IB Biology Paper 2 Section B

Draw a labeled diagram of the kidney and associated vessels. [5 marks]

Award [1] for each of the following correctly drawn and labeled: cortex - outer part of kidney; medulla - inner part of kidney shown with pyramids/variation in thickness; pelvis - in centre of kidney; ureter - leaving kidney from pelvis; renal vein - attached to concave side of kidney/to pelvis; (renal) artery - attached to concave side of kidney/to pelvis;

Draw a labeled diagram to show the structure of a motor neuron. [4 marks]

Award [1] for each of the following correctly drawn and labelled: a. cell body and nucleus - star shaped body with nucleus inside; b. dendrites - as multiple long/narrow protrusions from the cell body; c. axon - at least three times as long as the cell body not including the dendrites; d. myelin sheath/Schwann cells and nodes of Ranvier - sheath with gaps/narrowings; e. motor end plates - shown as widened ends of multiple branches of the nerve fibre; Reject the points for axon and myelin sheath if the labelling line does not clearly point to the structure.

Draw a labeled diagram of the carbon cycle. [6 marks]

Award [1] for each of the following shown using labelled arrows or notes on a diagram. Accept carbon dioxide or CO2 throughout. a. carbon dioxide/CO2 in atmosphere/water; b. (cell) respiration producing CO2 in atmosphere; c. photosynthesis (fixing) CO2 from atmosphere into producers/plants; d. death/decomposition transforming C in plants/animals to C in bacteria/fungi/saprotophs; e. fossilization converting carbon in organisms to fossil fuels/coal/oil/natural gas; f. combustion/burning of fossil fuels/coal/oil/natural gas/peat producing CO2 / weathering of shells/rocks releasing CO2; g. combustion/burning of producers/forests producing CO2; h. feeding (organic C) in producers/plants to (organic C) in consumers/animals; i. feeding (organic C) in consumers to other consumers; If candidates do not show on their diagram that carbon is in the form of carbon dioxide, do not award the first marking point but allow other marking points.

Draw a labelled diagram to show the structure of the heart. [5 marks]

Award [1] for each of the following structures clearly drawn and labelled correctly in a diagram of the heart. a. left ventricle/right ventricle - both left and right ventricles must be shown but the mark can be awarded if either is correctly labelled. The left must be thicker walled than right and both must be larger than the atria; b. left atrium/right atrium - both left and right atria must be shown with thinner walls than ventricles, but the mark can be awarded if either atrium is correctly labelled; c. atrio-ventricular valves/tricuspid and bicuspid valves - positioned between atria and ventricles, with both labelled and tri/bicuspid correct if these names are used; d. semi-lunar valves -shown at the start of the aorta and pulmonary artery, with the cusps facing in the right direction; Award [1] for any two blood vessels clearly drawn and correctly labelled. aorta - shown connected to the left ventricle; pulmonary artery - shown connected to the right ventricle; pulmonary vein - shown connected to the left atrium; vena cava - shown connected to the right atrium;

Draw a labelled diagram of a mature human egg. [5 marks]

Award [1] for each structure accurately drawn and correctly labelled. a. haploid nucleus; b. cytoplasm - with nucleus-to-membrane distance >4 times nucleus diameter; c. centrioles - two must be shown but only one needs to be labelled; d. cortical granules - needs to be drawn in vicinity of plasma membrane; e. plasma membrane - shown as a single line and approximately circular overall; f. polar cell / (first) polar body - needs to be drawn outside the egg cell; g. zona pellucida / layer of gel (outside the cell membrane); h. follicle cells / corona radiata (outside the cell membrane); i. size shown as 100 μm/0.1 mm; (accept 90 μm to 120 μm)

Draw a labelled diagram to show the structure of a sarcomere. [5 marks]

Award [1] for each structure clearly drawn and correctly labelled. a. sarcomere - clearly indicated between Z lines (whether Z lines named or not); b. Z lines - shown at the ends of a sarcomere; c. actin (filaments) - drawn as thin lines attached to Z lines; d. myosin (filaments) - drawn as thick lines interdigitating with thin/actin filaments; e. myosin heads - on both sides of at least one myosin filament; f. light band and dark band - indicating regions of actin only and myosin plus actin;

Draw a labelled diagram to show the structure of a motor neuron. [4 marks]

Award [1] for each structure clearly drawn and labelled. a. cell body - star shaped body at end of neuron with nucleus inside; b. dendrites - as multiple long/narrow protrusions from the cell body; c. axon - at least three times as long as the cell body not including the dendrites; d. myelin sheath/Schwann cells - surrounding the axon; e. nodes of Ranvier - periodic gaps in myelin sheath; f. motor end plates - shown as buttons at the end of multiple branches of axon; Reject the points for axon and myelin sheath if the labelling line does not clearly point to the structure. Accept a bracket label indicating the length of the axon.

Draw a labelled diagram of the human heart showing the attached blood vessels. [6 marks]

NB: Drawings must be correctly proportioned and clearly drawn showing connections between structures. The drawing may show the heart without contraction or in any stage of contraction. Award [1] for any correctly labelled part that has been drawn to the stated standards. a. atria/right atrium/left atrium - shown above the ventricles and must not be bigger than ventricles; b. ventricle/left ventricle/right ventricle - below the atria, must have thicker walls than atria; c. vena cava/superior vena cave/inferior vena cava - connected to right atrium; d. pulmonary artery - shown from right ventricle (to lungs); e. pulmonary vein(s) - shown (from lungs) to left atrium; f. aorta - shown as large artery from left ventricle out of heart; g. AV valves/atrioventricular valves / mitral/bicuspid and tricuspid - named correctly and shown between both atria and ventricles and labelled at least on one side; h. semilunar valves - shown in aorta/pulmonary artery; Valves need to open in correct direction.

