B2 H Mock Exam October 2014

Transcription

1 B2 H Mock Exam October 204 B2. - B minutes 64 marks 5x 4x2 2x3 Page of 34

2 Q. The diagram shows a cell. (a) (i) Use words from the box to name the structures labelled A and B. cell membrane chloroplast cytoplasm nucleus A... B... (2) The cell in the diagram is an animal cell. How can you tell it is an animal cell and not a plant cell? Give two reasons (2) (b) Oxygen will diffuse into the cell in the diagram. Why? Use information from the diagram () Page 2 of 34

3 (c) The cell shown in the diagram is usually found with similar cells. Draw a ring around the correct answer to complete the sentence. an organ. Scientists call a group of similar cells a system. a tissue. () (Total 6 marks) Q2. In a living organism, the cells are organised into organs, systems and tissues. (a) Use words from the box to complete the list of these structures in order of size. organs systems tissues The smallest structure is at the top of the list and the largest is at the bottom. cells organism () Page 3 of 34

4 (b) List A gives three tissues found in the human body. List B gives four functions of tissues. Draw a straight line from each tissue in List A to its correct function in List B. List A Tissue List B Function Covers many parts of the body Muscular tissue Contracts to cause movement Glandular tissue Divides by meiosis Epithelial tissue Releases hormones or enzymes (3) (Total 4 marks) Q3. Diagram shows the digestive system. Letters A to F show parts of the digestive system. Diagram (a) Answer each question by writing one letter, A to F, in each box. (i) Which letter shows the salivary glands? () Page 4 of 34

5 In which two organs does digestion happen? and (2) (iii) In which organ is bile made? () (iv) In which organ are faeces made? () (b) During absorption food moves from the small intestine into the blood. Diagram 2 shows part of the surface of the small intestine and a blood vessel. Diagram 2 (i) Food moves from the small intestine into the blood. Why? Tick ( ) one box. The concentration of food is... Tick ( ) higher in the small intestine than in the blood. lower in the small intestine than in the blood. the same in the small intestine as in the blood. () How does the food move from the small intestine into the blood? Draw a ring around the correct answer. by diffusion by digestion by dilution () (Total 7 marks) Page 5 of 34

6 Q4. Substances can move into and out of cells. (a) (i) How does oxygen move into and out of cells? Draw a ring around one answer. diffusion digestion photosynthesis () Diagram shows the percentage concentration of oxygen in three cells, A, B and C. Diagram Oxygen can move from cell to cell. Into which cell, A, B or C, will oxygen move the fastest? () (b) (i) How does water move into and out of cells? Draw a ring around one answer. breathing osmosis respiration () Page 6 of 34

7 Differences in the concentration of sugars in cells cause water to move into or out of cells at different rates. Diagram 2 shows three different cells, P, Q and R. The information shows the percentage concentration of sugar solution in cells P, Q and R. Diagram 2 Water can move from cell to cell. Into which cell, P, Q or R, will water move the fastest? () (Total 4 marks) Q5. The diagrams show a plant cell from a leaf and a bacterium. Plant cell from a leaf Bacterium Page 7 of 34

8 (a) List A shows parts of a cell. List B shows jobs of parts of a cell. Draw one line from each part of the cell in List A to its correct job in List B. List A Parts of a cell List B Jobs of parts of a cell Contains cell sap Vacuole Protein synthesis Cell wall Controls the passage of substances into the cell Cell membrane Strengthens the cell (3) (b) Genetic material controls the activities of a cell. Where is the genetic material in the plant cell? Tick ( ) one box. In the mitochondria In the nucleus In the ribosomes () Page 8 of 34

9 (c) There are differences between the plant cell and the bacterium. (i) In the plant cell photosynthesis makes food for the cell. The bacterium is not able to photosynthesise. Why? Use information from the diagrams to help you. () The bacterium absorbs dissolved food from outside the cell. Name the process by which dissolved food is absorbed into the bacterium. () (iii) Structure X in the bacterium is where most energy is released in respiration. Which part of the plant cell does the same job as structure X? Draw a ring around the correct answer. ribosome mitochondria chloroplast () (Total 7 marks) Q6. Cells in the human body are specialised to carry out their particular function. (a) The diagram shows a sperm cell. The sperm cell is adapted for travelling to, then fertilising, an egg. (i) How do the mitochondria help the sperm to carry out its function? () Page 9 of 34

