T1-1 1.
[247 marks]
[1 mark]
Markscheme D
Examiners report [N/A]
2.
[1 mark]
Markscheme D
Examiners report [N/A]
3.
[1 mark]
Markscheme C
Examiners report There were comments from some teachers about the electron micrograph used in this question. The mitochondrion that candidates had to identify has a sigmoid shape rather than the classic ovoid shape of a textbook diagram, but the internal structure is clearly the same as ovoid mitochondria elsewhere in the micrograph and cristae are visible, so there should not have been any confusion. Students should be able to recognise mitochondria in micrographs from the densely stained matrix and the invaginated inner membrane. The statistics show that some of the stronger candidates misidentified this organelle as a lysosome, but there are other single-membraned structures visible in micrograph that are more densely stained and nearly circular in outline and these are the lysosomes.
4.
[1 mark]
Markscheme C
Examiners report [N/A]
5.
[1 mark]
Markscheme C
Examiners report [N/A]
6.
[1 mark]
Markscheme A
Examiners report [N/A]
7.
[1 mark]
Markscheme B
Examiners report The guide clearly states that the cell wall is an extracellular structure; therefore candidates could not have confused the intracellular space with it.
8.
[1 mark]
Markscheme D
Examiners report [N/A]
9.
[1 mark]
Markscheme D
Examiners report There is a comment in the G2s about the fact that there are some prokaryotic organisms that do have internal-bound compartments. This is true, but most prokaryotes do not have these compartments, and this is only an exception. In Biology there are many exceptions to the rule. In a multiple choice question one expects the best suited answer, in this case, all the other answers were incorrect, so the fact that prokaryotes do not have membrane bound compartments was the most suitable answer. In all, the question turned out to be an easy question and a good discriminator.
10.
[1 mark]
Markscheme A
Examiners report [N/A]
11a.
[2 marks]
Markscheme a. living things are composed of cells; b. cells are the basic/smallest unit of life; c. cells come from pre-existing cells; Do not accept cells are the “smallest organisms”. Do not accept “cells are the building blocks” of life on its own.
Examiners report Most gained both marks for their knowledge of cell theory in part a.
11b.
[2 marks]
Markscheme a. I: locomotion; b. II: attachment to surfaces / holds bacteria together / conjugation; Do not accept “exchange material” on its own. If more than one function is given, mark the first answer only.
Examiners report Students who read the rubric correctly in b scored well. However approximately half of the students read "label" instead of "function".
11c.
[1 mark]
Markscheme ×15 000 (accept answers in the range of × 14 000 to × 16 000)
Examiners report A disappointing number had no idea how to calculate the magnification (15000X) and some answers showed no concept of scale, with answers such as 0.15 X or 5x10-7 X.
12a.
[5 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. a. (the genetic code is based on) sets of three nucleotides/triplets of bases called codons; b. bases include adenine, guanine, cytosine and thymine in DNA / adenine, guanine, cytosine and uracil in RNA; (do not accept ATCG) c. each codon is code for one amino acid; d. some codons are (start or) stop codons; e. DNA is transcribed into mRNA by base-pair matching/complementary base pairing; f. mRNA is translated into a sequence of amino acids/polypeptide; g. each gene codes for a polypeptide; h. polypeptides may be joined/modified to form proteins;
12b.
[5 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. a. channel proteins allow diffusion/osmosis/passive transport; b. large/polar molecules cannot cross the (hydrophobic) membrane freely; c. facilitated diffusion involves moving molecules through proteins down their concentration gradient/without requiring ATP; d. aquaporins (specific integral membrane proteins) facilitate the movement of water molecules/osmosis; e. some proteins (for facilitated diffusion) are specific to molecule/ions; f. active transport involves moving molecules through proteins against their concentration gradient/requiring ATP; g. (some) proteins in the membrane are pumps / pumps perform active transport / sodium potassium pump;
Examiners report Many were confused by the differences between channel proteins (passive) and protein pumps (active).
12c.
[8 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. a. ATP is a form of energy currency/immediately available for use; b. ATP is generated in cells by cell respiration (from organic compounds); c. aerobic (cell respiration) requires oxygen; d. anaerobic (cell respiration) does not require oxygen; e. glycolysis breaks down glucose into pyruvate; f. glycolysis occurs in cytoplasm; g. (by glycolysis) a small amount of ATP is released; h. ADP changes into ATP with the addition of a phosphate group/phosphoric acid / accept as chemical equation; i. in mitochondria/aerobic respiration produces large amount of ATP / 38 mols (for the cell, per glucose molecule); j. oxygen/aerobic respiration is required for mitochondrial production of ATP; k. in mitochondria/aerobic respiration pyruvate is broken down into carbon dioxide and water;
Examiners report There were several comments about how the students could gain 8 marks on a question about ATP. It was obvious that some students had studied option C, but this should not really have given them an advantage. In fact the students found this question much easier than the teachers thought, scoring well in this section.
13a.
