Describe the endosymbiotic theory.

Explain the need for halving the chromosome number during a sexual life cycle and how this is done.

Outline the binomial system of classification.

a. theory that eukaryotic cells evolved from prokaryotes
OR
origin of eukaryotic organisms based on some organisms living inside/engulfed by other organisms
OR
prokaryotic cell engulfed another prokaryote including it in cytoplasm without digesting it;
b. mitochondria/chloroplasts have double membranes;
c. mitochondria/chloroplasts have their own DNA/loop of DNA/naked DNA;
d. mitochondria/chloroplasts have similar size to prokaryotes;
e. mitochondria/chloroplasts can reproduce by binary fission;
f. mitochondria/chloroplasts have 70S ribosomes (same as prokaryotes);

a. chromosome number is halved so the zygote/offspring has same number as the parent / so that chromosome number is not doubled;
b. process is meiosis;
c. DNA/chromosomes replicate (so each chromosome consists of two chromatids);
d. homologous chromosomes pair in prophase I;
e. (these) separate in anaphase I into two cells;
f. (after meiosis I) cells are haploid;
g. in meiosis II chromatids are separated;
h. result is four haploid cells/gametes;
i. each gamete is genetically unique;
j. (uniqueness) is due to crossing over/independent assortment/random alignment of chromosomes;
k. fertilization results in the formation of a diploid zygote;
l. (fertilization) results in variation in a population

a. the binomial system of names for species is universal among biologists
OR
named according to a globally recognized scheme;
b. allows to classify organisms into groups based on similar characteristics/common ancestry/DNA;
c. every species is given a binomial name;
d. members of the same species can mate and reproduce fertile offspring
e. genus is written first, followed by species;
f. genus is capitalized, (followed by) species is lower case
OR
an underlined correct example/stated that it must be underlined or italicized;

The theory of endosymbiosis was quite well known. Common errors included the original engulfing process being carried out by a eukaryote, rather than a prokaryote.

This provided a departure from the usual questions requiring a straight recall of meiosis. In general, it was well attempted, with all but a few students failing to state that meiosis was at the heart of the question. Despite the question stating halving of the chromosome number, many insisted on writing about chromosomal errors such as Down syndrome, which was not pertinent to the question.

This part was about the use of the binomial system for naming organisms. Weaker students insisted on describing the complete classification starting from kingdom, which was not required and put themselves in danger of losing the clarity mark for including superfluous material. Most were able to gain 2 marks for saying that the genus was written before species and about the use of capital/lower case or underlining or italicising.

Describe briefly the endosymbiotic theory.

Outline how photosynthesis produces glucose.

Discuss the control of blood glucose levels and the consequences if they are not maintained.

a. eukaryotes evolved from prokaryotes ✔

b. prokaryotes engulfed other prokaryotes without digesting them ✔

c. engulfed aerobic cell/prokaryote became mitochondria ✔

d. engulfed photosynthetic cell/ prokaryotes became chloroplasts ✔

e. these organelles have a double membrane «due to the engulfing process» ✔

f. mitochondria/chloroplasts contain DNA/small ribosomes/70S ribosomes ✔

a. solar/light energy is converted to chemical energy ✔

b. energy needed to produce glucose ✔

c. only specific wavelengths are absorbed by chlorophyll
OR
red and blue absorbed most strongly.
OR
chlorophyll is the pigment that absorbs light energy ✔

d. H⁽⁺⁾/electrons from water are used to reduce compounds ✔

e. CO₂ is absorbed/used/reduced to produce carbohydrates ✔

f. correct word/balanced symbol equation of photosynthesis ✔

Accept correct reference to NADPH/ATP from AHL.

control: [6 max]

a. homeostasis is the maintenance of a constant internal environment ✔

b. the pancreas produces hormones that control the levels of glucose ✔

c. if glucose levels in blood are high, beta-cells «of the pancreas» produce insulin ✔

d. «insulin» causes the cells to take up /absorb glucose ✔

e. liver stores excess glucose as glycogen ✔

f. if glucose levels in blood are low, alpha-cells «of the pancreas» produce glucagon ✔

g. «glucagon» causes the liver to break down glycogen into glucose ✔

h. «glucagon» increase levels of glucose in the blood ✔

i. negative feedback controls the glucose levels ✔ OWTTE

consequences:

j. if the pancreas produces little/no insulin a person can develop type I diabetes ✔

k. a person with type I diabetes «usually» needs/is dependent on injections of insulin ✔

l. type II diabetes occurs when the body becomes resistant to insulin/cells do not respond to insulin ✔

m. type II diabetes can «sometimes» be controlled by diet and exercise ✔

n. named consequence of having diabetes «eg: eye damage» ✔

Award [6 max] if no consequences are given.

Endosymbiotic theory. Those who had been taught it gained at least one mark. Few mentioned that the cell that became the mitochondrion was aerobic, and that the one that became the chloroplast was photosynthetic.

Glucose and photosynthesis. Again, this was an example of leaping into an answer without planning. Despite G2 protestations, HL material was not expected. Better candidates were able to gain full marks by stating that the light was trapped by chloroplasts, processes converted this into chemical energy and energy was needed to make glucose and included a correct equation ( if a symbol equation, it needed to be balanced).

Control of blood glucose levels. Weaker candidates tied themselves in knots trying to explain. Weak candidates also described insulin and glucagon as enzymes, not hormones. Other common mistakes were Alpha cells and Beta cells do not move, they just produce the hormones and glucagon and insulin do not have any direct effect on the glycogen molecules. The causes and treatment of type 2 diabetes were quite well known. A large number of students used the word ‘digest’ incorrectly, stating that glucose was ‘digested’ to glycogen.

Pictured below are Louis Pasteur’s original drawings of swan-necked flasks.

Describe how Pasteur’s experiments provided convincing evidence to falsify the concept of spontaneous generation.

State the function of life in Paramecium that is carried out by:

cilia.

State the function of life in Paramecium that is carried out by:

the contractile vacuole. 

Discuss the advantages and disadvantages of the use of adult stem cells.

