2023 IGCSE Biology Past Papers

DIfficult Questions from 2023 IGCSE Biology Past Papers have been listed below along with specific and extremely detailed comments by examiners. Read them carefully, so as to avoid repeating the same mistakes in your own exams. Also this is the ideal exam preparation, as the comments come from the examiners themselves.

OCTOBER SESSION

MAY SESSION

May 2023 Paper 11:

Easy concepts included:characteristics of living things; the composition of a protein molecule and how the shape of the active site of an enzyme complements the substrate.
Difficult concepts inculded:osmosis; colour changes of hydrogencarbonate indicator solution; the importance of physical digestion and how to apply the magnification formula.Question Numbers: 5,7,8,10, 12, 15,16,17,18,19,34,36,37,38.
Examiners feel students need to work more methodologically for Questions 12 and 38.

May 2023 Paper 12:

Easy concepts included:how to calculate magnification; the pathway of water through a plant and the changes in the pupil.
Difficult concepts inculded:osmosis; colour changes of hydrogencarbonate indicator solution; the importance of physical digestion and how to apply the magnification formula.Question Numbers:
Examiners feel students need to work more methodologically for Questions 12, 16, 18 and 34.

May 2023 Paper 13:

Easy concepts included:the features of active transport; the components of the diet that can be broken down to release energy and interpreting tropic responses.
Difficult concepts inculded:: the processes involved in transpiration in plant leaves; identifying the right ventricle of the heart and the order which red blood cells flow through blood vessels in the human body.Question Numbers:
Examiners feel students need to work more methodologically for Question 12.

Extended Theory Paper

May 2023 Paper 41:

Examiner concerns and suggestions:

Comments on specific questions

Question 1 (a) Many gave three correct answers but did not seem to appreciate that they could give the same letter for more than one response. A small number of candidates wrote out the names of the parts of the digestive system but did not gain any credit even if correct. The question tested the ability of candidates to locate the structures in the diagram.
(b) (i) Candidates often realised that this question was testing knowledge of the roles of lipase and bile in the digestion of fat. There were good explanations that used the information given above Table 1.1, stating that over time the reaction mixtures in test-tubes B and C became acidic. This was ascribed to the formation of fatty acids as lipase digests fat molecules in the milk. The emulsification of fat by bile was stated to be responsible for the faster rate of reaction in test-tube C. However, many candidates did not realise that the question was about fat digestion and referred to the digestion of milk instead, or simply described the results in the table without any attempt at an explanation. A few candidates wrote about the enzyme ligase. Many simply described the colour changes but did not relate these to the action of lipase and bile. Several thought that lipase and bile were acidic and some thought that bile also digested the fats in the milk to fatty acids.
(ii) The role of test-tube A in the investigation was stated by many as the control experiment or more usually the control. Some used the term control variable, which was not accepted. Few candidates stated that test-tube A was used to show that lipase, and not bile, was necessary for the colour and/or pH change in the other test-tubes.
(c) The sketch graphs were not completed very well. Many candidates drew bell-shaped curves rather than curves that increased gradually to a peak and then decreased steeply to meet the x-axis. Very few indicated that the point where the line meets the x-axis shows the temperature at which all the lipase is denatured. Many labelled the peak or the descending part of the curve as the point of complete denaturation. Some candidates drew a line showing an increase in activity and then a horizontal line showing the activity was constant. The horizontal line was labelled incorrectly as the point of complete denaturation.
(d) Many candidates realised that enzymes are specific to their substrate and wrote good answers explaining that the shape of the active site of lipase is complementary only to fat and not to protein. However, many candidates omitted to use the word ‘shape’ in their answers. There were many correct references to enzyme-substrate complexes. Some described protease as the enzyme to digest proteins but did not relate their answer to lipase as required by the question. Many answers described how lipase digests fats, but not why the enzyme cannot digest proteins.
Question 2 (a) (i) Most candidates performed the calculation correctly. The best answers wrote out the formula for calculating percentage change and then showed the working to derive the answer of –13.28%. An error seen on some scripts was to use 1.11 as the denominator to give –15.45% as the answer. The principle of error carried forward was applied to candidates who made such an error.
(ii) There were many good answers to this question which showed excellent understanding of water potential and the movement of water from the potato cubes used in the experiment. Some answers made all six points on the mark scheme. Other answers revealed several misunderstandings, such as water moving into the potato or sucrose solutions moving. Some candidates ignored the instruction in the question and wrote about the concentrations of sucrose and water instead of using water potential terminology. Three of the mark points required the use of the term water potential. Some candidates missed marks because it was unclear whether their comparisons were between the two solutions or between the potato cubes and the solutions. A significant number did state that there was a larger decrease in percentage mass in the 0.8 mol dm–3 sucrose solution.
(iii) A large proportion of the candidates did not seem to realise that this question asked about a cell in the potato cube that had been placed into distilled water. Instead, they either described a cell that would have come from the 0.8 mol dm–3 sucrose solution or about the effect of immersion in water on the cube of potato rather than its cells. Others used most of the answer space to describe how and why water would move into the cell, rather than its appearance. Good answers stated that the cells from the potato in distilled water would be enlarged and turgid. Many also stated that the vacuole would be enlarged so that the cell membrane or cytoplasm would be pushed against the cell wall.
(b) Many candidates explained that active transport requires energy, uses carrier proteins, and involves moving substances, such as ions, against a concentration gradient. All of these are different from the features of osmosis. Many wrote about osmosis as well, although this was not necessary to answer the question. The wording of the question clearly asked how active transport differs from osmosis, not for a comparison between the two processes. There were many irrelevant comments about the need for a partially permeable membrane.
(c) Root hair cells or root hairs were the answers given by most candidates. Root cells and root were not accepted. Examples of incorrect answers included xylem and phloem. (d) There were many good answers to this question on the effect of magnesium ion deficiency on the colour of plant leaves. Candidates often stated that the areas of the leaf between the veins would turn yellow because magnesium is required to make chlorophyll. The term chlorosis was seen on some scripts. Many candidates stated that magnesium ions are used to make chloroplasts, this answer was not accepted.
