Sample essays and suggested plans for content

1. The process of diffusion and its importance in living organisms

Definition

Fick’s Law

Types of diffusion e.g. Facilitated diffusion, osmosis

Gas exchange in unicells, fish, mammals and plants

Digestion and absorption of products

Exchange of materials between blood in capillaries and tissues e.g. placenta

Transpiration, root pressure, water and ion uptake by roots

Translocation and mass flow hypothesis

Osmoregulation by blood and kidney, unicells e.g. Amoeba

Action potentials

Synaptic transmission

Muscle action

Intracellular diffusion e.g. mitochondria, chloroplasts, enzyme action, DNA replication and protein synthesis

2. The different ways in which organisms use ATP OR ATP and its roles in living organisms

The nature/structure of ATP and its importance as energy currency.

Production and use of ATP in cytoplasm by glycolysis

Production of ATP by mitochondria in Krebs cycle and ETS – aerobic respiration.

Anaerobic respiration.

Role of chloroplasts in ATP production via light independent reaction

Uses e.g. Active transport (carrier protein shape changes), Nerve action (maintaining resting potentials via Na+/K+ pump and resynthesis of ACh), selective reabsorption by nephron, absorption by gut, Calvin cycle, muscle contraction (cross bridge formation), Biosynthesis of organic compounds, Contractile vacuoles, Translocation (loading of phloem), cell division (movement of chromosomes via spindle), CP formation in muscles, Nitrogen fixation (Blue-green algae), Kidney function, movement of sperm, secretion of digestive enzymes in saprophytic fungi, cilia and flagella action

3. The movement of substances within living organisms (Jan 2003) OR Transport mechanisms in

living organisms

Diffusion e.g. Ion movement in Roots, Synapse, within a cell, O2/CO2 in lungs and gills, factors affecting rate

Facilitated diffusion e.g. Glucose uptake, action potentials

Osmosis e.g. Turgidity, uptake of water in plant roots, Kidney function

Active Transport e.g. Na+/K+ pump, Cl- in RBC, Glucose uptake in intestine, mineral ions in plant roots, neurotransmitters into presynaptic membranes, carrier proteins, mechanism

Endocytosis / exocytosis / Pinocytosis / phagocytosis e.g. Feeding in Amoeba

Mass flow e.g. Phloem, Xylem, Peristalsis, Ventilation in lungs, gills and insect tracheoles, Bloodstream, Excretion, Cilia

Unusual ideas e.g. Chromosome movement during cell division, organelle movement in cells, Sliding filament theory, reproductive cells

4. Mutation and its consequences

Definition.

Types of mutation – addition, deletion, substitution.

Causes e.g. spontaneous, radiation, mutagenic chemicals.

Effect of mutation on protein synthesis.

A change in base sequence may result in a change in amino acid sequence of a polypeptide, which affects the protein structure and its function.

Metabolic blocks as a result e.g. PKU.

Mutation in CFTR gene in cystic fibrosis.

Haemophilia.

Somatic mutations e.g. cancer and germ line mutations e.g. colour blindness.

Introns and exons – mutation may be removed by post-transcriptional modifications.

Diploid carriers e.g. sickle cell anaemia.

The role of mutation in evolution e.g. sickle cell anaemia.

Mutation as a source of genotypic variation e.g. bacteria and antibiotics.

Natural selection leading to changes in populations, changes within a species e.g. peppered moth, formation of a new species.

5. The properties of enzymes and their importance in living organisms OR The role of enzymes in

living organisms

What is an enzyme?

How do enzymes work – lock and key theory/induced fit and lowering activation energy/enzyme substrate complexes.

Enzymes as proteins.

Effects of extremes of temperature and pH – optimums – graphs.

Inhibition – competitive and non-competitive.

Activators, substrate concs.

Extra-cellular digestion - Fungal feeding.

Digestion in animals e.g. proteases, lipases, carbohydrases.

Enzymes in chemical processes e.g. Photosynthesis, Respiration, Nerve conduction, synapses, deamination, transamination, DNA replication, RNA production.

Synthesis reactions.

CO2 carriage.

Acrosome in sperm.

Effect of insulin on enzyme production in liver cells.

Gut symbionts and cellulase production.