Explain the role of decomposers in an ecosystem.

a. spontaneous generation is life appearing from nothing / from non-living / cells only come from pre-existing cells/life 

b. broth/culture medium (for bacteria) (used/placed) in flasks 

c. broth boiled/sterilized «in some flasks» to kill microbes 

d. no clouding/signs of bacterial growth/reproduction / microbes did not appear «in flasks of boiled broth» 

Allow bacteria or organisms instead of microbes.

e. after necks of flasks were snapped boiled broth became cloudy/growth of microbes 

f. because microbes from the air contaminated the «boiled» broth 

g. curved necks allowed indirect exposure to air but prevented entry of microbes

movement/locomotion
OR
feeding/nutrition

homeostasis
OR
maintain osmotic balance / expels «excess» water / maintains «cell» water content

Advantages:

a. «adult stem cells» can divide «endlessly» / can differentiate 

b. «adult stem cells» can be used to repair/regenerate «tissues» 

c. fewer ethical objections «than with embryonic stem cells» 

d. adults can give «informed» consent for use of their stem cells 

e. adult source is not killed / «source» would not have grown into new human / no death of embryos used to provide stem cells 

f. no rejection problems / patient’s own cells used 

g. less chance of cancer/«malignant» tumor development «than from embryonic stem cells» 

h. most tissues in adults contain some stem cells

Disadvantages:

i. difficult to obtain/collect/find in adult body/very few available 

j. some «adult» tissues contain few/no stem cells 

k. «adult stem cells» differentiate into fewer cell types «than embryonic cells» /OWTTE

a. saprotrophs/decomposers feed on/break down dead «organic» matter 

b. saprotrophs/decomposers release energy «heat» accelerating decomposition/warming soil 

c. saprotrophs/decomposers recycle nutrients / make nutrients available (to producers)
OR
improves soil fertility / returns nutrients (minerals/nitrates/phosphates/carbon)to soil/water/environment 

d. saprotrophs/decomposers detoxify waste

State processes occurring during interphase.

Using the letter C, label the stage on the diagram where chromosome supercoiling occurs.

Using the letter M, label the stage on the diagram where sister chromatids migrate to opposite poles.

Distinguish between the outcomes of a cell dividing either by mitosis or meiosis.

The mitotic index is an important prognostic tool for predicting the response of cancer cells to chemotherapy. Outline how the mitotic index is calculated.

a. DNA replication ✔

b. cell growth ✔

c. duplication of organelles/mitochondria / production of microtubules/protein synthesis ✔

Accept first two answers only.

prophase ✔

The stage should be clearly labelled.

If more than one stage is shown the candidate does not receive a mark.

anaphase ✔

The stage should be clearly labelled.

If more than one stage is shown the candidate does not receive a mark.

a. mitosis produces two daughter cells while meiosis four ✔

b. mitosis produces cells with same number of chromosomes (2n) while in meiosis they are halved (n) ✔

c. mitosis produces body cells but meiosis produces gametes
OR
mitosis produces genetically identical cells but meiosis does not ✔

Allow answers in a table.

Reference to both has to be present for the mark.

number of cells (seen under the microscope) undergoing mitosis divided by the total number of cells (observed in sample area) ✔

Can be given as a %.

There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.

There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.

There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.

There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.

There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.

Outline how the amphipathic properties of phospholipids play a role in membrane structure.

State the name of the structure shown.

X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.

a. part hydrophobic/not attracted to water/non-polar AND part hydrophilic/attracted to water/polar; Both needed.

b. bilayer formed (formed naturally by phospholipids in water);

c. hydrophilic heads/parts face outwards AND hydrophobic tails/parts face inwards;

Do not allow water loving/hating in mpa or mpc.

synapse/synaptic

a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives;

b. uptake of calcium / calcium ions diffuse in / calcium channels open;

c. structures containing neurotransmitter/vesicles move to/fuse with membrane;

d. neurotransmitter/acetylcholine released by exocytosis into cleft/binds to postsynaptic membrane/receptors;

Knowledge of amphipathic properties in part a was good. In b, most could state that the diagram shows a synapse. A variety of spelling is usually allowed, but in this case ‘synapsis’ was not allowed in English as this refers to the pairing of homologous chromosomes. There were some G2 comments that the X could be taken as the structure. However X clearly points to an arrow, not a structure. Most were able to gain some marks by describing the events, but some lost marks by not clearly indicating that it is the vesicle containing the neurotransmitter that moves.

State the main characteristic of stem cells.

Calculate the maximum diameter of the stem cell cluster on the micrograph, showing your working and giving the units.

..........

State one therapeutic role of stem cells.

Discuss how the use of stem cells to treat hereditary diseases could affect the person who received the treatment and their progeny.

undifferentiated/pluripotent/ability to divide/differentiate into any types of cells/differentiate along different pathways;

1. correct formula: 1.1cm = 500 μm, 2.7cm = length, $\frac{2.7\times 500}{1.1}=\mathrm{X\mu m}$;
2. correct answer with unit: 1227μm;

Allow answer in range of 1150 μm to 1350 μm.

treatment of Stargardt’s disease/leukemia/diabetes/heart disease/Parkinson’s disease;

Any other verifiable condition.

1. could improve quality/length of life of the treated person;
2. disease could still be passed on to progeny if defective gene/allele in gametes is not replaced/changed;

In a. most were able to say the stem cells were undifferentiated. Many put ‘unspecialised’ instead, which was not credited. There were several, justified G2 comments about the size of the micrograph, which made it difficult to measure the diameter accurately. However, this was generally very poorly answered, with over half failing to get the mark for either the correct answer or the correct calculation. In 1d the better candidates stated that the person could now live a normal life, but as it was not in the genome the progeny could still be affected. The word ‘progeny’ was commented on by several teachers, who pointed out that ‘children’, or ‘offspring’ would have been clearer for those working in an additional language.

Outline the stages in the production of mRNA by transcription.

Describe the functions of proteins in cell membranes.

Explain how natural selection can lead to speciation.

a. DNA is unwound/strands are separated «by RNA polymerase» ✔

b. new nucleotides attached to template strand «by RNA polymerase» ✔

c. complementary base pairing/base pairing with an example
OR
adenine with thymine/uracil with adenine/cytosine with guanine/guanine with cytosine ✔

d. mRNA detaches from template ✔

e. DNA rewinds ✔

a. facilitated diffusion by channel proteins ✔

b. active transport by protein pumps
OR
protein pumps eg sodium-potassium ✔

c. cell recognition by glycoproteins/protein receptors ✔

d. communication/receptors for hormones/signal molecules ✔

e. cell adhesion ✔

f. allow up to one additional mark for AHL material ✔

a. natural selection is caused by selection pressures in the environment
OR
example of a selection pressure ✔

b. natural selection requires that variation exists within a species ✔

c. variation arises randomly due to mutation
OR
variation is enhanced by meiosis/sexual reproduction ✔

d. over-production of offspring promotes selection
OR
natural selection occurs when there is competition/overpopulation/predators/environmental changes/changes in selection pressures ✔

e. well adapted individuals/individuals with best variations survive to reproduce/survival of fittest ✔

f. «frequency of» genes/alleles conferring an advantage are selected for
OR
genes/alleles conferring a disadvantage are selected against ✔

g. genetic divergence/difference increases
OR
natural selection «genetically» isolates members of a species so eventually they can no longer produce fertile offspring ✔

h. genetic divergence» leads to reproductive isolation ✔

i. geographical/behavioural/ecological factors may lead to «reproductive» isolation ✔

j. prolonged «reproductive» isolation leads to speciation ✔

k. up to one additional mark for AHL information ✔

Almost all students had a clear idea of complementary base pairing and that A pairs with U in RNA. However, this question revealed weakness in the understanding of transcription and the ability to distinguish transcription from DNA replication and RNA translation. Often times candidates had hybrid answers containing information from at least two, but sometimes all three processes. Many candidates were able to gain a couple of the easier marks in 7a on transcription despite having a poor understanding of the process.

