Biology Paper 2 Questions, 6 +11 Paper 2s, Biology Markscheme Active recall

2. Explain how a nerve message passes from one neuron to another neuron

- Nerve impulse travels to the end of the presynaptic neuron. There, depolarization causes calcium channels in the membrane to open, and calcium diffuses into the presynaptic neuron. Allowing the vesicles with neurotranmitters to fuse with the presynaptic membrane. The neurotransmitter is released into the synaptic cleft and diffuses across to attach to the receptor on the postsynaptic neuron. The postsynaptic neuron is depolarized, causing a new acion potential. The neurotransmitter is broken down or reabsorbed

Explain the relationship between the structure and function of arteries, capillaries and veins

Arteries: [3 max] a. thick walls to withstand high pressure/maintain blood flow/pressure; b. collagen fibres/elastic fibres/connective tissue (in outer layer) give wall strength/flexibility/ability to stretch and recoil; c. (smooth) muscle layer (contracts) to maintain pressure; d. narrow lumen maintains high pressure; e. smooth endothelium for efficient transport/reduced friction; Capillaries: [3 max] f. wall has one layer of cells allowing (fast) diffusion of substances; g. pores to allow lymphocytes/plasma to exit / to increase permeability; h. extensive branching increases surface area for exchange of materials; i. small diameter allows them to fit between cells/perfuse tissue; j. narrow diameter increases oxygen diffusion from RBC; Veins: [3 max] k. thin walls allow (skeletal) muscles to exert pressure on veins; l. thin outer layer of collagen/elastic/muscle fibres provide structural support; m. wide lumen allows great volume of blood to pass; n. valves prevent backflow; NB Every structure requires a function for the mark.

describe the causes of down syndrome

Down syndrome is caused by non-disjunction; occurs during meiosis; chromosome pairs fail to separate in meiosis I / chromatids in meiosis II / anaphase II; some gametes have an extra chromosome; can lead to zygotes/individuals with an extra chromosome / individual has 47 chromosomes; in Down syndrome this would be trisomy 21/extra chromosome 21; increased probability with increased age of mother/ages of parents;

Outline the role of the sodium-potassium pump in maintaining the resting potential.

a, sodium/potassium pump pumps sodium ions Na' out of axon and pumps potassium ions/K' in b. requires energy/ATP/against concentration gradients/active transport c. three sodium ions pumped out for every two potassium ions pumped in d results in charge difference between inside and outside where outside is positive relative to inside

Compare and Contrast hormonal and nervous communication

Similarities a both used for communication between cells/tissues/organs/parts of the body / WTTE b. both cause a response change in specific target cells OR both use chemicals that bind to receptors / hormones and neurotransmitters are both chemicals c. both can stimulate or inhibit (processes in target cells)/WITE k over long distances/between widely separated parts of the body/WTTE e both under (overall) control of the brain/CNS / brain (has role in) sending hormones and nerve impulses 1 both use feedback mechanisms/negative feedback / both used in homeostasis Differences Hormones Nerves 9 chemical (messenger) nerve impulse/electrical (signal) in transported in blood transported by neurons slower faster carried throughout body carned to single specific cell muscle fiber k all/wide range of tissues/organs affected only muscles/glands receive signals D(usually long term (persistence/response) short duration/short-lived (responses) m. example of use of hormonal and use of nervous communication LOOK AT TABLE SCREENSHOT

Hormones are distributed throughout the body by the blood. Outline the roles of two reproductive hormones during the menstrual cycle in women.

a FSH/follicle stimulating hormone stimulates the development of follicles/follicle cell division in the ovary to produce eggs b. LH/luteinizing hormone triggers ovulation development of the corpus luteum c estrogen stimulates development of the uterine lining/endometrium d. progesterone maintains the uterine lining endometrium OR inhibits other hormones by negative feedback eg, FSH e. HCG stimulates ovary to produce progesterone sin early pregnancy f. other verifiable hormone and roles relevant to the menstrual cycle

Describe the risk to the human population of indiscriminate use of antibiotics

a antibiotics block bacterial processes b. example of bacterial process c. variations exist naturally in a population / some are naturally resistant to the antibiotic d bacteria that are not resistant to this antibiotic will die / only resistant will survive (when antibiotic given) e this characteristic could be passed to next generation 1 (natural selection) leads to changes in the proportions/frequency in the population 9. human population will be exposed to antibiotic resistant bacteria and will not have antibiotic to kill them h. (antibiotic resistant bacteria) may pass resistance to other bacteria species types by means of plasmids (so other bacteria species turn resistant too)

Explain what happens to an enzyme if there is a change in pH.

a change in pH can cause a change in the tertiary structure of the enzyme OR enzyme denatured b. causing a change in the active site / substrate not able to bind c. the enzyme will not work as efficiently I decreased rate of reaction d. (may no longer be) the optimum/optimal pH for enzyme activity

outline the causes and consequences of blood clot formation in coronary arteries

a coronary heart disease/CHD/coronary artery disease/CAD occurs when there is reduction of oxygen to the heart muscle b. high ratio of LDL to HDL/fatty diet leads to plaque formation in arteries c. plaque breaks off causing damage that activates blood clot formation d. clots in the bloodstream> may block a coronary artery/coronary thrombosis reducing blood flow oxygen OR clots can cause heart attack/muscle death e sickle cell anemia scrisis produces blood clots that can cause coronary/arterial blockage

Explain how insects excrete nitrogenous waste

a excreted as uric acid b. excretion by Malpighian tubules c. nitrogenous waste ammonia caccumulates in hemolymph d. nitrogenous wastaammonia absorbed by Malpighian tubules e. ammonia converted to uric acid f. conversion to uric acid requires energy ATP high solute concentration in Malpighian tubules OR active transport of ions/Na/Kinto Malpighian tubules h water absorbed by osmosis flushes uric acid nitrogenous wastato chindo gut i. Waterlions reabsorbed from the feces and returned to hemolymph uric acid precipitates becomes solid forms a paste so can pass out with little water k. uric acid excreted egested with the feces water conservationlosmoregulation OR reduces mass of water ein body m. uric acid is non-toxic

Explain how amino acids in casein could reach the liver, starting from the moment when the person takes a bite of pastry cream pie.

a food is mechanically physically digested in the mouth through mastication chewing b. mixed with saliva (to form the bolus) in mouth c. moved through esophagus/peristalsis d. proteins digested in the stomach (pepsin) pancreas secretes enzymes into lumen of small intestine OR (endo)peptidases/trypsin) are secreted by pancreas enzymes digest macromolecules to monomers OR endopeptidases digest polypeptides to peptides amino acids 9. villi of small intestine absorb amino acids h. amino acids carried to blood capillaries 1 blood (capillaries) carry amino acids to (hepatic portal) veinblood vessel going to liver amino acids absorbed by active transport protein pumps in the villi.