Na+/K+ pump

6. The ways in which a mammal maintains constant conditions inside its body

Blood pH – decreased pH counteracted by secretion of HCO3- from distal convoluted tubule and NH4

+ from kidney cells and increased pH counteracted by secretion of H+ from distal convoluted tubule

Exercise and blood flow to parts of the body

Temperature regulation – hypothalamus, vasoconstriction/vasodilation, piloerection, shivering, metabolic rate, sweating

Blood glucose regulation – pancreas, islets of Langerhans, Insulin, glucagon, liver, gluconeogenesis, glycogenesis

Water balance/Osmoregulation – Kidney, Nephron, ADH, permeability of the Loop of Henle, hypothalamus, Pituitary, Cl- transport, Plasma sodium control by aldosterone

Regulation of hormones e.g. sex hormones

Negative feedback 7. Negative feedback in living organisms (June 2005)

principle of negative feedback – departure from a norm initiates changes which restore a system to the norm.

importance in homeostasis; principles of detection of change, role of receptors, corrective response, role of effectors.

Thermoregulation; roles of thermoreceptors and hypothalamus in detection; heat loss and heat gain centres; sweating and vasodilatation in heat loss; vasoconstriction, hair erection, shivering and increased metabolism in heat gain.

Regulation of blood glucose; role of receptors in pancreas, secretion of insulin or glucagons; effect of insulin on surface membrane receptors/carrier proteins in stimulating uptake of glucose and glycogenesis; role of glucagons glycogenolysis.

Regulation of blood water potential; role of receptors in hypothalamus; secretion of ADH from pituitary; effect of ADH on permeability of d.c.t and collecting duct; role of loop of Henle in maintaining high ion concentration in the medulla; effect on urine concentration.

Control of ventilation; stimulation of chemoreceptors in medulla; effect on inspiration; stimulation of stretch receptors in lungs; stimulation of expiratory cells in medulla.

Control of heartbeat; roles of chemoreceptors and pressure receptors; inhibitory and acceleratory centres in medulla; effect on SAN and rate of heartbeat; effect of change in rate on pH/pressure of blood.

Metabolic pathways; examples of build-up of a product in a metabolic pathway resulting in inhibition of its formation.

Population stability; effect of increasing competition/predation on increasing population size and restoration of balance.

(selection – stabilising selection resulting in constancy of species)

(oestrous cycle; effect of feedback on hormone production, e.g. oestrogen on FSH and progesterone on both FSH and LH. From Option 8)

Any other sensibly argued example showing negative feedback should be credited. In a good essay the description of the changes in a system should be clearly related to the principles of negative feedback, with sufficient detail for the relationship to be explained.

8. Chemical coordination in organisms

Need for chemical coordination

General principles of chemical coordination

Endocrine control in animals – nature of hormones, glands, principles of hormone action

Animal physiology – sexual reproduction, control of blood glucose, osmoregulation

PGR’s – auxins, gibberellins, ethane, cytokinins, ABA

Plant physiology – growth, seed dormancy, leaf fall, root growth, bud development

Ecdysis in insects

Chemotaxis 9. The production and elimination of metabolic waste products in living organisms

Requirement for removal of toxic metabolic waste products.

Mechanisms of removal via specialised pathways or organs.

CO2

Aerobic respiration

Diffusion by unicells

Stomata/lenticels

Carriage by plasma in mammals as HCO3-

Bohr shift

Mass flow in lungs after diffusion from blood

Control mechanisms by medulla

Removal by insects

Nitrogenous waste

Produced by deamination of amino acids

Urea formation in liver (via ornithine cycle)

Transport of urea by plasma

Ultrafiltration and elimination by kidneys

Removal in other animals e.g. uric acid in birds and insects

Oxygen removal after photosynthesis

Leaf abscission e.g. tannins

10. The biological importance of water (Jan 2003) OR The role of water in the lives of organisms

Structure - dipolar nature, hydrogen bonds

Solvent – Hydrophobic/hydrophilic interactions leading to stability of membranes, proteins, nucleic acids etc, diffusion of molecules, dilution of toxic compounds e.g. urea

Osmosis and turgidity and their effects on plant support

Transport medium – xylem, phloem, blood, lymph, secretion, excretion

High heat capacity – temperature regulation, constant external environment for aquatic organisms

High heat of vaporisation – cooling effect e.g. sweating, panting, transpiration

Surface tension and cohesion – Translocation, mosquito larvae, pond skaters

Chemical reagent e.g. in P/S it is a source of Hydrogen, hydrolysis reactions

Incompressibility – hydrostatic skeletons, eyes, joints, seed germination, amniotic fluid, shock absorption in brain