A wide variety of fairly well-developed answers. Often, they did not couple a type of protein with its function or missed marks by being too general. Saying “transport proteins” was not enough. Often the terms integral and peripheral proteins were mentioned without going beyond that. Channel proteins and facilitated diffusion was most commonly given. The mistaken idea that proteins offer structural support or strengthen the cell membrane was seen repeatedly.

There were some excellent explanations given in well-structured responses. Many candidates avoided talking about natural selection in genetics terms, losing marks in the process. Darwin’s finches, industrial melanism and the giraffe were common examples. Some students invented their own creative examples.

The idea that natural selection limits biodiversity appeared a few times. The flawed case of the peppered moth was given to exemplify speciation, however Darwin's finches were the most frequent example.

Outline four types of membrane transport, including their use of energy.

Draw the structure of a dipeptide.

Explain the action of enzymes in digestion and the different roles of at least two named enzymes that are produced in the pancreas.

a. simple diffusion is passive movement of molecules/ions along a concentration gradient ✔

b. facilitated diffusion is passive movement of molecules/ions along a concentration gradient through a protein channel «without use of energy» ✔

c. osmosis is the passage of water through a membrane from lower solute concentration to higher ✔ OWTTE

d. active transport is movement of molecules/ions against the concentration gradient«through membrane pumps» with the use of ATP/energy ✔ Active transport requires mention of the use of energy.

e. endocytosis is the infolding of membrane/formation of vesicles to bring molecules into cell with use of energy
OR
exocytosis is the infolding of membrane/formation of vesicles to release molecules from cell with use of energy ✔

f. chemiosmosis occurs when protons diffuse through ATP synthase «in membrane» to produce ATP ✔

The description of each type of transport should include the name and brief description.

mpa, mpb and mpc require reference to concentration.

a. two amino acids, one with NH₂/NH₃+end and one with COOH/COO– end ✔

b. peptide bond between C=0 and N—H correctly drawn ✔

c. «chiral» C with H and R group on each amino acid ✔

d. peptide bond labelled/clearly indicated between C terminal of one amino acid and N terminal of the second amino acid ✔

Labels not required for amino group and carboxyl group.

a. enzymes catalyse/speed up chemical reactions/lower the energy needed ✔ OWTTE

b. have specific active sites to which specific substrates bind ✔

c. enzyme catalysis involves molecular motion and the collision of substrates with the active site ✔ OWTTE

d. enzymes break macromolecules into monomers/smaller molecules indigestion ✔

e. smaller molecules/monomers more readily absorbed ✔

f. <<pancreas>> secretes enzymes into the «lumen of» small intestine ✔

g. the small intestine has an alkaline pH ✔

h. enzymes have maximum action at specific pHs
OR
enzymes can be denatured at other pHs ✔

i. amylase breaks down starch into sugars/disaccharides ✔

j. lipase breaks lipids/triglycerides into monoglycerides/fatty acids and glycerol ✔

k. endopeptidase/protease breaks «peptide» bonds in proteins/polypeptides ✔

l. accept any other valid pancreatic enzyme, substrate and product ✔

Award [6 max] if there is no mention of two specific groups of enzymes.

Membrane transport – In spite of the question asking about energy, many lost easy marks by forgetting to refer to it. Others did not mention the gradients. In osmosis, please stress to the students which concentration they are talking about. They should be talking clearly about water potential or solute concentration.

Structure of the dipeptide – candidates who also do chemistry were at an advantage here. Diagrams went from the superb to something Picasso might have produced.

Enzymes in digestion. A disturbing number of candidates saw the word pancreas and wrote about insulin and glucagon. These are hormones, produced by ENdocrine glands not enzymes produced by EXocrine glands. Better candidates scored nearly full marks, by describing enzyme action and correctly describing the three main enzymes from the pancreas. Weaker candidates could not string the correct sequence together and scored very few marks. Better candidates wrote some sort of plan before starting, using the space below the instructions for Section B. This should be encouraged.

The structure of prokaryotic cells has been investigated using electron microscopy. Draw a labelled diagram to show prokaryotic cell structure.

Outline the reasons for differences between the proteomes of cells within a multicellular organism.

Discuss the cell theory and its limitations.

a. cell wall — a uniformly thick wall ✔

b. pili — hair-like structures connected to cell wall
OR
flagellum — at one end only, longer than pili ✔

c. plasma/cell membrane — represented by a continuous single line ✔
May be labelled as the innermost wall line

d. «70S» ribosomes — drawn as small discrete dots not circles ✔

e. naked DNA/nucleoid — region with DNA not enclosed in membrane ✔

f. cytoplasm — the non-structural material within the cell ✔

Award [1] for each structure clearly drawn and correctly labelled

Award [2 max] if any eukaryotic structure is drawn and labelled

a. all the genome is the same in all the cells of an organism  ✔

b. the genome/DNA/genes instructs the production/expression of proteins/proteome ✔

c. the proteome is all the proteins produced by a cell ✔

d. the proteome varies with the function/location/cell differentiation/environmental conditions of the cell ✔

e. specific genes are expressed/turned on/off in different cells ✔

f. «turning on/off» according to a required function ✔

Accept a specific example (eg: insulin only produced in pancreas)

cell theory:

a. cell theory is the accepted explanation of life ✔

b. organisms are composed of «one or more» cells ✔

c. cells are the basic/fundamental/smallest units of life ✔

d. cells can only come from pre-existing cells ✔

e. spontaneous generation of life has been disproven ✔

limitations:

f. striated muscle cells contain many nuclei «while most eukaryotic cells have one nucleus»
OR
red blood cells have no nucleus «while most eukaryotic cells have one nucleus» ✔

g. giant algae have complex single cell structure
OR
organisms as large as giant algae would be expected to be multicellular, but they have only one cell with one nucleus ✔

h. aseptate fungal hyphae are tube-like structures that contain no cell membranes between the many nuclei
OR
slime molds contain many nuclei ✔

i. viruses have some characteristics of living organisms but are not cells ✔

j. if all cells come from pre-existing cells, where did the first one come from? ✔

Allow description of Pasteur’s experiments

Do not accept a list of limitations without explanation

Outline the significance of surface area to volume ratio in the limitation of cell size.

Describe transport across cell membranes by osmosis.