Outline how sperm are produced from diploid cells in the testis and how this production can be sustained over many decades of adult life.

a germinal epithelium divide endlessly (by mitosis giving rise to spermatagonia) b. spermatogonia are diploid/2n C. spermatogonia divide by mitosis / provide a continuous supply throughout adult life d. (some) spermatogonia enlarge forming primary spermatocytes e primary spermatocytes undergo the first division of meiosis/meiosis f. secondary spermatocytes produced are haploidin secondary spermatocytes undergo the second division of meiosis (to produce spermatids) ✓ spermatids develop tails OR spermatids differentiate into spermatozoa / spermatids associate with Sertolicells

Describe the genetic and hormonal control of male sexual characteristics in a human.

a male if (X and Y chromosomes present bgene on Y chromosome/SRY promotes development of testes (from embryonic gonads) c. testes secrete testosterone d. testosterone stimulates sperm production/spermatogenesis e testosterone stimulates development (in fetus) of male genitals/primary sexual characteristics f. testosterone stimulates development of male secondary sexual characteristics OR testosterone causes changes to become adult male during puberty

Outline the actions taken by the body to avoid infection when the skin is cut.

a platelets/cut tissues release clotting factors b. «clotting factors» activate thrombin from prothrombin c. thrombin converts fibrinogen to fibrin d. «fibrin forms a clot/scab/mesh that seals the cut e. phagocytic white blood cells ingest pathogens

State one use of monoclonal antibodies.

a pregnancy testing kits/detection of hCG (to diagnose pregnancy) b. produce antibodies for treating arthritis C difficile/anthrax/psoriasis/ulcerative colitis/asthma/ankylosing spondylitis/Crohn's disease/multiple sclerosis/HIV/other named disease if verified/targeting tumor cells in treatment of cancer OR gives artificial/passive immunity (if injected) c. blood typing/testing urine for drugs/other verified specific use of monoclonal antibodies.

Outline the role of lymphocytes in defence against disease

a produce antibodies b. memory cells confer immunity c. specific immunity results from production of antibodies specific to a particular antigen d. recognize pathogens e destroy foreign cells/cancer cells

Explain how valves control the flow of blood through the heart

a valves open and close in response to changes in blood pressure/heart contraction/pumping b. valve prevents backflow/maintains direction of blood flow c. valves allow heart chambers to fill to empty

Outline the functions of villi in the small intestine.

a, increase the surface area for absorption b. absorption of digested foods/nutrients c. absorption of mineral ions/vitamins

The light-dependent reactions in photosynthesis take place on the thylakoid membranes. Explain the light- [8 marks] dependent reactions

a. (chlorophyll/pigments/antenna complex) in photosystem II absorb light; b. light/photoactivation produces an excited/high energy/free electron; c. electrons pass from carrier to carrier/along electron transport chain/e.t.c.; d. protons pumped across thylakoid membrane/into thylakoid space; e. ATP produced (by the light dependent reactions); f. ATP production by chemiosmosis/by ATP synthase/ATP synthetase; g. electrons from photosystem II passed to photosystem I; h. light/photoactivation excites electrons in photosystem I (to higher energy level); i. production of NADPH/reduction of NADP(+) (using electrons from photosystem I); (reject NAD in place of NADP. Accept reduced NADP instead of NADPH) j. electrons from photolysis (needed) for photosystem II; k. oxygen from photolysis is a waste product/by-product/passes out/excreted; l. in cyclic photophosphorylation electrons from photosystem I return to it;

Outline the processes that occur during the first division of meiosis

a. (consists of) prophase, metaphase, anaphase and telophase; b. chromosome number halved/reduced/(diploid) to haploid; c. homologous chromosomes pair up/form a bivalent/synapsis in prophase; d. crossing over between non-sister chromatids/chromatids of different homologues; e. nuclear envelope breaks down (at end of prophase/start of metaphase); f. tetrads/bivalents/homologous pairs move to/align on equator/cell centre/on metaphase plate in metaphase; (accept homologous chromosomes without pairs if pairing has already been described) g. attachment of spindle fibres/microtubules to centromeres/kinetochores; h. (homologous) chromosomes separate/pulled to opposite poles in anaphase; i. nuclear envelopes reform/do not reform (because of meiosis II) in telophase; Accept the above points in a series of annotated diagrams. Reject answers with single chromatids forming pairs in metaphase or separating or moving to opposite poles in anaphase.

Cell membranes separate aqueous environments in cells. Explain how the properties of phospholipids help to maintain the structure of cell membranes.

a. (labelled) phospholipid consisting of head and two tails; b. head is glycerol and phosphate; c. tails are fatty acid chains; d. head hydrophilic and tails hydrophobic; [8 marks] e. hydrophilic molecules/heads attracted to/soluble in water; f. hydrophobic molecules/tails not attracted to water but attracted to each other; g. (properties of phospholipids leads to) formation of double layer in water; h. stability in double layer because heads on outer edge are attracted to water and tails are attracted to each other in middle; i. phospholipid bilayer in fluid/flexible state because of attraction of non-polar tails to each other; j. (fluidity) allows membranes to change shape/vesicles to form or fuse with membrane/(fluidity) allows cells to divide; k. non-polar amino acid side chains attracted to (hydrophobic) tails;

Outline how depolarization of the membrane of an axon occurs.

a. (local depolarization) causes ion / sodium / voltage gated channels to open ✓ b. altering membrane permeability to sodium ions/Nat/positive ions / Nat diffuses into the cytoplasm ✓ c. membrane potential of the axon) changes from negative to positive d. a threshold potential is reached and an action potential is generated ✓

explain the causes and consequences of PKU

a. (point) mutation of gene; b. defective enzyme/phenylalanine hydroxylase (PAH); c. phenylalanine/Phe not broken down to tyrosine/Tyr; d. phenylalanine/Phe accumulates; e. (if not treated) symptoms mental retardation/seizures; f. diet free of phenylalanine/Phe to avoid symptoms;

Describe four different types of transport of substances across a membrane.