10 The nucleus of the sperm cell is different from the nucleus of body cells. Give one way in which the nucleus is different. () (b) Stem cells from human embryos are used to treat some diseases in humans. Explain why (2) (Total 4 marks) Page 0 of 34

11 Q7. The diagram shows two cells, a bacterial cell and a plant cell. (a) (i) Both the bacterial cell and the plant cell contain ribosomes. What is the function of a ribosome? () The plant cell contains mitochondria but the bacterial cell does not contain mitochondria. Give one other way in which the plant cell is different from the bacterial cell. () Page of 34

12 (b) (i) Both cells are drawn the same length, but the magnification of each cell is different. The real length of the bacterial cell is 2 micrometres. Calculate the real length, X, of the plant cell. Give your answer in micrometres. Show clearly how you work out your answer. X =... micrometres (2) Most mitochondria are about 3 micrometres in length. The plant cell contains mitochondria but the bacterial cell does not contain mitochondria. Use your answer to part (b)(i) and the information in the diagram to suggest why. () (Total 5 marks) Page 2 of 34

13 Q8. Diagrams A, B and C show cells from different parts of the human body, all drawn to the same scale. (a) Which cell, A, B or C, appears to have adaptations to increase diffusion into or out of the cell? Give one reason for your choice () (b) (i) Cell C is found in the pancreas. Name one useful substance produced by the pancreas. () Use information from the diagram to explain how cell C is adapted for producing this substance. (2) (Total 4 marks) Page 3 of 34

14 Q9. The diagrams show a cheek cell from a human and a leaf cell from a plant. (a) The two cells have a number of parts in common. (i) On the cheek cell, label three of these parts which both cells have. In the table, write the names of the three parts you have labelled above and describe the main function of each part. (3) Part Function (3) (b) Blood contains white cells and red cells. State the function of each type of cell in the blood. White cells..... Red cells (2) (Total 8 marks) Q0. Some molecules can move into and out of cells across the cell membrane. (a) Dissolved substances move into and out of cells. Name this process.... () Page 4 of 34

15 (b) Diagram shows a model of a cell surrounded by water. The model cell contains a solution of two molecules, A and B. In the diagram, the circles represent molecules of A and B. The cell membrane contains small holes that allow molecules to pass through. Diagram (i) Describe what will happen to the number of molecules of A and of B in the cell and in the water, in the next few hours. (3) Explain the reasons for your answer to part (b)(i). (2) Page 5 of 34

16 (c) Oxygen can pass through membranes into cells. Oxygen passes from the lungs into the blood. Diagram 2 shows a blood vessel and cells at the surface of the lung. Diagram 2 (i) Why do cells need oxygen? () Blood moves along the blood vessel all the time. In terms of oxygen passing into the blood from the lungs, why is the movement of blood important? (2) (Total 9 marks) Q. Diagram shows a typical animal cell. Diagram Page 6 of 34

17 In multicellular organisms, cells are specialised to carry out particular functions. There are two types of cell lining the windpipe. Ciliated cells have cilia on their surface. The cilia move mucus out of the windpipe. Goblet cells produce mucus. Mucus contains a sticky protein that traps microorganisms and dust particles. Diagram 2 shows these two types of cell. Diagram 2 Ciliated cells and goblet cells are both specialised to carry out their functions. (a) Suggest one cell part that you would expect to find a lot of in the cytoplasm of ciliated cells. Explain your answer. Cell part... () Explanation (2) (b) Suggest one cell part that you would expect to find a lot of in the cytoplasm of goblet cells. Explain your answer. Cell part... () Explanation (2) (Total 6 marks) Page 7 of 34

18 M. (a) (i) A = nucleus B = (cell) membrane any two from: ignore shape no (cell) wall no (large / permanent) vacuole no chloroplasts / chlorophyll 2 (b) because high to low oxygen / concentration or down gradient allow more / a lot of oxygen molecules outside ignore along / across gradient (c) a tissue [6] M2. (a) in sequence: 2 = tissue(s) 3 = organ(s) 4 = system(s) Page 8 of 34

19 (b) mark for each correct line extra line(s) from one tissue cancel 3 [4] M3. (a) (i) A B and E either order, one mark each 2 (iii) F (iv) D (b) (i) higher in the small intestine than in the blood by diffusion [7] M4. (a) (i) diffusion apply list principle A apply list principle (b) (i) osmosis apply list principle Page 9 of 34