Explain the adaptations of the small intestine to its function.

a. surface area of the cell affects the rate of material exchange;
b. when the cell increases in size, so does its chemical activity/metabolism;
c. (when the cell increases in size/grows) more substances need to be taken in / more waste products need to be excreted;
d. as the volume of the cell increases, so does the surface area, however not to the same extent
OR
when the cell gets bigger, its surface area to volume ratio gets smaller;
e. substances will not be able enter the cell fast enough/cell volume will not be supplied

OR
metabolic rate will exceed the rate of exchange
OR
when the surface area: volume ratio is higher, the diffusion rate increases;
f. some cells have adaptations to increase their surface area/flatten/microvilli/shape of red blood cells;
g. cells in growth areas tend to divide and remain small
OR
cells divide when maximum size is reached;

a. form of diffusion;
b. osmosis is the movement of water molecules;
c. (movement) across a selectively/semi/partially permeable membrane/cell membrane;
d. from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)
OR
movement of water molecules from a high concentration of water to a low concentration of water molecules;
e. it is a passive transport mechanism/does not use ATP;
f. channel proteins/aquaporins are used;

a. small intestine is where nutrients are absorbed into the bloodstream;
b. very long to maximize absorption;
c. (the small intestine) is lined with (smooth) muscle to allow for the mixing/ and moving of digested food;
d. muscles are circular and longitudinal;
e. that perform peristalsis;
f. the pancreas (and gall bladder) secretes substances into the small intestine to aid digestion;
g. contain villi, to increase surface area;
h. villi have microvilli to increase surface area even more;
i. villi absorb products of digestion/mineral ions/vitamins/glucose;
j. dense capillary network rapidly transports absorbed products;
k. lacteal absorbs lipids from the intestine (into the lymphatic system);
l. (most of the) chemical digestion (into monomers) occurs in small intestine/description of specific enzyme action;

Accept annotated diagrams as part of the explanation.

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Most knew that as the cell increases in size, the SA:volume ratio decreases but had difficulty explaining its significance.

Most gained at least 2 marks describing osmosis. Common mistakes were not making it clear whether the concentration was referring to water or to the solute. A surprising number of students did not refer to water at all.

The structure and function of the small intestine was quite well known. Many missed a mark for omitting to say that the products of digestion are absorbed into the blood. Some of the descriptions of microvilli were not clear, not making it evident that they were on the epithelial cells of the villi. The presence and functions of the muscle layers were well known.

Draw a labelled diagram to show the fluid mosaic model of the plasma membrane.

Unicellular and multicellular organisms share the same functions of life. Outline four functions of life.

The structure of organisms is based on organic molecules containing carbon. Explain the cycling of carbon in an ecosystem.

a. two correctly oriented layers of phospholipids/phospholipid bilayer shown with heads facing in opposite directions 

b. phospholipids shown with two parts labelled hydrophilic/phosphate head AND hydrophobic/hydrocarbon tail

c. protein (any) shown as a globular structure embedded in one/both layers of phospholipid 

d. peripheral protein, shown as globular structure at the surface of the membrane AND integral protein shown as embedded globular structures 

e. glycoprotein shown as embedded globular structure with antenna-like carbohydrate protruding / carbohydrate shown as a branched/antenna-like structure either on a protein or on a phospholipid
OR
channel protein(s) shown with a pore passing through it
OR
pump protein shown as a transmembrane globular structure 

f. cholesterol shown in between adjacent phospholipids

Do not award the mark unless the structure is labelled with the underlined name.

a. nutrition: process by which organisms take in and make use of food//nutrients OWTTE 

b. metabolism: conversion of organic molecules/chemical reactions in an organism 

c. growth: increase in size/mass/number of cells within an organism

d. response/irritability/sensitivity: reactions/responsiveness to stimuli/factors 

e. homeostasis: regulating/maintaining constant/stable interior environment 

f. reproduction: production of similar cells/organisms from existing ones/offspring 

g. excretion: elimination of (metabolic) wastes

a. autotrophs/producers absorb carbon (dioxide} from atmosphere/air/water 

b. autotrophs make carbohydrates/organic compounds / perform photosynthesis 

c. carbon (compounds) pass along food chains/trophic levels (as consumers feed) 

d. respiration releases carbon (dioxide) into atmosphere/water 

e. carbon (dioxide} is released from dead matter /by decomposition/respiration 

f. methane is produced during anaerobic respiration of organic matter / by methanogens in cattle/herbivores

g. methane is oxidized into carbon dioxide in the atmosphere 

h. fossil fuels/peat were made from partially decomposed organic matter 

i. combustion of fossil fuels/forest fires/biomass releases carbon (dioxide} into the atmosphere 

j. volcanic eruptions may add large quantities of carbon (dioxide) into the atmosphere 

k. limestone (from shells/reefs)/trees/permafrost are sinks of carbon

The image is an electron micrograph.

Determine, with a reason, whether the image is of a prokaryotic cell or eukaryotic cell.

(i) State the process that divides one nucleus into two genetically identical nuclei.

(ii) Explain how the cell cycle is controlled.

eukaryotic because nucleus/membrane-bound organelles/named organelle other than ribosome «eg, mitochondria, vesicles» internal membranes «ER»/multicellular

(i) mitosis

(ii)

a. cell cycle is a sequence of stages / cell cycle is G₁, S, G₂ and mitosis

b. (control of the cell cycle) by cyclins/cyclin

c. levels of cyclins rise (and fall)/fluctuate during the cell cycle/surge at different times/have to reach a certain concentration

d. conditions inside as well as outside the cell affect regulation

e. four cyclins/different cyclins to enter different stages of/events in the cell cycle / cyclins regulate the sequence/timing of the cell cycle / cyclins trigger the next stages

The idea of different cyclins acting at different phases must be clear.

f. cyclin-dependent kinases / cyclins bind to kinases and activate them

g. kinases phosphorylate other proteins

h. phosphorylated proteins perform specific functions in the cell cycle

Describe the origin of eukaryotic cells according to the endosymbiotic theory.

Explain how hormones are used to control the human menstrual cycle.

Outline natural methods of cloning in some eukaryotes.

a. mitochondria and chloroplasts are similar to prokaryotes

b. «host» cell took in another cell by endocytosis/by engulfing «in a vesicle»

Allow “taking in” in place of “engulfing”

c. but did not digest the cell/kept the «ingested» cell alive

    OR

    symbiotic/mutualistic relationship «between engulfed and host cell»

d. chloroplasts and mitochondria were once independent/free-living «organisms»

e. DNA «loop» in chloroplast/mitochondrion

f. division/binary fission of chloroplast/mitochondrion

g. double membrane around chloroplast/mitochondrion

h. 70s ribosomes «in chloroplast/mitochondrion»

Award up to [2] for evidence from mpe to mph

[Max 4 Marks]

a. FSH stimulates the development of follicles

b. follicles produce estrogen

c. estrogen stimulates the repair of the uterus lining

d. estrogen stimulates LH secretion

e. LH causes/stimulates ovulation

f. LH causes/stimulates the development of the corpus luteum

g. corpus luteum secretes progesterone

h. progesterone causes/stimulates thickening of the uterus lining

    OR

    prepares uterine lining for implantation

    OR

    maintains the endometrium

i. progesterone/estrogen inhibits the secretion of LH/FSH

j. falling progesterone levels at the end of the cycle allow FSH production/menstruation

k. negative/positive feedback «control» described correctly

l. LH/FSH are pituitary hormones

[Max 8 Marks]

a. clones are genetically identical organisms

    OR

    group of cells derived from a single parent cell

b. asexual reproduction in plants such as tubers/runners/bulbs

Allow other verifiable examples of plants

c. common in non-vertebrates such as budding in hydra

Allow other verifiable examples of invertebrates

d. budding in yeast/fungi

Allow other verifiable examples of fungi

e. identical twins «in humans» are clones because they originate from
the same cell

State the genus of this organism.

