T1-2 [94 marks] Markscheme. Examiners report. [1 mark] 1a. grasses

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1 T1-2 [94 marks] 1a. grasses 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. 1b. 6 months Most were able to state that the total volume was greatest at 6 months. 1c. 50 (%) lmost all could state 50% for a. 1d. highest: ffar; lowest: Tigray; (both needed) lmost every candidate gave the correct answers of ffar and Tigray. 1e. 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) ccept any other correct comparisons.

2 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. 1f. reduces glycogen levels In b, the command term was state, but many tried to explain at length, usually on extension sheets. 1g. a. evidence of high malnutrition rates / some areas with many mothers below 18.5 MI; b. large range/15 40% range (in mothers below 18.5 MI); c. many/6 regions in the range of % / many/5 regions in the range of % (are below 18.5 MI); d. lowest in ddis and highest in ffar/gambela; In b, even though the question was about mothers, many wrote about the sons, but also correctly commented on the large range. 1h. feeding time on grasses (slightly) reduces / feeding time on bushes increases 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. 1i. feeding time on grasses (greatly) reduces / feeding time on bushes increases 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. 1j. feeding is similar without predators; more feeding on grass by adults with predators;

3 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. 1k. 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; 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. 1l. a. hypothesis not supported; (do not award if unqualified) b. no clear relationship / as malnutrition (mothers below 18.5 MI) increases, there is no clear change in percentage male offspring; c. however, male birth percentage is usually higher than female (above 50 %) regardless of MI / 9 of the regions are above/2 regions are below; In c most were able to comment that the hypothesis was not supported as there was no clear relationship. 1m. 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; In c i and ii most were able to obtain 1 mark, with only the better candidates obtaining both. 1n. 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; In c i and ii most were able to obtain 1 mark, with only the better candidates obtaining both.

4 1o. 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; ccept other reasonable responses. Many could correctly suggest a reason why the feeding differs. 1p. 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; 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. 1q. a. no measurement of glycogen levels in fast/type II muscle fibres; b. no mention of sample number/sex; c. data shows no S or SE; 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. 1r. a. no data about sex of the mothers other children; b. MI 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; In d many noted that there was no data about the sex of the mothers other children or the age of the mothers.

5 1s. 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; 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. 1t. food shortages / famine / insufficient food / poor food quality / warfare / epidemics / poverty 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. 2. C This question was a poor discriminator in spite of being relatively easy, and most candidates chose option instead of the correct response of C. In the G2 forms, some teachers comment that the addition of by mitosis at the end of item II could interfere with the assessment of the students understanding of cell theory. However, it was felt that this had not been a significant problem for the candidates since a large number had chosen the correct answer

6 5. 6. In question 4, more candidates than was expected thought that prokaryotes have mitochondria and so chose answer This question discriminated well, and many candidates chose option, which is a correct statement, but is not answering the question asked.

7 10. C lthough this question discriminated well, a large proportion of candidates chose option C instead of the correct response of (10nm). It was thought that students were confusing the different units used in those two options C

8 This question was a good discriminator, which was testing two elements of understanding, those of the condensation process and where in the cell amino acids are assembled into polypeptides. Just over half of candidates gave the correct answer of C, with many being drawn to, the Golgi apparatus. lthough this question discriminated well, a large proportion of candidates chose option instead of the correct response of (endocytosis). It was thought that perhaps students had been drawn by the connection of osmosis and the word fluidity in the question a. ward [1] for each structure clearly drawn and correctly labelled. phospholipid bilayer with head and tails; hydrophilic / phosphate / polar heads and hydrophobic / hydrocarbon / fatty acid / non-polar tails labelled; integral/intrinsic protein embedded in the phospholipid bilayer; protein channel integral protein showing clear channel/pore; peripheral/extrinsic protein on the surface; glycoprotein with carbohydrate attached; (carbohydrate should project outwardly from membrane protein) cholesterol shown embedded in bilayer; (must appear in hydrophobic region) thickness indicated (10 nm); (allow answers in the range of 7 nm to 13 nm) [6 marks]

