (m) explain the role of natural selection as a possible mechanism for evolution Term

Definition

Natural selection

Mechanism that brings about adaptation to the environment and evolution

Link to evolution  Different variants are selected for or against by different environment factors that act as selective pressures  Organisms with favourable traits that are genetically determined will survive better and reproduce  Offspring will inherit their traits over time, increasing the frequency of alleles for favourable traits and decreasing the frequency of alleles for nonfavourable traits

(n) give examples of artificial selection such as in the production of economically important plants and animals Production

Procedure

Improving plants by hybridisation

 To cultivate a variety of wheat that has two main desirable traits, two parents each with one of the two traits is crossed  Some new hybrids will have preferred combination of genes from both parents (desirable traits)  The hybrid is propagated by vegatative means to prevent any repeats of hybridisation for the next generations as offspring is not identical

Improving animals by inbreeding

 Similar process of hydrisation as above for new breeds of animals (e.g. cattle)  Mating carried out instead of crossing  Inbreeding maintains the improved breed by breeding among closely related individuals

Differences

Natural selection

Artificial selection

Definition

Nature selects for organisms with favourable genes and traits that help them survive unique habitats

Produced by selective breeding by humans

Varieties

Produced by mutations

Occurence

When natural environment conditions change

Importance

Possible mechanism for evolution, which is the process by which present forms of living organisms have arisen from simpler ancestral forms

When humans select organism varieties to suit their needs, producing more diversity


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THEME IV: MAN AND HIS ENVIRONMENT Overview All living organisms are part of a complex network of interactions called the web of life. This section focuses on the interrelationships among living things. These include two major processes. The first is the cycling of nutrients, as illustrated by the carbon cycle. The second major process is the flow of energy from sunlight to organisms further down the food chain. Human activities can upset natural ecosystems, causing permanent damage not just to local environments but also the global environment. As a part of this environment, humans must show a sense of responsibility for its maintenance. Extracted from BIOLOGY GCE ORDINARY LEVEL (2014) Syllabus Document

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16. Organisms and their Environment Content • Energy Flow • Food Chains and Webs • Carbon Cycle • Effects of Man on the Ecosystem • Environmental Biotechnology • Conservation Learning Outcomes: Candidates should be able to: (a) briefly describe the non-cyclical nature of energy flow Non-cylical

Heat energy

Supply

Respiration

Excretion, egestion

Light energy

Energy does not flow in a cycle

Heat energy cannot be recycled nor used to do work

Energy needs to be constantly supplied to the ecosystem

Carbon dioxide is produced for photosynthesis

Carbon dioxide is produced when these waste products are decomposed

Combines with chlorophyll to release chemical energy

(b) explain the terms producer, consumer and trophic level in the context of food chains and food webs Term

Explanation

Producer

Organisms that convert energy from the Sun into chemical energy and store it as food during photosynthesis

Consumer

Organisms that obtain energy by feeding on other organisms

Trophic level

Stage of a food chain (e.g. producers are always located at the first trophic level)

(c) explain how energy losses occur along food chains, and discuss the efficiency of energy transfer between trophic levels How energy is lost  Uneaten body parts  Faeces as waste products  Excretory products, undigested matter egested  Heat loss during respiration

Amount of energy lost  We usually assume 90% of energy is lost when energy is transferred to the next trophic level  10% is passed down

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Efficiency of energy transfer  Short food chains are more efficient in energy transfer  Less energy is lost to the environment along the food chain  More energy is available to the final consumer


syllacon.weebly.com (d) describe and interpret pyramids of numbers and biomass Term

Explanation

Pyramid of numbers

To compare the number of organisms present in each trophic level at a particular time

Pyramid of biomass

To compare the mass of organisms present in each trophic level at a particular time

Pyramid of numbers

Pyramid of biomass

 If organisms at the top

 If organisms at the bottom

 Organisms at the bottom

 are greater in numbers

 are smaller in numbers

 are always smaller in numbers

 compared to those in the previous trophic level

 compared to those in the next trophic level

 compared to those in the next trophic level

 they are likely parasitic

 they are likely to be a producer

 They also have higher rates of reproduction

 and hence small in size

 that is large in size (e.g. a tree)

Diagrams Pyramid of numbers

Pyramid of biomass

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syllacon.weebly.com (e) describe how carbon is cycled within an ecosystem Removal of carbon dioxide Photosynthesis