20 R apply list principle [4] M5. (a) mark for each line do not award mark for part if more than one line is drawn from that part 3 (b) In the nucleus (c) (i) (has) no chloroplasts allow (has) no chlorophyll diffusion allow active transport ignore absorption (iii) mitochondria [7] M6. (a) (i) release energy allow provide / supply / give energy do not accept produce / create / generate / make energy do not allow release energy for respiration contain half the (number of) chromosomes or contains one set of chromosomes or contains 23 chromosomes allow genetic information / DNA / genes / alleles instead of chromosomes accept haploid Page 20 of 34

21 (b) any two from: (stem cells) are unspecialised / undifferentiated allow description eg no particular job are able to become differentiated or can form other types of cell / tissue / organ stem cells can / able to divide / multiply 2 [4] M7. (a) (i) makes / produces / synthesises protein / enzyme plant cell has nucleus / vacuole / chloroplasts / chlorophyll or plant cell is much larger It = plant cell allow correct reference to DNA or chromosomes allow plant cell has fewer ribosomes allow cellulose (cell wall) (b) (i) 200 correct answer with or without working gains 2 marks if answer incorrect, allow mark for or 00 or 2 bacterial cell is too small / bacterial cell about same size as a mitochondrion / no room ignore references to respiration [5] M8. (a) B no mark for B, alone large(r) surface / area or large(r) membrane accept reference to microvilli accept reasonable descriptions of the surface do not accept wall / cell wall ignore villi / hairs / cilia Page 2 of 34

22 (b) (i) any one from: insulin / hormone if named hormone / enzyme must be correct for pancreas enzyme / named enzyme many ribosomes (ribosomes) produce protein accept insulin / hormone / enzyme named is (made of) protein or allow many mitochondria () provide energy to build protein or to make protein () accept ATP for energy [4] M9. (a) (i) the three features correctly labelled on cheek cell (which are referred to in part label lines should touch or end very close to part no marks if leaf cell labelled nucleus cytoplasm cell membrane mitochondrion accept mitochondria or one of these could be labelled vacuole 3 Page 22 of 34

23 any three from feature function nucleus controls cell accept contains genetic material or genes or chromosomes or stores information do not credit the brain of the cell cytoplasm where respiration occurs accept contains food or mitochondria or reactions occurs membrane less water or chemicals accept surrounds the cell or lets some things in but not others do not credit keeps things out or protection in and or out (b) mitochondria where energy released ecf from leaf cell labelling accept chloroplasts make sugar or glucose accept vacuole contains sap accept if cell wall mis labelled on cheek cell, support or hold together fight or ingest or kill bacteria or germs or viruses or microbes accept produce antitoxins or antibodies fight disease (organisms) do not credit fungus 3 (transport) oxygen or carry haemoglobin accept transport carbon dioxide or helps form scabs [8] M0. (a) diffusion ignore absorption Page 23 of 34

24 (b) (i) any three from max 2 marks for A or B only (the number of) A decreases in the cell (the number of) A increases in the water if neither of first two bullet points given allow mark for A moves out of cell / membrane or A moves into water until (number of) A is equal inside and outside cell or until (number of) A is half what it was at beginning (in cell) accept the idea that the concentrations of A in the cell and in the water will become (close to) equal (the number of) B stays the same in the cell there are no (molecules of) B in the water if neither bullet point 4 nor 5 is given allow mark for B does not move out of cell or B does not move into the water 3 (molecules of) A small enough to pass through holes / membrane allow membrane permeable to A or membrane not permeable to B or (molecules of) B too large to pass through holes / membrane allow reference to size of holes (in membrane) being too small for B or large enough for A, to pass through once concentration of molecules of A is the same inside and outside cell there will be no (net) movement allow this idea in terms of numbers of molecules or A moves from high concentration (in cell) to low concentration (in water) (c) (i) for (aerobic) respiration ignore references to energy or uses of energy eg contraction or to respire do not accept anaerobic respiration Page 24 of 34

25 any two from: removes oxygen that has diffused / passed into blood keeps difference (in concentration) between lungs and blood high accept idea of maintaining diffusion / concentration gradient increases speed of diffusion / passage of oxygen into blood if no other mark given allow mark for so oxygen can reach the cells / (named) parts of the body 2 [9] M. (a) Cell part: mitochondria allow mitochondrion Explanation: release energy ignore produce / make energy or reference to respiration for movement of cilia (b) Cell part: ribosome(s) Explanation: reference to synthesis of protein for production of mucus / sticky (substance) reference to production of sticky protein gains 2 marks allow for 3 marks cell part mitochondria, explanation: to release energy for production of protein [6] Page 25 of 34