Density – floats when frozen and insulates

Transparent – light penetration for aquatic organisms

Medium for movement e.g. gametes, seed dispersal, oceanic migration, mucus in alimentary canal

Protection e.g. lachrymal fluid, mucus

Factor for evolution e.g. terrestrial organisms have to adapt to conserve water

Water vapour can act as a greenhouse gas 11. The importance of proteins in living organisms

Structure and chemical composition of amino acids, amphoteric nature

Essential and non-essential amino acids

Peptide bond, ionic bonds, disulphide bonds, hydrogen bonds

Denaturation by heat, heavy metals, pH

Primary, secondary, tertiary and quaternary structures

Fibrous (Collagen in tendons and bone, myosin in muscle, silk in spiders webs, keratin in hair, horn, nails and feathers) and globular (Enzymes, antibodies, hormones e.g. insulin, histones for compacting DNA) proteins

Conjugated proteins e.g. phosphoproteins (Casein in milk), Glycoproteins (Mucin), Nucleoproteins (viruses), chromoproteins (HB, Phytochrome, cytochrome), Lipoprotein (Membranes and for lipid transport in the blood), Flavoprotein (FAD in ETS), metal proteins (nitrate reductase in plants)

Structural collagen in connective tissue, keratin in skin etc, elastin in ligaments, sclerotin in insect exoskeletons, mucoproteins in mucus, capsid proteins in viruses

Enzymes: RUBISCO, any named

Hormones: Insulin, glucagon

Transport: Hb, Mb, serum albumin for lipid transport

Protective: Antibodies, fibrinogen and thrombin for blood clotting

Contractile: myosin and actin

Storage: ovalbumin in egg white, casein in milk

Toxins: snake venom, diphtheria toxin

12. How the structure of proteins is related to their functions (Jan 2004)

Structure o Primary structure – peptide bond o Secondary structure o Tertiary structure – Globular (bonds between R groups give spherical shape – shape

determines function – active sites and receptor sites) o (Allow quaternary structure – Hb incorporates ions for oxygen transport)

Structural proteins o Fibrous – regular pattern of H bonds – coiling, o (e.g. keratin coils twist together to form rope like structures – flexible and strong, e.g.

collagen – coils more tightly bound – more rigid)

Transport o Channel – complementary shape – charges-gated o Carrier – complementary shape – can change shape o Active transport – phosphate group attached by energy from ATP – can change shape

Enzymes o Active site, enzyme-substrate complex o Activation energy reduction – explanation e.g. brings molecules closer

Receptors o Synapse o Insulin / glucagons o ADH o Rhodopsin

Muscle o Actin thin – binding site o Myosin thick – cross bridges o Tropomyosin – block binding sites

13. The importance of lipids in living organisms

Structure and chemical composition

Properties e.g. fats and oils, saturated and unsaturated, insolubility in water

Functions e.g. energy storage, insulation, protection of major organs, hydrophobic/hydrophilic interactions, membranes, lipoproteins, myelin sheath in nerve action, buoyancy (aquatic organisms), metabolic water on hydrolysis (kangaroo rats), waterproofing (leaf cuticle, insect exoskeleton, synthesis of steroid sex hormones, glycolipids, structural (beeswax in honeycombs), Scents, Pigments (carotenoids and chlorophyll), cholesterol, rubber

14. The importance of carbohydrates in living organisms OR The structure and functions of carbohydrates (June 2003)

Contain C, H, O.

Monosaccharides: glucose (blood transport) and fructose, monomers of which other carbohydrates are composed. Glucose as a source of energy; a substrate in aerobic and anaerobic respiration; brief outline of biochemistry of respiration. Structural formula.

Disaccharides: condensation reactions to form sucrose (glucose and fructose) used in phloem transport and Maltose (glucose and glucose)- and poly- saccharides, formula, glycosidic bond, hydrolysis.

Energy source e.g. glucose, fructose, galactose released via respiration

Respiration intermediates e.g. glyceraldehydes, dihydroxyacetone

Photosynthesis intermediates in light independent reaction e.g. Ribulose bisphosphate – formation of carbohydrates, CO2 accepted by RuBP, reduction of gycerate-3-PO4 to carbohydrate and regeneration of RuBP.