Outline the process of in vitro fertilization (IVF). [6 marks]

a. (at the start) drugs/hormones given to stop ovulation b. ovarian hyperstimulation/fertility drugs/ hormones/named drug injected in mother; c. development of multiple follicles; d. inductionofeggmaturation; e. retrieval of eggs through (minor) surgery; f. sperm collected (in vitro); g. fertilizationinvitroofeggandsperm; h. (if sperm count is low) intracytoplasmic sperm injection (ICSI) is performed; i. fertilized egg is grown in medium; j. fertilized egg is introduced/implanted in uterus;

Describe the action of the heart in pumping blood. [5 marks]

a. (both) atria collect blood (from veins); b. sinoatrial/SA node sends impulses to muscle/fibres initiating contraction; c. blood is pushed to ventricles by contraction of atria/atrial systole; d. AV (atrioventricular) valves are open (as atria contract); e. semilunar valves are closed so that ventricles fill with blood; f. ventricles contract / ventricular systole; g. AV (atrioventricular) valves close ( preventing backflow); h. (blood is pushed through the) semilunar valves/pulmonary artery and aorta; i. when ventricles relax /diastole, semilunar valves close preventing back flow of blood; Do not accept the description of blood flow without a clear action. Do not accept general statements such as systole = heart contraction and diastole = heart relaxation. [4 max] if answer suggests that left and right sides are contracting at different times or simultaneous contraction not indicated.

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

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. [6 marks]

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.

Giving one specific example, discuss genetic modification in organisms including the potential benefits and possible harmful effects. [8 marks]

a. (genetically modified organisms) are organisms where characteristics are altered/changed by addition or removal of a gene; b. reference to the specific gene transferred to the host organism; c. verifiable example of genetic modification; (eg BT- corn/other valid examples) d. universal genetic code (allows genes to be transferred between species); e. gene transfer involves splicing genes into a suitable vector/host DNA; f. after placed in host, host cells are cloned; potential benefits: 1st potential benefit; (eg increased yields/productivity) 2nd potential benefit; (eg allows for the introduction of a characteristic that wasn't present within the gene pool (selective breeding could not have produced desired phenotype)) 3rd potential benefit; (eg less use of chemical pesticides) harmful effects: 1st harmful effect; (eg possibility of cross pollination) 2nd harmful effect; (eg could have currently unknown harmful effects / toxin may cause allergic reactions) 3rd harmful effect; (eg reduces genetic variation/biodiversity) Specific harmful effects related to the named examples.

Outline how the human body responds to high blood glucose levels. [5 marks]

a. (high blood glucose levels) detected by pancreas islet cells/beta cells; b. insulin secreted in response (to high blood glucose/glucose above threshold level); c. insulin stimulates cells to absorb glucose; d. glucose used in cell respiration (rather than lipids); e. glucose converted to glycogen (in liver/muscle cells); f. glucose converted to fatty acids/triglycerides/fat; g. negative feedback process;

Outline two factors that affect the rate of photosynthesis. [5 marks]

a. (increase in) light (intensity) increases rate (of photosynthesis); b. until a plateau is reached at higher light intensities/when another factor is limiting; c. light needed for light dependent reactions/example of light dependent reaction; d. (increase in) temperature/heat increases the rate (of photosynthesis); e to an optimum temperature above which the rate drops; f. temperature/heat affects rate of Calvin cycle/enzyme activity/rubisco activity; g. (increase in) carbon dioxide (concentration) increases rate (of photosynthesis); h. until a plateau is reached at higher CO2 levels/when another factor is limiting; i. CO2 needed for light independent reactions/Calvin cycle/carboxylation of RuBP/production of glycerate phosphate;

Outline the energy flow between trophic levels in a food chain. [6 marks]

a. (original) source of energy in a food chain is from (sun)light; b. captured by plants/autotrophs/producers/first trophic level; c. by means of photosynthesis/converted to chemical energy/organic molecules; d. plants use part of energy for own energy requirements/lost through cell respiration; e. consumers use energy for own requirements from organisms in previous trophic level; f. energy travels between trophic levels/producer to 1st consumer/1st consumer to 2nd consumer/2nd consumer to 3rd consumer; g. not all material is assimilated/consumed/not digested/lost in faeces / OWTTE; h. only a small amount of energy/(approximately) 10-20% is passed between trophic levels / most/80-90%/a large amount of the energy of a trophic level is lost (and not transferred); i. loss of energy from organisms in form of heat; j. energy is not recycled in an ecosystem (but nutrients are);

Describe the process of endocytosis. [5 marks]

a. (plasma) membrane encloses/engulfs solid particles/droplets of fluid/molecules; b. fluidity of the membrane allows endocytosis; c. plasma membrane forms pit/forms indentation/pulled inwards/invaginates; d. membrane pinches off/seals back on itself/edges fuse; e. vesicle/vacuole formed; f. inside of plasma membrane becomes outside of vesicle membrane / converse; g. vesicle breaks away from plasma membrane/moves into cytoplasm; h. active process / endocytosis/vesicle formation requires energy; (plasma) membrane encloses/engulfs solid particles/droplets of fluid/molecules; Accept any of the above points clearly described in an annotated diagram.

