1.1 Biological compounds contain a limited number of chemical elements. These are combined in small organic molecules which may be further linked to form very large molecules.

(a) The main elements found in living organisms. Some elements are needed in trace amounts (details not required).

Key elements are present as inorganic ions: Mg²⁺, Fe²⁺, K⁺, Na⁺, Ca²⁺, PO₄^3– , SO₄^2– , NO₃^– , Cl^– , HCO₃^– .

2.1

Figure 3 in spread 2.1 shows the main elements found in living organisms.

Trace elements and their importance in the human diet are considered in spread 9.8. See the index for references to individual elements.

The importance of water in terms of its polarity, ability to form hydrogen bonds, surface tension, as a solvent, thermal properties, as a metabolite.

2.3, 2.4

For importance of water as a metabolite, see condensation and hydrolysis (spread 2.6), and photolysis (spread 5.3).

(b) Structure properties and functions of carbohydrates: monosaccharides (triose, pentose, hexose sugars); disaccharides (sucrose, lactose, maltose); polysaccharides (starch, glycogen, cellulose). Alpha and beta structural isomerism in glucose resulting in storage and structural carbohydrates as illustrated by starch and cellulose. Chemical properties enabling the use of starch and glycogen as storage and cellulose as structural compounds.

2.6

2.7

Note that these spreads give an introduction to carbohydrates only. For more details of individual carbohydrates, see the index.

Particularly important figures are 1 and 2 on spread 2.6, and 2 and 5 on spread 2.7.

Structure, properties and functions of lipids as illustrated by triglycerides and phospholipids.

Lipids as an energy store.

Implications of saturated and unsaturated fat on human health.

2.8

See also spread 4.6 for role of phospholipids in cell membranes; spread 9.6 for energy content of lipids, spread 9.7 for role of lipids in a balanced diet; spread 16.8 (especially the box on lipoproteins) for implications of fat on human health.

Structure and role of amino acids and proteins. The peptide link.

Relation of molecular structure to function.

Primary, secondary, tertiary and quaternary structure of proteins.

Globular and fibrous proteins

2.9

2.10

Do not forget that enzymes (the main subject of chapter 3) are proteins.

Candidates should be able to use given structural formulae (proteins, triglycerides and carbohydrates) to show how bonds are formed and broken by condensation and hydrolysis, including peptide, glycosidic and ester bonds.

(Candidates should be able to recognise and understand but not reproduce the structural formulae of the above molecules).

 2.6 to 2.10

Important figures: spread 2.6, figures 1 and 2 (structural formulae of carbohydrates; condensation and hydrolysis; glycosidic bond); spread 2.8 figure 1 (structural formulae of triglyceride; ester bond); spread 2.9, figures 1 and 2 (structure of amino acid; peptide bond).

Practical Activities: Iodine-Potassium iodide test for starch; Benedict's test for reducing and non-reducing sugars; biuret test for protein.

App.

Brief descriptions of each test (how to carry out the test, expected results, and the basis of the test) are given in the Appendix.

1.2 The basis of biological organisation is the cell.

(a) The internal membranes of eukaryotic cells and their importance.

4.6

The structure of the following organelles: mitochondria; endoplasmic reticulum (rough and smooth); ribosomes; golgi body; lysosomes; centrioles; chloroplasts; vacuoles; nucleus; chromatin; nuclear envelope; nucleolus; plasmodesmata.

The function of these organelles.

4.3

4.4

See also spreads 6.4 (role of mitochondria in respiration); 18.7 and 18.8 (role of endoplasmic reticulum and ribosomes in protein synthesis); 4.11 (centrioles); 5.12 (role of chloroplasts in photosynthesis).

Structure of prokaryotic cells and viruses.

Comparison of the structure of animal, plant and prokaryote cells and viruses.

4.4

4.4 gives a brief introduction; more details about viruses are given in spread 17.1.

A fuller comparison of prokaryotes and eukaryotes is given in spread 21.2.

(b) Levels of organisation: aggregation of cells into tissues. Brief histology of: epitheluim, cuboidal and ciliated; muscle, smooth and striated; connective tissue, collagen. Aggregation of tissues into organs.

4.13

This spread discusses levels of organisation, but does not give a full description of individual tissue types. See index for references to individual tissue types.

Practical Activities: The use of the light microscope. Calibration of microscope using a stage micrometer and eye piece graticule. Use of the units mm and mm. Measurement using microscope. Calculation of the magnification of drawings. Examination of a range of living cells e.g. Spirogyra, onion epidermis, Elodea cells, potato tuber cells. Temporary preparations using simple materials e.g. iodine in potassium iodide, methylene blue, dilute glycerine.

Examination of slides showing: epithelia, muscle, collagen.

A study of a range of electron micrographs of prokaryote and eukaryote cells to show structure.

Advanced Biology does not cover practical work. However, theoretical aspects of light and electron microscopy are covered in spread 4.2; calibration of microscope using a stage micrometer and eye piece graticule is described in the Appendix.

Electron micrographs figure in several spreads, but see in particular spread 4.3 for electron micrographs of several organelles of eukaryotic cells.

1.3 Living cells take up nutrients and other requirements, secrete chemicals and communicate with each other. The boundary of the cell has unique properties which permit these diverse activities.

(a) The principal components of the plasma membrane and the fluid mosaic model. Factors affecting permeability of the membrane.

4.6

4.7

The general structure and function of the plasma membrane (= cell surface membrane) is covered, including the fluid mosaic model. Membrane permeability is included in spread 4.7, but it is also important to note that factors such as high temperature and detergents, which break down the plasma membrane, will increase its permeability to substances.