Synthesis of e.g. Nucleic acids are pentoses (ribose and deoxyribose) – sugar phosphate backbone provides strength, coenzymes (NAD, NADP, CoA, FAD), AMP, ADP, ATP, Disacs (sucrose, lactose, maltose), Polysaccharides (Starch/amylose, glycogen, cellulose, callose, inulin) - No osmotic effects, compact molecules, easily converted into sugars, relationship of structure to function, starch, glycogen and cellulose are all polymers of glucose differing in the number and arrangement of the glucose molecules. Starch – helical shape for compact storage, insoluble for storage (osmotically inactive), large size cannot pass through membranes, provides large numbers of glucose molecules for respiration.

Glycogen – similar to starch but more branches, insoluble storage compound in liver and muscles. Conversion of glucose to glycogen for storage. Importance of control of blood glucose.

Structural e.g. cellulose (long straight chains, OH groups linked by H bonds forming microfibrils and macrofibrils. Layers of fibrils orientated in different directions are interwoven and embedded in a matrix providing a rigid cell wall; gaps in layers provide permeability), pectins, hemicellulose, murein

Optical isomers – only D forms used in nature

Transport e.g. sucrose in phloem

Food store e.g. lactose in milk, starch in plants, glycogen in animals.

Glycoproteins, glycolipids, mucopolysacs (chitin – insect exoskeletons, nails, murein – bacterial cell walls, pectins – form gels, hemicellulose, heparin - anticoagulant, hyaluronic acid, chondroitin – very viscous component of synovial fluid and cartilage and cornea, gums and mucilage – drought resistance)

15. How the structure of cells is related to their function (June 2002)

Leaf mesophyll cells – chloroplasts, thylakoids for P/S

Xylem – waterproof, no end walls, lignified for support and water transport

Phloem – minimal cytoplasm, end plates for sucrose transport

Guard cells – mechanisms of controlling gas exchange by stoma control

Epidermal cells – flattened for protection

Sclerenchyma – polygonal for support

Root endodermis – casparian strip for regulating entry of substances

Collenchyma – cells thickened at corner for support

Pollen grains – hooks for attaching to insects

Ciliated tracheal epithelium – moving material away from lungs

Squamous epithelium of alveoli and bowmans capsule – thin for diffusion

Gut epithelial cells - microvilli for absorption

Cornified cells of skin – flattened and keratinised for protection

Nerve cells – long, myelin sheath, mitochondria, neurotransmitters

RBC – shape for increased SA, Hb for carrying O2, no nucleus

Sperm cells - tail and mitochondria for swimming

Egg cells

Muscle cell – actin and myosin for contraction

Secretory cells e.g. goblet cells – secretory vesicles, sER

Rods and Cones in retina – light sensitive pigments etc

Pyramidal neurones in brain – many dendrites = parallel processing

Bacterial cells – flagella for movement, capsule for defence/adhesion 16. Natural selection and the effects of environmental change

Natural selection o Variety amongst individuals of same species o Survival characteristics o Selective advantages o Survival, breeding genes/alleles passed on to next generation o Advantageous characteristics become common

Change in gene pool Environment and selection pressure o environmental factors exert pressure o e.g.’s of environmental factors e.g. climate change, pollution, predation, food

availability, disease o Environmental change favours certain characteristics o Differential mortality/natality o Stabilising selection o Directional selection o Disruptive selection o Isolation and speciation

Specific examples o Industrial melanism in the peppered moth o Heavy metal tolerance in plants o Insecticide/antibiotic resistance o Sickle cell anaemia in Afro-American population o Banding patterns in Cepaea

17. Gas exchange in animals and flowering plants

Surface area: volume

Specialised surfaces e.g. gills alveoli

Diffusion

Plants o Lenticels o Leaf structure, mesophyll and stomata

Animals o Transport mechanisms o Fish – gills o Insects – tracheoles and spiracles o Protozoans

Mammals o thorax structure, alveoli, ventilation, breathing control

18. The importance of molecular shape in living organisms

Receptor interactions o Drugs and Toxins o Immunoglobulins or antibody/antigen o Hormones – second messenger or direct action o Neurotransmitters and synapses

Carbohydrates o Structural (cellulose), storage (starch, glycogen)

Proteins o levels of structure, globular, fibrous, enzymes, specificity, properties, channel

proteins

Lipids o Phospholipids, storage, structural (beeswax)

Water o Dipole – polarity, cohesion, adhesion

Haemoglobin o Quaternary structure and O2 binding/release

DNA Double helix o accurate copying, stability, base pairing etc

Pigments o Rhodopsins/opsins, chl, phytochrome

Isomers

19. The factors affecting the growth and size of populations

Population defined

Description and explanation of typical population growth curve

Carrying capacity

Population change (Birth + immigration) – (death + emigration)