Research is being undertaken by scientists in some countries to develop methods of therapeutic cloning. Discuss the ethical issues of therapeutic cloning in humans. [8 marks]

a. (therapeutic cloning) is the creation of an embryo to supply embryonic stem cells for medical use; b. transfer of nucleus from somatic cell in to an (a nucleated) egg; c. stimulated by shock to begin cell division; pros: d. stem cells from embryos have greater flexibility; e. pluripotent cells can give rise to all cells in the body / new organ could be grown as needed; f. no (danger of) rejection of the transplant because the organ DNA would match the patient's DNA (exactly); g. elimination of pain/inconvenience/shortened life span of organ recipient; h. would eliminateorganandtissueshortages; i. no need for immunosuppressive drugs; cons: j. manipulation/destruction of human embryos not ethically acceptable; k. the process of extracting stem cells involves killing the embryo; l. many attempts before success is attained;

Outline the effects of a base substitution mutation in the case of sickle-cell anemia. [5 marks]

a. DNA changes from GAG to GTG/CTC to CAC b. mRNA changes from GAG to GUG; c. affecting the process of translation/causes different primary structure of polypeptide; d. causing glutamic acid to be replaced by valine; changing the form of hemoglobin; e. changes the shape of the red blood cells / red blood cells become sickle shaped; f. transport oxygen less efficiently/less oxygen gets to tissues; g. sickled cells block capillaries; h. muscular pain/severe anemia/slow growth; i. (allow other appropriate symptom) correlated with protection against malaria in heterozygotes;

Explain how DNA is used to pass on genetic information to offspring accurately but also produce variation in species. [8 marks]

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;

Prior to cell division, chromosomes replicate. Explain the process of DNA replication in prokaryotes. [8 marks]

a. DNA replication is semi-conservative; b. each (molecule formed) has one new strand and one from parent molecule; c. helicase uncoils DNA; d. helicase separates the two strands by breaking hydrogen bonds between bases; (reject unzips as an alternative to uncoils but accept as alternative to separates if breakage of hydrogen bonds is included) e. RNA primase adds primer / primase adds (short) length of RNA; f. DNA polymerase III binds to/starts at (RNA) primer; g. DNA polymerase (III) adds nucleotides/bases in a 5' → 3' direction; h. bases according to complementary base pairing / A-T and C-G; i. (leading strand) built up continuously (towards the replication fork); j. (lagging strand) built up in pieces/short lengths/Okazaki fragments; k. DNA polymerase I removes RNA/primers and replaces them with DNA; l. ligase seals gaps between nucleotides/fragments/makes sugar-phosphate bonds; m. nucleoside triphosphates provide the energy to add nucleotides; Accept the above points in annotated diagrams.

Explain the processes involved in the Krebs cycle. [8 marks]

a. Krebs cycle only occurs in aerobic conditions; b. the Krebs cycle occurs in the mitochondria; c. acetyl CoA from the link reaction releases an acetyl group; d. NADH+H+ and CO2 are formed (with each decarboxylation); e. decarboxylation/removal of CO2 involves oxidation/oxidative decarboxylation; f. and the release of energy; g. acetyl group is joined to a 4-carbon molecule/C4/oxaloacetate to form a 6-carbon molecule/citrate; h. (decarboxylation changes citrate) to 5-carbon molecule/C5; i. (decarboxylation changes glutamate) to a 4-carbon molecule/C4; j. then converted into the original 4-carbon molecule/C4/oxaloacetate and the cycle repeats; k. one (molecule) of ATP is made during this step; l. reduced H-carriers/ NADH and FADH2 and carbon dioxide are end-products of Krebs cycle;

Muscle contraction is a chemical process involving proteins. Explain how skeletal muscle contracts. [8 marks]

a. actin and myosin filaments are the proteins involved in muscle contraction; b. (a motor neuron stimulates the) release of calcium ions; c. from the sacroplasmic reticulum; d. calcium reveals the binding sites on actin; e. myosin heads form cross-bridges with binding sites on actin; f. ATP binds to myosin heads; g. breaking cross bridges to actin; h. ATP hydrolyzed to ADP (+phosphate); i. causing myosin heads to change angle/become cocked with energy from ATP; j. myosin heads bind to new sites on actin further from centre of sarcomere; k. ADP is released; l. actin filaments slide inwards to centre of sarcomere/power stroke;

Compare the processes of spermatogenesis and oogenesis. [8 marks]

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); Oogenesis: a. eggs/ova produced in the ovaries b. process starts during development of embryo/fetus c. meiosis breaks occur in prophase I/ prophase II/ metaphase II d. cytoplasm split unequally / larger cell and smaller cells e. one cell/egg (per meiosis) / some become polar bodies f. one gamete (usually) at a time/per month/per menstrual cycle g. timing of release: on about Day 14/in middle of menstrual cycle/at ovulation h. stops at menopause Spermatogenesis: a. sperm (atozoa) produced in the testes b. process starts during puberty/adolescence c. no breaks in meiosis d. equal division of cytoplasm e. four sperm (per meiosis) / all cells become sperm f. many/far more/(hundreds of) millions daily/at a time gametes produced g. timing of release: continuously (from testis) / by ejaculation/intercourse h. goes on (throughout adult life/until death)