State the domain in which it is classified.

Outline the method of nutrition carried out by P. caudatum.

Outline one aspect of how P. caudatum carries out homeostasis.

Apart from the ribosomes, explain the evidence for the endosymbiotic theory of the origin of eukaryotic cells.

Paramecium

eukaryotes

heterotroph/consumer as it feeds on bacteria/algae/yeast/smaller single celled organisms
OR
heterotroph/consumer as it does not have chloroplasts

Heterotrophic must be qualified.

a. lives in fresh water so water enters cell (by osmosis);

b. contractile vacuoles collect and expel water;

c. homeostasis is keeping internal conditions within limit/constant / involves osmoregulation/regulating water content/potential;

a. mitochondria/chloroplasts show features in common with prokaryotes/similar size;

b. multiply by binary fission/in same manner;

c. have naked loop of DNA/circular DNA/own DNA;

d. surrounded by a double membrane;

In a about half of the candidates named the genus correctly (Paramaecium), but significantly fewer could state the correct domain (eukaryota). The most common wrong answers were prokaryote and eubacteria. Only the better candidates were able to outline the method of nutrition (heterotrophy) in b and describe how homeostasis is carried out, in spite of being specifically stated in the syllabus. The endosymbiotic theory was quite well known.

Outline how acidified sea water could affect the shells of the oyster.

Outline the trends shown in the data in the graph.

Estimate how much smaller drilled oysters raised in seawater at a high CO₂ concentration were than drilled oysters raised in seawater at a normal CO₂ concentration.

Deduce from the data in the bar charts which factors were and were not correlated significantly with the number of oysters drilled by the gastropods.

Suggest reasons for the differences in the numbers of oysters drilled, as shown in the bar charts.

The radula in a gastropod is hard but not made of calcium carbonate. Outline how this statement is supported by the drilling success of the gastropods in seawater with normal or high CO₂ concentrations.

Using all the data, evaluate how CO₂ concentrations affect the development of oysters and their predation by gastropods.

Shells might dissolve/deteriorate / become smaller/thinner/weaker / OWTTE
OR
shell formation reduced / more difficult

a. positive correlation between shell thickness and shell size
OR
as shell thickness increases, shell size «also» increases 

b. (positive correlation) occurs at two different CO₂ concentrations / both high and normal concentrations 

c. trend for thickness is «slightly» lower with high CO₂

«approximately» 0.2 mm²
OR
«approximately» 40 % «smaller» 

unit required

a. significant factor: concentration of CO₂ in which oysters were raised 

b. insignificant factor: concentration of CO₂ at which oysters were presented to gastropods

a. (because) shells are thinner/smaller when the oyster is raised in high CO₂/lower pH
OR
«because» lower pH/higher acidity prevents/reduces deposition of calcium carbonate 

b. gastropods target smaller/thinner-shelled oysters more 

c. gastropods can eat/drill thin-shelled/smaller oysters at a faster rate (and move onto another) 

d. eating smaller oysters «from high CO₂ environments» means given population of gastropods require more oysters for same food intake

a. data shows that similar numbers are drilled regardless of conditions 

b. since radulas are not affected by acidification
OR
radulas not made of calcium carbonate so (remain) strong/successful at drilling

a. the data/trend lines indicate that a higher CO₂ concentration diminishes the shell thickness, making gastropod predation more successful
OR
the bar graphs suggest that oysters raised in a higher CO₂ concentration are smaller, making gastropod predation more successful 

b. CO₂ concentrations «during feeding» do not change the occurrence of drilling/predation «by gastropods» 

c. «limitation» no information about how exaggerated the CO₂ concentrations were
OR
«limitation» no information about numbers of gastropods used «in each setting»

Identify the stage of mitosis labelled X in the image, giving a reason.

[Source: Copyright 2002, The Trustees of Indiana University]

Outline the use of a karyogram during pregnancy.

telophase because the chromosomes/chromatids have reached the poles
OR
«late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔

OWTTE

a. is a photograph/diagram of homologous pairs of chromosomes that can be analysed ✔

b. information may be used to determine other chromosome abnormalities/changes in chromosome numbers/possible birth defects ✔

c. Down syndrome/trisomy can be detected if there are three copies of a chromosome Not just “Down syndrome”.
OR
accept any other valid example ✔

d. other missing or extra pieces of chromosomes can be detected ✔

e. sex can be determined as the Y chromosome is shorter than the X ✔ Or correct ref to X and Y.

Most were able to correctly state (late) anaphase or telophase but did not give a reason as clearly asked. Many students seem to have excellent eyesight as they claimed to see that the chromosomes were unwinding and that the nuclear membranes had formed. Please encourage the students not to go beyond what can be seen.

Most knew what a karyogram was. However, the question was about use, which does not involve a detailed description, taking up half the space about how the sample was obtained and the risks involved. Most knew that it was to do with the chromosomes, few stated that it was a diagram or a picture of the homologous pairs. An explanation of how it is used to confirm sex was needed.

Glands are organs that secrete and release particular chemical substances. Melatonin is an important hormone secreted in the pineal gland in the brain. Describe its role in mammals.

State the principal product of this cell.

Using the table, identify the organelles labelled I and II on the electron micrograph with their principal role.

a. controls circadian rhythms/biological clocks «in mammals» 

b. production is controlled by amount of light detected by the retina 

c. high production/secretion in the dark
OR
no production/secretion in the day
OR
production/secretion is directly proportional to night time duration 

d. affects «seasonal» reproduction/sleep-wake cycles/jet lag

«digestive» enzymes

The Davson-Danielli model of membrane structure was proposed in the 1930s. When electron micrographs of membranes were first produced, they were used as evidence for this model. The micrograph shows two adjacent membranes (indicated with arrows).

[Source: DENNIS KUNKEL MICROSCOPY/SCIENCE PHOTO LIBRARY.]

Explain how the appearance of membranes in electron micrographs was used as evidence to support the Davson-Danielli model.

1. the black lines represent proteins;
2. forms a ‘sandwich’/2 layers;
3. there is a clear layer in the centre;
4. (the clear layer) is composed of phospholipids;
5. reference to both membranes being similar;

Some students stated that they could ‘clearly see’ the hydrophilic heads and the hydrophobic tails. They were describing the wrong model. Once again, this image came under some criticism for being far too small. Only the better prepared candidates used the evidence from the micrograph, and it was obvious that many students had not encountered this on their course.

Outline the use of human embryonic stem cells (hESC) to treat Stargardt’s disease.