(b) Transport mechanisms: diffusion and factors affecting the rate of diffusion, osmosis and water potential, pinocytosis, facilitated diffusion, phagocytosis, secretion (exocytosis), active transport and influence of cyanide.

4.7

4.9

4.8

Note in particular Fick’s Law which summarises the relationship between surface area, concentration gradient, and length of diffusion path on rate of diffusion.

Practical activities: Determination of water potential by measuring changes in mass, and solute potential by measuring the degree of incipient plasmolysis.

Practical activities are not covered, but note that the water potential of a cell wall will be the same as the water potential of the external solution when there is no change in mass of the cell. The solute potential of a plant cell equals the water potential of the surrounding, external solution when the cell is at the point of incipient plasmolysis (the point at which the plasma membrane begins to lose contact with the cell wall; for practical purposes, incipient plasmolysis is assumed to occur when 50% of the cells are plasmolysed).

1.4 Most biological reactions are regulated by enzymes.

(a) Metabolism is a collection of enzyme controlled reactions.

The protein nature of enzymes. Enzymes may act intracellularly or extracellularly. (ref to 1.2, 1.6)

Active sites interpreted in terms of three dimensional structure, theory of induced fit as illustrated by lysozyme.

3.6

3.1

2.9, 2.10

3.2

Intracellular and extracellular enzymes defined in spread 3.6 – see also 17.1 (extracellular enzymes of fungi) and 18.4 (intracellular enzymes involved in protein synthesis).

The induced fit model is illustrated by hexokinase. Lysozyme, a bacteriocide found in tears (spread 10.11) has a similar mode of action. It catalyses the hydrolysis of peptidoglucan, a component of bacterial cell walls, causing the breakdown of the wall.

(b) The meaning of catalysis; the lowering of the activation energy. Influence of temperature, pH, substrate and enzyme concentration on rate of activity.

Inactivation and denaturation.

Functions of the following enzymes in the human alimentary canal: salivary amylase, rennin, pepsinogen/pepsin, trypsinogen/trypsin, enterokinase, lipase. Physiological significance of the effects of temperature, pH, activation, inactivation on digestive enzymes.

3.1, 3.2, 3.3

9.4

9.5

The term ‘catalysis’ is not referred to specifically, but as it is the chemical action brought about by catalysts, it is covered in spread 3.2.

(c) The principles of competitive and non competitive inhibition (references to reversible and irreversible action not required) as illustrated by succinic dehydrogenase and potassium cyanide.

End product inhibition.

3.4

Principles of inhibition covered, but not by reference to succinic hydrogenase (an enzyme which normally acts on succinate, but is competitively inhibited by malonate, a substance with similarly shaped molecules) or potassium cyanide (a non-competitive inhibitor of cytochrome oxidase – an enzyme involved in aerobic respiration – spread 6.4).

Practical Activities: Investigations into the effect of enzyme and substrate concentrations on enzyme activity. The importance of buffers for maintaining a constant pH.

Investigation into the immobilisation of enzymes e.g. pectinase.

Theoretical aspects of these practical activities are covered in spreads 3.3 and 3.6 (immobilised enzymes).

1.5 Medical and industrial applications of enzymes.

(a) Biosensors and their use giving rapid, accurate and sensitive diagnosis in medicine as illustrated by glucose oxidase testing of urine for diabetes.

3.7

Figure 3, spread 3.7 shows a plan of a typical biosensor.

(b) The importance of immobilised enzymes. Industrial processes utilise immobilised enzymes enmeshed in an inert solid support so allowing enzyme reuse and improving stability.

3.6

See in particular figure 2, spread 3.6.

1.6 The nature of the genetic code and how it determines the nature of organisms.

(a) Structure of nucleotides (pentose sugar, phosphate, organic base) as illustrated by ATP and as subunits of nucleic acids.

2.11

Structure of nucleic acids: DNA bases: purines-adenine and guanine, pyrimidines-cytosine and thymine, complementary base pair rule, hydrogen bonding and the double helix (triple and double bonding not required), antiparallel strands.

18.1

Comparison between the structure of RNA and DNA.

18.7

tRNA, mRNA and rRNA described, see figure 4 spread 18.7 for a description of tRNA.

(b) The two major functions of DNA: replication and protein synthesis. The semi-conservative replication of DNA catalysed by DNA polymerase.

Evidence from Meselson and Stahl experiment.

The genetic code. The triplet code for amino acids.

18.3

18.6

18.7

18.8

Figure 1, spread 18.3 shows semi-conservative replication.

18.6 describes the nature of the code which is given in full in the Appendix.

Protein synthesis includes transcription (spread 18.7) and translation (spread 18.8).

(c) The transcription of DNA to produce messenger RNA.

Translation by ribosomes and transfer RNA, which has an anticodon and a specific amino acid binding site, to synthesize proteins (other details of the structure of tRNA not required).

18.7

18.8

See figure 2, spread 18.7.

Figure 1, spread 18.8.

'One gene - one polypeptide' hypothesis.

Polypeptides may be further modified and combined.

18.5

(d) There is an international project sequencing the genetic code of human chromosomes.

Access

The potential uses, disease treatment, and abuses of this human genome project such as eugenics, false hopes of cure for disease, genes as a predictor of health.

19.6

The human genome project is described, but its potential uses are not discussed fully. Students are advised to use the website referred to in the specification.

A risk, difficulty and advantage of using gene therapy for the treatment of disease as illustrated by cystic fibrosis. Use of liposomes to insert the new DNA fragment.

19.10

See figure 2, spread 19.10 for a description of the use of liposomes.

Formation of recombinant DNA by insertion of foreign DNA into bacterial plasmids and cloning of the bacteria to produce useful molecules as illustrated by insulin.