Density dependent and density independent factors

Examples of abiotic factors e.g. light, inorganic ions, oxygen, temperature

Competition for abiotic factors

Examples of biotic factors e.g. food supply, spread of disease/parasitism, predator prey relationships, interspecific competition, intraspecific competition, competitive exclusion

Demographic changes in human populations/ population pyramids

Birth control. 20. Cycles in Biology (June 2003)

Ecological cycles o N cycle – role of microorganisms in the processes of saprophytic nutrition, deamination,

nitrification, nitrogen fixation and denitrification. o C cycle – role of microorganisms in the breakdown (respiration) of complex organic

compounds into CO2 making it available for reuse

Metabolic cycles o Kreb’s cycle: acetyl CoA combines with a 4C molecule to produce a 6C molecule which

enters Kreb’s cycle; the 4C compound is regenerated during the cycle involving a series of oxidation reactions and the release of CO2; production of ATP and reduced NAD and FAD.

o ETS: cyclical reduction and oxidation of NAD, FAD and other ‘carriers’. o Synthesis and breakdown of ATP o Light independent reactions – CO2 accepted by RuBP to form 2 molecules of Glycerate-

3-PO4, reduction of Glycerate-3-PO4 to carbohydrate, and regeneration of RuBP.

Physiological cycles o Negative feedback mechanisms: regulation of body temp/blood glucose/blood water

potential. o Cardiac cycle: relate pressure and volume changes in the heart and aorta to

maintenance of blood flow. o Role of tropomyosin, calcium ions and ATP in the cycle of actomyosin bridge formation. o Nerve function – depolarisation/repolarisation of a neurone in terms of differential

membrane permeability and cation pumps, synthesis and resynthesis of Ach (synaptic transmission)/rhodopsin (rods) and restoration of a resting potential.

o Menstrual cycle. o Ventilation in fish, mammals, insects.

Life cycles o Mitosis / cell cycle – explanation of stages of mitosis, importance in growth and sexual

reproduction – vegetative reproduction. o Meiosis – importance of maintaining a constant chromosome number from generation

to generation; outline of process (no detail). o E.g.’s of life cycles might be provided in terms of mitosis, meiosis, fertilisation, and

chromosome number. o DNA replication – semi-conservative replication. o Predator / prey cycles.

21. The causes of variation and its biological importance (Jan 2004)

Gene mutation o Addition o Deletion substitution o Effect on alleles o Effect on polypeptide / protein

Sexual reproduction o Crossing over o Independent assortment o Random fusion of gametes o (allow chromosome mutation)

Environmental o Nutrients o Disease o Light o Temperature

Biological importance o Enables adaptation o Natural selection o Speciation o Evolution

22. The process of osmosis and its importance to living organisms (June 2004)

definition

effects on cells

turgidity and support

plasmolysis (idea)

lysis

cystic fibrosis

importance in animals role in relationship between plasma and tissue fluid

role in medulla of kidney

reabsorption in gut

sweat production neutral

importance in plants

role in movement of water from soil to leaves in plants

role in mass flow hypothesis for movement in plants

23. Energy transfers which take place inside living organisms (June 2004)

ATP

Synthesis from ADP and P

Role as an energy source

Photosynthesis o excitation of electrons o generation of ATP and reduced NADP o photolysis o reduction of glycerate phosphate to carbohydrate o structure of chloroplast in relation to energy transfer

Respiration o net gain of ATP in glycolysis o production of ATP in Krebs cycle o synthesis of ATP associated with electron transfer chain o ATP production in anaerobic respiration o Structure of mitochondrion in relation to energy transfer

Uses of energy in biological processes o active transport o muscle contraction o nerve transmission o synthesis o translocation o kidney function o nitrogen fixation o receptors

24. How microscopes have contributed to our understanding of living organisms (Jan 2005)

reference to both light and electron microscopes o e.g. resolution, magnification, techniques. o good candidates e.g. clear distinction of advantages disadvantages of each, historical

developments, reference to wavelength employed and limitations.

cell structures (typically) visible with each o good candidates – how observation of structures can inform about function; viewing

isolated organelles and their internal structure.

tissue structure o e.g. histology of digestive system related to function, muscle structure, kidney tubules,

leaf structure. o good candidates – explanation linking appearance of features to understanding function

observation of processes o e.g. cell division, fertilization, capillary circulation o good candidates – appreciation of using microscopes to observe dynamic processes, use

of tracers.

observation of organisms; classification o e.g. bacteria and viruses, taxonomic differences in small organisms. o good candidates – importance in understanding of disease.

other uses o e.g. understanding effects of disease/cancer, opportunities to improve/alter/etc living

organisms.