a. (simple) diffusion when molecules move down a concentration gradient directly through membrane/unaided by carrier molecule; b. (passive transport by) facilitated diffusion through (specific) channel proteins; c. osmosis of water via aquaporins/from area of low solute concentration to area of high solute concentration; d. active transport against a concentration gradient using protein pumps/ATP; e. vesicles attach to plasma membrane and release materials to exterior/ exocytosis; f. cell membrane invaginates/pinches off to bring material to interior / endocytosis / phagocytosis;

Describe the genetic code and its relationship to polypeptides and proteins

a. (the genetic code is based on) sets of three nucleotides/triplets of bases called codons; b. bases include adenine, guanine, cytosine and thymine in DNA / adenine, guanine, cytosine and uracil in RNA; (do not accept ATCG) c. each codon is code for one amino acid; d. some codons are (start or) stop codons; e. DNA is transcribed into mRNA by base-pair matching/complementary base pairing; f. mRNA is translated into a sequence of amino acids/polypeptide; g. each gene codes for a polypeptide; h. polypeptides may be joined/modified to form proteins;

Many cell functions, like synthesis of macromolecules and transport, require energy in the form of ATP. Explain how ATP is generated in animal cells.

a. ATP is a form of energy currency/immediately available for use; b. ATP is generated in cells by cell respiration (from organic compounds); c. aerobic (cell respiration) requires oxygen; d. anaerobic (cell respiration) does not require oxygen; e. glycolysis breaks down glucose into pyruvate; f. glycolysis occurs in cytoplasm; g. (by glycolysis) a small amount of ATP is released; h. ADP changes into ATP with the addition of a phosphate group/phosphoric acid / accept as chemical equation; i. in mitochondria/aerobic respiration produces large amount of ATP / 38 mols (for the cell, per glucose molecule); j. oxygen/aerobic respiration is required for mitochondrial production of ATP; k. in mitochondria/aerobic respiration pyruvate is broken down into carbon dioxide and water;

Describe the use of DNA profiling to determine paternity

a. DNA from child, mother and possible father(s) used to establish paternity; b. (DNA profiling is done) for legal reasons / divorce / inheritance; c. (DNA profiling is done) for personal reasons / self-esteem issues for children/fathers/parents; d. DNA copied/amplified using PCR; e. DNA cut using restriction enzymes; f. (gel) electrophoresis used to separate DNA fragments; g. pattern of bands is produced (in gel); h. analysed for matches between child with mother and possible father; i. (about) half the child's bands will match the father (while the other half will match the mother);

Explain the consequences of celiac disease for absorption of digested nutrients.

a. celiac disease/gluten causes) much smaller villi/flattened villi/smaller surface area (of villl) / no villi b. (smaller villi leads to) less efficientless/slower/poor absorption OR nutrients/energy lost/ fatigue/malnutrition may result c. (celiac sufferers) must eat a gluten-free diet/WTTE

Explain how DNA is used to pass on genetic info, but also include variation

a. DNA is replicated/copied semi-conservatively/from a template; b. mutations can be a source of variation / resulting protein has new or different functions; c. mutations/changes in the DNA may not result in changes in the amino acid for which the triplet codes; d. genetic code is redundant; e. genes occur as paired alleles which can be different; f. crossing-over occurs; g. recombines linked alleles producing new combinations; h. random orientation of bivalents / homologous chromosomes (in metaphase I); i. large genetic variation in (haploid) gametes / 2n / 223; j. random recombination of alleles during fertilization (leads to variation); k. different phenotypes among members of the same population; l. natural selection may lead to enhanced survival of recombinants;

Hormones such as FSH (follicle stimulating hormone) and LH (luteinizing hormone) affect the development of [6 marks] certain cells by binding to receptors in the plasma membranes. Outline the role of FSH and LH in the menstrual cycle

a. FSH stimulates estrogen secretion by follicle cells; b. at start of menstrual cycle; c. leading to development of endometrium; d. (FSH and) LH (rise to a peak and) causes egg to be released/ovulation; e. causes follicle cells to secrete less estrogen/more progesterone; f. progesterone maintains endometrium/uterine lining g. LH promotes change of follicle to corpus luteum; h. secretion of LH and FSH regulated by negative feedback; i. regulated/inhibited by high estrogen and progesterone levels; j. low progesterone levels cause menstruation;

Explain the process of gas exchange taking place in the alveoli

a. O diffuses into blood and CO2 diffuses out from blood b. blood entering the alveoli is high in CO/low in 02 OR air in alveolus is high in O/low in CO2 c diffusion (in either direction) take place due to concentration gradients d. concentration gradients maintained by ventilation/blood flow large surface area created by many alveoli/spherical shape of alveoli for more efficient diffusion 1. rich supply of capillaries (around alveoli) allows efficient exchange type I pneumocytes are thin to allow easy diffusion/short distances h gases must dissolve in liquid lining of alveolus in order to be exchanged 1 type il pneumocytes secrete surfactants to reduce surface tension/prevent lungs sticking together type Il pneumocytes create moist conditions in alveoli

explain the cause and consequences of biomagnification using one named example.

a. a process in which chemical substances become more concentrated at each trophic level; b. valid named example (for example mercury, organophosphorous pesticides, DDT, TBT); c. these substances cannot be broken down / are broken down slowly by metabolism; d. are often stored in (adipose) tissues; e. each organism consumes large quantities of the trophic level below it; f. so substance accumulates/increases to reach toxic levels; If no example is given award [3 max].

Explain how acetylcholine initiates an action potential in a postsynaptic membrane.

a. acetylcholine binds to the receptor protein b. (causing a) change in tertiary structure / conformation of protein c diffusion/entry of ions / Na through the receptor channel protein allowed

Describe how water is carried through a flowering plant.

a. active transport of solutes from soil into roots; b. draws water by osmosis c. root hairs provide a large surface area for water uptake; d. carried through xylem vessels; e. transpiration is the loss of water (vapour) from leaves and stems / stomata; f. (transpiration) creates suction/pull/negative pressure; g. cellulose wall with rings of lignin give strength to resist (low) pressure; h. water pulled up due to capillary action/cohesion/adhesion; i. continuous column of molecules/transpiration stream;

Outline adaptive radiation (2 points)

a. ancestral species occupies new environment / survives natural disaster; b. different members of the species are exposed to different selection pressures; c. gives rise to new species that share common structures adapted to new environment / occupy all niches; d. example of divergent evolution/homology; e. accept valid example eg Galapagos finches, vertebrate pentadactyl limb;

Explain the evolution of antibiotic resistance in bacteria.