The most common form of Stargardt’s disease is known to be autosomal recessive. Using a Punnett grid, deduce the probability of a child inheriting Stargardt’s disease, if both of the parents are carriers of the disease but do not have the disease themselves.

a. «an inherited form of» degeneration of retinal layer/photoreceptor cells/blindness 
OR
eye genetic disorder 

OWTTE

b. «hESC/stem cells» can provide/differentiate into healthy retinal cells 

c. injecting «hESC/stem cells» into the retina/eye can restore vision in animal/human trials

a. correct allele identification 
«eg: S=dominant/normal; s=recessive/disease»

b. correct Punnett grid

c. correct phenotypic ratio/outcome

example:
s =recessive, disease-causing form of gene,
S =dominant,
normal form parents =Ss.
Any letter can be used as capital and lower case but a legend/key is not required if correct notation is used.

Do not award mp b if the gametes do not show heterozygous organisms

phenotypic ratio:
normal :  with disease
OR
3 normal : 1 with disease
OR
«75 % normal :» 25 % disease

Outline the cell theory.

State two functions of life.

List three characteristics of eukaryotic homologous chromosomes.

Using the following table, compare and contrast anaerobic cell respiration in yeasts and in humans. The first row has been completed as an example.

a. cells can only arise from preexisting cells ✔

b. living organisms are composed of cells/smallest unit of life ✔

c. organisms consisting of only one cell carry out all functions of life in that cell/cells perform life functions «at some point in their existence» ✔

d. although most organisms conform to cell theory, there are exceptions ✔

a. nutrition ✔

b. metabolism/respiration ✔

c. growth ✔

d. response/irritability ✔

e. excretion ✔

f. homeostasis ✔

g. reproduction ✔

Do not allow “feeding”, plants do not “feed”.

Mark the first two answers only.

a. linear DNA molecules
OR
DNA associated with histone «proteins» ✔

b. carry the same sequence of genes ✔

c. «but» not necessarily the same alleles «of those genes» ✔

d. both are present when nucleus is in diploid state ✔
OR
occur in pairs ✔

e. have same size/length/banding patterns ✔

f. centromeres are in the same position ✔

Award [1] per correct row.

Draw an annotated diagram of the fluid mosaic model of membrane structure.

Describe the processes involved in absorbing different nutrients across the cell membrane of villus epithelium cells lining the small intestine.

Explain the events that occur during a nerve impulse and how the impulse is propagated along an axon.

a. phospholipid bilayer – with head and tails 

b. hydrophilic/phosphate/polar heads AND hydrophobic/hydrocarbon/fattyacid/non-polar tails labelled. Both needed.

c. integral/intrinsic protein – embedded in the phospholipid bilayer 

d. protein channel – integral protein showing clear channel/pore 

e. peripheral/extrinsic protein – on the surface 

f. glycoprotein with carbohydrate attached 

g. cholesterol – shown embedded in bilayer

Award [1] for each structure clearly drawn and correctly labelled.

a. «simple» diffusion of nutrients along/down a concentration gradient 

b. example of simple diffusion, eg: fatty acids 

c. facilitated diffusion of nutrients involves movement through channel proteins 

d. example of nutrient for facilitated diffusion eg: fructose 

e. active transport of nutrients against a concentration gradient / involving protein pumps 

f. example of active transport, eg: (iron) ions/glucose/amino acids 

g. endocytosis / by means of vesicles 

h. example of nutrient for endocytosis, eg: cholesterol in lipoprotein particles

a. nerve impulses are action potentials propagated along axons of neurons 

b. resting potential is −70 mV
OR
relatively negative inside in comparison to the outside 

c. Na⁺/K⁺ pumps maintain/re-establish «the resting potential» 

d. more sodium ions outside than inside «when at the resting potential»
OR
more potassium ions inside than outside «when at the resting potential» 

e. action potential stimulates «wave of» depolarization along the membrane/axon 

f. «when neuron is stimulated» if threshold potential is reached Na⁺ channels open 

g. sodium ions diffuse/move in 

h. «Na⁺ move in» causing depolarization / inside of the neuron becomes more positively charged than the outside of the neuron 

i. potassium ion channels open
OR
potassium ions diffuse/move out 

j. «K⁺ move out» causing repolarization 

k. local currents
OR
description of Na⁺ ion diffusion between depolarized region and next region of axon to depolarize 

l. myelination increases propagation speed/allows saltatory conduction

Accept any of the points clearly explained in an annotated diagram.

Identify which electron micrograph shows a mitochondrion, providing one observation to support your choice.

Discuss the evidence for the theory that mitochondria may have evolved from free-living prokaryotes by endosymbiosis.

«micrograph» C cristae/double membrane is visible/«folds of» membranes inside ✔

Must state observation

a. «double» membrane may have formed when engulfed ✔

b. replicate by binary fission like free-living prokaryotes
OR
reproduce separate from «host» cell replication ✔

c. they have their own «circular» DNA AND reproduce on their own ✔

d. they have «70s» ribosomes AND can manufacture «their own» proteins ✔

e. have organelle«s» similar to free-living prokaryotes ✔

f. similar in size to free-living prokaryotes ✔

g. mitochondrial inner membranes manufacture ATP like bacterial membranes ✔

h. currently there is no free-living prokaryote like a mitochondrion ✔

Most candidates identified the correct micrograph but for the wrong reason such as 70S ribosomes visible, has a matrix, or correct shape. Only starch granules were visible in the image, not ribosomes.

The command term for this question was “discuss”. Connections were not made as many candidates just gave a list of features of mitochondria with no attempt at explanation or discussion. There was some confusion between the words endocytosis and endosymbiosis. In spite of the many shortcomings, there were a few brilliant responses

Draw a section of the Singer-Nicolson model of an animal cell membrane.

Outline the principles used by scientists to classify organisms.

Explain the movement of energy and inorganic nutrients in an ecosystem.

a. bilayer of phospholipids with both “tails” towards the inside «of the bilayer» ✔ This can be taken unlabeled from diagram.

b. hydrophilic/polar and hydrophobic/non-polar annotation ✔

c. cholesterol between phospholipid tails ✔

d. glycoprotein ✔

e. integral proteins/channel proteins ✔

f. peripheral proteins ✔ Allow this if it does not extend across the membrane

Elements should be clearly drawn, correctly positioned and annotated.

a. use of the binomial system ✔

b. agreed/developed by scientists / OWTTE ✔

c. hierarchy of taxa used ✔ Names of the seven taxa not required. 

d. three domains used/three domain names ✔ OWTTE

e. genome/DNA sequence similarities
OR
amino acid sequence of specific proteins ✔

f. species from a common ancestor are grouped together
OR
included in the same clade/branch in cladogram ✔

g. use evidence of evolutionary origin ✔ Allow example e.g. fossil record comparison

h. shared characteristics within a group
OR
similar embryonic development ✔

a. autotrophs/producers/plants obtain inorganic nutrients from the «abiotic» environment ✔

b. energy provided «mainly» by sunlight ✔

c. light energy converted «to chemical energy» through photosynthesis ✔

d. photosynthesis/producers/autotrophs convert inorganic carbon/carbon dioxide and water into carbon/organic compounds ✔

e. «these» carbon compounds/foods contain/are a source of «useable» energy «for life» ✔

f. carbon compounds/energy are transferred along food chains when eaten by consumers/heterotrophs ✔ Allow OWTTE for mpf for passed up trophic levels.

g. respiration returns carbon «dioxide» to the environment ✔

h. respiration releases stored/chemical energy as ATP/heat ✔

i. energy/ATP is used to carry out life functions/synthesis/growth/movement ✔

j. energy is lost/not recycled ✔

k. nutrients are recycled / example of recycled nutrient e.g. carbon ✔

l. decomposers recycle minerals/inorganic nutrients ✔

Outline reasons for the therapeutic use of stem cells.