Distinguish between the absorption of red light, blue light and green light by plants. [4 marks]

a. chlorophyll is the main photosynthetic pigment; b. high levels of absorption in red light and blue light; (both needed) c. greatest absorption in blue light; d. least/lowabsorptioningreenlight; e. green light is reflected; f. other pigments absorb other wavelengths/colours;

Outline outcomes of the human genome project. [4 marks]

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;

Describe the importance of water to living organisms. [5 marks]

a. coolant in sweat/in transpiration; b. water has a high heat of vaporisation / heat taken when hydrogen bonds break; c. water is cohesive so can pulled up/so can be moved under tension in xylem; d. water is an excellent/universal solvent/dissolves many different substances; e. medium for transport in blood/xylem/phloem; f. medium for metabolic reactions / (metabolic) reactions happen dissolved in water; g. surface tension due to cohesion allows organisms to live on water surface; h. water has high heat capacity so much energy required to change its temperature; i. ice floats so lakes/oceans do not freeze allowing life under the ice; j. high heat capacity so stable habitat/so temperature of water changes slowly; k. used in chemical reactions/photosynthesis/hydrolysis in organisms;

Describe the use of DNA pro ling in forensic investigations. [4 marks]

a. cut DNA into fragments using restriction enzymes/endonucleases; b. satellite DNA/(short) repeated sequences are used; c. PCR used to amplify/copy many times (satellite) DNA; d. DNA fragments separated by size / DNA separated by gel electrophoresis; e. pattern of bands/fragments compared to bands of suspected person/criminal;

In a given population some variations of a protein are expressed more frequently than others. Outline how evolution through natural selection can lead to the expression of one version of a protein rather than another. [6 marks]

a. different alleles for proteins exist in nature / a gene for a protein shows variations; b.selection pressure acts on organisms/change in external environment/example of selection pressure (eg: use of antibiotic); c. organisms expressing one allele/protein have advantage over those expressing others; d. organisms expressing one allele/protein have greater chances of survival/by natural selection the better adapted organisms survive; e. organisms expressing one allele/protein can reproduce more/leave more descendants; f. expression of the given allele/protein is inherited by these organisms; g. population expressing the given allele/protein increases (while the ones expressing the other protein decreases); h. after a few generations, the characteristic of the species gradually changes;

The leaves of plants are adapted for photosynthesis. Draw a labelled plan diagram of a leaf to show the distribution of tissues in a leaf. [5 marks]

a. epidermis - shown and labelled on either the upper or lower surface or both; b. upper and lower epidermis - both labelled; c. palisade layer / palisade mesophyll; d. spongy layer / spongy mesophyll; e. xylem (in upper part of a major or minor vein); f. phloem (in a major or minor vein); (accept whether upper or lower) g. guard cells; (do not accept stoma or stomata only) Do not penalize diagrams that show individual cells rather than tissues.

Outline type II diabetes. [5 marks]

a. excess glucose in blood / hyperglycemia; b. symptoms are excessive thirst / frequent urination / dehydration / fatigue; c. unresponsive to insulin / insulin resistance / not enough insulin produced; d. linked to/risk factor is obesity/diets high in sugar/fat; e. late onset / onset is usually adulthood/after childhood; f. insulin not required (usually) / insulin ineffective as a treatment; g. treated with low sugar diets/low GI/glycemic index foods; Reject weight loss as a symptom of Type II diabetes. Reject no insulin. Reject low carbohydrate diet. Do not award a mark simply for stating that glucose is present in the urine as this is in the question.

Outline the structure and functions of nucleosomes. [4 marks]

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;

Using a named example, discuss the effects of genetically modifying an organism. [8 marks]

a. genetic modification is transfer of genes/DNA from one organism to another; b. named example of organism modified; c. Accept binomials or common names. d. name of gene transferred / name of organism from which gene was obtained; eg a. corn/maize crops modified; b. using gene from Bacillus thuringiensis/Bt toxin gene; benefits: a. makes corn resistant to pest/corn borer; b. producing higher crop yields; c. less land needed for crops (as is more efficient) / more land for wildlife; d. less pesticide needed; harmful effects: a. non-target/beneficial insects might be harmed / non-target specific; b. gene might spread to other plants (by cross-pollination); c. (possibility of) allergic reactions when crop is eaten / side effects in humans; d. only favoured countries have the technology / increases inequality;

Accurate transmission of base sequences to offspring depends on successful gamete production. Describe how spermatogenesis occurs in humans. [6 marks]

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;

Explain the presence of glucose in the urine of a diabetic person and its absence in the urine of a person with type I diabetes that is being successfully treated. [8 marks]

a. glucose filtered out of blood (plasma) in glomerulus; b. glucose reabsorbed from filtrate in proximal convoluted tubule; c. by active transport; d. reference to specific pumps for glucose / limited capacity for glucose uptake; e. in diabetic patients glucose concentration in plasma is high; f. not all glucose can be reabsorbed (in PCT) /capacity for reabsorption exceeded; g. no glucose reabsorption after the proximal convoluted tubule; h. glucose still present at end of nephron/collecting duct/in the ureter/bladder; i. type I diabetes treated with insulin; j. insulin reduces the glucose concentration of blood/plasma/filtrate; k. all glucose reabsorbed from filtrate in Type I diabetics if treated; Do not award a mark simply for stating that glucose is present in the urine as this is in the question. Reject regulates glucose concentration.

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. [7 marks]

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; Names of phases are required to earn the mark. Award marks for a clearly drawn correctly annotated diagram.