a. antibiotics (are chemicals) used to treat bacterial diseases; b. within populations, bacteria vary in their (genetic) resistance to antibiotics/fitness; c. resistance arises by (random) gene mutation; d. when antibiotics are used antibiotic-sensitive bacteria are killed; e. (natural) selection favours those with resistance; f. resistant bacteria survive, reproduce and spread the gene / increase allele frequency of resistant bacteria; g. the more an antibiotic is used, the more bacterial resistance/the larger the population of antibiotic-resistant bacteria; h. genes can be transferred to other bacteria by plasmids; i. doctors/vets use different antibiotics but resistance develops to these as well; j. multiple-antibiotic resistant bacteria evolve/it becomes difficult to treat some infections;

Compare oogenesis and spermatogenesis

a. both produce haploid cells / both produce (mature/male/female) gametes; b. both have mitosis at start/in epithelium / both involve mitosis and meiosis; c. both have cell growth before meiosis; d. both involve differentiation (to produce a specialised gamete);

explain the roles of actin and myosin in muscle contraction

a. calcium/Ca2+ frees myosin binding sites on actin/thin filament; b. ATP (linked to myosin head) hydrolysed to ADP + P(i); c. myosin head cocked/assumes high energy configuration; d. myosin head binds to actin / forms a cross-bridge; e. actin filament slides towards center of sarcomere / dark band; f. combined sliding of actin filaments shortens muscle fiber / muscle; g. ATP binds to myosin head and breaks cross-bridge; Accept answers with properly annotated diagrams.

Explain the role of cells in the defense against infectious disease

a. cells of skin provide a physical barrier/produce fatty acids/lactic acid/lysozyme which stops entry of microbes OR mucous membranes produce mucus to trap pathogens OR stomach cells produce hydrochloric acid which kills microbes b. platelets start the clotting process preventing access of pathogens c. (two types of) white blood cells fight infections in the body d. phagocytes ingest pathogens (by endocytosis/phagocytosis): f. production of antibodies by lymphocytes/B cells g. in response to particular pathogens/antigens h gives specific immunity i. lymphocyte/B cell makes only one type of antibody i plasma cells produce large quantity of (one type of) antibody k some lymphocytes act/remain as memory cells 1. can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered: m. results in faster defence against second exposure to specific antigen/pathogen/disease;

Outline the role of proteins in active and passive transport of molecules through membranes.

a. channel proteins allow diffusion/osmosis/passive transport; b. large/polar molecules cannot cross the (hydrophobic) membrane freely; c. facilitated diffusion involves moving molecules through proteins down their concentration gradient/without requiring ATP; d. aquaporins (specific integral membrane proteins) facilitate the movement of water molecules/osmosis; e. some proteins (for facilitated diffusion) are specific to molecule/ions; f. active transport involves moving molecules through proteins against their concentration gradient/requiring ATP; g. (some) proteins in the membrane are pumps / pumps perform active transport / sodium potassium pump;

Explain cladistics as a method to classify organisms

a. cladistics uses cladograms/tree diagrams; b. show clades/branches (in parallel) that begin at a point/node; c. each clade includes a (common) ancestral organism/node and all its descendents; d. members of a clade share derived/inherited characteristics; e. clades are nested/subsets of larger clades; f. cladograms show evolutionary history/origin of organisms / phylogeny; g. branch length (of clade) can indicate (relative) amount of genetic change/time; h. clades based on (objective) molecular analysis/genetic evidence / differ in amino acid sequences/DNA base changes/mutations; i. fewest number of differences/maximum parsimony determines branch separation; j. predictability of DNA base changes/mutation rates suggests evolutionary timelines; k. problems arise when gene change varies (greatly) from one gene to the next; l. cladograms may not match traditional/Linnaean classification; m. (mismatch) prompts re-examination of data / reclassification of a group; Some of the above points may be included in a correctly annotated diagram clearly stating above points.

Describe the process of blood cloting

a. clotting factor released by platelets/damaged tissue/cells; b. cascade/series of reactions; c. prothrombin (activated) to thrombin; d. soluble fibrinogen to insoluble fibrin / thrombin converts fibrinogen to fibrin; e. mesh of fibrin/fibres seals wound/traps platelets/red blood cells;

Explain the inheritance of color blindness

a. colour blindness caused by recessive allele / colour blindness is recessive; b. gene located on X chromosome/sex-linked; c. Xb is allele for colour blindness and XB is allele for normal colour vision/dominant allele; d. male has one X and one Y chromosome; e. male has only one copy of gene(s) located on X chromosome; f. X chromosome (in males) comes from female parent; g. any male receiving allele from mother will express the trait; h. XbY is genotype for colour blind male; i. many more males have colour blindness than females; j. female will express colour blindness only if is homozygous recessive/Xb Xb; k. heterozygous/XB Xb female is a carrier; l. colour blind female could be born to colour blind father and carrier mother;

outline the outcomes of the human genome project

a. complete human DNA/chromosomes sequenced; b. identification of all human genes / find position/map (all) human genes; c. find/discover protein structures/functions; d. find evidence for evolutionary relationships/human origins/ancestors; e. find mutations/base substitutions/single nucleotide polymorphisms; f. find genes causing/increasing chance of/develop test for/screen for diseases; g. develop new drugs (based on base sequences) / new gene therapies; h. tailor medication to individual genetic variation / pharmacogenomics; i. promote international co-operation/global endeavours;

Outline the process of inhalation

a. diaphragm contracts / moves downwards/flattens b. external intercostal muscles contract C (muscle contraction) moves the rib cage upwards and outwards d. increases volume of the thorax/lungs o difference in pressure/decreasing pressure causes air to flow into lungs / lungs inflate

Following fertilization, cells in the developing embryo differentiate. Outline a technique for cloning using differentiated cells

a. differentiated/somatic/diploid cells taken from donor animal/sheep udder; b. (diploid) nucleus from donor cells removed; c. ova/eggs cells removed from (donor) animal/female sheep; d. (haploid) nucleus removed from eggs/ova; e. (diploid/donor's) nucleus is fused with/inserted into egg/ovum (to form zygote); f. embryo (from cell with donor nucleus and egg from surrogate) implanted in uterus of surrogate mother; g. normal pregnancy and birth is completed; h. offspring is a genetic copy/clone of the donor mother/diploid nucleus WTTE; [5 marks]

In the placenta, many substances are transported across membranes. Explain the structure and role of the [8 marks] placenta.

a. disc shaped structure b. embedded in uterus wall; c. connected to fetus by umbilical cord; d. contains fetal and maternal structures/tissues; e. placental villi/maternal intervillous space provide large surface area for exchange of materials; f. blood of fetus and mother flow close to each other (but no mixing); g. materials exchanged/diffuse (through membranes) between mother and fetal blood; h. oxygen/nutrients/antibodies/other substances diffuse (through membranes) to fetus; i. CO2 and wastes diffuse (through membranes) to mother; j. caffeine/drugs/alcohol/viruses from mother may damage fetal development; k. takes over role of corpus luteum (to produce hormones); l. produces hormones/estrogen/progesterone/HCG;

Explain the advantages of using hybridoma cells in the production of monoclonal antibodies.

a. endless cell divisions/unregulated mitosis (in hybridoma cells) b. large clone/population of identical cells produced c. all cells in clone) produce same type of antibody d. large amount of chosen) antibody can be produced.