[2 marks]
Markscheme a. living things are composed of cells; b. cells are the basic/smallest unit of life; c. cells come from pre-existing cells; Do not accept cells are the “smallest organisms”. Do not accept “cells are the building blocks” of life on its own.
Examiners report Most students earned these marks. A small number demonstrated knowledge of the properties of cells but seemed to be unfamiliar with the cell theory itself.
13b.
[1 mark]
Markscheme attachment to surfaces / holds bacteria together / conjugation Do not accept “exchange material” on its own. If more than one function is given, mark the first answer only.
Examiners report A number failed to state a correct function. The pilus plays a role in adhering to surfaces and in bacterial conjugation. A number annotated the picture with the name of the structure without stating a function.
13c.
[1 mark]
Markscheme × 15 000 (accept answers in the range of × 14 000 to × 16 000)
Examiners report About half of candidates correctly answered this question. A number were making order of magnitude errors such as writing 150 000x and 1500x. Some were unfamiliar with the interpretation of the metric prefix.
13d.
[1 mark]
Markscheme helicase: unwinds /unzips the DNA (into two strands) / breaks H bonds;
Examiners report Most were able to explain the function of helicase.
13e.
[1 mark]
Markscheme DNA ligase: joins/seals the nick between the (Okazaki) fragments;
Examiners report Similar to primase, the mechanism of action of ligase was very rarely accurately described, most limiting it to bond formation between Okazaki fragments, not acknowledging that ligase has a role on the leading strand as well.
14a.
[8 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. 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;
Examiners report Students tended to perform well on this question though it was rare for students to demonstrate detailed knowledge of the mechanism of active transport in terms of ion exchange.
14b.
[3 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. 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.
Examiners report Students found it easier to list the conditions required for germination rather than outlining the conditions required.
14c.
[7 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. 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.
Examiners report Many students earned marks by outlining the stages of mitosis though a number were not clear on when spindle fibres form and when they attach, commonly indicating that this occurs in metaphase. Some students muddled the mechanisms of meiosis and mitosis. The distinctions between cytokinesis in plant and animal cells does not seem to be well understood. The events that occur in the different stages of interphase appears to be less well known.
15a.
[5 marks]
Markscheme a. cell wall – uniformly thick and drawn outside the plasma membrane; b. plasma membrane – a continuous single line; c. cytoplasm/cytosol; d. nucleoid/(naked) DNA – shown as a tangle of thread or irregular shape without a nuclear membrane; e. (70S) ribosomes – drawn as a small circle or dark dot; f. pili – hair like structures / flagellum – shown to be longer than any pili; g. plasmid – circular ring of DNA; h. capsule – drawn outside the cell wall; Award [1] for each structure clearly drawn and labelled which conforms to the italicized guidelines given above.
Examiners report Those that drew a prokaryotic cell did well but there were also quite a few eukaryotic cells as the diagram showed and labeled organelles such as mitochondria, lysosome and endoplasmic reticulum.
15b.
[7 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. a. skin/mucus membranes act as barrier (to pathogens); b. sebaceous glands secrete lactic acid/fatty acids/sebum / make surface of skin acidic; c. (skin/stomach) acid prevents growth of many pathogens; d. lysozyme in mucus can kill bacteria; e. pathogens caught in sticky mucus and removed from body; f. inflammatory response/inflammation can cause swelling/redness/fever (to inhibit the pathogen); g. phagocytes/macrophages/leucocytes/white blood cells (non-specifically) identify (pathogens/bacteria/fungi/viruses) as foreign; h. (phagocytes macrophages/leucocytes/white blood cells) ingest pathogens; i. specific lymphocytes recognize one specific antigen; j. (antigen-specific) lymphocytes clone themselves; k. lymphocytes/leucocytes produce antibodies; l. antigen-antibody complex formed and stimulates destruction of pathogen;
Examiners report There were a generous number of marking points for this question. However, candidates were expected to earn some of them describing the first and second lines of defence as well as some of them from the immune response. This answer was generally done well when students weren't confused by extra material, many students had been over taught this area and confused the functions of macrophages / B cells / T cells / memory cells. Terminology and concepts found in HL were presented by students. Those were not accepted in the mark scheme as there were sufficient marks allotted to show understanding of the broad picture expected at SL. Those who used the HL material successfully generally had most of the marks in the mark scheme plus HL information. Unfortunately many got muddled as stated above.
15c.
[6 marks]
Markscheme a. antibiotics (are chemicals) used to treat bacterial diseases; b. within populations, bacteria vary in their (genetic) resistance to antibiotics/fitness; c. resistance arises by (random) gene mutation; d. when antibiotics are used antibiotic-sensitive bacteria are killed; e. (natural) selection favours those with resistance; f. resistant bacteria survive, reproduce and spread the gene / increase allele frequency of resistant bacteria; g. the more an antibiotic is used, the more bacterial resistance/the larger the population of antibiotic-resistant bacteria; h. genes can be transferred to other bacteria by plasmids; i. doctors/vets use different antibiotics but resistance develops to these as well; j. multiple-antibiotic resistant bacteria evolve/it becomes difficult to treat some infections;
(Plus up to [2] for quality)
Examiners report Capable candidates answered this question very well and with clear explanation. The best responses extended their answers to include the occurrence of multiple-antibiotic resistant bacteria. Weaker and mid-range candidates mentioned that bacteria evolve to gain resistance to antibiotics but rarely that it occurs through gene mutation or suggested that mutations that give resistance occurred because bacteria required them rather than randomly. There were many vague answers as candidates seemed to have some grasp of the mechanism but difficulty explaining it.