Outline how the rate at which the heart beats is controlled. [6 marks]

a. heart cells can contract on their own / myogenic (muscle contraction); b. contractions/heart beat controlled by/starts at pacemaker/sinoatrial node; c. pacemaker/sinoatrial node is in the wall of the right atrium; d. signal to contract transmitted from across the atria/heart muscle/heart wall; e. nerves/impulses from medulla (of brain) to heart; f. fone nerve increases rate and another nerve decreases it; g. epinephrine/adrenalin increases rate; Reject noradrenalin. Details of events in the cardiac cycle are not relevant and should not be rewarded. Do not award marks for reference to the autonomic, sympathetic or parasympathetic nervous systems as these are Option E topics.

All parts of the body change the composition of the blood. Explain how the nephron changes the composition of blood. [7 marks]

a. higher nitrogen/urea as blood enters nephron/Bowman's capsule than when it leaves the nephron (in the renal vein); b. most small soluble molecules/glucose/nutrients/ions are removed from blood in Bowman's capsule; c. through ultrafiltration; d. proteins / blood cells / large molecules remain in the blood; e. as filtrate moves through the nephron (tubule), water is returned to the blood (by osmosis); f. glucose/nutrients is returned to blood by active transport (and diffusion) / selective reabsorption; g. in the proximal convoluted tubule; h. urea / uric acid remain in the filtrate / removed from blood; i. sodium is pumped into the medulla in the loop of Henlé; j. water reabsorption is enhanced by a high sodium gradient (in the medulla); k. permeability of the collecting duct membrane is regulated by hormones / ADH; l. water concentration in urine is variable to maintain homeostasis in the blood; m. more oxygen/less carbon dioxide in blood entering (kidney) than in blood leaving (kidney);

Explain how nerve impulses pass from one neuron to another neuron. [8 marks]

a. impulse/message/action potential/depolarization reaches the pre-synaptic membrane; b. calcium channels open; c. calcium diffuses into/calcium ions enter (pre-synaptic) neuron; d. vesicles of neurotransmitter fuse with membrane (of pre-synaptic neuron); e. release of neurotransmitter by exocytosis; diffusion of neurotransmitter across cleft/synapse; f. neurotransmitter binds to receptor in (post-synaptic) membrane/neuron; g. ion channels open and sodium/positively charged ions enter; h. depolarization/action potential/impulse in post-synaptic neuron/membrane; i. neurotransmitter broken down by enzymes; Apart from point d, acetylcholine or another specific neurotransmitter is acceptable in place of neurotransmitter.

Describe codominance and multiple alleles using inheritance of ABO blood groups as an example of them. [6 marks]

a. in multiple alleles there are more than two alleles of a gene; b. codominant alleles both affect the phenotype (in the heterozygote); c. IA and IB and i are the three alleles controlling blood groups; d. in ABO blood group IA and IB are codominant and i is recessive; e. when A and B both present, both are expressed/will give AB; f. i is recessive to both IA and IB / type A and type B can be heterozygous; g. only homozygous/ii organisms are blood group O; h. example of inheritance of blood groups/Punnett square showing inheritance;

Explain how the distribution of tissues in the leaf of a dicotyledonous plant is adapted to production and distribution of products of photosynthesis. [8 marks]

a. leaf has large surface area for absorption of light; b. upper epidermis (thin) allowing light to pass; c. (waxy translucent) cuticle to (allow light in and) prevent water loss; d. palisade mesophyll contains many (cells with) chloroplasts; e. palisade mesophyll close to upper layer to receive more light; f. spongy mesophyll contains chloroplasts which allow photosynthesis; g. spongy mesophyll (cells loosely packed) allows gaseous exchange; h. stoma allow CO2 for photosynthesis to diffuse in; i. stoma allow O2 produced in photosynthesis to diffuse out; j. xylem brings water (for reactions); k. phloem carries away products of photosynthesis/sucrose; l. guard cells open and close stoma (for gas exchange);

Explain how abiotic factors affect the rate of transpiration in terrestrial plants. [8 marks]

a. less transpiration/water loss as (atmospheric) humidity rises; b. air spaces inside leaf are saturated/nearly saturated (with water vapour); c. smaller concentration gradient with higher atmospheric humidity; d. more transpiration/water loss as temperature rises/with more heat; e. faster diffusion / more kinetic energy (of water molecules); f. faster evaporation (due to more latent heat available); g. more transpiration/water loss as wind (speed) increases; h. humid air/water vapour blown away from the leaf; i. increasing the concentration gradient (of water vapour); j. more transpiration/water loss in the light; k. light causes stomata to open / stomata closed in darkness; l. low CO2 concentration inside leaf in bright light so stomata open wider; Accept any of the points if clearly made on an annotated graph.

Outline how light intensity and concentration of carbon dioxide affect photosynthesis. [6 marks]

a. low light intensity affects light-dependent reactions; b. fewer electrons are excited/less photolysis occurs; c. less NADPH and ATP produced at low light intensities; (both needed) d. rate-limiting step is the reduction of G3P/glycerate 3-phosphate/PGA phosphoglycerate; e. graph showing: effect of light intensity on rate of photosynthesis; f. low carbon dioxide concentration affects the Calvin cycle/light-independent stage; g. fixation of CO2 is decreased; h. less ribulose bisphosphate joins to CO2 to form G3P/glycerate 3-phosphate /PGA phosphoglycerate; i. graph showing: effect of CO2 concentration on rate of photosynthesis;

Explain how minerals move into plants. [8 marks]

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 the potential overproduction of offspring. [5 marks]

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 modi ed crop, discuss the specific ethical issues of its use. [6 marks]

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 non- target species; g. another specific harmful effect; eg, concerns about contamination of neighbouring non-GMO crops affecting trade; To award [6] responses need to address the name, description and the effect of the modification. Effects have to be linked to the specific example discussed. Marks have to be all linked to one example. Assistant examiners are required to research examples.