The use of restriction endonuclease, DNA ligase, reverse transcriptase, antibiotic marker gene.

Advantages and disadvantages of genetic engineering.

Issues associated with genetically modified food crops such as tomatoes and soya.

18.9

18.10

Production of insulin by recombinant DNA technology shown in figure 1, spread 18.10.

Genetically modified organisms considered in spread 23.3 – see in particular ‘Food for thought’ for reference to soya beans genetically engineered to give herbicide resistance.

Genetic fingerprinting of an individual produces a unique pattern of bands of DNA.

Uses of this technique.

18.11

1.7 Genetic information is copied and passed on to daughter cells.

(a) Interphase (no subdivisions required). Significance of mitosis as a process in which daughter cells are provided with identical copies of genes. Main stages of mitosis. The importance of meiosis and fertilisation in sexual reproduction giving rise to variation. Main stages of meiosis (names of subdivisions of prophase 1 not required). Cytokinesis in animal cells.

4.10

4.11

4.12

Main stage of mitosis given in figures 1 and 2 spread 4.11.

Main stage of meiosis given in figure 1 and 2, spread 4.12.

(b) Advantages and disadvantages of sexual and asexual reproduction.

12.1

Practical activities: Observation of prepared slides of root tip for mitosis and developing anthers for meiosis.

Practical activities are not covered

2.1 All organisms need transport systems. This requirement increases with increasing size and complexity.

(a) Unicellular organisms. Diffusion. High surface to volume ratios.

(b) Multicellular organisms. Decreasing surface to volume ratio and division of labour in cells. Properties to aid uptake and supply of requirements.

Development of exchange surfaces and transport systems.

21.3

21.4

4.7

4.13

Spread 21.3 and 21.4 are devoted to protoctists, the group to which unicells belong. Spread 21.4 focuses on Amoeba and Euglena, two common unicells, and mentions their dependence on diffusion for exchange of materials. Surface area/volume relationships are dealt with in spread 4.7 and spread 4.13 (which also discuses multicellularity and specialisation).

2.2 Gas exchange is an essential feature of organisms.

(a) Species are adapted to survive in particular environmental conditions.

The influence of size and environmental conditions on the exchange of gases as illustrated by Amoeba, earthworm, bony fish.

21.4, 21.12

See figure 3, spread 21.12 which shows gaseous exchange in an earthworm.

The importance of counter current flow and ventilation movements in the bony fish.

21.17

The principles of counter current exchange are described in spread 8.7; 21.17 considers gaseous exchange in bony fish.

The structure and function of human breathing system to include: epiglottis, trachea, bronchi, bronchioles, alveoli, pleural membranes, ribs, intercostal muscles, diaphragm. Ventilation movements including role of intercostal muscles, diaphragm, pleural membranes and pleural cavity and exchange of gases in alveoli. Role of surfactant.

7.1

7.2

7.3

Figure 2, spread 7.1 shows the human respiratory system.

Figure 1, spread 7.2 shows the ventilation movements.

Figure 4 and the box in spread 7.3 deal with lung surfactants.

Principles of spirometry and lung capacities including interpretation of data (practical work not required).

7.3

Figure 2, spread 7.3 shows a spirometer.

Effects of pulmonary disorders on lung function as illustrated by asthma and emphysema.

16.2

16.6

Spread 16.6 also considers the effects of smoking on lung function.

(b) Structure of the angiosperm leaf to include: cutide, epidermis, palisade mesophyll, spongy mesophyll, vascular bundle, air space, stomata, guard cells. The role of these structures in allowing the plant to photosynthesise effectively.

13.1

13.7

Figure 1, spread 13.1 shows the structure of a typical dicotyledenous leaf; stomata are described in spread 13.7. See also Chapter 5 for the biochemistry of photosynthesis.

The leaf as an organ of gaseous exchange; intercellular spaces. Stomatal opening and closing. Xerophytes may open stomata at night.

5.6

Spread 5.6 discusses Crassulacean Acid Metabolism, which enables some xerophytes to open stomata at night and close them by day to conserve water.

Practical Activities: Examination of epidermal strips and/or replicas. T.S. dicotyledonous leaf Ligustrum (Privet). Examination of fish gill.

Practical activities are not covered

Transverse section of dicotyledonous leaf shown in figure 1, spread 18.1; figure 2, spread 21.7 shows the structure of a fish gill.

2.3 Substances are transported from and to exchange surfaces.

(a) Structure of root of dicotyledon. Absorption of water.

Movement through the root, apoplast and symplast, structure and role of endodermis. The structure of xylem. Movement of water from root to leaf.

Transpiration, cohesion-tension theory to describe the transpiration stream.

Environmental factors affecting transpiration. Xerophytic adaptations as illustrated by marram grass.

13.3, 13.4

13.5, 13.6

22.15

See also figure 2, spread 13.8 for role of endodermis.

See figure 1, spread 13.6 for apoplast and symplast route.

See figure 3, spread 13.5 for cohesion-tension theory.

Figure 2, spread 22.15 shows transverse section of marram grass.

Active uptake of mineral ions and their movement in the transpiration stream.

13.8

See also 4.8 for a discussion of active transport.

The structure of phloem as seen by light and electron microscope.

Translocation of organic materials from source to sink. Phloem transport: diffusion; cytoplasmic strands; mass flow models.

13.9

13.10

Structure of phloem as seen with light microscope and electron microscope described in 13.9 – no electron-micrographs.

Note that it has been suggested that cytoplasmic strands occur in the phloem which convey materials by cytoplasmic streaming (see box spread 13.10).

Practical Activities: Examination of T.S. dicotyledon primary stem and root.