16a.
[5 marks]
Markscheme a. O connected to 2 H forming a V shape; b. line between O and H of same molecule labelled as covalent bond; c. three water molecules bonded together with dashed/dotted lines between O on one molecule and H on another; d. dotted/dashed line labelled as hydrogen bond; e. O labelled as partial negative charge/ and H labelled as partial positivecharge/ ;
Examiners report Almost all candidates knew the V shape for water molecules but few labeled covalent bonds and still fewer were exact in describing the negative charge on O as partial or the positive charge on H as partial. The mark scheme assumes a stick model of water. Answers often used a bubble diagram, undercutting one possible mark. Even so, full marks could be earned. Bonding within and among water molecules was the part most often neglected.
16b.
[6 marks]
Markscheme a. warming results in melting (arctic/polar) ice (cap) / loss of ice habitats; b. (warming) raises sea level / floods coastal areas / destroys coastal habitats; c. (warming) of habitat would change species/flora/fauna that can be supported (named examples can be used); d. decrease in size of population(s) / possible extinction of species; e. temperate species move into area / arctic species adapt/move; f. change in distribution of species/changes in migration patterns; g. (ecological) changes will affect higher trophic levels/food webs/food chains; h. increased rates of decomposition of detritus from (melting) permafrost; i. increased success of pest species including pathogens;
Examiners report This question was generally well answered displaying good knowledge of the effect of global warming on arctic ecosystems. Often this answer was reasonably well started, but often did not have enough follow-through. Weak answers included some odd understandings. It is not melting glaciers that are the issue, it is the melting ice cap and the sea ice. Some answers were glib, repeating the cases made by the public media rather than research-based information regarding the plight of endangered animals. There are no penguins in the Arctic.
16c.
[8 marks]
Markscheme a. (labelled) phospholipid consisting of head and two tails; b. head is glycerol and phosphate; c. tails are fatty acid chains; d. head hydrophilic and tails hydrophobic; e. hydrophilic molecules/heads attracted to/soluble in water; f. hydrophobic molecules/tails not attracted to water but attracted to each other; g. (properties of phospholipids leads to) formation of double layer in water; h. stability in double layer because heads on outer edge are attracted to water and tails are attracted to each other in middle; i. phospholipid bilayer in fluid/flexible state because of attraction of non-polar tails to each other; j. (fluidity) allows membranes to change shape/vesicles to form or fuse with membrane/(fluidity) allows cells to divide; k. non-polar amino acid side chains attracted to (hydrophobic) tails; Marks may be earned using suitable labelled/annotated diagrams illustrating the points given above. (Plus up to [2] for quality)
Examiners report This question expected students to approach the topic from a slightly different position than the usual. As such, it discriminated well between stronger and weaker candidates. Many students misinterpreted what was being asked and wrote long detailed answers on structure of the cell membrane and how transport occurs through the proteins - rather than concentrating on the properties of the phospholipids which give the cell membrane its structure. Answers needed more attention to interaction of phospholipid with water. Few knew that the phospholipid head is glycerol and phosphate and virtually nobody mentioned anything about non-polar amino acid side chains being attracted to (hydrophobic) tails.
17.
[4 marks]
Markscheme a. microorganisms/prokaryotes taken into cell by endocytosis; b. kept inside cell and perform respiration/photosynthesis; c. developing into mitochondria/chloroplasts; d. mitochondria/chloroplasts have double membranes (as expected in cells taken in by endocytosis); e. mitochondria/chloroplasts have (circular naked) DNA (as prokaryotes); f. mitochondria/chloroplasts have 70S ribosomes (as prokaryotes); g. mitochondria/chloroplasts grow and divide like (prokaryotic) cells;
Examiners report Most candidates scored some points in questions 11 and 12 with the top candidates achieving full marks.
18.
[1 mark]
Markscheme D
Examiners report N/A
19.
[1 mark]
Markscheme B
Examiners report N/A
20.
[1 mark]
Markscheme D
Examiners report There is a comment in the G2s about the fact that there are some prokaryotic organisms that do have internal-bound compartments. This is true, but most prokaryotes do not have these compartments, and this is only an exception. In Biology there are many exceptions to the rule. In a multiple choice question one expects the best suited answer, in this case, all the other answers were incorrect, so the fact that prokaryotes do not have membrane bound compartments was the most suitable answer. In all, the question turned out to be an easy question and a good discriminator.
21.