Outline the effect of carbon dioxide on the rate of photosynthesis and how this can be measured by oxygen release. [4 marks]

a. no photosynthesis at very low/no CO2 concentration; b. positive correlation between increasing amount of CO2 and photosynthesis rate; c. at high CO2 concentration (rate of photosynthesis) reaches a plateau; d. carbon dioxide used in the light independent reactions/Calvin cycle; e. oxygen release measured by counting/measuring volume of bubbles in water; f. (changes in) oxygen concentration measured using oxygen probe/electrode; g. oxygen is a product of light dependent reactions so it is a measure of the rate; Points above may be awarded if clearly shown on an annotated graph.

Explain the control of blood glucose concentrations in humans. [8 marks]

a. pancreatic cells monitor the blood glucose concentrations; b. alpha and beta cells are in the islets of Langerhans; c. negative feedback mechanisms; d. send hormones (through bloodstream) to target organs; e. if too high, β cells (in pancreas) produce insulin; f. insulin stimulates liver/muscle cells to take up glucose; g. glucose is converted into glycogen (stimulated by insulin); (do not award this marking point where it is stated that insulin directly converts glucose) h. lowering blood glucose level; i. other cells are stimulated to absorb glucose and use it in cell respiration; j. if glucose levels too low, α cells (in pancreas) produce glucagon; k. glucagon stimulates liver/muscle cells to break down glycogen; (do not award this marking point where it is stated that glucagon directly breaks down glycogen) l. and release glucose into the blood; m. raising the blood glucose level;

Draw a simple labeled diagram to show the structure of a double stranded DNA molecule, comprising four nucleotides. [5 marks]

a. phosphate labelled and each phosphate shown joined to C5 of sugar; b. nucleotides in each chain linked by a bond from phosphate to C3 of sugar; c. deoxyribose labelled and each shown joined to a base by C1; d. hydrogen bonds labelled and shown linking each base to another base; e. adenine/A joined to thymine/T and guanine/G joined to cytosine/C; f. two strands shown inverted/antiparallel to each other as indicated by the sugars; g. phosphate end labelled 5' and sugar end labelled 3' at ends of both strands;

Draw a simple labeled diagram to show the structure of a double stranded DNA molecule, comprising four nucleotides. [6 marks]

a. phosphate labelled and each phosphate shown joined to C5 of sugar; b. nucleotides in each chain linked by a bond from phosphate to C3 of sugar; c. deoxyribose labelled and each shown joined to a base by C1; d. hydrogen bonds labelled and shown linking each base to another base; e. adenine/A joined to thymine/T and guanine/G joined to cytosine/C; f. two strands shown inverted/antiparallel to each other as indicated by the sugars; g. phosphate end labelled 5' and sugar end labelled 3' at ends of both strands;

Draw a labelled diagram to show the structure of the plasma membrane. [5 marks]

a. phospholipid bilayer - with head and tails; b. hydrophilic/phosphate/polar heads and hydrophobic/hydrocarbon/fatty acid/non-polar tails labelled; c. integral/intrinsic protein - embedded in the phospholipid bilayer; d. protein channel - integral protein showing clear channel/pore; e. peripheral/extrinsic protein - not protruding into the hydrophobic region; f. glycoprotein with carbohydrate attached - carbohydrate should be outside the bilayer; g. cholesterol - positioned across one half of bilayer and not protruding; h. thickness indicated (10 nm); (allow answers in the range of 7 nm to 13 nm)

Explain chemiosmosis as it occurs in photophosphorylation. [8 marks]

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; Award marks for a clearly drawn correctly annotated diagram.

Outline a technique used for gene transfer. [5 marks]

a. plasmid used for gene transfer/removed from bacteria; b. plasmid is a small/extra circle of DNA; c. restriction enzymes/endonucleases cut/cleave DNA (of plasmid); d. each restriction enzyme cuts at specific base sequence/creates sticky ends; e. same (restriction) enzyme used to cut DNA with (desired) gene; f. DNA/gene can be added to the open plasmid/sticky ends join gene and plasmid; g. (DNA) ligase used to splice/join together/seal nicks; h. recombinant DNA/plasmids inserted into host cell/bacterium/yeast;

Outline the four levels of protein structure. [4 marks]

a. primary structure is the (number and) sequence/order of amino acids in a polypeptide; b. secondary structures are regularly repeating structures/β-pleated sheets/α-helices (held together by H-bonds); c. tertiary structure is the (specific) 3-dimensional structure of the polypeptide (held by bonds/ionic bonds/H-bonds/hydrophobic interactions/disulfide bridges/interactions between R groups); d. quaternary structure links two or more polypeptides (to form one protein)/and/or describes non protein groups associated with the polypeptide;

Draw the stages of mitosis. [4 marks]

a. prophase - with chromatin condensed/chromosomes visible and nuclear membrane still present/disappearing; b. metaphase-chromosomes at the equator with spindle fibers present; c. anaphase - sister chromatids migrating to opposite poles with spindle fibres present; d. telophase-two nuclei being formed (and nuclear membrane present/reappearing);