26 E. This question was well answered by most students. (a) (b) (c) Most knew that structure A in the diagram of the cell was the nucleus and that structure B was the cell membrane. More than three quarters knew this was not a plant cell either because it had no cell wall or because it had no (large) vacuole or no chloroplasts. Some included a reference to the shapes of plant and animal cells which was ignored by examiners. Others gave incorrect points about whether ribosomes or mitochondria were present. In this question students had to use the distribution of oxygen molecules shown in the diagram to explain why oxygen was able to diffuse into the cell. This was often poorly answered; some merely repeated the information in the question without adding to it. Others made statements like oxygen can pass through the cell membrane or there is no wall to stop it. Some students wrote about the cell s need for oxygen. A minority recognised the difference in concentrations inside and outside of the cell as being relevant and were able to explain clearly that the oxygen would diffuse down the concentration gradient. Three quarters of students correctly chose tissue as the correct term to describe a group of similar cells. E2. (a) Almost half of the students were able to list tissues-organs-systems in the correct size order. (b) The distracters in this section proved very distracting and less than half the students could assign the correct function to all three types of tissue muscular, glandular and epithelial. Page 26 of 34

27 E3. (a) (i) The vast majority of students correctly identified A as the salivary glands. (iii) (iv) Slightly more students identified that E, the small intestine, was one site where digestion happens, than identified B, the stomach. Approximately two-thirds of the students gave at least one of these responses, with D, the large intestine, being a common error. Knowledge of the site of production of bile was less secure, with less than half of the students identifying F, the liver. The most common error here was C ; examiners suspecting that many of these students were unsure what organ C was and were similarly unsure what bile was, so logically put the two together. The examiners were pleased that most students recognised organ D, (the latter part of) the large intestine, as the site of production of faeces. (b) (i) Almost all students were aware that movement would be due to a difference in concentrations of food between the small intestine and the blood, thus very few selected the third alternative. Well over half of the students realised that there would need to be a higher concentration in the intestine than in the blood for movement to occur out of the intestine. Digestion proved to be a powerful distracter here, with almost as many students selecting this as those who chose the correct diffusion. This was disappointing, as the examiners might have hoped that most students would realise that food is not absorbed by digestion, or that digestion is a break-down process occurring within the small intestine; however, the examiners also realise that few students would use diffusion in an everyday context. However, relatively few opted for dilution, which is perhaps a more well-known term in other situations. E4. (a) Most students knew that diffusion is responsible for the movement of oxygen into or out of cells and many of these recognised the significance of the oxygen concentrations shown in the cells, selecting A. Those who got part (a) wrong usually chose B, the cell oxygen will pass out of the most quickly. (b) (i) Similarly, most students recognised that osmosis is responsible for the movement of water into or out of cells. This part proved more problematic. More students selected P, than selected the correct answer R, presumably as a result of not understanding the significance of high and low solute concentrations for osmosis. Once more the least attractive answer was the cell with the middle concentration in the range. Page 27 of 34

28 E5. (a) Most students were able to match at least two of the cell parts to their correct function. The vacuole was least well known and inevitably some students confused cell membrane with cell wall. (b) A high proportion of students knew that genetic material is found in the nucleus of plant cells. (c) (i) This required a specific reference only to the bacterial cell lacking chloroplasts or chlorophyll; here many students tried the scattergun approach, naming all the organelles from the plant cell that were not in the bacterial cell. This approach was not accepted, as the lack of any of the others would not, in itself, preclude photosynthesis. Students should be aware that the list principle applies to responses such as this, i.e. that any incorrect answer disqualifies a correct answer. Consequently students should be encouraged to give one answer, rather than several, as it is highly likely that multiple answers will result in no marks. (iii) This also proved to be tricky for many students. Absorption was a common response which examiners ignored due to it being in the question, twice. Instead diffusion was sought but was not frequently given. Mitochondria being the site for respiration were identified by well over half of the students, with the two distractors proving to be roughly equally enticing. Page 28 of 34