[1 mark]
Markscheme A
Examiners report N/A
22.
[1 mark]
Markscheme D
Examiners report Some proteins synthesized in the free ribosomes will be used in the nucleus (for example polymerases), but these are only a few, most of them are used in the cytoplasm, therefore C is the best answer.
23a.
[5 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. Award [1] for each structure clearly drawn and correctly labelled. 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)
Examiners report Structure of the plasma membrane Of the three diagrams tested on this exam paper, this was drawn most successfully with many candidates scoring full marks. Some candidates misinterpreted the question and drew a diagram of a whole eukaryotic cell with a plasma membrane around its margin. On diagrams showing the expected structure the commonest errors were to place particular types of proteins or cholesterol in the wrong position.
23b.
[8 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. 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;
Examiners report Light-dependent reactions of photosynthesis Answers were polarised with strong candidates writing accurate and detailed accounts of the light dependent reactions but other candidates revealing very little knowledge. Diagrams were sometimes included at the start of the answer but they often didn’t help because they were not annotated fully enough to make any of the points on the mark scheme.
23c.
[5 marks]
Markscheme Remember, up to TWO “quality of construction” marks per essay. 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; If the candidate outlines more than two factors, only mark the first two. Accept the first two points relating to each factor if clearly shown on a graph with both axes appropriately labelled. Accept level instead of concentration, intensity or rate. Do not accept enzyme denaturation as a reason for reductions in photosynthesis at higher temperatures.
Examiners report Factors affecting the rate of photosynthesis Only light intensity, temperature and carbon dioxide concentration were accepted here. Candidates could score two marks for any two of these factors by showing the trend in a graph or by describing it in text but for other marks the answer had to include a cause of the effect of the factor, for example rising temperature increasing the activity of enzymes in the Calvin cycle. Denaturation was not accepted as a cause of decreasing photosynthesis at higher temperatures because the decreases happen at much lower temperatures than would cause denaturation.
24a.
[2 marks]
Markscheme a. mitochondria/chloroplasts were once (independent) prokaryotes; b. taken in by (larger) heterotrophic/host cell (through endocytosis); c. new living arrangement mutually beneficial / depend on each other to exist as single organism;
Examiners report While many candidates were able to get 1 mark, and some 2, few wrote clearly or accurately about the endosymbiotic theory. The question was not asking for evidence of the theory which is what some candidates wrote about.
24b.
[1 mark]
Markscheme all the alleles/genes of a population (at a particular time)
Examiners report The definition of gene pool in (ii) was answered better than in previous years.
25.
[3 marks]
Markscheme a. ancestral eukaryote cell engulfs free living prokaryote; b. free living prokaryote not digested; c. symbiotic relationship develops between ancestral eukaryote cell and engulfed prokaryote; d. ancestral eukaryote cell and engulfed prokaryote reproduce as a unit; e. the engulfed prokaryote provides energy by aerobic respiration for the eukaryote; f. prokaryote gains protection/nutrition; g. organelles have double membranes; h. organelles have DNA/ribosomes; i. theory cannot be falsified/tested;
Examiners report There was sound knowledge of endosymbiosis
26.
[1 mark]
Markscheme B
Examiners report N/A
27a.
[1 mark]
Markscheme Golgi apparatus/complex/body Reject Golgi vesicle and Golgi unqualified.
Examiners report About half of the candidates identified the structure correctly as Golgi apparatus, with the others mostly suggesting rough endoplasmic reticulum even though there were no ribosomes on the outside.
27b.
[1 mark]
Markscheme endocytosis/phagocytosis/pinocytosis Reject exocytosis.
Examiners report Again about half of candidates answered correctly with endocytosis or a variant of this process. A wide range of other answers was given by other candidates.
27c.
[2 marks]
Markscheme fluidity of membrane allows change of shape/invagination/formation of vesicles; phospholipids can move / phospholipid bilayer makes membrane fluid/flexible; weak bonding between phospholipid tails; bends/kinks in the phospholipid tails prevent close packing; cholesterol affects membrane fluidity;
Examiners report This question was answered moderately well. Candidates were expected to link the fluidity of the phospholipid bilayer to the movement involved in vesicle formation.
28a.
[4 marks]
Markscheme Award [1] for each structure clearly drawn and correctly labelled, up to [4 max]. a. cell wall – a uniformly thick wall; b. pili – hair-like structures connected to cell wall / flagellum – at least length of the cell; c. plasma/cell membrane – represented by a continuous single line; (may be labelled as the innermost wall line) d. ribosomes (70S) – drawn as small discrete dots; e. naked DNA/nucleoid – region with DNA not enclosed in membrane; f. plasmid – circular ring of DNA; g. cytoplasm – the non-structural material within the cell; Award [2 max] if any eukaryotic structure is shown.
Examiners report Overall, candidates performed very well on this question. The diagram in 5a was well drawn by most. A number of students included eukaryotic structures in their drawings. Flagella were often drawn too short in relation to the overall length of the cell. Pilli were often poorly drawn being shown not connected to the cell. The diameter of ribosomes was often too large in relation to the rest of cell structures.