T.S. and L.S. of primary xylem and phloem. T.S. marram grass leaf. The use of a simple potometer.

Computer modelling may be used to extend this investigation.

Practical activities are not covered

Figure 3, spread 13.2, shows T/S dicotyledonous stem; figure 2, spread 13.3 shows T/S of dicotyledonous root; xylem and phloem are shown in figures 2 and 3, spread 13.4.

See figure 2 spread 13.5 for potometer.

(b) The circulatory system in human. The names of the main blood vessels associated with the heart. Structure of heart, artery, vein and capillary in relation to functions. The cardiac cycle and the maintenance of circulation to include graphical analysis of pressure changes. Role of sinuatrial mode and Purkinje fibres.

7.4

7.5

7.6

7.7

In spread 7.4, figure 2 shows the structure of blood vessels; figure 3 shows the double circulatory system.

In spread 7.5, figure 1 shows the structure of the human heart.

In spread 7.6, figure 1 shows the cardiac cycle; figure 2 is a graph of pressure changes;

See spread 7.7 for a description of the role of the sinoatrial node and Purkinje fibres (= Purkyne fibres)

The function of red blood cells and plasma in relation to transport of respiratory gases, dissociation curves of haemoglobin of mammal (adult and foetus) and llama. Böhr effect and chloride shift. Transport of nutrients, hormones, excretory products and heat.

7.8

7.9

Böhr effect = Böhr shift.

See also spreads 8.10 and 8.11 for accounts of the role of the circulatory system in temperate regulation.

The formation of tissue fluid and its importance in exchange. Excess fluid drains into the lymphatic system. The effect of low blood proteins on capillary filtration resulting in oedema as illustrated by kwashiorkor.

7.11

Oedema is considered as a result of blockage of lymph vessels, but kwashiorkor (characterised by swollen abdomen due to accumulation of fluid resulting from lack of protein in the diet) is not.

Practical Activities: Examination of T.S. of artery and vein. Observation of erythrocytes and leucocytes in prepared blood smears.

Practical activities are not covered

Figure 1 spread 7.8 shows the components of blood; note leucocytes = leukocytes.

2.4 There is a continuous transfer of energy and materials between organisms.

(a) The concept of ecosystems. The sun is the source of energy for the ecosystem.

The concept of habitat and community. Transfer of energy from plants to animals. Trophic levels and the efficiency of energy transfer. Gross and net production.

22.2

22.3

22.4

Spread 22.2 gives a general introduction to ecosystems.

Spread 22.3 considers food chains, food webs and pyramids of numbers, biomass and energy.

Spread 22.4 considers efficiency of energy transfer, and gross and net production.

The differences between autotrophic and heterotrophic methods of nutrition.

Modes of heterotrophic nutrition: holozoic, herbivores, carnivores,

omnivores; detritivores; parasites and saprophytes. Pyramids of number, biomass and energy

9.1

22.2

22.3

Pyramid diagrams shown in figure 4, spread 22.3.

(b) Food chains and food webs. The importance of organic breakdown in recycling nutrients.

22.3

22.12

The nitrogen cycle with bacteria referred to as nitrifying, denitrifying and nitrogen fixing (species names not required). Significance of nitrates in proteins and nucleic acids.

The importance of ploughing and drainage in producing the aerobic conditions needed for nitrification.

22.12

See also 23.1 for the effects of soil management in nitrification, and 23.5 for effects of deforestation on the nitrogen cycle.

The carbon cycle.

22.13

Figure 2, spread 22.13 summarises the carbon cycle

Eutrophication and algal blooms.

23.7

In spread 23.7, eutrophication and algal blooms considered in relation to sewage.

Greenhouse effect and global warming.

23.6

Spread 23.6 covers the greenhouse effect and global warming in relation to air pollution.

2.5 The supply of nutrients is only one of the factors controlling population size.

(a) Populations and the way in which they grow - a simple quantitative treatment. Immigration, emigration, birth and death rates.

Graphs showing population growth.

Factors affecting population growth: weather, predation, parasitism, food supply, living space, competition, carrying capacity.

Distinguish between factors which slow growth and those which cause a population crash.

Regulation by density dependent and density independent factors.

22.6

22.7

Graphs showing population growth are given in 22.6 (figures 1, 2, and 3) and 22.7 (figures 1, 3, and 4). The sigmoid growth curve shows in figure 1, spread 22.6, is particularly important and students might be asked to describe and explain each of the phases.

(b) Principles of succession as illustrated by the change from bare rock to woodland.

Use of terms primary and secondary succession, pioneers, sere and climax community.

22.10

In spread 22.10, figure 2 shows succession from bare sand to woodland; figure 3 shows succession from a ploughed field to woodland – The ‘Fact of Life’ box gives an account of primary succession from bare volcanic rock to woodland on Surtsey Island.

2.6 Human activities can impose far reaching effects on the environment.

(a) Agricultural exploitation. Conflicts between production and conservation as illustrated by:

1. forests: reasons for forest destruction, consequences, managed forests.

23.5

Management of forests is covered only briefly in relation to sustained development, detailed descriptions of methods of management are not covered.

2. oceans: the problems of over-fishing and attempts at regulation as illustrated by the principle of quotas, exclusion zones and restricted net mesh size.

23.4

(b) The principles of chemical and biological control of pests and their relative advantages and disadvantages,

The use of pyrethroids to control pest insects in agriculture and the parasite Encarsia formosa to control the glasshouse white fly Trialeurodes vaporariorum.

23.2

Pyrethroids are not mentioned by name in the text, but they are examples of contact pesticides described in spread 23.2; they break down quickly, do not harm plants, and are not very toxic to vertebrates.