29 E6. (a) (i) Here the question required candidates to explain how mitochondria help a sperm cell to carry out its function. It was, therefore, not enough to simply write they are the sites of respiration, as this does not link the mitochondria to a function in sperm cells. Candidates had to go one step further to state that they release energy. Although it was acceptable to use synonyms such as provide, supply or give in lieu of release, the all too common references to the idea of energy being produced or made were not credited. No mark was awarded either if candidates said that mitochondria contained energy or that the energy they released would be used in respiration, this latter being another common misconception. Some candidates gave very confused answers implying that respiration made glucose or provided the cell with oxygen. Many answers were too vague, referring to mitochondria being needed to help the sperm swim, whilst others simply gave incorrect roles such as protein synthesis or contains the genetic information. Under half the candidates had the correct idea and gave an answer which implied that the nucleus contained only half the usual number of chromosomes. Candidates occasionally failed to read the question properly, however, and saw it as a continuation of part (i) asking for a function rather than a difference. Answers such as carries genetic information or controls the activities of the sperm, therefore, gained no credit. It was quite common to see responses which gave a comparison between sperm cells and body cells in terms of size, shape or position of the nucleus, with a particularly common idea that the nucleus of the sperm cell is bigger (than that of a body cell) showing that the concept of scale had not been considered or that it is not in the middle, indicating that candidates take basic cell diagrams as representing all cells. (b) Many candidates conveyed the idea that stem cells are able to form other types of cells. Fewer, however, made the points that they are unspecialised or that they have the capacity to divide, the latter being seen only rarely. Some answers failed to gain credit because the language used was too loose or vague. Consequently, no marks were given for answers such as stem cells have no function or can be made to do jobs or can be turned into anything needed. Incorrect ideas included stem cells have no DNA, contain chemicals to cure diseases, make humans immune, or help to repair damaged cells. Some candidates, unfortunately, focused only on the two words embryo and disease in the question and mistakenly answered in terms of genetic screening, whilst a few implied almost magical, cure-all properties on these cells, describing them as fighting disease. Page 29 of 34

30 E7. (a) (i) Almost two-thirds of students knew that ribosomes were the site of protein synthesis. Some clearly confused ribosomes with mitochondria and thought they were for energy release. There was also a range of curious suggestions by those who did not know the answer but were able to use their imaginations. While most could choose either the presence of a vacuole, a nucleus, or chloroplasts as a feature that distinguished the plant cell from the bacterial cell, there were many students who selected common features, such as the cell wall, cytoplasm or cell membrane. (b) Almost two-thirds of students were able to calculate that the length of the plant cell was 200 micrometres. This involved appropriate manipulation of the two given scale factors. Those who did this incorrectly, answering 0.02 micrometres, ought to have considered which of the two types of cell, plant or bacterium, was the larger in real life. Most students, who used their answer from part (i) as instructed, realised that a bacterium was too small to contain any mitochondria. Those who ignored this instruction invented various improbable reasons for the absence of mitochondria in bacteria, such as bacteria not needing to respire. Page 30 of 34

31 E8. (a) The examiners were looking for a clear understanding that increased diffusion may be achieved by increased surface area. However, there appears to be some confusion as to what diffusion is, many believing that it requires energy, suggesting that the high numbers of mitochondria in cell C would provide the necessary energy to drive the process. The diagrams also caused difficulties, with candidates sometimes thinking that the dots, keyed as ribosomes, represented concentrations of substances; this latter resulting in candidates suggesting inward diffusion to cell A, as it has a low concentration, or outward diffusion from cell C, due to its high concentration. Although there were many descriptions of the microvilli on cell B, knowledge of this term is not required in the specification, so terms such as stringy extensions were accepted, if linked to the explanation regarding increased surface area. Those who believed these provided channels or openings or were used to draw in substances did not gain the mark. A few conferred unexpected structures on their chosen cell, offering stomata, root hairs or guard cells or described parts of the cell wall, despite being told the diagrams represented cells of human origin. (b) (i) Most candidates were able to name a suitable substance, with insulin by far the most common, followed by protease and amylase. A few managed to spell glucagon correctly but there were also several unacceptable hybrids of this and glucose or glycogen. This part gave the candidates the opportunity to make a simple observation of cell C and link it to their understanding. A good majority of candidates recognised the significance of lots of ribosomes and went on to explain that these are involved in protein synthesis. However, some only repeated the substance they had named in part (b)(i) and did not gain the second mark. Those candidates who chose to go down the more mitochondria route frequently failed to link the energy release to protein production. A surprising number of candidates missed the large numbers of organelles in cell C and decided that the excretory vesicles in the upper membrane were active sites for the attachment of substrates, showing a complete misunderstanding of the differences in scale of enzyme and cell. A minority of candidates reversed the functions of the organelles, suggesting that mitochondria produce protein or that ribosomes release energy. E9. Foundation Tier Many of the weaker candidates did not attempt to label the diagram at all perhaps they simply did not see this part of the question. Of those who did label the diagram, the nucleus was well known, but the cytoplasm and mitochondria less so. The function of each part proved to be a discriminating question, with many candidates simply asserting that the nucleus was the brain of the cell. The functions of the red and white blood cells were pleasingly well known by many candidates, although inevitably a few had them the wrong way round. The weaker candidates appeared to believe that the red cells were veins or arteries, as it was common to read answers such as... carries the blood around the body. Page 3 of 34