28b.
[6 marks]
Markscheme a. transcription is the copying of a strand of DNA into RNA/RNA formation; b. RNA polymerase binds to promoter region of DNA; c. anti-sense strand as template / only one strand copied; d. RNA polymerase unwinds DNA/separates the strands; e. RNA nucleotides/nucleoside triphosphates pair with complementary bases on DNA; f. Adenine to Thymine, Cytosine to Guanine, and Uracil to Adenine; (do not accept letters alone) g. added at 3' end / strand grows 5' to 3' ; h. RNA nucleotides joined with covalent/sugar-phosphate bonds; i. RNA polymerase separates from DNA when reaches terminator/termination sequence; j. no introns/post-transcriptional modification/RNA splicing (as occurs in eukaryotes);
Examiners report Overall, candidates performed very well on this question. Many were able to outline transcription successfully. Some confused transcription with replication. A number referred to helicase as the enzyme responsible for separating and unwinding the helix.
28c.
[8 marks]
Markscheme a. vaccines contain a dead/weakened form of the pathogen/bacteria/virus; b. vaccine introduced to the body by injection/on surface of skin/orally; c. antigens in the vaccine cause antibody production; d. antigen/pathogen engulfed by macrophage/phagocyte; e. each type of lymphocyte recognizes specific antigen; f. macrophages activate helper T-cells; g. which activate B-cells; h. B-cells divide to form clones/memory cells; i. B-cells divide to form plasma cells/antibody producing cells; j. result is (specific) immunity; k. vaccination/first exposure causes slow production of antibodies and lower level of antibodies; (this idea can be illustrated on a diagram or graph) l. contact with the disease leads to rapid production and higher level of antibodies; (this idea can be illustrated on a diagram or graph) m. second/booster shot to stimulate memory cells/more production of antibodies;
Examiners report Overall, candidates performed very well on this question. Most scored well on part c of the question. An area of misunderstanding surrounds what happens upon second exposure to the antigen. It should be noted that antibodies are produced more rapidly and to a higher level.
29a.
[4 marks]
Markscheme Must be description of types not a list. a. (simple) diffusion when molecules move down a concentration gradient directly through membrane/unaided by carrier molecule; b. (passive transport by) facilitated diffusion through (specific) channel proteins; c. osmosis of water via aquaporins/from area of low solute concentration to area of high solute concentration; d. active transport against a concentration gradient using protein pumps/ATP; e. vesicles attach to plasma membrane and release materials to exterior/ exocytosis; f. cell membrane invaginates/pinches off to bring material to interior / endocytosis / phagocytosis;
Examiners report Question 8 was the least popular question. In part a, few discussed exocytosis and endocytosis. The distinction between simple diffusion and passive diffusion was often confused. Reference to aquaporins was rare. Discussion of osmosis was generally well done.
29b.
[6 marks]
Markscheme a. FSH stimulates estrogen secretion by follicle cells; b. at start of menstrual cycle; c. leading to development of endometrium; d. (FSH and) LH (rise to a peak and) causes egg to be released/ovulation; e. causes follicle cells to secrete less estrogen/more progesterone; f. progesterone maintains endometrium/uterine lining g. LH promotes change of follicle to corpus luteum; h. secretion of LH and FSH regulated by negative feedback; i. regulated/inhibited by high estrogen and progesterone levels; j. low progesterone levels cause menstruation;
Examiners report Question 8 was the least popular question. In part b, the knowledge of students was adequate. The challenge for this question was structuring the response to address the demands of the question as the events within the ovary had to be linked to the events within the uterus. The role of estrogen in developing the uterine lining was well known as was the role of progesterone in maintaining the lining. They were also reasonably successful in discussing the role of LH. Students were less commonly successful with discussing the specific actions of FSH and the regulation of hormone levels.
29c.
[8 marks]
Markscheme a. disc shaped structure b. embedded in uterus wall; c. connected to fetus by umbilical cord; d. contains fetal and maternal structures/tissues; e. placental villi/maternal intervillous space provide large surface area for exchange of materials; f. blood of fetus and mother flow close to each other (but no mixing); g. materials exchanged/diffuse (through membranes) between mother and fetal blood; h. oxygen/nutrients/antibodies/other substances diffuse (through membranes) to fetus; i. CO2 and wastes diffuse (through membranes) to mother; j. caffeine/drugs/alcohol/viruses from mother may damage fetal development; k. takes over role of corpus luteum (to produce hormones); l. produces hormones/estrogen/progesterone/HCG;
Examiners report Question 8 was the least popular question. Answers to part c were adequate, though it was common for the use of terminology to be poor. Most candidates were able to identify the placenta as a disc shaped structure embedded in the uterine wall that was connected to the mother via the umbilical cord. Most showed adequate understanding of the types of material exchanged within the placenta. Fewer showed adequate comprehension of the mechanism of materials exchange between the mother and the fetus. Few adequately described the structure of the placental villi or the relationship between maternal and fetal blood flow.