The effects of human activities on the carbon cycle. Economic importance of the nitrogen cycle in relation to food production and fertiliser application.

22.12, 22.13

23.1, 23.5, 23.7

See spreads 22.13 and 23.5 for effects of human activities on the carbon cycle.

See spread 22.12 and 23.1 for economic importance of nitrogen cycle.

4.1 Energy is essential for the maintenance of living systems.

(a) The importance of chemical energy in biological processes.

The central role of ATP as an energy carrier and its use in the liberation of energy for cellular activity.

2.11

See also 3.1 for a discussion of energy and living organisms.

(b) The synthesis of ATP by means of a flow of protons through the enzyme ATP synthetase.

The similarity between mitochondrial and chloroplast membrane function in providing a proton gradient for ATP synthesis.

5.3

6.4

ATP synthetase is referred to as ATPase in spread 6.4 and ATP synthase in spread 5.3. It is an enzyme complex which uses the energy from proton flow to make ATP – see box Chemiosmotic theory: How ATP is synthesised spread 6.4, and Fact of Life spread 5.3.

(c) The maintenance of the proton gradient by proton pumps driven by electron energy. The alternate arrangement of pumps and electron carriers to form the electron transport chain. (Names of proton pumps and electron carriers in the electron transport system are not required).

As above

4.2 Respiration releases chemical energy from organic molecules in order to synthesize ATP for the maintenance of life.

(a) All living organisms carry out respiration in order to provide energy in the cell.

The role of reduced NAD as a source of electrons and protons for the electron transport system.

6.1

6.2

See also spread 6.4 for the use of protons from reduced NAD for the electron transport system.

(b) The Krebs cycle as a means of liberating energy from carbon bonds to provide ATP and reduced NAD with release of carbon dioxide.

6.3

Figure 2 summarises the cycle.

(c) Glycolysis as a source of triose phosphate, pyruvate, ATP and reduced NAD. The formation of acetyl CoA.

(The names of glycolysis and other Krebs cycle intermediates are not required.)

6.2

Note that glyceraldehyde 3-phosphate (figure 1, spread 6.2) is a triose phosphate, but triose phosphates are not referred to by name in the text.

(d) The energy budget of the breakdown of glucose under aerobic and anaerobic conditions.

6.4

The efficiency of ATP production under aerobic and anaerobic conditions is given in terms of number of ATP molecules produced for each glucose molecule respired.

Fat and amino acid utilisation in respiration as illustrated by long distance running and starvation.

6.3

See ‘Fact of Life’, spread 6.3. Amino acid utilisation as a respiratory substitute increases during starvation and leads to muscle wastage (see Anorexia in spread 16.9). Beta oxidation of fats is important in long distance running.

Practical Activities: Demonstration of dehydrogenase activity using artificial hydrogen acceptors, as illustrated by methylene blue or DCPIP or tetrazolium compounds.

Practical activities are not covered

4.3 Photosynthesis uses light energy to synthesize organic molecules.

(a) The distribution of chloroplasts in relation to light trapping.

Chloroplasts as transducers converting the energy of light photons into the chemical energy of ATP.

Light harvesting. Absorption of various wavelengths of light by chlorophyll and associated pigments and energy transfer to reaction centres.

5.1

5.2

5.3

See also 13.1 for distribution of chloroplasts in leaf cells.

(b) Basic features of Photosystems I and II.

Cyclic and non-cyclic photophosphorylation sources of electrons for the electron transport chain. Loss of electrons as a form of oxidation. The hydroxide ion as a source of electrons for Photosystem II.

Reduction of NADP by addition of electrons and hydrogen ions; occurs in the stroma maintaining the proton gradient.

5.3

See in particular figure 2, spread 5.3 which summarises the events which take place in the light-dependent stage of photosynthesis.

(c) The light independent stage and the formation of glucose; uptake of carbon dioxide by ribulose bisphosphate to form glycerate 3-phosphate.

Reduction of glycerate 3-phosphate to triose phosphate (carbohydrate), with the regeneration of ribulose bisphosphate.

Reduced NADP as a source of reducing power and ATP as a source of energy for these reactions.

Other carbohydrates, lipids and amino acids can be made from the triose phosphate. (No details of chemistry of these processes needed).

5.4

Figure 2, spread 5.4 summarises the events occurring in the light-independent stage.

(d) The effect of light, carbon dioxide concentration and temperature on the rate of photosynthesis.

The concept of limiting factors.

5.5

Figure 5, spread 5.5. illustrates how light, carbon dioxide concentration and temperature interact to affect the rate of photosynthesis according to the law of limiting factors.

The role of inorganic nutrients in plant metabolism as illustrated by the utilisation of nitrogen and magnesium.

13.8

The role of inorganic nutrients is covered briefly.

Practical Activities: Separation of chloroplast pigments by chromatography.

A quantitative investigation of the effects of different coloured/wavelength light on the rate of photosynthesis. Computer modelling may be used to extend this investigation.

Practical activities are not covered

Chromatography is covered in the appendix.

Comparison of absorption spectrum with the action spectrum is shown in Figure 3, spread 5.2.

4.4 The uptake of energy and nutrients.

(a) Structure and function of the human alimentary canal. Histological structure of the ileum. Mechanical breakdown in the mouth and stomach.

The role of the secretions of the mouth, stomach, liver, pancreas and small intestine in digestion. (link with 1.4)

Peristalsis.

9.2

9.3

9.4

9.5

See figure 2, spread 9.2 for a diagram of alimentary canal.

9.3 figure 3

Table 1, spread 9.3 shows how circular and longitudinal muscles work antagonistically to cause peristalsis.