Question 3 (a) (i) Most candidates stated the role of the goblet cell shown in the photomicrograph in Fig. 3.1 as secreting mucus for trapping pathogens and/or dust. A common error was to fail to notice the information at the top of the question and state that the cell was in the digestive system secreting mucus for the lubrication of food.
(ii) Many candidates identified the cell labelled X as a ciliated epithelial cell or simply as a ciliated cell. The same candidates who made the common error in (i) stated that the cell has microvilli for absorption. Some candidates described cilia as hair-like, but many also simply called them small hairs, not mentioning cilia at all. Some described the cilia as moving bacteria, rather than moving the mucus containing the bacteria. (iii) In this question, it was expected that candidates would identify another region of the breathing system such as the bronchi or bronchioles. In fact, these answers appeared rarely as the most common answers were the small intestine, stomach, and oesophagus. Ciliated cells are widely distributed in the mammalian body so almost anywhere other than the digestive system was accepted. Nose and oviduct were the most common correct answers. Nostrils and lungs were not accepted. Lung was too imprecise as the organ contains blood vessels and alveoli do not have cilia.
(b) Many candidates completed Table 3.1 showing the correct actions of the breathing system to achieve inspiration. Giving unsuitable answers for the external intercostal muscles and the ribs were common reasons for less than full marks. Candidates often stated that the external intercostal muscles relax, and the ribs expand during inspiration rather than saying that the muscles contract and the ribs move upwards and/or outwards. Candidates often stated that the pressure increased in the thorax. A few candidates tried to write lengthy descriptions within the table, so that their answers took up much more than the space provided.
(c) Almost all candidates named carbon dioxide as the gas excreted.
(d) There were many good answers to this question on features of gas exchange surfaces other than good ventilation. Most candidates gave a large surface area, some way in which the distance for diffusion of gases is short and having a good blood supply. Thin and one cell thick were common answers. Two answers that were not accepted were thin cell wall and thin cell membrane. (e) Most candidates identified the gas exchange surface in humans as the alveoli. Several different spellings of the term were accepted if they were recognisable.
Question 4 (a) Fig. 4.1 showed the effect of three different variables on the rate of photosynthesis. In the investigation that generated these results, three groups of plants were exposed to different light intensities and kept in different environmental conditions as shown at the end of the lines on the graph. A logical approach to this question was to describe the shape of lines B and C, ignoring line A. An explanation of the shapes of these two lines then followed, with reference to limiting factors. Candidates who did this were often awarded high marks. Candidates often wrote that as light intensity increased the rate of photosynthesis increased until an intensity where the rate became constant or reached a plateau. These candidates noticed that at low light intensities the rates are the same, but line B becomes constant at a higher light intensity than C so that light intensity remains limiting to a higher value. Candidates explained that the rate became constant for B at a higher rate because the carbon dioxide concentration is higher. The use of light to provide energy and carbon dioxide as a reactant in photosynthesis were sometimes mentioned. Temperature acts as a limiting factor for B at high light intensities since increasing the temperature from 15 °C to 25 °C shows that the rate increases even though the carbon dioxide concentration is the same. Many candidates did not approach the question quite as logically as this. It was quite rare to see a clear description of the shapes of lines B and C. Many candidates were distracted by the carbon dioxide levels, apparently forgetting (or not understanding) that they also needed to think about the increasing light intensity. Only a small percentage of candidates referred to light providing energy or being a limiting factor over the first part of the graph.
In addition, common errors were: •
Thinking that only one of the limiting factors applied to the whole graph.
Stating that photosynthesis in each line (group of plants) stops when the line shows the rate becoming constant. Some stated that carbon dioxide was used up very quickly and photosynthesis came to an end.
Thinking that the temperature increases as the light intensity increases, even though the annotations on the graph state that the temperatures were 15°C and 25°C.
Not using the term limiting factor anywhere in the answer to explain the shapes of the lines.
Interpreting the annotations on the line as meaning that the plants somehow reached those temperatures and carbon dioxide concentrations at the end of the experiment.
Not relating their explanations to light intensity, the variable on the x-axis.
Writing statements which applied to the whole of a line, instead of recognising that there were different limiting factors when each line was increasing and when each line reached a plateau.
