Essay Titles + Markschemes

1. Essay Titles + Markschemes

2. Cells are easy to distinguish by their shape. How are the shapes of cells related to their functions? (25 marks)

5. Movement in cells (25 marks)

7. Transfer through ecosystems (25 marks)

9. The part played by enzymes in the functioning of different cells, tissues and organs (25marks)

11. The ways in which organisms use ATP(25 marks)

12. The role of ATP could have been described in: • Muscle contraction • Active transport • Maintaining resting potential • Re-synthesis of acetylcholine and rhodopsin • Glycolysis of respiration • Light independent reactions of photosynthesis • Synthesis (anabolism) • Kidney function • Translocation • Nitrogen fixation At least 50% of candidates went into great detail about ATP production and consequently lost 1 relevance mark.

13. Introduction could include reference to DNA as a polynucleotide and the nature of the genetic code as a sequence of bases • Structure of a mononucleotide • Bases in DNA, deoxyribose and phosphate • Adenine and guanine as purines, cytosine and thymine as pyrimidines • Condensation reactions between mononucleotides to form polynucleotides • Complementary base pairing and the double helix - • Reference to transcription and translation of genetic code • Point mutations illustrated by base deletions, insertions, and substitutions • Effects of point mutation on amino acid sequences, reference to HbS The structure of DNA and the effects of point mutation

14. The causes of genetic variation. Introduction could include reference to the importance of genetic variation – Sexual reproduction involves fusion of gametes leading to genetic variation – Gamete formation involves reduction division (meiosis) – Behaviour of chromosomes during first and second divisions of meiosis – Chiasmata formation – Crossing over – Autosomal linkage and recombinants in relation to events of meiosis – Significance of mutations – Causes of mutations, chemical mutagens and radiation – Point mutations – Chromosome mutations – Translocation – Polysomy – Polyploidy –

15. Chemical coordination in animals and plants Introduction could include reference to the concept of homeostasis and its importance, reference to negative feedback mechanisms The nature of mammalian hormones Principles of hormonal action Regulation of blood glucose, factors which lead to variation in blood glucose levels Roles of insulin, glucagon and adrenaline in the control of blood glucose levels Role of the liver - ADH and the regulation of body water Hormones in reproduction, FSH, LH, oestrogen, progesterone, oxytocin, prolactin Plant growth substances, auxins, cytokinins, gibberellins, ABA and ethene Emphasis should be on the principle of coordination

16. The roles of proteins in living organisms. Introduction could include outline of protein structure and diverse roles Specific roles of proteins: Enzymes, illustrated with examples such as digestive enzymes, enzymes in DNA replication – Structural proteins, e.g. collagen – Hormones, illustrated by insulin and glucagon, ADH, other protein /peptide hormones – Membrane transport proteins – Haemoglobin and myoglobin – Antibodies – Rhodopsin and iodopsin – Rubisco –

17. The structure of enzymes and their uses in commercial processes. The structure of enzymes as globular proteins – The concept of active site – Enzyme specificity – Use of pectinases in production of fruit juices – Immobilised enzymes in commercial procedures – Reference to lactase – Roles of enzymes in gene technology – Reverse transcriptase – Endonucleases – DNA ligase – Chymosin from genetically modified yeast and its use – DNA polymerase in PCR –

18. Introduction could include reference to the structure of xylem tissue in plants • Roles of diffusion and active transport in the uptake of mineral ions – • Structure of the root – • Movement of water (plus dissolved mineral ions) through the plant – • Apoplast, symplast and vascular pathways – • Role of the endodermis – • Functioning of the transpiration stream – • Structure of vessels and their contribution to the movement of water – • Nitrate ions – • Phosphate ions – • Magnesium ions – • [some candidates might refer to the transport of mineral ions to sinks in the phloem] The uptake, transport and roles of mineral ions in flowering plants. .