30.
[1 mark]
Markscheme B
Examiners report N/A
31.
[1 mark]
Markscheme B
Examiners report Question 3 was answered much less successfully than expected. Some teachers reported on G2 forms that it was too difficult without calculators, but the math was in fact very easy. A large number of candidates were unable to convert 70µm into 0.07mm by moving the decimal point three places to left. Students should be taught that S.I. units are increased by a factor of 1000 so conversion from micrometres to millimetres is accomplished by dividing the length by 1000.
32.
[1 mark]
Markscheme A
Examiners report Question 4 had a very low discrimination index which sometimes indicates a problem with a question. In this case it merely showed that a high proportion of candidates answered the question correctly, despite the fears expressed by some teachers in G2 forms that the micrograph was not clear enough.
33.
[1 mark]
Markscheme B
Examiners report N/A
34.
[1 mark]
Markscheme C
Examiners report N/A
35.
[1 mark]
Markscheme D
Examiners report N/A
36.
[1 mark]
Markscheme B
Examiners report N/A
37.
[1 mark]
Markscheme A
Examiners report N/A
38.
[1 mark]
Markscheme C
Examiners report N/A
39a.
[1 mark]
Markscheme Golgi apparatus/complex/body Reject Golgi vesicle and Golgi unqualified.
Examiners report Most candidates correctly identified the organelle as Golgi apparatus; otherwise, it was usually mistakenly labelled as rough ER.
39b.
[1 mark]
Markscheme endocytosis/phagocytosis/pinocytosis Reject exocytosis.
Examiners report Instead of answering “endocytosis”, candidates often stated “exocytosis” and lost the mark.
39c.
[2 marks]
Markscheme a. fluidity of membrane allows change of shape/invagination/formation of vesicles; b. phospholipids can move / phospholipid bilayer makes membrane fluid/flexible; c. weak bonding between phospholipid tails; d. bends/kinks in the phospholipid tails prevent close packing; e. cholesterol affects membrane fluidity;
Examiners report This follow-up question involved application of knowledge about membrane structure. Sadly, candidates had trouble linking fluidity in membranes to vesicle formation. Though the phospholipid bylayer was sometimes mentioned it was not seen as giving fluidity/flexibility. Weak bonding between the phospholipid tails was rarely included. A few candidates did mention the presence of cholesterol in membranes but not much on their role in membrane fluidity. The idea that bends/kinks in the phospholipid tails prevents close packing, thereby contributing to flexibility, was never given. Some candidates confused fluidity with permeability.
39d.
[3 marks]
Markscheme a. moves substances up/against a concentration gradient / from lower to higher concentration; b. protein/pump (in membrane) that moves material; (reject channels) c. ATP is used; (reject energy alone) d. example/labeled diagram showing mechanism;
Examiners report Many candidates gained partial or full marks on their explanations of active transport across membranes. Movement up/against a concentration gradient was often mentioned, along with the necessity of ATP. Energy, by itself, was rejected. There was confusion over protein pumps/carrier proteins and channel proteins. The latter were unacceptable since they are used in passive transport to enable solutes to diffuse down concentration gradients.
40a.
[3 marks]
Markscheme a. growth (of cells); b. transcription/protein synthesis/translation; c. DNA replication / genetic material copied; d. production of organelles/mitochondria/chloroplasts; e. named normal activity of cell (eg active transport, movement, secretion); NB Do not accept G1, S, G2 unless linked to correct process.
Examiners report Various cellular processes occur during interphase. Any three of the following were accepted: growth (of cells), protein synthesis/translation, DNA replication, production of organelles or named normal activity (e.g. active transport, movement, secretion etc.). It was not necessary to name the sub phases such as G1, S or G2. If that was done the sub phase had to be linked to a correct process to achieve a mark. It should be noted that cells grow in all three phases by producing proteins and organelles. DNA replication, however, only occurs in the S phase.
40b.
[3 marks]
Markscheme a. sexual reproduction promotes variation in species; b. independent assortment of genes / random orientation of chromosomes in metaphase/meiosis; c. crossing-over provides new combinations of alleles; d. production of great variety of gametes (by meiosis) / different combinations of chromosomes in gametes; e. (random) combination of gametes from both parents (in fertilization); f. (genetic) variation allows natural selection which leads to evolution;
Examiners report Explaining how sexual reproduction can lead to variation and then evolution challenged many candidates. Some candidates began with the premise that sexual reproduction produces variation, but did not explain how the variation occurs.This was the heart of the question. Others tried to answer what evolution is, instead of explaining how sexual reproduction allows it to occur. Too many answers just stated the terms independent assortment, crossing over, random fertilization and natural selection without further developing them, i.e. their effect on genes, allele combination or gametes. Sometimes mutation was mixed into the answer gaining no credit.
41a.