Explain how an impulse passes along the axon of a neuron. [8 marks]

a. resting potential is -70 mV / relatively negative inside in comparison to the outside; b. Na+/K+ pumps maintain/re-establish (the resting potential); c. more sodium ions outside than inside (when at the resting potential); d. more potassium ions inside than outside (when at the resting potential); e. nerve impulse is an action potential that stimulates a (wave of) depolarization along the membrane/axon; f. if neuron is stimulated/threshold potential/-50 mV is reached sodium ion channels open; g. sodium ions diffuse/move in; h. (Na+ move in) causing depolarization; i. potassium ion channels open / potassium ions diffuse/move out; j. (K+ move out) causing repolarization; k. local currents / description of Na+ ion diffusion between depolarized region and next region of axon to depolarize; Accept any of the above points clearly explained in an annotated diagram

Draw a labelled diagram of the human adult male reproductive system. [5 marks]

a. scrotum - shown around testes; b. testes/testis/testicles - shown inside scrotum; c. epididymis - shown adjacent to testis and connected to sperm duct; d. sperm duct/vas deferens - double line connecting testis/epididymis to urethra; e. seminal vesicle - sac shown branched off sperm duct (not off the urethra); f. prostate gland - shown positioned where sperm duct connects with urethra; g. urethra - shown as double line linking bladder to end of penis; h. penis - with urethra passing through it; Award [1] for each structure clearly drawn and labelled that conforms to the italicized guidelines given.

Explain how skeletal muscle contracts. [8 marks]

a. sliding filament model / filaments/actin and myosin slide past each other; b. action potential/depolarisation/nerve impulse arrives at end of motor neurone; c. neurotransmitter/acetylcholine released causing action potential (in muscle sliding filament model / filaments/actin and myosin slide past each other; fibre); d. sarcoplasmic reticulum releases calcium ions; e. calcium ions cause binding sites on actin/for myosin to be exposed; f. myosin heads bind to sites on actin/form cross-bridges; g. myosin (head) moves actin filament using energy from ATP; h. actin moved towards the centre of sarcomere/M line/M band; i. sarcomeres shortened; j. (binding of) ATP causes release of myosin head from actin; k. conversion of ATP to ADP and Pi causes myosin heads to change angle; l. cycle (of events) repeated (during muscle contraction); Accept the above points in annotated diagrams.

Explain the process of translation. [8 marks]

a. translation involves initiation, elongation/translocation and termination; b. ribosome slides along the mRNA to the start codon; c. translation takes place in 5′ → 3′ direction; d. start codon is AUG/codes for methionine; e. tRNA activating enzymes; f. link amino acids to a specific tRNA; g. ribosome binds the tRNA with the mRNA; h. anticodon of tRNA pairs with codon on mRNA; i. using complementary base pairing; j. second tRNA binds (to the codon) at the adjacent/next binding site; k. peptide bond forms between amino acids; l. translocation occurs moving the tRNA into the next site; m. reference to A, P and E sites; n. tRNA that has lost its amino acid detaches; o. this proceeds until stop codon is reached;

Explain how the structure and functions of the placenta maintain pregnancy. [8 marks]

a. transport facilitated by proximity of mother and embryo blood vessel; b. chorionic villi increase surface area for exchange; c. oxygen and food reach embryo; d. carbon dioxide and waste matter carried from embryo to mother; e. immune system of mother protects embryo; f. barrier function as bloods do not mix; g. endocrine function as it secretes hormones; h. human chorionic gonadotropin/HCG prevents degeneration of corpus luteum; i. production of estrogen maintains endometrium; j. estrogen increases mammary gland growth; k. progesterone maintains endometrium; l. progesterone prevents uterine contractions; transport facilitated by proximity of mother and embryo blood vessel;

Explain the role of the nephron in maintaining the water balance of the blood in the human body. [8 marks]

a. ultrafiltration in the glomerulus produces (large volumes of) filtrate; b. 80 %/most of water in filtrate is (always) (re)absorbed in proximal convoluted tubule; c. water reabsorbed from filtrate in descending loop of Henle; d. pituitary gland secretes ADH if blood solute concentration is too high; e. ADH makes the collecting duct/distal convoluted tubule more permeable to water; f. ADH moves aquaporins into the membranes (of cells in the tubule wall); g. more water reabsorbed from filtrate/into blood due to ADH; h. blood becomes more dilute / small volume of urine with high solute concentration; i. with low/no ADH less water is reabsorbed in the collecting duct; j. blood becomes more concentrated / large volume of dilute urine; k. water reabsorption in collecting duct due to high solute concentration of medulla; l. active transport of Na+ ions from filtrate in ascending limb of loop of Henle;

Explain how evolution may happen in response to environmental change with evidence from examples. [8 marks]

a. variation in population; b. (variation is) due to mutation/sexual reproduction; c. valid example of variation in a specific population; d. more offspring are produced than can survive / populations over-populate; e. competition / struggle for resources/survival; f. example of competition/struggle for resources; g. survival of fittest/best adapted (to the changed environment)/those with beneficial adaptations / converse; h. example of changed environment and adaptation to it; i. favourable genes/alleles passed on / best adapted reproduce (more) /converse; j. example of reproduction of individuals better adapted to changed environment; k. alleles for adaptations to the changed environment increase in the population; l. example of genes/alleles for adaptations increasing in a population; m. evolution by natural selection; n. evolution is (cumulative) change in population/species over time / change in allele frequency; Suitable examples are antibiotic resistance and the peppered moth but any genuine evidence-based example of adaptation to environmental change can be credited.