9 Candidates knew their hydrophilic heads and hydrophobic tails! Overall performance on this question was good. s noted earlier, improvement was seen in the quality of the drawings. However, some details needed to be more exact: peripheral/extrinsic protein should have appeared on the membrane surface, not fully embedded and flush with the surface; channel proteins, by definition, required a channel or pore. 19b. diffusion/facilitated diffusion and osmosis are passive; do not require energy/tp; diffusion is movement from high to low concentration/down a (concentration) gradient; facilitated diffusion uses (protein) channels/carrier proteins; osmosis is water movement from lower to higher solute concentration / from higher to lower water potential/concentration; across a partially permeable membrane; active transport/formation of vesicles require energy; in the form of TP; active transport moves materials up/against the (concentration) gradient/from low to high concentration; protein pumps required; endocytosis into cells / exocytosis out of cells; [8 marks] example of active or passive transport; (e.g. sodium potassium pump for active transport / oxygen exchange in alveoli for passive transport) Explanations of passive and active transport (.S , 2.4.6) involved many ideas that candidates seemed to know. Responses were generally well organized. Easy marks were gained for knowing which type of transport required TP and for knowing details about different concentration gradients. Candidates did stumble when they confused protein pumps needed in active transport for protein channels used in facilitated diffusion. Some candidates also forgot that osmosis involves the movement of water molecules, not just particles, from lower to higher solute concentration gradients across semi-permeable membranes. Instead of explaining osmosis in terms of solute concentration, other candidates correctly wrote about movement of water molecules from higher to lower water potential

10 Only two thirds of candidates answered this apparently easy question on the differences between prokaryote and eukaryote cell structure correctly. This was most likely due to candidates not reading carefully enough and choosing it as their answer, even though they did know that prokaryotes contain N. If they had carried on and read they would probably have chosen it. 25. C 26. There were some comments about the quality of the electron micrograph. lthough most candidates answered this question correctly, many believed X was pointing at the Golgi apparatus and others at the endoplasmic reticulum. The discrimination index was poor for this question, as many stronger candidates did not answer it correctly.

11 27. This question was well answered by most candidates, showing that they could easily identify the mitochondrion form the micrograph. 28. This question was too easy for candidates and not a good discriminator. This shows most candidates were familiar with the process of facilitated diffusion Many candidates were not able to do this calculation correctly and convert µm to mm. lthough the size of the drawing calculated was admittedly too small for a real drawing, there was no reason why the correct conversion could not be made. It did discriminate as the more able candidates got this correct while the others guessed between the other choices of answers. 31. C This question proved difficult. Many candidates answered the correct option C but many went for. They seemed to equate the cell wall with only plant cells and did not consider that prokaryote cell walls exist as well.

12 C 36. C 37.

13 Some teachers believed that mitosis could be considered a correct answer for the prokaryotic cell division, but this mechanism only occurs in eukaryotes (it requires the presence of chromosomes). Most candidates did very well in this question and it was a very good discriminator Seemed to be an easy question and had a good discrimination index, this means good candidates had it right and weaker candidates were incorrect. 40. Most candidates recognized that the embryological development required mitosis. Many weak candidates believed it was cell growth

14 Some teachers complained about the quality of the diagram, but the examiners did not agree with this conception. 43. In the G2 forms, some teachers comment that answer C is also correct, as there are some unicellular organisms that perform meiosis before cell division. This may be true; nevertheless answer is more correct as it applies to all unicellular organisms. Most good candidates had this answer correct, this question turning out to be a good discriminator This seemed quite an easy question. Many candidates were confused with the 70S and 80S ribosomes. This statement is clearly addressed in the teacher notes

15 48. lthough many candidates realized that a greater surface are to volume ratio increased the rate at which heat was lost, many candidates wrongly believed it slowed down the rate of exchange of waste materials. Some teachers complained that the distracters were ambiguous, but it was believed at the grade award that this was not the case. 49. Some teachers commented that answer was not quite specific and could confuse the candidates. This was the least chosen option. Most candidates went for the correct answer, making this question quite an easy one for most and a very good discriminator. 50. teacher complained in the G2s that a nucleolus is not in the syllabus, therefore an inappropriate distracter. It would be possible to only use terms present in the syllabus, but this is very limiting and sometimes it is not sensible to do so. Very few candidates went for that option. This turned out to be an easy question and a good discriminator. 51. There were many comments on this question respecting the presence of 70S ribosomes in mitochondria and chloroplasts. lthough this is true, was still the best answer of the available choices, as all others were present only in eukaryotes. 52.

16 Some teachers complained that in some books the synthesis of proteins is in G2 not G1. In all sources checked, the synthesis of proteins is shown in G1. There is synthesis of spindle proteins and histones in G2, but this is not the main activity occurring in this gap stage. This question turned out to be a bad discriminator and was the most difficult question on the paper. There was a spread of choices amongst the four options. It is obvious that this topic was not known well, although it is present in the syllabus. 53. This question discriminated well. Many candidates answered the correct option, but many went for C. This clearly showed they did not know the difference between mitosis and meiosis. The question may have been badly worded, as candidates might have been looking for a process that occurred in both the stages rather than either of them. In this case there would have been no correct answer. International accalaureate Organization 2017 International accalaureate - accalauréat International - achillerato Internacional