25. Enzymes and their importance in plants and animals (Jan 2005)

principles of enzyme action o e.g. catalysis, protein structure, active site, activation energy, enzyme-substrate

complex, specificity. o good candidates relate protein structure to specificity/active site, catalysis to activation

energy

factors affecting enzyme action o e.g. temperature, pH, enzyme/substrate concentration, inhibition o good candidates – relate changes in activity to denaturing/tertiary structure; effects of

concentration to active site availability, distinguish competitive/non competitive inhibition.

enzyme synthesis o reference to protein synthesis; link to genes, gene expression, effects of mutation. o good candidates – appreciation of connection between genes and enzyme production,

e.g. ‘one gene, one enzyme’. o roles and functions of enzymes in different processes. In each case good candidates

should specify enzyme and its function.

digestion o enzymes involved in mammalian digestive system, breakdown of polymers in other

circumstances, e.g. saprophytic digestion/mobilisation of storage compounds o good candidates – range of enzymes giving source and action in sequence in mammalian

digestion; reference to other breakdown.

metabolic pathways – photosynthesis and respiration o e.g. light independent reaction, Krebs cycle, ATP formation. o good candidates – reference to specific roles e.g. in light independent reseaction,

distribution in mitochondria/chloroplasts.

other specific examples o e.g. in nervous system, such as role of acetylcholinesterase in synapses, o in homeostasis, such as in glycogenesis, o in muscle action, such as role of ATPase, o in fertilisation, such as enzymes in acrosome, o in transcription/translation, such as role of polymerase.

26. Mean temperatures are rising in many parts of the world. The rising temperatures may result in physiological and ecological effects on living organisms. Describe and explain these effects. (June 2005)

Principle of destabilising effect of rising temperature on metabolic systems within organisms and on balance in ecosystems.

effect on rate of diffusion/gaseous exchange; possible consequences, e.g..

increased evaporation, more rapid uptake of ions by plants.

effect on proteins; possible increased rate of denaturation of tertiary structure. Increased rate of enzyme activity; possible increased dislocation of metabolic pathways.

Effect on photosynthesis (light independent reaction); increased rate with small increases, disruption with larger; increased rate of growth of (some) plants; possible increased rate of crop growth; effect of other limiting factors.

Effect on transpiration; increased rate of water loss and hence wilting /dehydration; reduced stomatal opening may effect photosynthesis; possible consequences of drought on ecosystem

Effect on respiration and metabolism; increased effect on growth and activity, especially of ectotherms.

Ecological effects of disruption of food webs and the dynamics of ecosystems, with changes in niches and hence communities.

Effect on species; extinction of species that are unable to adapt, especially ones with specialised requirements, limited opportunity for plants and some animals to spread to more suitable conditions as climate changes.

Effect on agriculture, increased growth of some crops and loss of others, and effect on productivity; possible redistribution to different parts of the world, and overall loss of agricultural land.

Ecological effect of increased rates of growth and reproduction, especially of bacteria, insects and pests; possible increased incidence of disease.

role of natural selection in adaptation to change. There are many possible alternative approaches to this essay and any biologically sensible effect of increasing change in temperature on living organism should be credited. In a good essay the specific effects of rising temperature will be explained and explicitly linked to their possible effects on physiology or ecology. A good candidate will also recognise the complex interactions involved and avoid giving simplistic explanations and doomsday scenarios.

27. The transfer of substances containing carbon between organisms and between organisms and

the environment

Transfer between organisms: o food chains and feeding relationships o carbon cycle o nitrogen cycle o digestion o cell transport

Transfer to/from the non-living environment o photosynthesis o respiration o exchange surfaces o (production and) removal of urea o human activities o agricultural ecosystems

Transfer of substances containing carbon between organisms and the environment

Transfer between organisms: o Food chains and feeding relationships o plants producers o idea of food chains as feeding relationships o with transfer energy o in substances containing carbon o Digestion and absorption (possible link to bacteria and fungi) o digestion/hydrolysis of large carbon-containing compounds o by enzymes o producing small/soluble compounds o which can be absorbed o Transport of organic molecules in and out of cells/across exchange surface o (possible link to bacteria and fungi o organic molecules (including sugars and amino acids) cross cell membranes o by facilitated diffusion o active transport o which requires ATP from respiration o involving carrier proteins and/or enzymes