Plants absorb CO2 from air to manufacture carbohydrates

Carbon compounds

Glucose is converted to other C compounds like fats, amino acids and proteins

Animals

Animals feed on plants and C compounds enter their bodies

Fossil fuels

When organisms die, C compounds can be preserved in fossil fuels as coal, natural gas and oil

Release of carbon dioxide Respiration

When organisms respire, C compounds are broken down and carbon dioxide is released to the environment as a byproduct

Decay

The bodies of dead organisms decay and are broken down into simple substances by decomposers

Combustion

When fossil fuels undergo combustion, C compounds preserved are broken down and carbon dioxide is released to the environment

Diagram of carbon cycle

Inferences  Energy flow is non-cyclical  Carbon flow is cyclical

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syllacon.weebly.com (f) evaluate the effects of: • water pollution by sewage and by inorganic waste • pollution due to insecticides including bioaccumulation up food chains and impact on top carnivores Pollution form Insectides

Sewage

Inorganic waste

Description Poisonous chemicals used to kill insects

Waste matter from homes or industries

Waste matter with poisonous materials like lead, mercury

Effects

Result

Bioaccumulation

 Some insecticides (e.g. DDT) are insoluble in water, cannot be excreted and cannot be broken down, therefore have to be stored in fatty tissues of organisms  They accumulate in bodies of living organisms and pass along food chains, causing the consumers at the end of the food chain to contain high levels of insectides

Bioamplification (final impact on top carnivores)

These insectides end up in high concentrations in the bodies of the carnivores on the top of the food chain, and as they are in large amounts, they are poisonous and harmful to these organisms

Epidemic

Untreated sewage may cause bacteria to enter drinking water and affect humans with diseases like cholera

Eutrophication

Phosphate and nitrate nutrients promote growth of algae and water plants, blocking out sunlight for submerged ones and they die by lack of food from photosynthesis (elaborate in terms of plant nutrition)

Death of fish

 Phosphate and nitrate nutrients promote growth of bacteria  Bacteria use more oxygen, so competing organisms like fish die due to lack of oxygen for release of energy

Death, blinding and paralysis to humans when they eat fish that have consumed matter containing these metals through bioaccumulation

Differences between bioaccumulation and bioamplification Bioaccumulation

Bioamplification

Increase in amount (e.g. volume)

Increase in concentration

In an organism‘s body

Across a food chain

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syllacon.weebly.com (g) outline the roles of microbes in sewage disposal as an example of environmental biotechnology Molecules or tanks involved

Description

Type of microbes

Bacteria and fungus

Primary settling tank

 Used water is channelled from households to water reclamation plants  Heavy solids settle to the bottom and removed as sludge in settling plant

Partially treated sewage component Remaining used water

Sludge

Systems involved

Description

Aeration tank

 Liquid is drained and mixed with bacteria  Bacteria secrete enzymes to digest organic pollutants to harmless soluble substances and CO2

Final settling tank

 Microorganisms removed from treated water  Remaining liquid is discharged into sea

Anaerobic digesters

Sludge is treated with anaerobic digesters

Dewatering

Water is removed and disposed as soil conditioner

(h) discuss reasons for conservation of species with reference to the maintenance of biodiversity, management of fisheries and management of timber production Reasons

Description Drugs and insecticides

 Nearly 25% of medicinal drugs have originated from plant species of rainforests (e.g. Morphine is a pain-supressing drug from poppy plant)  Certain poisonous animals in rainforests may contain chemicals with medicinal value

Food provision

Rice, pineapple and banana are some examples of food plants developed from rainforest plants

Gene pool

Agricultural produce can be improved by cross breeding different plant varieties of wild plants and animals of favourable species

Fisheries

Prevent overfishing

While banning harvesting of endangered species and limiting fishing, fisheries (e.g. hatcheries) raise endangered species and release them into fishing grounds of dwindling fish population

Timber production

Industries

Tropical plants provide raw materials for industries (e.g. rattan used to make furniture, timber for cupboards)

Protection of wildlife

 Forests are a major source of oxygen as well as protection and shade for soil  Trees felled for timber have to be cut down at a regular and selective rate to ensure that the functions of forests are not lost

Biodiversity


-End-

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