19. The structure of a typical mesophyte leaf and the effects of environmental factors on photosynthesis. Introduction could include relationship between structure and function of a leaf – External and internal structure of a mesophyte leaf – Upper and lower epidermis, palisade mesophyll, spongy mesophyll – Xylem – Phloem – Structure and roles of stomata – Effect of light intensity on photosynthesis – Effect of wavelength on photosynthesis – Effect of carbon dioxide concentration – Effect of temperature – Effect of air pollution – Concept of limiting factors – Compensation point –

20. Digestion and absorption of carbohydrates and the regulation of blood glucose. Introduction could include reference to the nature of carbohydrates, monosaccharides, disaccharides and polysaccharides – Digestion of starch, salivary amylase and pancreatic amylase – Digestion of maltose – Digestion of sucrose – Digestion of lactose – Absorption of monosaccharides – Relationship between structure and function of ileum – Digestion of cellulose in ruminants, saprobiotic digestion Absorption of glucose, leading to an increase in blood sugar level – Roles of insulin, glucagon and adrenaline in control of blood glucose levels – Roles of the liver in glucose-glycogen metabolism –

21. The structures and functions of different types of plant cells. Introduction could include reference to generalised structure of a plant cell Expect descriptions of structure and functions of: Palisade cell with reference to structure of chloroplasts and photosynthesis – Guard cell – Spongy mesophyll cell – Xylem vessel – Fibre – Sieve tube element – Companion cell – Epidermal cell – Root hair – Expect discussion of relationship between structure and function

22. Polymers have different structures. They also have different functions. Describe how the structures of different polymers are related to their functions

23. Polymers as molecules associated with storage • Biological molecules, carbohydrates and proteins • The release of energy from carbohydrate • The control of blood glucose Polymers as informational molecules • Enzymes • DNA as genetic material, structure of nucleic acids • Principles of immunology • The transport of respiratory gases Polymers as structural molecules • Cell ultrastructure, cell walls • Biological molecules, carbohydrates and proteins

24. Heat and many different substances are transferred within the human body and between the body and the environment. Explain how surface area is linked to this transfer.

25. Principles Diffusion and Fick’s law Size and surface area to volume ratio Substances Blood and blood vessels The exchange of respiratory gases in the lung The structure and functions of the placenta. Absorption of the products of digestion Transfer of heat The relationship between

26. Carbon dioxide in organisms and ecosystems.

27. Biochemistry • The biochemistry of photosynthesis • The biochemistry of respiration • C4 photosynthesis in maize • Physiology • Gas exchange surfaces • Changes in cardiac output and pulmonary ventilation with exercise • The transport of respiratory gases • Ecology • The effect of carbon dioxide on productivity • Decomposition and recycling maintain the balance of nutrients in an ecosystem • The greenhouse effect is not specifically mentioned but should be credited hereif discussed

28. Why the offspring produced by the same parents are different in appearance

29. Genes • Genes incorporate coded information which influences phenotype • Gene mutation • Environment • Environment variation • Dietary requirements of insects • Chromosomes and cells • Meiosis • Principles of Mendelian inheritance • Polygenetic inheritance • Gametes and gamete formation. Fertilisation

30. Hydrogen bonds and their importance in living organisms.

31. Hydrogen bonds associated with the properties of water • The passage of water through a plant and cohesion tension Hydrogen bonds associated with secondary and tertiary structure • The structure of proteins, starch and cellulose • Enzymes • Hydrogen bonds associated with nucleic acids • DNA as genetic material, structure of nucleic acids • Gene technology

32. How nitrogen-containing substances are made available to and are usedby living organisms.

33. Nutrient cycling • Nitrogen cycle • The influence of deforestation of nitrogen cycling The uses of proteins • Proteins as biological molecules • Enzymes and enzyme action • Haemoglobin and the exchange of respiratory gases • The use of membrane proteins in the nervous system The uses of nucleic acids and other nitrogen-containing substances • DNA and protein synthesis • Chlorophyll, NADP and photosynthesis • ATP and respiration