Transfer to/from the non-living environment o Carbon cycle (and relevant parts of nitrogen cycle) o carbon enters biotic by photosynthesis o leaves biotic by respiration/combustion o role of bacteria/fungi as decomposers o of dead organisms/ faeces/ excretory products/urea

Photosynthesis o light-independent reaction o carbon dioxide reacts with ribulose bisphosphate o glycerate 3-P reduced to sugar o reduced NADP and ATP from light-dependent reaction o Calvin cycle

Respiration o link reaction/Krebs cycle o oxidation of intermediates o generation of reduced coenzymes o loss of carbon dioxide o Exchange surfaces - for carbon dioxide o for animals o and plants o large surface area - alveoli - mesophyll cells o short diffusion pathways - epithelium and endothelium - thin leaves and many stomata o maintaining diffusion gradient - capillary and respiration - photosynthesis and o respiration in mesophyll cells (time of day) o ventilation - breathing - via air spaces in leaf

28. Cells are easy to distinguish by their shape. How are the shapes of cells related to their

function? (June 2006)

Epithelial cells in animals o epithelial cells from small intestine o epithelial cells of alveoli, gill lamellae

Epidermal cells in plants o palisade mesophyll cells o stomatal guard cells o root hair cells

Reproduction o differences between egg and sperm cells

Transport of substances in organisms o red blood cells o endothelial cells of capillaries o xylem vessels o phloem sieve cells

Nervous coordination o neurones o rod and cone cells

Muscle o skeletal muscle

Animals: o Epithelial cells - intestinal, alveolar, kidney tubule, gill lamellae o Two examples allowed o As appropriate, relating to transport function(s)

(collectively) large SA flattened - short diffusion pathway folded membrane - larger SA for stated function podocytes - pores for filtrate formation

o Blood – transport red blood cells biconcave shape - increase SA for oxygen exchange move through capillaries

o Blood - exchange endothelial cells of capillaries

flattened - short diffusion pathway fenestrated in glomerulus

o Blood white cells phagocytes/macrophages amoeboid properties. related to movement into tissues/engulfing e.g. bacteria

Nervous system - neurones (and Schwann cells) o dendrites - make synaptic connection to other neurons o axon/dendron - carry nerve impulses over long distances o shapes of relay, motor and sensory o related to function o myelin sheath - faster transmission of impulses o Nervous system - receptors - NB could be other than light o cone/rod cells with distinctive ’heads’ - containing pigment o detect light o dendrites to synapse with bipolar/ganglion cell(s)

Muscle o elongated - contain rows of sarcomeres o leads to contraction in length o force generated in particular plane o branched in cardiac - give contraction in more than one plane

Ciliated o cells lining air passages/oviducts o push mucus/eggs along o remove trapped microorganisms/towards uterus

Sperm o sperm have beating tail/flagellum o streamlined shape o help sperm to move o find egg cell o acrosome with (digestive/hydrolytic) enzymes o digest way into egg cell

Plants and any other organisms: o Hair cells - of root o root - extension of epidermal cell o increases SA o for absorption of water and mineral ions o Hair cells - of leaf o leaf - extension of epidermal cell o reduces air flow/traps air near leaf surface o reduces water potential gradient for diffusion of water o reduces water loss by transpiration o Leaf cells (guard cell structure not in spec., but could be known and used) o palisade mesophyll are elongated o allows more to be packed side by side o to absorb maximum amount of light for photosynthesis o Transport in xylem and/or phloem o elongated cells o xylem vessels no end walls/ phloem sieve cells end plates o rows end to end to form ’tubes’

o no/less resistance to flow o Bacterial cells flagellum rotates pushes against external medium moves bacterium o Fungal hyphae (though usually cyncitial) o hyphae grow and branch through substrate increasing SA for absorption

29. Movements inside cells. (June 2007)

Plasma membranes and movement across

Protein synthesis

Movement through ER and Golgi

Cell division and chromosome movement

Water movement in plants/xylem

Translocation

Neurones and synaptic vesicles

Actin and myosin

DNA replication and mutation

Electron transport chains

Molecular/atomic/ionic movement Any other sensible example of movement inside cells should be credited. In a good essay, the emphasis should be on movement.