(b) Products of digestion and absorption, transport to the liver, deamination and storage of glycogen. (Reference to the control of digestive juice secretion is not required.)

Fat absorption as fatty acids and glycerol into lacteal, through lymphatic system to blood stream.

Practical Activities: Examination of T.S. ileum.

9.5

8.4

Table 1, spread 9.5, lists the products of digestion.

Spread 8.4 covers the structure and role of the liver, and deamination (figure 3).

The structure of the ileum is shown in figure 1, spread 9.5 and related to its role of absorption. See also spread 7.11 for an account of the lymphatic system.

4.5 Basic microbiology and disease

(a) Bacteria may be grouped according to their shape (cocci/round, bacilli/rods and spiral) and by their reaction to the Gram stain.

17.2

17.3

Figure 2, spread 17.2 shows the shape of common bacteria.

Figure 5, spread 17.3 shows the reaction of bacteria to Gram stain.

Culture of microorganisms in the laboratory. Conditions necessary for growth; suitable temperature, water, pH, nutrient supply and oxygen level.

Principles of aseptic techniques and use of sterile equipment.

17.4

This topic is covered only briefly and students should consult a specialist textbook on bacteria for details.

Practical Activities: Examination of bacteria in order to recognise bacilli and cocci. Safe handling using aseptic technique. Use of simple stains e.g. methylene blue for staining bacteria (from milk) and examination using the light microscope.

Gram staining and microscopic investigation of yoghurt

Practical activities are not covered

Although practical details are not given, some bacteriological techniques are considered in spread 17.4 and in the Appendix.

Principles underlying a simple batch culture fermenter.

17.7

Batch culture of penicillin is described.

(b) Counting microorganisms to monitor population growth, viable count, using serial dilutions, plating and counting colonies.

17.4

See figure 4, for description of making a serial dilution. See Appendix for theoretical consideration of method for counting colonies and testing milk for freshness.

Practical Activities: Investigation into the numbers of bacteria in fresh and stale milk, using techniques of serial dilution, plating and counting colonies.

Practical activities are not covered

The theory behind some bacteriological techniques are given in the appendix.

4.6 Pathogens, spread of human disease and control of infection.

(a) Pathogens are organisms which cause disease in a favourable host tissue.

Meaning of the following terms: infectious disease, carrier, animal reservoir, endemic, epidemic, vaccine, antibiotic, resistance, vector, toxin, antigenic(sero) types.

15.1 and through Ch. 15

See box Trypanosomiasis, spread 15.4 for an example of animal reservoir.

Spreads in which terms are defined: infectious disease (15.1), carriers (19.8 for genetic diseases. The term also applies to people who carry pathogenic organisms but are not themselves affected by them – see spread 15.2 for an account of symptomless carriers of HIV), resistance (see immune system, 15.5), vector (15.4), toxin (15.7), antibiotics (15.9), antigenic (sero) types (15.7).

The causative organism, tissue affected and symptoms (in brief), source of infection, mode of transmission, prevention and control methods, including vaccines, for the following diseases:

Salmonellosis;

Cholera;

Influenza;

5.3

The influenza virus is mentioned in spread 15.1 and shown in figure 1, spread 17.1; figure 1, spread 15.1 shows how the influenza virus can be transmitted, difficulty of treating influenza by vaccination is discussed in spread 15.7.

Malaria: Main stages (names of stages not required) of the life cycle of Plasmodium (parasite in salivary gland of mosquito, passes into blood stream when mosquito bites, invades liver cells, invades red blood cells, taken in when mosquito bites, passes to salivary gland) to illustrate suitable points at which the cycle can be broken by preventing transmission, controlling life cycle of vector. Advantages and disadvantages of control methods of Malaria.

15.4

Figure 2, spread 15.4 summarises the main stages of the life cycle of Plasmodium.

(b) Treatment: antibiotics may be bacteriostatic or bactericidal and act on bacteria by interfering with specific metabolic pathways, as exemplified by penicillin acting on cell wall formation in Gram positive bacteria. Viruses are not susceptible to antibiotics. Plasmodium is susceptible to some drug treatment when outside cells in the blood stream.

15.4

15.7

See box ‘Mechanics of antibiotic action’ for a discussion of mode of action of antibodies.

Note bacteriostatic antibiotics are examples of biostatic antibodies; bacteriocidal antibodies are an example of biocidal antibiotics  which act specifically on bacteria.

4.7 Human defence mechanisms

(a) Natural barriers against infection. Influence of vitamin C and natural skin flora.

Localised defence by inflamation.

Immune responses as a result of foreign antigens.

Humoral and cell mediated immunity.

Antigen-antibody interactions; the role of T lymphocytes and B lymphocytes.

15.5

The role of skin flora is not considered. See spread 9.8 (table 2) and 16.6 for references to vitamin C.

(b) Medically induced immunity which may be active, as illustrated by Rubella or passive as illustrated by Rabies.

15.7

Rubella is a virus which can be transmitted across the placenta (see 16.1), children can be immunised against it in a manner similar to immunisation against polio; immunity to rabies can be induced passively in a manner similar to that for tetanus.

4.8 Applications and contemporary issues.

(a) Industrial application of a batch culture fermenter as exemplified by penicillin production.

17.7

Applications of monoclonal antibodies as illustrated by pregnancy testing kits and drug targetting.

15.6

See also Fact of Life, spread 12.8 for the use of monoclonal antibodies in pregnancy testing kits.

(b) Problems of antibiotic resistance, due to over use.

Relative effectiveness of vaccination programmes, as illustrated by the eradication of smallpox and the continued epidemics of influenza.

Ethical considerations for vaccination programmes.