[2 marks]
Markscheme a. magnification measured length of bar actual size bar represents/4 mm 1 μm / spore micrograph size real size / OWTTE; b. 4000;
Examiners report Candidates scored marks for a good working, but did not measure correctly, so failed to obtain the second mark. This question seemed to cause some confusion with candidates measuring the picture rather than the scale bar. Also, many wrote down very large magnifications without thinking about plausibility.
41b.
[2 marks]
Markscheme a. rate of exchange of materials/gas/energy is a function of its surface area; b. rate of production of heat/waste/resource consumption is a function of its volume; c. surface area to volume ratio decreases with increase in size / OWTTE; d. at low surface area to volume ratios, exchange of materials takes longer/reduced efficiency of exchange / vice versa;
Examiners report Confusing answers led to interpret that many candidates do not clearly understand this topic, writing wrong memorized concepts instead.
42a.
[5 marks]
Markscheme lysosome: a. (from Golgi apparatus) with digestive enzymes / break down food/organelles/ cell; Golgi apparatus: b. site that processes/modifies/packages and releases proteins; free ribosomes: c. site of synthesis of proteins (released to cytoplasm); plasma membrane: d. controls entry and exit of materials/substances in cell; rough endoplasmic reticulum: e. synthesis and transport of proteins; (both needed)
Examiners report Question 6 was the most popular to answer. The major confusions were found when explaining the functions of the Golgi Apparatus and the rough endoplasmic reticulum. Some candidates did not make any reference to proteins when explaining the function of the Golgi, for which they did not receive the mark.
42b.
[4 marks]
Markscheme
Award [1] for each contrasting characteristic. Table format is not necessary for the marks.
Examiners report Marks were not awarded generally for incomplete answers. E.g. Not mentioning one of the end products of anaerobic respiration, either CO2 or ethanol or in products of aerobic respiration, water was often omitted. The comparisons were sometimes difficult to spot, given that they did not use a chart or did not follow a proper order. Finally some candidates simply failed to compare, explaining only one type of cell respiration.
42c.
[9 marks]
Markscheme a. inspiration/inhalation brings air into lungs; b. external intercostal muscles contract; c. and move rib cage upwards and outwards; d. diaphragm flattens/contracts; e. increasing thoracic volume; f. pressure decreases from atmospheric pressure so air rushes into lungs; g. expiration/exhalation forces air out; h. internal intercostal muscles contract / external intercostal muscles and diaphragm relax; i. abdominal/abdomen wall muscles contract and push diaphragm upwards; j. decreasing thoracic volume; k. increasing pressure in lungs so air is forced out; l. a concentration gradient between air sacs and blood needs to be maintained;
Examiners report There were quite a few students who gave very good descriptions of gas exchange and even respiration in some cases, and the properties of the alveoli that made them well adapted for gas exchange. Unfortunately the question was "Explain the mechanism of ventilation in the lungs in order to promote gas exchange for cell respiration". Many candidates did not read the question correctly. Some candidates even gave more detail of aerobic respiration here than they did in part b. Among the most common errors found were to say that "...inspiration brings oxygen into the lungs" and that "...expiration releases CO2". In some of the answers there was no differentiation between external and internal intercostal muscles. Some candidates referred to changes in the lung volume, instead of thoracic volume.
43.
[1 mark]
Markscheme A
Examiners report N/A
44.
[1 mark]
Markscheme A
Examiners report N/A
45.
[1 mark]
Markscheme C
Examiners report There similar complaints from a few teachers about Question 9. At Standard Level students are not expected to have studied transpiration, but the examining team felt that the answer referring to water moving from a leaf into the atmosphere could have been eliminated without knowing details of transpiration because movement of water molecules from a liquid state inside the leaf to the gases of the air outside cannot be osmosis.
46.
[1 mark]
Markscheme D
Examiners report N/A
47.
[1 mark]
Markscheme C
Examiners report N/A
48.
[1 mark]
Markscheme A
Examiners report N/A
49a.
[1 mark]
Markscheme grasses
Examiners report There were some comments on the G2 forms that said that these graphs were confusing. In fact the vast majority of candidates gained all three marks on parts a and b.
49b.
[1 mark]
Markscheme 6 months
Examiners report Most were able to state that the total volume was greatest at 6 months.
49c.
[1 mark]
Markscheme 50 (%)
Examiners report Almost all could state 50% for a.
49d.
[1 mark]
Markscheme highest: Affar; lowest: Tigray; (both needed)
Examiners report Almost every candidate gave the correct answers of Affar and Tigray.
49e.
[2 marks]
Markscheme a. no clear trend in the inner layer whereas there is a decrease in the outer layer; b. outer layer is higher (than inner layer) at 2 months and lower at 18 months; (do not accept statements that are not comparisons) Accept any other correct comparisons.
Examiners report Most were able to gain a mark for spotting that there is no clear trend in the inner layer but a decrease in the outer. Few gained the second mark. There were many correct statements, but few correct comparisons.
49f.
[1 mark]
Markscheme reduces glycogen levels
Examiners report In b, the command term was state, but many tried to explain at length, usually on extension sheets.