Outline how a protein such as gluten is digested.

a. enzymes/protease required b. (protease/peptidase) breaks peptide bonds/bonds between amino acids c. hydrolysis adds water molecules/breaks peptide bonds between amino acids d. protein/macromolecule converted to monomer/amino acids e. endopeptidase/enzymes/protease/trypsin secreted by the pancreas

Structure and function of nucleosomes

a. found in eukaryotes; b. consists of DNA wrapped around proteins/histones; c. histones are in an octamer/group of eight; d. are held together by another histone/protein; e. in linker region; f. help to supercoil chromosomes / to facilitate DNA packing; g. (function is to) regulate transcription / gene expression;

Explain how spermatogenesis

a. germinal cells / spermatogonia undergo mitosis to keep a supply of germinal cells present; b. some germinal cells / spermatogonia grow larger to become primary spermatocytes; c. primary spermatocytes go through meiosis I; d. to form secondary spermatocytes; e. these secondary spermatocytes go through meiosis II; f. to produce spermatids; g. spermatids differentiate/grow a tail and reduce their cytoplasm h. spermatids associated with nurse cells (Sertoli cells); i. sperm detach from Sertoli cells and enter lumen of the seminiferous tubule; j. testosterone stimulates sperm production;

Outline how and where energy is stored in plants

a. glucose (from photosynthesis) stored as starch; b. starch stored (as granules) in chloroplast/in plastids; c. (starch stored) in seeds/storage roots/stem tubers; d. stored as lipids/oils; e. (lipid/oils storage) in seeds; f. lipids store twice as much energy per gram as starch;

state two symptoms of type 2 diabetes

a. glucose in urine; b. high blood glucose; c. frequent urination / dehydration/excess thirst; d. constant hunger; e. weight loss; f. tiredness;

Following germination of seeds, plants undergo a rapid increase in the number of cells. Describe stages in the cell cycle that result in this increase of cells.

a. growth phase/G-1: synthesis of proteins/cytoplasm/organelles; b. synthesis phase/S-phase: replication of DNA; c. second growth phase/G-2: continued growth of cytoplasm/molecular synthesis/duplication of organelles; d. prophase: chromosomes super-coil to prepare for mitosis / nuclear envelope disappears / spindle fibres form; e. metaphase: chromosomes line up at equatorial/metaphase plate / spindle fibres attach to centromeres/chromosomes; f. anaphase: chromatids move along microtubules/spindle fibres move chromatids toward opposite poles; g. telophase: nuclear membranes form around each cluster of chromosomes; h. cytokinesis: new plasma membrane forms between the nuclei / cell plate forms; i. a new cell wall forms; j. (mitosis) results in two cells with identical nuclei;

describe how the liver helps to maintain human health

a. helps regulate blood glucose level / converts glucose to glycogen and back; b. prevents excess glucose that could damage cells / lack of glucose could limit cell growth/activity / OWTTE; c. stores/recycles iron; d. stores vitamin A/vitamin D; e. synthesizes plasma proteins/cholesterol; f. provides essential substances for cell growth/hormone production; g. detoxifies substances / protects the body from damage from toxic substances (as alcohol); h. breaks down erythrocytes/hemoglobin; i. production of bile for digestion (of fats); j. (production of bile) reduces build-up of bilirubin in the blood / prevents jaundice;

Outline how males inherit hemophilia and how females can become carriers for the condition

a. hemophilia is due to a recessive allele/is a recessive trait / XH is normal allele and Xh is hemophilia allele; b. hemophilia is sex linked; c. allele/gene is on the X chromosome; Reject disease/hemophilia carried on X chromosome. d. (sex chromosomes in) females are XX while males are XY; e. Y chromosomes do not have the allele/hemophiliac males are XhY; f. males inherit their X chromosome from their mother/do not pass the allele to sons; g. males have only one copy so recessive trait/allele is not masked; h. males have a 50% chance of hemophilia/receiving the allele if mother is a carrier; i. carrier is heterozygous for the gene/is XHXh; j. dominant/normal allele masks the recessive allele (so clotting is normal); k. females inherit one X chromosome from father and one from mother; l. affected/hemophiliac males have carrier daughters; m. hemophilia allele could have been inherited from either parent; [8 marks Accept the points above explained either in text or clearly using a Punnett grid or genetic diagram, but not for simply reproducing an unlabeled Punnett grid or diagram without explanation.

Explain the possible health consequences of a diet rich in protein

a. high amount of one nutrient may cause deficiency in another one; b. excess protein not stored as protein by the body / converted to fat; c. results in weight/mass loss in many people (due to fat/carbohydrate deficiency); d. health problems such as kidney stones/other health problems; e. high protein as part of a weight/mass loss diet;

Explain the mechanism of ventilation in the lungs in order to promote gas exchange for cell respiration.

a. inspiration/inhalation brings air into lungs; b. external intercostal muscles contract; c. and move rib cage upwards and outwards; d. diaphragm flattens/contracts; e. increasing thoracic volume; f. pressure decreases from atmospheric pressure so air rushes into lungs; g. expiration/exhalation forces air out; h. internal intercostal muscles contract / external intercostal muscles and diaphragm relax; i. abdominal/abdomen wall muscles contract and push diaphragm upwards; j. decreasing thoracic volume; k. increasing pressure in lungs so air is forced out; l. a concentration gradient between air sacs and blood needs to be maintained;

describe the features of alveoli in human lungs that adapt them for efficient absorption of oxygen

a. large surface area from having many alveoli; b. single/flattened layer of (thin) cells in wall; Reject one-cell membrane/thin membrane. c. (surrounded by) dense network of capillaries/capillary bed; d. short distance for gases/oxygen/carbon dioxide to diffuse; e. moist lining / film of moisture on inside of alveolus; f. moisture allows oxygen/gases to dissolve; g. diffusion of oxygen down concentration gradient;

outline how leucocytes defend the body against pathogens

a. leucocytes/phagocytes/macrophages can recognize pathogens/foreign matter; b. (phagocytes) engulf pathogens by endocytosis/phagocytosis; c. migration to tissues/squeezing out of capillaries; d. each pathogen has specific antigens; e. leukocytes/lymphocytes produce antibodies by reacting to specific antigen/ pathogens; f. antibody joins to (specific) antigen inactivating/destroying them; g. lymphocyte makes a clone/copies itself; h. thus increasing the total number of (specific) antibodies;