15.2

15.7

Spread 15.2 describes why the eradication of smallpox was effective; spread 15.7 explains why diseases such as influenza are difficult to eradicate. See 15.9 and 20.5 for antibiotic resistance.

Vaccination strategies are considered in spread 15.7, but ethical considerations for vaccination programmes are not.

5.1 All organisms are variable in form and function.

(a) Alleles as different forms of the same gene.

An understanding of the principles of monohybrid and dihybrid Mendelian inheritance. Codominance (Monohybrid only).

Sex linkage as illustrated by haemophilia.

Chapter 19

Alleles are considered in spread 19.1, monohybrid inheritance in 18.3; dihybrid inheritance in 19.5, codominance in 19.4, and sex linkage and haemophilia in 19.8.

(b) Gene mutation as illustrated by sickle cell anaemia and chromosome mutation as illustrated by Down's syndrome. Mutagens and carcinogens.

Random assortment, crossing over and fertilisation as sources of variation.

Chapter 19

Gene mutation (19.1), sickle cell anaemia (16.1), Down’s syndrome (19.9).

See 16.5 for an account of cancer.

Gene mutations are covered in 19.1, sickle cell anaemia in 16.1 (see also 20.6), Down’s syndrome in spread 19.9, carcinogens and cancer in spread 16.5, random assortment and crossing over in spread 19.6, variation in spread 19.1.

Practical Activities: One experiment to illustrate gene segregation (Drosophila, maize cobs and tomato plants are suitable, but other material may be used).

Practical activities are not covered

5.2 Genetic variation is the raw material for evolutionary change.

(a) Genetic and environmental factors produce variation between individuals.

Variation - continuous and discontinuous; heritable and non-heritable.

19.1

Distinction between genotype and phenotype, continous and dis-continuous variation is made in this spread.

Practical Activities: Investigation of continuous variation in a locally occurring species including use of students t test e.g. comparison of florets

on north and south facing Ivy or wing length in fruits of Sycamore (t test will only be examined through the practical assessment).

Practical activities are not covered

Inter and intra-specific competition for breeding success and survival.

Selective agencies (e.g. supply of food, breeding sites, climate).

20.4

Selective agencies referred to as selection pressure or environmental resistance.

The gene pool and genetic drift.

Selection can change the frequency of alleles in a population.

20.4, 20.6

Genetic drift is included in the Food for Though, spread 20.6; this spread also includes the Hardy-Weinberg equation for calculating allele frequencies.

(b) Isolation and speciation.

20.8

Separation of populations by geographical, behavioural, morphological seasonal and isolation mechanisms. Hybrid sterility.

20.9

Hybrid sterility occurs when two different species interbreed to produce offspring which are infertile (see ‘The story of Spartina’ in spread 20.9)

Darwin's theory of evolution that existing species have arisen through modification of ancestral species by natural selection.

20.1 and 20.4

The formation of new species as illustrated by Darwin's finches. Ancestral species evolved by adaptive radiation to occupy vacant niches, free from competition, in the Galapagos islands.

20.2

Figure 2, spread 20.2 shows some of ‘Darwin’s finches’

(c) Human influence on the environment has created new selection pressures as illustrated by warfarin resistance in rats, and antibiotic resistant forms of bacteria. Artificial selection.

20.5

20.7

Warfarin resistance in rats is not covered specifically, but its evolution is similar to antibiotic resistance in bacteria.

Artificial selection of wheat considered in detail.

Biodiversity. Reasons for species becoming endangered and causes of extinction. The conservation of gene pools in the wild and in captivity.

22.11

23.10

23.11

Practical Activities: Investigation of endangered species using secondary sources (ICT is suitable).

Practical activities not covered

5.3 Sexual reproduction is of major importance for plant productivity.

(a) The generalised structure of wind, Lolium (ryegrass) and insect, Primula (primrose) pollinated flowers.

The development of pollen and ovules.

Pollination and self pollination.

Cross pollination as illustrated by Primula. Advantages and disadvantages.

Fertilisation. Double fertilisation.

14.1

14.2

14.3

14.4

The basic structure of an insect pollinated plant is illustrated by the buttercup in figure 2, spread 14.1, but the two types of Primula which favour cross-pollination are shown in figure 3, spread 14.3.

(b) Formation of seed and fruit. Structure and germination of Vicia faba (broad bean).

14.4

14.6

Figure 1, spread 14.6 shows hypogeal germination of broad bean.

Practical Activities: Dissection/examination of wind and insect-pollinated flowers. Examination of prepared slides of anthers, ovaries and developing fruits e.g. Capsella (Shepherds purse).

Starch agar diffusion technique to illustrate amylase action from cut surfaces of germinating bean.

Practical activities are not covered

5.4 Sexual reproduction in human.

(a) The structure and function of the reproductive systems in human.

Spermatogenesis and oogenesis to produce spermatozoa and secondary oocyte. Sexual intercourse, fertilisation and implantation.

12.2

12.3

12.5

12.7

Figure 1, spread 12.2 shows the mammalian male reproductive system; figure 2 shows the female reproductive system.

12.3 considers gametogenesis; the production of spermatozoa and egg cells.

Figure 2, spread 12.5 shows fertilisation; figure 2, spread 12.7 shows implantation.

(b) Endocrine control, of reproduction in the female, menstrual cycle, birth and lactation by reference to follicle stimulating hormone, luteinizing hormone, oestrogen, progesterone, oxytocin and prolactin. Role of the placenta including hormonal control.

12.4

12.6

12.8

12.9

Figure 1, spread 12.4 summarises the human menstrual cycle; table 1 gives the hormones involved.

12.6 deals with birth; 12.8 with pregnancy and 12.9 with the placenta.