34. The biological importance of plants to humans.

35. Ecological cycles • The role of plants in the nitrogen cycle • Photosynthesis and respiration in giving rise to short-term fluctuations and longterm • global balance of oxygen and carbon dioxide; Plants and food • Digestion and absorption • Diet and dietary requirements Energy transfer • Transfer of energy through food chains and food webs • Biochemistry of photosynthesis

36. Humans and microorganisms

37. Microorganisms as part of the environment • Decomposition and recycling maintain nutrient balance Pathogens • Bacteria and viruses are examples of pathogenic organisms • Plasmodium and malaria Making use of microorganisms • 12.6 Gene technology may be used in combating disease

38. The transfer of substances containing carbon between organisms and between organisms and the environment (25 marks)

40. The part played by the movement of substances across cell membranes in the functioning of different organs and organ systems (25 marks)

42. Old Essay Titles – bit off the syllabus?

43. The roles of water in the lives of organisms Introduction to include reference to the physical properties / dipolar Solvent properties important in role of transport Cohesive properties Transport medium in animals - constituent of body fluids / blood Transport medium in plants - for mineral ions - for products of photosynthesis – Adhesive properties in transport in xylem Water as a cellular constituent - role in metabolic reactions – hydrolysis Role of water as a reactant in photosynthesis - source of hydrogen ions Role of water in fertilisation - transport of gametes Role of water in support – turgidity of tissues in herbaceous plants - maintenance of shape Water as a lubricant – synovial fluid - tears Water as a coolant - ref. to loss of heat on vaporisation - sweating and heat loss Water as a habitat – Thermal properties of water - reference to freezing – surface tension

44. The roles of pigments in living organisms Introduction to include a definition of a pigment - some reference to the range of pigments in living organisms Respiratory pigments: Haemoglobin - myoglobin - oxygen carriage Cytochromes and electron transport – Visual pigments:Rhodopsin - occurrence in rods - vision at low light intensities lodopsin - occurrence in cones - comment on colour vision - ref. to role of colour vision Chlorophylls and photosystems - roles in photosynthesis Other photosynthetic pigments - carotenes - credit other references Phytochromes - role in flowering - photoperiodic effects – Plant growth and development – Flower pigments - anthocyanins / xanthophylls in flowers – Role in pollination - flower markings Melanins in skin - functions Roles of pigments in camouflage - warning - courtship - mimicry

45. The effects of light on flowering plants. Introduction could include reference to the need for detection of external stimuli – References to light intensity and wavelength and effects on photosynthesis – Reference to the detection of light duration by phytochrome – Interconversion of P660 and P730 (or Pr and Pfr) – Examples of phytochrome effects such as Photoperiodism and Germination of light sensitive seeds Etiolation Detection of light direction – Auxin and phototropism – Effects on stomatal opening and closing and transpiration –

46. The production of gametes in humans, fertility and the implications for world population trends. Introduction could include reference to gamete production involving reduction division Spermatogenesis - Spermatogonia Primary and secondary spermatocytes Spermatids and sperm maturation – Oogenesis: Oogonia Primary and secondary oocytes Ova Credit references to the roles of mitosis and meiosis – Variations in fertility Factors affecting fertility - could include references to birth control Demographic changes, reference to growth curves or population pyramids Consequences for population trends

47. The production and transport of metabolic wastes in mammals. Introduction could include explanation of term metabolic waste –Function of circulatory system in transport of metabolic wastes –Specific references to production of carbon dioxide in respiration – In ( link reaction and) Krebs cycle – Production of urea in liver – From excess amino acids – Deamination –Outline of ornithine cycle – Transport of urea in plasma from liver to kidneys Transport of carbon dioxide from respiring tissues to lungs– As HCO3 In solution in plasma As carbamino compounds – Reference to metabolic water Reference to lactic acid –