Describe how leaf cells make use of light energy.

Explain how cells and cell components in the blood defend the body against infectious disease.

1. unspecialized/undifferentiated stem cells can divide / differentiate along different pathways;
2. (stem cells are accessible as they) come from embryos/bone marrow/umbilical cord blood/adult tissue;
3. (stem cells) can regenerate/repair diseased/damaged tissues in people;
4. valid specific example;
5. drugs can be tested on stem cells (in laboratories to see if they are harmful);

1. leaf cells contain chloroplasts;
2. light is absorbed by chlorophyll (in chloroplasts);
3. other pigments absorb different wavelengths;
4. light energy is used in photosynthesis;
5. (light is needed) to combine water and carbon dioxide/fix carbon dioxide;
6. carbon compounds/organic compounds/glucose/starch/carbohydrate are produced;
7. blue and red light is absorbed;
8. perform photolysis
   OR
   split water molecules;

Wavelengths accepted for mpg.

Platelets: [3 max]

1. damage/cuts to blood vessels causes platelets to be activated;
2. the platelets release clotting factors;
3. initiates cascade of reactions
   OR
   fibrinogen is converted to fibrin;
4. forms a mesh over the damaged area;
5. prevents pathogens from entering the body;
   
   Phagocytes: [3 max]
   
6. phagocytes/phagocytic white blood cells in the blood travel to the site of infection;
7. (phagocytes) squeeze between the capillary cells;
8. (phagocytes) engulf/ingest/take in pathogens;
9. the pathogen is digested/broken down by/within the phagocyte;
   
   Lymphocytes: [3 max]
10. lymphocytes recognize a particular fragment/antigen of a pathogen;
11. (lymphocytes) release antibodies;
12. (antibodies) provide specific immunity;
13. memory cells provide rapid response giving long-term immunity (to pathogens previously recognized);
14. antibodies destroy pathogens;

ECF may be applied when candidates use white blood cells in place of specific terms.

Some excellent answers; stem cells was usually well answered, leaf cells was often more complex than necessary but marks were usually able to be gained, though many answers were missing the obvious, for example leaf cells contain chloroplasts. Defence against disease; far too often over-complicated and confused answers. It is important that students are aware of the level they need to know. There is no need to over-complicate and risk loss of understanding, which was evident across many answers and which was so confused across the roles of macrophages, B cells and T cells. Equally, for cell components, more often than not this was ignored or mistakenly discussed as skin and mucus over platelets.

Mostly well done. Appropriate examples provided for stem cell therapies. It seems that many candidates think that all stem cells can differentiate into "any" type of cells, which is not correct. Other candidates showed understanding of the discrimination between the source and the potential of the cells. Occasionally candidate showed confusion about the term "stem" in that "stem cells show the way plants grow"; sometimes therapeutic use of stem cells was confused with gene editing.

Generally speaking, students know how leaf cells make use of light energy; at least three marks were usually gained. Some candidates made the answer too complex and involved, when a simple straight-forward answer would have been better.

Among all candidates, there was knowledge of how each of the blood components (platelets, phagocytes, lymphocytes) can defend against infectious disease; each of the marking points in the mark scheme was eventually awarded; popular ideas were that fibrin is formed, phagocytes engulf pathogens and antibodies provide specific immunity.

Correct terminology was confused or was not employed in too many answers.

Label the area where cellulose is found in the micrograph of a plant cell.

[Source: BIOPHOTO ASSOCIATES/Getty Images]

Cellulose is the most abundant organic polymer on Earth. Describe the structure of cellulose.

Outline one reason for humans being unable to digest cellulose.

Explain the advantages of having both lipid and carbohydrate as energy stores in the human body.

label placed anywhere along outside perimeter/cell wall of plant cell ✔

a. unbranched/straight chain of glucose molecules
OR
unbranched/straight-chain polysaccharide ✔

b. formed of beta glucose;

c. formed by condensation reactions/glycosidic bonds
OR
1, 4 linkage ✔

d. hydrogen bonds form between cellulose chains 

e. form microfibrils ✔

Award marks to an accurate annotated diagram

Do not allow carbohydrate

humans lack cellulase/appropriate enzyme ✔

a. lipid is long-term energy storage
OR
carbohydrate is short-term energy storage/readily available ✔

b. lipids are insoluble, so easier to store
OR
carbohydrates/sugars are soluble, so easy to transport by blood ✔

c. lipids store more energy «per gram»
OR
lipids occupy less space «per energy/kJ» ✔

OWTTE

Deduce the concentration of ZDV that would cause a 50 % reduction in root growth compared to the control.

Identify the root length, as a percentage of the control, resulting from a ZDV concentration of $400 \text{μmol}$.

Compare and contrast the effect of ZDV and NVP on the growth of Allium roots.

Based on the information, suggest with a reason which of the labelled cell types will become more common in Allium root tips treated with ZDV.

Allium root tips continue to show some growth even at high concentrations of NVP. Suggest a possible reason for the growth seen in root tips with 800μmol NVP.

Deduce the change in mitotic index after 72 hours compared to the control.

Based on the data, evaluate the evidence for leptin promoting regeneration of liver tissue.

Outline the role of leptin in appetite control.

75 μmol ✔

Allow answers in the range of 70 µmol–80 µmol.

24 % ✔

Allow answers in the range 23 %–25 %.

Similarities:

a. reduce root length (compared to the control) ✔

b. (ZDV and NVP) have greatest change (in growth) at lowest concentrations (of ZDV and NVP) ✔

c. same effect at 200 μmol ✔

d. above/at about 400 μmol effect levels off ✔

Differences:

e. the change/differences become significant after 200 μmol ✔

f. ZDV has a (slightly) larger effect / NVP has a (slightly) smaller effect / WTTE
OR
above 400 μmol effect of ZDV remains higher / NVP remains lower ✔

Answer must contain one similarity and one difference.