Misusing the word ‘steep’, which should be a description of the gradient of a line, to describe the difference in the rate of photosynthesis at which the lines levelled off.
(b) Almost all candidates gave O2 as the answer. Many prefixed the formula with a 6 and some even wrote out the whole equation for photosynthesis. Both answers were credited. Some candidates ignored the question and simply wrote the name of the element without giving the formula. No mark was awarded for this answer.
(c) There were many good answers outlining the fate of the glucose made in photosynthesis. Some candidates gave all the examples listed in the mark scheme. The most common answers were: used to provide energy, stored as starch, converted to sucrose for transport, converted to cellulose to make cell walls, and used to make nectar to attract pollinators. Some candidates misread the question and wrote about how glucose is made in photosynthesis, mentioning at best only one of the uses of carbohydrates in plants. Some discussed many of the uses of energy in the plant rather than answer the question.
Question 5 (a) (i) Many candidates identified the three components shown in the diagram of protein synthesis. Weaker responses named Y correctly as mRNA but did not give a correct name for the other two.
(ii) Many gave the sequence of bases in DNA, mRNA or a gene as the feature that determines the sequence of amino acids in proteins. There were also many vague answers such as DNA, RNA, and gene, with no mention of the sequence or order of bases.
(iii) Many did not read the question carefully and wrote about receptor cells rather than receptor molecules. Correct answers were very few and far between, but some candidates correctly stated that the receptor molecule must have a shape complementary to the neurotransmitter to allow the neurotransmitter to bind to the receptor, and that it is the sequence of amino acids that determines the shape of the protein receptor.
(b) Candidates appeared not to have read the question carefully as they thought this was a question about what happens to stem cells, although they had not been mentioned earlier in the question. The link to protein synthesis was not made by many candidates. Few candidates realised that cells with different functions use only some of the genes in their nuclei. Good answers here referred to gene expression. The very best answers stated that the genes that are expressed are those that code for the proteins required by cells to fulfil their specialist roles in the body. They could have used as an example the goblet cells and the ciliated cells from Question 3 (a) which are specialised cells found in the same tissue. An exceptional answer would have been: goblet cells express genes that code for the enzymes required to make mucus and ciliated cells express the genes that code for the proteins that form the components of cilia.
(c) Many candidates gave the definition of allele given in the syllabus. Some candidates did not make it clear that an allele is an alternative form of a gene. Many mentioned that an allele can be recessive or dominant but did not state the meaning of the term.
(d) Most candidates identified the role of humans in artificial selection. Other common answers were that artificial selection leads to less genetic variation, is faster and is of benefit to humans. Some gave examples of characteristics that are chosen such as disease resistance, drought resistance and higher yield. As with Question 2 (b) many wrote a great deal about natural selection when this was not required by the question. (e) The main sources of genetic variation in populations listed in the syllabus, other than mutation, are meiosis, random mating, and random fertilisation. Some candidates gave other acceptable answers, including hybridisation or inter-specific breeding. Some went beyond the requirements of the syllabus, mentioning the events that occur during meiosis to give rise to genetic variation – crossing over and independent assortment. Some candidates did not read the question and incorrectly referred to causes of mutation, such as radiation. Many gave natural selection and artificial selection as their answers. Sexual reproduction was not accepted as this includes self-pollination that does not introduce any genetic variation.
Question 6 (a) Most candidates read the graph in Fig. 6.1 correctly to state that the pH in muscles during exercise decreases from 7.07 to 6.55. A common error was to give 7.7. Most identified oxygen as the missing term in the next two gaps, but many misread the time for the muscle pH to return to its initial level after exercise. The accepted answer was 31 or 32 minutes or anything in between, such as 31.5 minutes. Many stated that lactic acid is transported in the blood. Blood vessels or named blood vessels, such as veins, were not accepted as the lactic acid is dissolved in the blood plasma. Liver and heart were given by many as the last two answers. Many gave muscles instead of liver. Pulse was accepted as an alternative to heart.
(b) (i) The correct answer for the balanced equation for anaerobic respiration in yeast was given by many candidates. However, many did not write the formula for ethanol correctly or did not balance the equation. Some rewrote the question by adding 6O2 to glucose and completing the equation for aerobic respiration.
(ii) Almost all the candidates identified the cell wall as a cell component present in yeast cells but not in animal cells. Vacuole, sap vacuole and large vacuole were also given and accepted. Candidates should know that yeast cells do not have hyphae.