Outline the basic techniques used for the gene transfer of hemophilia treatment using Factor IX

a. mRNA/gene coding for factor IX extracted from human cell/tissue; b. mRNA copied to DNA/cDNA (using reverse transcriptase); c. plasmids used (for gene transfer); d. restriction enzyme/endonuclease used to open plasmid/cut DNA; e. complementary bases/sticky ends on gene and plasmid/link gene to plasmid; f. sealed using ligase; g. recombinant plasmid/plasmid containing desired gene taken up by bacteria; h. isolate/clone the recombinant/transformed bacteria; i. bacteria cultured/grown in fermenter to produce factor IX;

Outline how plasma cells become activated.

a. macrophages/phagocytes recognize engulf pathogen and display antigens b. antigen binds to T cell helper T cell / antigen causes activation of T cell c, antigen binds to antibodies in membrane of B cells d. (activated) T cells activate B cells (that have the antigen bound to them) e. activated B cells divide to produce a clone of cells active plasma cells develop from the clone of cells/from activated B cells

Meiosis in humans produce cells that participate in fertilization. Outline the processes involved in meiosis.

a. meiosis reduces a diploid cell into (four) haploid cell(s); b. (during prophase I) homologous chromosomes pair up/synapsis; c. chromatids (break and) recombine / crossing over d. (metaphase I) (homologous chromosomes) at the equator of the spindle / middle of cell; e. (anaphase I) (homologous) chromosomes separate and move to opposite poles; f. (telophase I) chromosomes reach poles and unwind WTTE; g. (prophase II) chromosomes (condense and) become visible, new spindles form; h. (metaphase II) chromosomes line up at the centre of the cells/equator; i. (anaphase II) sister chromatids separate; j. (telophase II) chromatids reach the poles and unwind;

Discuss the endosymbiotic theory for the origin of eukaryotes.

a. microorganisms/prokaryotes taken into cell by endocytosis; b. kept inside cell and perform respiration/photosynthesis; c. developing into mitochondria/chloroplasts; d. mitochondria/chloroplasts have double membranes (as expected in cells taken in by endocytosis); e. mitochondria/chloroplasts have (circular naked) DNA (as prokaryotes); f. mitochondria/chloroplasts have 70S ribosomes (as prokaryotes); g. mitochondria/chloroplasts grow and divide like (prokaryotic) cells;

Explain how minerals move into plants.

a. minerals bound to soil particles; b. examples of three nutrients from: phosphate, nitrate, magnesium, iron, calcium, potassium, sodium, magnesium; c. minerals dissolve in water; d. mass flow causes movement of minerals with movement of water through soil; e. minerals diffuse down a concentration gradient towards roots (as the mineral concentration next to the roots is continuously decreasing); f. minerals enter the plant through roots; g. by active transport / use of ATP; h. branching of roots increases surface area for absorption of minerals; i. root hairs increase surface area (for the absorption of minerals); j. hypha of (mutualistic) fungi may enhance movement of selected ions into roots / increase surface area; k. root hairs have many mitochondria to provide energy/ATP for active transport; l. export of H+ creates electrochemical gradient / displaces ions bound to soil/clay; m. that causes positive mineral ions to diffuse into (root) cells; n. negative mineral ions cross membrane linked to H+ ions moving down (H+) gradient;

Describe the consequences of overproduction of offspring

a. more (offspring) than the environment can support / carrying capacity reached; b. increased mortality/lower life expectancy/more deaths; c. competition (for resources) / struggle for survival; d. food/mates/nest sites/territory/other example of resource shortage / example of greater need; e. variation between members of population / example of variation; f. better adapted more likely to survive / converse; (reject Lamarckian statements such as those who adapt survive) g. better adapted reproduce / pass on (favourable) genes/traits / converse; h. natural selection / (survival of fittest) leads to evolution;

Using a named example of a genetically modifed crop, discuss ethical issues.

a. named example of verified genetically modified crop; eg, Bt corn / golden rice; Example must be verifiable. b. specific gene added / new protein synthesized by the crop plant / specific modification; eg gene from Bacillus thuringiensis / cry protein; c. biological effect of the modification; eg, makes the plant toxic to (herbivorous) insects / insect pests / corn borers; [2 max] for benefits and [2 max] for harmful effects / costs; d. a benefit of specific genetic modification; eg, increased crop yields / less land needed; e. a second benefit of this specific modification; eg, reduced need for use of chemical pesticides; f. a harmful effect of specific genetic modification; ingestion of toxin by nontarget species; g. another specific harmful effect; eg, concerns about contamination of neighbouring non-GMO crops affecting trade;

Explain the control of body temp in humans

a. normal body core temperature constant/36.5 to 37.5°C; (accept single values within this range) b. regulated by negative feedback/homeostatic mechanisms; c. hypothalamus is the centre of thermoregulation; d. hypothalamus sends impulses to the body to increase/decrease temperatures; [8 marks] e. release of sweat (by sweat glands in the skin) if skin temperature rises; f. evaporation of water cools the body; (concept of evaporation must be mentioned) g. heat is transferred by blood; h. transfer of heat from body core in blood to surface; i. if temperature rises, increased flow of blood/heat to the skin/vasodilation of skin blood vessels/arterioles; (do not accept veins, arteries or capillaries) j. if temperature drops, decreased flow of blood/heat to the skin/vasoconstriction of skin blood vessels/arterioles; (do not accept veins, arteries or capillaries) k. shivering increases heat production (in muscles); l. example of one behavioural mechanism; (eg reducing activity (to lower body temperature) / reducing exposed surfaces (to reduce heat loss)

explain the process of photophosphorylation in chloroplasts

a. occurs in stroma (of chloroplast); b. energy/ATP and NADPH provided by the light-dependent reactions; c. Calvin cycle; d. carbon dioxide fixed to RuBP / carboxylation of RuBP/ribulose bisphosphate; e. by RuBP carboxylase/rubisco; f. forms unstable 6C compound / forms 6C compound which splits; g. glycerate 3-phosphate (is produced by carbon fixation); h. (glycerate phosphate) to triose phosphate/3C sugar by reduction/adding hydrogen; i. using NADPH/reduced NADP; j. triose phosphate/3C sugar converted to form hexose/glucose (phosphate); k. most/5/6 of triose phosphate used for regeneration of RuBP; l. ATP used to regenerate RUBP/convert glycerate 3-phosphate to triose phosphate;