32 Higher Tier This was a relatively easy, high scoring question to start the paper. Some candidates, however, failed to read the question sufficiently carefully and lost marks by not answering part (a)(i). The other carelessness was that a few labelled the leaf cell. Whilst many candidates correctly identified the cell membrane, cell wall was often given. Good answers to the functions were given by many, but there was some confusion as to the roles of red and white cells. For example, white cells are thought by weaker candidates to carry antibodies and red cells to carry food. E0. (a) Although most students correctly identified diffusion, reference to osmosis was also commonly seen. (b) (i) Many students referred to molecules of A and B jointly, suggesting that they would both move through the membrane into the surrounding water, paying scant notice to the size of the holes in the membrane. In most cases students referred to the molecules moving (or not) through the membrane, rather than answering the question which asked about how the numbers of molecules might change. There were five possible routes to gaining the three marks available here; however, very few students referred to the eventual achievement of equilibrium for molecules of A.Examiners expected that, had students answered the question asked, far more of them would have gained two or three of the marks available. Examiners were also surprised at the number of students who referred to the movement of water into the model cell by osmosis apart from not having been asked for, osmosis does not crop up until Biology Unit 3. The examiners were also concerned about the number of students who failed to follow the command word describe and added explanations to this part of the question. When these students came to part (b), they failed to give these same explanations which would have gained them at least one of the marks. A significant proportion of students failed to offer any response here. Many of these had already given, in part (b)(i), what would have been creditworthy responses, but had now exhausted their ideas. This is also true for many of those who made an attempt to answer but had already given a correct answer previously and now looked for something different. To award one mark, examiners were looking only for some reference to a consequence of the size of the holes compared with that of the molecules. The second mark here was more demanding and as expected, only particularly able students achieved this. (c) (i) The examiners were surprised that so few students could identify respiration. All sorts of alternative processes were offered instead. It appeared that most students had not understood the significance of the first part of the question, to give an answer in terms of oxygen passing into the blood from the lungs, as very few students appeared to have any idea of the importance of diffusion gradient. Most of the students who gained one mark here did so for explaining why the movement of blood is important, referring to the delivery of oxygen to body cells. Page 32 of 34

33 E. Having been given a labelled diagram of the parts of a cell given in the specification, the examiners were surprised at the frequently poor quality of spelling of these parts, in responses. Students were expected to use the information to make sensible suggestions of relevant organelles and to explain their choices. It would appear that a considerable proportion of students merely skimmed over the information, or ignored it completely, in their haste to get on with the questions. Hence what was written for both parts of the question did not reflect the information given. (a) (b) It was expected that students would identify the movement of cilia described in the information and recognise that ciliated cells would need large numbers of mitochondria. The role of these mitochondria is to respire in order to release energy for the movement of the cilia. Unfortunately many students got off to a relatively poor start, suggesting some other organelle. However examiners did not link the named organelle to the explanation, so even with the wrongly identified organelle, it was still possible to gain the two explanation marks. As usual with this type of description students scientific language skills let them down, often describing respiration as using energy or producing energy, neither of which are allowable at this level. It was very common for students to incorrectly describe the energy released as being for the mucus to move rather than for the cilia to move. Students choosing the wrong organelle were not precluded from gaining both marks for an appropriate explanation. Here more students seemed comfortable with ribosomes than had been with mitochondria in part (a). These were also frequently linked to protein synthesis, although the extra link to mucus containing protein, derived from the information, was not often made clearly. Page 33 of 34

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