May 2023 Paper 42:

Examiner concerns and suggestions:

Comments on specific questions:

Comments on specific questions Question 1 (a) Many candidates explained why a leaf is an organ. Some candidates expanded their answers to include examples of specific functions of leaves.
(b) There were many detailed explanations about how the two layers in the diagram of the cross-section of the leaf are adapted for their functions. Almost all candidates focused their answers on the role of the layers in photosynthesis, with fewer referring to transpiration. Most candidates started their answers with correct identifications of layers B and C. All the mark points were regularly awarded to candidates apart from the evaporation of water from the surfaces of the spongy mesophyll cells.
(c) (i) Almost all candidates recognised the cells around the stomata in the sketches as guard cells. (ii) Slightly fewer candidates stated the main function of the stomata. Some common misconceptions included allowing water vapour to be taken into the leaf or thinking that stomata were cells.
(iii) Many candidates correctly stated that closing the stomata would reduce water loss in the plant with a minority describing the prevention of wilting. Most candidates did not consider the context of the investigation and wrote absolute statements, such as preventing water loss with little consideration for water loss through the leaf cuticle or other areas in the plant. Nevertheless, these statements were accepted.
(d) Although most candidates correctly predicted that the stomata would open for longer, the explanations of the effect of high humidity on the stomata was less well known. Very few candidates made correct reference to the gradient of water vapour concentration or of guard cells and their role.
Question 2 (a) Almost all candidates drew a circle to correctly identify a pair of bases on the diagram of the DNA molecule. However, some drew their circle around two pairs of bases and occasionally around a single base.
(b) Many candidates correctly calculated the percentages of guanine bases in the species. Common wrong answers were 71, 79 and 29, suggesting that those candidates did not consider that there are two strands, four bases, or how the bases pair with each other.
(c) (i) Almost all candidates knew that gene is the term for a length of DNA coding for a protein. Some candidates also correctly stated that this could be an allele. Common incorrect answers included mRNA and amino acids.
(ii) Some very detailed descriptions of protein synthesis were seen. Almost all candidates knew of the involvement of ribosomes in protein synthesis, and many were also able to explain the role of mRNA. All the mark points were regularly awarded, except for the requirement for energy for the process. However, there were several common misconceptions and contradictions. These included: • mRNA first moves into the nucleus and then later out of the nucleus • mRNA leaves the cell • mRNA is converted into amino acids at the ribosome • ribosomes make amino acids.
(iii) The most common cell membrane proteins given were enzymes and protein pumps, although a few candidates also accurately recalled that receptors for neurotransmitters are also proteins found in membranes. However, many wrong answers were seen many of which were neither proteins nor structures found in membranes.
Question 3 (a) (i) Most candidates used the correct y-axis and read off the correct values from the graph to calculate the percentage change in bacterial infections resistant to erythromycin. These candidates also usually went on to do the correct calculation and round their answers to two significant figures. A small minority simply subtracted the two values, rather than calculate the percentage change. However, there was a significant minority of candidates who either read the value from the wrong y-axis or used the wrong two bars for 1993 and 1995. Often these candidates showed their working and were then able to gain some credit for the next steps in the calculation. Very few candidates rounded their answers incorrectly or gave their answers to the wrong number of significant figures.
(ii) Most candidates accurately described at least one of the sets of data shown in Fig. 3.1, with many giving a comprehensive account of both sets. It was common for candidates to notice that the number of bacterial infections resistant to erythromycin was first recorded in 1991, but a few candidates incorrectly described this observation as people resistant to erythromycin or bacterial infections without any reference to them being those infections resistant to the antibiotic. Many candidates used the years to describe the two peaks, but those candidates who chose to describe the number of daily doses or number of infections often did not include the correct units with their data values and hence could not be given credit. A common misunderstanding of the data was to describe that in 1991 there were similar numbers of doses and bacterial infections resistant to erythromycin,suggesting that those candidates had not understood that the data were plotted on different axes.
© 2023 (iii) Many candidates correctly suggested that the decrease in the number of bacterial infections resistant to erythromycin was due to a decrease in use of the antibiotic. However, fewer candidates went on to give other suggestions, such as using new antibiotics or treatments, using vaccines, and taking the antibiotics as instructed or only when necessary. A significant minority of candidates did not answer the question, but rather discussed how the resistance had occurred, rather than how the number of resistant bacteria had decreased.
(iv) Most candidates knew that mutations were involved in the process whereby bacteria become resistant to antibiotics. Many of these candidates were also able to outline several of the other steps in the process of natural selection in this context. A significant number of candidates did not mention a gene or allele providing resistance at any point in their response, with many referring to passing on traits or characteristics. Few candidates mentioned variation in the population and even fewer related this to the degree of antibiotic resistance. However, some candidates confused immunity and resistance, attributing mutations to components of an immune system, such as memory cells. Others incorrectly stated that the mutations were caused by the antibiotics, rather than occurring randomly.
(b) (i) The most common correct features of all prokaryotes that were stated included circular DNA, cell wall and cell membrane. A few candidates did not read that the feature should be of all prokaryotes, and listed plasmids and capsules among their answers. Other candidates mentioned features that prokaryotes do not have, such as a nucleus, but did not go on to mention that they do have DNA.
(ii) Almost all candidates knew that the function of a flagellum is movement.
Question 4 (a) (i) Most candidates drew a food web from the student’s notes. The most common errors were either the omission of arrowheads or the arrowheads pointing in the wrong direction. There was evidence that several candidates needed to redraw their food webs after an initial attempt. Very few candidates drew the food webs as individual food chains, but some did include incorrect connections between organisms or did not draw each organism at a separate place in the food web.