49g.
[2 marks]
Markscheme a. evidence of high malnutrition rates / some areas with many mothers below 18.5 BMI; b. large range/15– 40% range (in mothers below 18.5 BMI); c. many/6 regions in the range of 20–30 % / many/5 regions in the range of 22–25 % (are below 18.5 BMI); d. lowest in Addis and highest in Affar/Gambela;
Examiners report In b, even though the question was about mothers, many wrote about the sons, but also correctly commented on the large range.
49h.
[1 mark]
Markscheme feeding time on grasses (slightly) reduces / feeding time on bushes increases
Examiners report There were some comments on the G2 forms that said that these graphs were confusing. In fact the vast majority of candidates gained all three marks on parts a and b.
49i.
[1 mark]
Markscheme feeding time on grasses (greatly) reduces / feeding time on bushes increases
Examiners report There were some comments on the G2 forms that said that these graphs were confusing. In fact the vast majority of candidates gained all three marks on parts a and b.
49j.
[2 marks]
Markscheme feeding is similar without predators; more feeding on grass by adults with predators;
Examiners report In c there were often very wordy answers that did not get to the point, not being proper comparisons. Only the better candidates were able to narrow it down to the fact that the feeding in adults and instars is similar without predators, but there is more feeding on grass by adults with predators.
49k.
[2 marks]
Markscheme a. volume of neurons remains the same; b. synapse density in the outer but not the inner layer decreases with age; c. number of neurons may not be reduced even with fewer synapses;
Examiners report In c most were able to state that the volume of neurons remains the same and that the synapse density in outer but not inner decreases with age.
49l.
[2 marks]
Markscheme a. hypothesis not supported; (do not award if unqualified) b. no clear relationship / as malnutrition (mothers below 18.5 BMI) increases, there is no clear change in percentage male offspring; c. however, male birth percentage is usually higher than female (above 50 %) regardless of BMI / 9 of the regions are above/2 regions are below;
Examiners report In c most were able to comment that the hypothesis was not supported as there was no clear relationship.
49m.
[2 marks]
Markscheme a. both lower the glycogen level; b. much greater reduction with 6000 m programme; c. no moderate (glycogen) levels exist after 6000 m programme / far more with no glycogen;
Examiners report In c i and ii most were able to obtain 1 mark, with only the better candidates obtaining both.
49n.
[2 marks]
Markscheme a. lower levels after 6000 m programme because more energy needed for longer swim; b. lower levels after 6000 m programme because the pace of swimming was faster; c. blood systems cannot supply glucose as fast as it is used during intense exercise; d. slow (type I) muscle fibres only have moderate stamina so are not ideal for faster swimming; e. less aerobic in 6000 m programme / vice versa;
Examiners report In c i and ii most were able to obtain 1 mark, with only the better candidates obtaining both.
49o.
[1 mark]
Markscheme a. instars are more protected from predators/camouflaged when feeding in bushes; b. adults can escape predator attacks more easily/camouflaged when feeding in grasses; c. adults are bigger and less easily captured; Accept other reasonable responses.
Examiners report Many could correctly suggest a reason why the feeding differs.
49p.
[2 marks]
Markscheme a. smell perception may fall in aging humans; b. changes in smell perception may change food eating habits/reduce quality of life; c. ageing human brains may lose synapses but not neurons (as previously thought); d. losing synapses in one part of the brain may be repeated in other parts of the brain;
Examiners report In d most were able to gain the mark for loss of synapses, but not neurons, but only the more astute candidates could link it back to the introduction and talk about smell perception.
49q.
[1 mark]
Markscheme a. no measurement of glycogen levels in fast/type II muscle fibres; b. no mention of sample number/sex; c. data shows no SD or SE;
Examiners report Many were able to obtain the mark in d for stating that there was no mention of the sex of the swimmers or comparison of fitness.
49r.
[1 mark]
Markscheme a. no data about sex of the mothers’ other children; b. BMI below 18.5 means individual is underweight but not necessarily malnourished; c. the number of mothers sampled in each region is not known; d. no comparison between town and country; e. no information about age of mothers;
Examiners report In d many noted that there was no data about the sex of the mothers’ other children or the age of the mothers.
49s.
[2 marks]
Markscheme a. water purifier is effective in removing bacteria; b. no bacteria in 12/15 test sites, regardless of temperature or flow rate; c. flow rate is less important than temperature; d. no information about how contaminated the water was before various treatments; e. no information about how effective the water purifier is in removing other harmful bacteria/substances;
Examiners report In e most were able to say that it was effective in removing bacteria, but few were able to spot that there was no information on how contaminated the water was beforehand or how effective it would be in removing other bacteria.
49t.
[1 mark]
Markscheme food shortages / famine / insufficient food / poor food quality / warfare / epidemics / poverty
Examiners report In e many did not relate back to the stem and remember that it was about Ethiopia, resulting in some nebulous answers about ‘lack of essential nutrients‘ etc.
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