Endocrine control of reproduction in the male: luteinising hormone, testosterone.

12.3

In 12.3, the gonadotrophin, which stimulates testosterone production, in luteinising hormone (see 10.1).

Human chorionic gonadotrophin production by the embryo and its use in pregnancy detection tests.

12.8

See Fact of Life in 12.8 for description of pregnancy detection tests

Practical Activities: Histology of the ovary and testis.

Practical activities are not covered

5.5 Applications of reproduction and genetics.

The principles involved in cloning as illustrated by: separating cells of developing animal embryos, nuclear transplants from somatic cells into egg cells, tissue cultures of animals, micropropagation of plants. The advantages and disadvantages.

18.10

14.8

Figure 2, spread 18.10 – how Dolly the sheep is believed to have been cloned.

Figure 3, spread 14.8 gives an outline of micropropagation.

5.6 Species are classified into groups using shared derived features.

(a) Characteristic features of Kingdoms:-

Prokaryotae, Protoctista, Plantae, Fungi, Animalia.

21.1

(b) The concept of the species. The binomial system. The principle that modern classification should reflect closeness of evolutionary relations. The example of the Tiger should be used simply to illustrate the concept of each taxon and main features only.

Kingdom: Animalia; Phylum: Chordata; Class: Mammalia; Order: Carnivora; Family: Felidae; Genus: Panthera; Species: P. tigris.

20.8

21.1

See box “Problems in defining species” in spread 20.8 for a discussion of the species concept.

The wolf, Canis lupus, is given as an example of classification in spread 21.1; note the similarity with the tiger, P. Tigris.

5.7 Control systems co-ordinate and regulate life processes.

(a) The concept of homeostasis and its importance in maintaining the body in a state of dynamic equilibrium.

The role of negative feedback in restoring conditions to their original levels.

8.1

(b) Structure of the mammalian kidney including nephron. Adaptations of the cells of the proximal tubule for reabsorption.

Functions of the mammalian kidney including nitrogenous excretion and water regulation. Adaptations of the loop of Henlé to different environments.

Endocrine glands contribute to homeostatic balance as illustrated by the role of the posterior pituitary gland in the secretion of antidiuretic hormone.

The role of antidiuretic hormone.

8.5

8.6

8.7

8.8

Figure 2, spread 8.5 shows the structure of the human kidney.

8.6 deals with the proximial tubule ( = proximial convoluted tubule).

8.7 deals with the loop of Henlé and the counter current multiplier.

8.8 discusses the role of antidiuretic hormone.

Practical Activities: Gross low power study of prepared slides of the kidney.

Practical activities are not covered

5.8 All living organisms show responses to stimuli which increase the chance of survival.

Responding to a stimulus requires information from a receptor to be relayed to an effector.

Some animals have developed complex structures for the reception of stimuli.

10.1

The ear, structure and function, for receiving, amplifying and transducing sound waves into electrical impulses for interpretation by the brain. (The ear as an organ of balance is not required).

10.9

10.10

Figure 2, spread 10.9 shows the structure of the human ear.

Figure 2 spread 10.10 shows how the ear transduces sound waves into electrical impulses.

5.9 The structure of the nervous system of mammals permits a rapid transmission and processing of information.

(a) The structure of the motor neurone, to include drawing and labelling of diagram.

10.1

Figure 2, spread 10.1 shows a motor neurone.

The nature of the nerve impulse and the way it is transmitted: resting potential; membrane depolarisation and the action potential; 'all or nothing' law; refractory period; passage of sodium and potassium ions. Analysis of oscilloscope traces.

The structure and role of the synapse and synaptic transmission.

Chemicals such as organophosphates and psychoactive drugs (in brief) affect transmission.

10.4

10.5

10.6

16.11

Figure 1, spread 10.4, shows an oscilloscope trace; 10.4 also deals with the resting and action potentials.

10.5 considers transmission of a nerve impulse, ‘all or nothing’ and refractory period.

Figure 3, spread 10.6 summarises the events that occur during synaptic transmission -– see also psychoactive drugs considered in box in spread 16.11.

(b) The structure of the human brain - the position of the cerebral hemispheres, hypothalamus, cerebellum, medulla oblongata.

The main functions of the cerebellum, medulla oblongata, hypothalamus.

10.13

Position of brain structure shown in figure 1, spread 10.13.

The hypothalamus is the link between nervous and endocrine regulation.

10.14

The pivotal role of the hypothalamus is discussed in spread 10.14; see also figure 1, spread 8.10 which shows the location of the hypothalamus.

(c) Voluntary actions involve coordination by the cerebral hemispheres and relay of information through the spinal cord.

The main areas of the spinal cord: central canal, grey matter, white matter.

The basic pattern of spinal nerves in relation to the spinal cord. Dorsal root and ventral root.

The simple reflex arc as the basis for protective, involuntary actions.

Flexion of the arm in response to a hot surface.

10.7

11.8

Figure 2, spread 10.7 shows a transverse section through a spinal cord.

Figure 2, spread 11.8 shows the spinal cord in relation to a reflex arc; although not labelled, the dorsal root is the pathway taken by the sensory neurone into the spinal cord, whereas the ventral root is the pathway taken by the motor neurone out of the cord.

(d) Effectors are either muscles or glands.

Structure and ultra structure of skeletal muscle.

Sliding filament theory to include actin, myosin and actomyosin only.

11.4

11.5

11.4 deals with the structure of skeletal muscle; 11.5 focuses on the sliding filament theory of muscle action.

Practical Activities: Examination of T.S. of spinal cord. The histology of skeletal muscle. Examination of electron micrographs of skeletal muscle.

Practical activities are not covered