(ii) Most candidates identified a primary consumer and a secondary consumer from the food web. Some of these candidates named the next trophic level as tertiary consumer and identified an example from the food web. However, far fewer candidates knew that the last trophic level in this food web is called the quaternary consumer. Even though many candidates did know that the example was the heron, this was only part of the answer. A common misconception was that decomposer was the highest level in the food chain.
(iii) Most candidates correctly stated that energy from the primary consumers was transferred to the secondary consumers. This was often described in the context of the inefficient transfer along a food chain, suggesting that most candidates had not read the question carefully and were expecting to describe the inefficiency in the transfer, rather than how the energy is used to produce biomass. Those candidates who did understand the question went on to write comprehensive answers covering the full range of mark points.
(iv) There were many excellent predictions on the impact of the overharvesting of salmon on the food web. Those candidates who used the names of the organisms in the food web often gained full credit, but a few chose to use the terms primary consumer and secondary consumer not realising that the same trend was not true of all the organisms at each trophic level. Some candidates who followed the impact through the food web very carefully wrote some excellent explanations as to why it was not possible to predict the impact on the aquatic plants because of two different interactions from the midges and from the mayflies and shrimps. A minority of candidates did not understand the impact of overharvesting salmon and described the reverse impact. However, the error carried forward rule ensured that these candidates gained some credit for this mistake.
(b) Although most candidates knew that decomposers feed on dead organic material, only very few added that they receive their energy from this material.
(c) There were some comprehensive answers to this question on why it is more energy efficient for humans to eat crop plants than livestock. Most candidates described how energy transfers are inefficient and gave examples of how energy is lost along a food chain. Some candidates found it challenging to apply their understanding of energy transfer in food chains to the number of trophic levels in the chain. A common misconception, which linked with the misreading of Question 2 (b)(iii),
was that energy is lost to growth and reproduction. Another misconception seen frequently was that plants contained more energy than livestock, when discussing the organism rather than the trophic level; some even went on to say that when consumers eat crop plants, they get 100% of the energy.
Question 5 (a) Many candidates identified the cell structure in the photomicrograph as a mitochondrion and correctly stated its function. A small minority of candidate incorrectly stated that it produces energy, rather than releases energy. A number of candidates thought that the label was pointing to cytoplasm, and this was credited as was an appropriate function of the cytoplasm. Many of those candidates who misidentified the cell structure, were able to gain a mark for correctly stating the function of their stated cell structure.
(b) Most candidates knew that the magnification is required to calculate the actual length of the cell structure, but were often too vague about the measurement required, i.e. the image length, often stating image size which is ambiguous.
(c) Almost all candidates converted the length in millimetres to micrometres, with only a small minority giving answers that were out by factors of 10 or 1000.
Question 6 (a) (i) Many candidates stated that the bean shoots in the Petri dish that was supported in a fixed vertical position grew upwards and that the roots grew down. However, a sizeable minority misread the question and only described the response in either root or shoots, but not both.
(ii) Many candidates also knew that the growth response is gravitropism. Many candidates did not realise that the investigation was carried out in the dark and stated that the growth response was phototropism. Others gave the answer tropism or simply wrote gravity.
(iii) Those candidates who had not noticed that this investigation was carried out in the dark invariably explained the effect of auxin in terms of phototropism. Nevertheless, these candidates were able to access many of the mark points if they knew where auxin was produced, how it moves, and that it causes cell elongation. Most candidates described gravitropism and wrote some very detailed and accurate answers. Common omissions were to describe elongation more generally, rather than to be specific in stating that the cells elongate, or to describe the shoots as bending, rather than the idea that they are growing or elongating. Two misconceptions were seen. Some candidates stated that auxin is produced in the area in which the effect occurs, and others stated that auxin moves against gravity in roots. Those candidates had often misread the question and attempted to explain the phenomena in roots, rather than shoots.
(b) (i) Almost all candidates stated an environmental condition that affects germination, with temperature being the most common. A few candidates suggested humidity and moisture, which implied they had not read the stem of the question before writing their answer.
(ii) There was a good range of correct suggestions for why oxygen and water are required for germination, with many candidates giving very detailed accounts of the use of water in activating enzymes and allowing solutes to dissolve. However, there were also many candidates who mentioned respiration without being explicit that oxygen would be required for aerobic respiration. Others mentioned photosynthesis in their answers, even though seeds do not contain chlorophyll and have no requirement for photosynthesis to germinate.
Question 7 Many candidates correctly completed each sentence in the passage about enzymes. The exception being the first marking point, when many candidates did not give small soluble molecules as being the products of chemical digestion. Common incorrect answers included liver as the site of trypsin production, low rather than high pH needed and digestion as the role of bile rather than emulsification.

May 2023 Paper 43:

Importance of the IGCSE Biology Past Papers-DIfficult -Questions Section

You will be able to assess your performance by referring to the above list.
You will understand your areas of concern and begin to work on those concepts thus preventing yourself from losing marks during your actual board exams. You will be able to, not just save your exams , but ace them as well.
You will know if you also find the same concepts hard like the other students who actually appeared for the above board examsor you find even the easier questions challenging. That will help you decide upon the level of your preparation.

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