Credit may be given for numeric differences when accurately stated.

a. Y (will become more common) ✔

b. spindle not formed yet
OR
cells x and z have spindles ✔

c. cells in Y cannot progress (into Z/into metaphase) ✔

a. still some mitosis ✔

b. individual cells grow/elongate (expand by absorbing water) ✔

c. NVP is not 100 % effective / does not enter all of the cells / not all cells have come in contact with NVP ✔

d. roots have reached maximum saturation of NVP and are no longer functionally affected ✔

e. some cells are resistant to the drug ✔

Accept reasonable suggestions. 

0.3 / 100 % increase / doubling ✔

Do not penalize errors in significant figures. For example, 0.34 would be acceptable.

a. mitotic index in treatment greater than in control/leptin appears to promote mitosis ✔

b. mitotic index increases with time suggests ongoing regeneration/growth 
OR
positive correlation between exposure to leptin and increased mitotic index ✔

c. but experiment limited to 72 hours/regeneration/recovery may take longer than 72 hours ✔

d. no error bars shown/no information on significance/sample size ✔

Acknowledge WTTE.

a. acts on receptors in the hypothalamus/appetite centre ✔

b. inhibits appetite ✔

Accept WTTE for mpb.

Part (ii) was better answered than part (i) as many answers provided were outside the acceptable range of answers.

Part (ii) was better answered than part (i) as many answers provided were outside the acceptable range of answers.

There was a tendency to describe data rather than interpreting it. Instead of writing that root length was reduced, students simply compared numbers. Commonly either a comparison or a contrast was missing.

Many students correctly identified cell type Y but reasoning was less accurate.

Most candidates earned this mark; some gave imaginative answers.

Those who had experience calculating mitotic index did well with this question.

Many students were able to extract conclusions from the data but did not take the evaluation into discussion of shortcomings of the design or error bars in the data.

Many answered the function of leptin correctly; some gave the opposite answer. Some reasoned that the action of leptin to inhibit cancer would require energy so hunger would be increased. Though the reasoning was interesting, they obviously did not understand the role of this hormone.

Draw the ultrastructure of a prokaryotic cell based on electron micrographs.

Outline what occurs in cells in the first division of meiosis.

Explain the role of cells in the defence against infectious disease.

a. cell wall;

b. plasma membrane; Clearly shown as a separate line under the cell wall or the inner line

c. cytoplasm AND 70S ribosomes; Do not allow (small) circles

d. nucleoid/naked DNA;

e. plasmid
OR
pili
OR
flagella/flagellum;

Structures correctly drawn and labelled.

Award [2 max] if any exclusively eukaryotic structures are shown.

Do not allow cilia as they are not found in prokaryotes.

a. halves the chromosome number/produces haploid cells;

b. at start of meiosis each chromosome consists of two sister chromatids attached by a centromere;

c. prophase (I): pairing of homologous chromosomes;

d. crossing over occurs;

e. chromosomes condense by supercoiling;

f. metaphase (I): pairs of homologous chromosomes/bivalents move to equator of spindle
OR
metaphase (I): orientation of pairs of homologous chromosomes (prior to separation) is random;

g. anaphase (I): centromeres do not divide
OR
anaphase (I): spindle fibre pulls chromosome/whole centromere with two sister chromatids to opposite poles;

h. telophase (I): arrival of centromere with sister chromatids at opposite poles;

Some of these can be awarded for correctly annotated diagrams.

No credit for events in meiosis II.

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);

e. gives non-specific immunity to diseases / ingest any type of pathogen;

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;

j. plasma cells produce large quantity of (one type of) antibody;

k. some lymphocytes act/remain as memory cells;

l. 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;

In part (a) many candidates were penalised for drawing clear eukaryotic structures such as mitochondria. The general level of the drawings was better than in the past. However a prokaryote should not be represented as a square. Ribosomes must be shown as dots, not circles.

In part (b), those who had been well prepared easily gained the 5 marks, but there was a significant proportion who did not know the difference between mitosis and meiosis.

In part (c), defence against infection was well known. Poor candidates lost marks by using loose, non-biological expressions such as the ‘white blood cells eat the infection/disease’. However, most had a fair idea of the cellular response to infection.

State the name of the structures labelled I and II.

Outline the function of the structure labelled III.

The plant from which this cell was taken is in the group angiospermophyta. State one characteristic that is unique to this group of plants.

Distinguish between autotrophic nutrition and heterotrophic nutrition.

Explain how energy and nutrients are transferred in ecosystems.

I. cell wall 

II. nucleus/chromatin

Both needed.

a. necessary for photosynthesis/converts light energy into chemical energy

b. contains chlorophyll to absorb light

c. (contains enzymes) for production of carbohydrate/glucose/starch

a. produce flowers 

b. enclosed seeds/have fruit

Table format not required.
Must be paired statements.

a. energy enters ecosystems from the Sun / continuous supply from the Sun 

b. light energy is converted into chemical energy and lost with movement along food chains
OR
energy needs to be «constantly» added «to ecosystem» as lost with movement along food chains / energy lost as heat with movement along food chains 

c. nutrients are recycled within ecosystems / nutrients in an ecosystem are finite and limited 

d. nutrients not lost but transformed into different compounds 

e. nutrients «carbon compounds»/energy flow through food chains by means of feeding

Outline the structures in M. tuberculosis that are not present in a human cell.

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

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

a. cell wall ✔

b. pili/flagella ✔

c. 70S ribosomes ✔

d. nucleoid / circular DNA
OR
naked DNA ✔

e. plasmids ✔

As candidates do not need to know the structure of Mycobacterium tuberculosis, all prokaryotic structures are accepted.

Ignore references to membrane bound organelles.

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 ✔

f. each lymphocyte produces just one type of antibody ✔

g. (this is) specific immunity ✔

h. (part of the) antibody/immunoglobulin binds to the antigen / specific antibody binds to the specific antigen ✔

i. antibodies are proteins/immunoglobulins ✔

j. (some) plasma cells become memory cells ✔

k. memory cells reproduce quickly ✔

l. memory cells prevent infection in the future ✔

Allow annotated diagrams to explain the process.

a. antibiotics block bacterial processes ✔

b. example of bacterial process ✔ e.g. cell wall formation

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 ✔

f. (natural selection) leads to changes in the proportions/frequency in the population ✔

g. 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) ✔

(attempted by about 60 % of the cohort)

Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.

(attempted by about 60 % of the cohort)

Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.

(attempted by about 60 % of the cohort)

Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.

State a reason for using an electron microscope to view this virus rather than a light microscope.

Rotavirus causes diarrhea and vomiting. Explain why viral diseases cannot be treated using antibiotics.

State an application of plasmids in biotechnology.

electron microscope has greater resolution/magnification

OR

70 nm is too small/viruses are too small to be viewed by a light microscope

a. viruses are not living

b. viruses lack metabolism/lack enzymes «for metabolism»/lack cell walls

c. antibiotics target metabolic «pathways»/cell wall production

[Max 2 Marks]

transfer/vector of genetic material/genes/DNA fragments

OR

to produce insulin/useful protein