Draw an annotated graph of the effects of light intensity on the rate of photosynthesis. [4 marks]

a. vertical axis labelled as "rate of photosynthesis" and horizontal axis labelled as "light intensity"; b. drawn showing that at low light intensities, increased intensity leads to increased rate of photosynthesis (sharply); c. drawn with plateau formed at high light intensities; d. plateau annotated as maximum rate of photosynthesis; e. curve intersecting horizontal axis at a value above zero; f. arrows added to axes or student annotates axis with "rate of photosynthesis increases" and "light intensity increases"

Outline the metabolic processes during germination of a starchy seed. [5 marks]

a. water must be absorbed by the seed (to become metabolically active); b. gibberellin is produced (in the embryo); c. stimulates production of amylase; d. which catalyses digestion of starch to maltose; e. maltose diffuses to the growing embryo root and shoot/growth regions; f. maltose is converted to glucose for (aerobic) cell respiration (to release energy); g. or to synthesize materials/cellulose for plant growth;

Outline the conditions needed for the germination of a typical seed. [3 marks]

a. water to rehydrate the seed / activate metabolic processes; b. oxygen for aerobic respiration as seed germinates; c. suitable temperature for enzyme activity; d. each type of seed has specific temperature requirements / temperature requirements ensure that seeds germinate at the correct time of year; Do not accept a simple list of factors without details.

Distinguish between aerobic and anaerobic respiration. [5 marks]

anaerobic respiration: a. does not require oxygen; b. in cytoplasm; c. pyruvate reduced; d. low yield of ATP; e. lower yield of NADH; f. end products ethanol and carbon dioxide (yeast/plants) and lactate (animals/humans); g. can only use sugars; h. does not involve oxidative phosphorylation or electron transport chain i. does not involve Krebs cycle aerobic respiration: a. requires oxygen; b. in cytoplasm and mitochondrion; c. oxgen reduced; d. high yield of ATP; e. high yield of NADH; f. end products carbon dioxide and water; g. can only use fast/proteins; h. involves oxidative phosphorylation or electron transport chain i. involves Krebs cycle

Carbon dioxide is released during cell respiration. Explain anaerobic and aerobic respiration. [8 marks]

anaerobic respiration: a. glucose transformed into (two molecules of) pyruvate/pyruvic acid; b. oxidation reactions using NAD/NAD+ / producing reduced NAD/NADH; smaller amount of energy released/ATP produced than in aerobic; c. NAD/NAD+ regenerated by reducing pyruvate/transfer of hydrogen to pyruvate; d. pyruvate to CO2 and ethanol in yeast/in alcoholic fermentation; e. pyruvate to lactic acid in humans/in lactic/lactate fermentation; aerobic respiration: a. pyruvic acid/pyruvate fully oxidized/fully broken down; b. by the link reaction and Krebs cycle; c. reduced NAD/NADH passes electrons to electron transport chain; proton/H+ gradient generated; d. oxygen required as terminal electron acceptor; e. proton gradient used by ATP synthase/synthetase to produce ATP;

Active skeletal muscle requires a good supply of oxygen. Outline the mechanism of ventilation in the lungs. [6 marks]

during inhalation: a. external intercostal muscles contract moving rib cage up and out; b. diaphragm contracts becoming lower/flatter; c. increase in volume and decrease in pressure (of thorax); d. air flows into lungs as atmospheric pressure is higher; during exhalation: e. internal intercostal muscles contract so ribs move in and down; f. diaphragm relaxes and returns to domed shape; g. decrease in volume and (therefore) increase in pressure (of thorax); h. air moves out until pressure in lungs falls/is equal to atmospheric pressure; i. abdominal muscles can be used to make a stronger/forced exhalation;

Describe the lock and key model of enzyme activity and how the induced fit model extends it. [6 marks]

enzymes are (globular) proteins that are catalysts/lower activation energy of chemical reactions; lock and key model: a. explains specificity of enzyme-substrate; b. the substrate (key) fits into/has complementary shape to the active site (lock) of the enzyme; c. the active site can be changed by different chemicals/temperatures/pH so substrate cannot bind; induced-fit model: a. changes in the active site/conformational changes to allow substrate to bind; b. the substrate induces the active site to change; c. bonds weakened in the substrate (so easier to break); d. explain reduction of activation energy/wider substrate specificity; Accept the above points in the form of a clearly drawn annotated diagram. Award [3 max] if only one model addressed.

State the source, substrate, products and optimum pH conditions for one named amylase. [4 marks]

salivary amylase source: salivary glands substrate: starch products: maltose optimum pH: 6.2-7.0/slightly acidic/neutral pancreatic amylase source: pancreas substrate: starch products: maltose optimum pH: 7.0-8.0/slightly basic/alkaline

State four functions of proteins, giving a named example of each. [4 marks]

transport: eg: hemoglobin; transport of molecules across membrane: eg: sodium potassium pump; structure: eg: collagen; catalysis: eg: amylase; immunity/protection: eg: IgA / antibodies (named antibody not required); movement: eg: myosin; regulation/homeostasis: eg: insulin; binding sites for hormones (named)/neurotransmitters (name not needed);