Explain the production of antibodies when a patient is infected with TB bacterium

a. phagocytes/lymphocytes are white blood cells b. TB bacterium has a specific antigen c. this antigen is recognised by white blood cells d. a clone of lymphocytes/plasma cells/B cells are produced e. antibodies are produced by lymphocytes 1. each lymphocyte produces just one type of antibody 9. (this is) specific immunity h. (part of the) antibody/immunoglobulin binds to the antigen / specific antibody binds to the specific antigen 1. antibodies are proteins/immunoglobulins j. (some) plasma cells become memory cells k. memory cells reproduce quickly 1. memory cells prevent infection in the future

Explain chemiosmosis as it occurs in photophosphorylation

a. photophosphorylation is the production of ATP; b. (some of the) light absorbed by chlorophyll / photosystem II; c. photolysis/splitting of water separation of hydrogen ion from its electron; d. the electron transport system moves the electrons through a series of carriers; e. (electron transport system occurs) in the thylakoid membrane; f. electron transport linked to movement of protons into thylakoid space; g. a proton gradient builds up (in the thylakoid space); h. small thylakoid space enhances the gradient; i. hydrogen ions move by diffusion through the ATP synthase; j. ADP + inorganic phosphate (Pi) forms ATP; k. (the kinetic energy from) movement of hydrogen ions (through ATP synthase) generates ATP; l. ATP synthase is a protein complex in the thylakoid membrane; m. formation of proton gradient / ATP synthesis linked to electron transport is chemiosmosis;

explain how the process of photosynthesis affects carbon dioxide concentrations in the atmosphere during a typical year and the likely consequences on Earth of the yearly rises in CO2

a. photosynthesis uses carbon dioxide; b. CO2 fixed/made into organic molecules/compounds by photosynthesis; c. lowering carbon dioxide level in atmosphere; d. annual/seasonal fluctuations of carbon dioxide levels could be related to photosynthesis; e. caused by increased photosynthesis during spring/summer; Consequences: [5 max] f. enhanced greenhouse effect caused by raised levels of carbon dioxide; g. causing global warming; h. rising of ocean levels / melting of polar ice caps/glaciers; i. changes in weather (patterns); j. ocean acidification; k. alter food webs; l. changes/loss of habitat; m. changes in distribution of plants and animals; n. may lead to extinction;

outline the use of named enzymes in gene transfer using plasmids

a. plasmids are removed/obtained from bacteria; b. endonuclease/restriction enzymes cut the plasmids at target sequences; c. DNA fragments of other organism are cut with the same restriction enzymes; d. in both DNA and plasmid, complementary sticky ends/staggered cut are produced; e. DNA segment added to the opened plasmid; f. spliced together by ligase; g. reverse transcriptase makes DNA copies of mRNA / DNA polymerase to increase the amount of DNA; h. recombinant plasmids inserted into new/host cells; i. cultured/cloned to produce the new genes/more genetically modified cells; Award [3 max] if no specific enzyme names are given. Do not accept the word "enzyme" on its own.

Outline the functions of the liver

a. produces bile for digestion/emulsification of fats/lipids; b. regulates blood glucose level through glucose-glycogen reaction; c. detoxification/example of detoxification (eg contains catalase for the breakdown of hydrogen peroxide); d. manufactures plasma proteins/albumins/fibrinogen; e. manufactures cholesterol; f. destroys red blood cells by phagocytosis; g. breaks down haemoglobin from red blood cells; h. stores iron; i. stores vitamin A and D; j. deaminates excess amino acids/formation of urea;

Describe what is shown in the pyramid of energy

a. pyramid of energy shows the flow of energy from one trophic level to the next (in a community); b. units of pyramids of energy are energy per unit area per unit time/kJ m-2 yr -1; c. bar width is proportional to the energy stored (in the biomass) in that trophic level; d. the first/lowest trophic level is producers; e. second level is primary consumers/herbivores; f. third level of secondary consumers/carnivores; g. only a small amount (10 to 20 %) of energy of one level is passed to the next; h. bar width/energy stored in the trophic level decreases (proportionally) as you go up each level; i. pyramid shows that there is a limit to the length of food chains;

explain the consequences of releasing raw sewage and nitrate fertillizer into rivers

a. raw sewage contains pathogens; b. can contaminate drinking water / cause disease/death; c. nitrate fertilizers cause algal blooms/(aquatic) plant development; d. algae release toxins that can contaminate drinking water; e. more organic matter results / eutrophication; f. more oxygen required to decompose organic matter / increase in BOD; g. (leading to) death of aquatic animals/organisms; h. recovery follows since algae/plants release more oxygen

Outline the changes that take place in the abiotic environment with primary succession

a. rocks begin to break down; b. minerals begin to accumulate; c. soil begins to develop; d. water retention increases; e. erosion of soil is reduced (by rhizoids and roots);

Bacteria are prokaryotes that sometimes act as pathogens. Describe how the body can defend itself against pathogens.

a. skin/mucus membranes act as barrier (to pathogens); b. sebaceous glands secrete lactic acid/fatty acids/sebum / make surface of skin acidic; c. (skin/stomach) acid prevents growth of many pathogens; d. lysozyme in mucus can kill bacteria; e. pathogens caught in sticky mucus and removed from body; f. inflammatory response/inflammation can cause swelling/redness/fever (to inhibit the pathogen); g. phagocytes/macrophages/leucocytes/white blood cells (non-specifically) identify (pathogens/bacteria/fungi/viruses) as foreign; h. (phagocytes macrophages/leucocytes/white blood cells) ingest pathogens; i. specific lymphocytes recognize one specific antigen; j. (antigen-specific) lymphocytes clone themselves; k. lymphocytes/leucocytes produce antibodies; l. antigen-antibody complex formed and stimulates destruction of pathogen;

Discuss ethical issues of therapeutic cloning in humans

a. therapeutic cloning involves producing embryos from which embryonic stem cells can be harvested for medical use; argument in favour: b. (to many people) any procedure that reduces pain and suffering is ethically/morally justified; c. stem cells can be used to replace organs/tissues that have been lost/damaged in a patient; d. (thus) pain and suffering can be reduced/lives can be saved/life quality improved; e. cells can be removed from embryos that have stopped developing and would have died anyway; f. cells are removed at a stage when no pain can be felt by the embryo; g. use embryos from IVF that would otherwise be destroyed; Accept up to one additional reasonable argument in favour. argument against: h. embryonic stem cells are no longer needed as adult stem cells can be used without causing loss of life; i. there is danger of embryonic stem cells developing into tumour cells/harmful effects are not yet known; j. every human embryo is a potential human with the right to development; k. more embryos may be produced than can be used and so some would be killed; l. (to many people) any procedure that harms a life/kills is unethical/morally wrong; Accept up to one additional reasonable argument against.