30. Transfers through ecosystems. (June 2007)

Photosynthesis – energy transfer

Respiration – energy transfer

Carbon cycle

Nitrogen cycle

Food chains

Ecological pyramids

Pesticide toxicity/bioaccumulation

Eutrophication

Digestion and absorption

Transfer of genetic material

Water cycle Any other sensible example of transfer through ecosystems should be credited. In a good essay,

the emphasis should be on transfers.

31. The part played by the movement of substances across cell membranes in the functioning of different organs and organs systems (June 2008).

Plasma membranes and movement across

Gaseous exchange system/ lungs

Digestive system/small intestine

Blood vascular system

Transpiration/root/stem

Mass flow/leaf/stem

Nervous system/eye

Excretory system/ kidney

Muscle systems

Liver, blood glucose

Root mineral ions

Lungs cystic fibrosis Any other sensible example of the movement of substances across cell membranes in the functioning of different organs and organ systems should be credited. In a good essay, the emphasis should be on movement across membranes involving organ function.

32. The part played by enzymes in the functioning of different cells, tissues and organs (June 2008)

Action of enzymes

Enzyme properties

Extracellular digestion

Nutrient cycles

Digestion in humans

Replication of DNA

Protein and enzyme synthesis

Metabolic pathways

Mutations

Coenzymes and enzyme action

Homeostasis

Neurone/synapse

Muscle contraction

Pesticide toxicity Any other sensible example of the part played by enzymes in the functioning of different cells, tissues and organs should be credited. In a good essay, the emphasis should be on the part played by enzymes.

33. Ions and Organisms (June 2009)

Osmosis and turgor

Haemoglobin dissociation, pH and carbon dioxid

Uptake/movement of water/mineral ions by/in plants

Ions in biological molecules

Hydrogen, photosynthesis and respiration

Anaerobic respiration and lactate

Nerve impulses and synaptic transmission

Regulation of blood water potential/kidney function

Muscle contraction

Nitrogen cycle

Eutrophication

Movement across membranes

Cystic fibrosis Any other sensible example of the role of ions, or exchange of ions by organisms should be credited. In a good essay, the emphasis should be on the ions rather than describing a process and then linking an ion to the process.

34. DNA and the transfer of information (June 2009)

Genes/how information is carried on DNA

Replication of DNA

Cell division - Mitosis and meiosis

Transcription and translation

Mutation

Genetic engineering

Gene therapy

Genetically modified organisms

Variation (in populations)

Evolution

Inheritance Any other sensible example of the transfer of information involving DNA should be credited. In a good essay, the emphasis should be on the transfer of information.

35. Carbon dioxide may affect organisms directly or indirectly. Describe and explain these effects. (June 2010)

Carbon dioxide affects the physiology of organisms o Pulmonary ventilation and the mechanism of breathing o Light-independent reaction of photosynthesis. Limiting factors o Role of chemoreceptors in controlling heart rate

The direct effects of increasing carbon dioxide concentration o Respiration, photosynthesis and human activity giving rise to short-term fluctuations

and long-term change. o Yield of crop plants

Carbon cycle o Indirect effects of increasing carbon dioxide concentration o Role of carbon dioxide in producing global warming o Life cycles and number of insect pests o Distribution of animals and plants o Effect of temperature on enzymes

36. The causes of disease in humans (June 2010).

Pathogens o Pathogens include bacteria, viruses and fungi o Pathogens cause disease by damaging cells and producing toxins o Cholera bacteria produce toxins resulting in diarrhoea o Symptoms and transmission of pulmonary tuberculosis o Horizontal gene transmission and MRSA

Lifestyle o Risk factors associated with cancer and coronary heart disease o The effects of fibrosis, asthma and emphysema on lung function o The biological basis of heart disease

Genetics o Differences in bases may lead to non-functional enzymes o Relationship between the cell cycle and cancer o Proto-oncogenes and tumour suppressor genes o Gene mutations

37. The role of carbon containing compounds in living organisms 38. The role of nitrogen containing compounds in living organisms 39. The roles of membranes in living organisms 40. The role of DNA in living organisms 41. Applications and implications of gene technology 42. Genetic variation and speciation 43. Control of the internal environment in living organisms 44. The movement of molecules and ions through membranes 45. Roles of pigments in living organisms 46. Light and life 47. Support and movement in living organisms 48. The chemical and biological control of insect pests