Outline transcription in prokaryotes.

a. transcription is the copying of a strand of DNA into RNA/RNA formation; b. RNA polymerase binds to promoter region of DNA; c. anti-sense strand as template / only one strand copied; d. RNA polymerase unwinds DNA/separates the strands; e. RNA nucleotides/nucleoside triphosphates pair with complementary bases on DNA; f. Adenine to Thymine, Cytosine to Guanine, and Uracil to Adenine; (do not accept letters alone) g. added at 3' end / strand grows 5' to 3' ; h. RNA nucleotides joined with covalent/sugar-phosphate bonds; i. RNA polymerase separates from DNA when reaches terminator/termination sequence; j. no introns/post-transcriptional modification/RNA splicing (as occurs in eukaryotes)

Some prokaryotes cause infectious disease in humans. Explain the principles of vaccination.

a. vaccines contain a dead/weakened form of the pathogen/bacteria/virus; b. vaccine introduced to the body by injection/on surface of skin/orally; c. antigens in the vaccine cause antibody production; d. antigen/pathogen engulfed by macrophage/phagocyte; e. each type of lymphocyte recognizes specific antigen; f. macrophages activate helper T-cells; g. which activate B-cells; h. B-cells divide to form clones/memory cells; i. B-cells divide to form plasma cells/antibody producing cells; j. result is (specific) immunity; k. vaccination/first exposure causes slow production of antibodies and lower level of antibodies; (this idea can be illustrated on a diagram or graph) l. contact with the disease leads to rapid production and higher level of antibodies; (this idea can be illustrated on a diagram or graph) m. second/booster shot to stimulate memory cells/more production of antibodies;

Aquatic and other environments are being affected by a global rise in temperature. Outline the consequences [6 marks] of this on arctic ecosystems

a. warming results in melting (arctic/polar) ice (cap) / loss of ice habitats; b. (warming) raises sea level / floods coastal areas / destroys coastal habitats; c. (warming) of habitat would change species/flora/fauna that can be supported (named examples can be used); d. decrease in size of population(s) / possible extinction of species; e. temperate species move into area / arctic species adapt/move; f. change in distribution of species/changes in migration patterns; g. (ecological) changes will affect higher trophic levels/food webs/food chains; h. increased rates of decomposition of detritus from (melting) permafrost; i. increased success of pest species including pathogens;

State the action of the acetylcholinesterase enzyme.

breaks down acetylcholine into acetyl and choline

explain the causes of sickle cell anemia

caused by gene mutation; (sickle-cell anemia) due to a base substitution (mutation); changes the code on the DNA; which leads to a change in transcription / change in mRNA; DNA changes from CTC to CAC/GAG to GTG / mRNA changes from GAG to GUG; (accept DNA changes from CTT to CAT/GAA to GTA / mRNA changes from GAA to GUA) which (in turn) leads to a change in translation / change in polypeptide chain/ protein; (the tRNA) adds the wrong amino acid to the polypeptide chain; glutamic acid replaced by valine; produces abnormal hemoglobin; causing abnormal red blood cell/erythrocyte shape / sickle shape; which lowers the ability to transport oxygen; sickle-cell allele is codominant; homozygote/HbS HbS have sickle cell anemia/is lethal / heterozygote/HbS HbA has the sickle trait/is carrier (and is more resistant to malaria);

Define: Chromosomes, genes, alleles, and genome

chromosome: structure formed by DNA and proteins; gene: a heritable factor that controls a specific characteristic; allele: one specific form of a gene occupying the same gene locus as other alleles of the gene; genome: the whole of the genetic information of an organism;

state the source, substrate, products and optimal pH conditions for lipase in the digestive system

eg source: pancreas; substrate: triglycerides / lipids / fats / oils; product: glycerol and (three) fatty acids; (both needed) optimal pH: 8; (accept answers in the range of 7 to 8) Accept other correct examples

Many people cannot digest lactose and benefit from a diet containing no lactose. Outline the production of lactosefree milk

milk contains lactose / lactose is milk sugar; lactose is broken down to glucose and galactose; by (the enzyme) lactase; which is lacking in people with lactose intolerance; lactose-free milk is sweeter than milk containing lactose; lactase produced by small intestine / produced by yeast sometimes found in milk; can be added directly to milk; immobilized in beads / biotechnological techniques; ultrafiltration of milk to remove lactose;

describe how human skin color is determined genetically

skin colour is an example of polygenic inheritance; many/more than two genes contribute to a person's skin colour; due to the amount of melanin in the skin; combination of alleles determines the phenotype; allows for range of skin colours / continuous variation of skin colour; phenotypes do not follow simple Mendelian ratios of dominance and recessiveness; the environment also affects gene expression of skin colour / sunlight/UV light stimulate melanin production; the more recessive alleles there are, the lighter the skin colour; (vice versa)

Explain how the kidney helps to retain useful substances in the blood and eliminate substances which the body does not need.

ultrafiltration occurs in the glomerulus; basement membrane acts as a filter; preventing proteins/cells from passing; (filtered) substances pass to the Bowman's capsule; to proximal convoluted tubule (PCT); (where there is) selective reabsorption; (in PCT) all glucose/amino acids are reabsorbed; (in PCT most) water reabsorbed; surrounding the loop of Henle, is an area of high solute concentration; in distal convoluted tubule, ions are exchanged between filtrate and blood; collecting duct has role in osmoregulation; ADH regulates the amount of water reabsorbed; substances not reabsorbed are eliminated as urine;

outline the abiotic factors that affect the distribution of plant species in an ecosystem

water (distribution) for turgor/biochemical reactions/photosynthesis; mineral / inorganic content / salinity of soil/water; temperature (max, min, range, seasonal changes) / altitude; light (intensity, duration, wavelength) for photosynthesis; pH (range, average, changes) of soil/water; wind (direction, strength);