GCSE HUMAN HEALTH AND PHYSIOLOGY

Transcription

1 GCSE HUMAN HEALTH AND PHYSIOLOGY 44151F Topics in Human Health and Physiology Report on the Examination 4415 June 2015 Version: 1.0

2 Further copies of this Report are available from aqa.org.uk Copyright 2015 AQA and its licensors. All rights reserved. AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre.

3 General There were some very good answers to most of the questions, with candidates demonstrating a sound understanding of the material in the Specification and an ability to apply it to the solution of problems in novel situations. The majority of candidates appeared to have been entered for the correct tier as there were relatively few at Foundation Tier who might have had access to higher grades if they had been entered for the Higher paper, although a few weaker candidates, whose work showed clearly that that they were unlikely to aspire to anything higher than a grade C, were inappropriately entered for the Higher Tier paper. There were a few areas that caused particular difficulty for many candidates, such as the properties of an exchange surface question 13ai; the concept of energy release (not production ) questions 12bii and 13c. Questions involving calculations, particularly percentages and the use of a scale for calculating size, were also found to be very low scoring. Errors frequently occurred when figures had to be read from a graph, such as questions 13bi, ii, iii. Also, when a calculated value did not fit the graph given in a subsequent section, this should have indicated that an error had been made and the calculation should have been checked, for example, question 7biv. It is also important that candidates read carefully the information given in the stem of the question. This sets the scene and is provided to help candidates find their way through what might otherwise be a complex situation. Candidates should make sure that they understand what they are being asked in any particular question and give sufficient detail in their answer and to keep to the point in their answers there are no marks available for irrelevant material or for repetition of the wording of the question. There were also a number of occasions when candidates gave an answer they were told specifically not to give. For example, Give two other causes... or...three other structures... It would also help if candidates could practise comparison style questions as these require comparative points to be made in the answer for example, question 12bii. Candidates must make sure that they communicate information clearly and unambiguously. Use of terms such as affect, food and harm, or protect and fight (with reference to disease), unless qualified, are often meaningless. Sentence construction need not be complex and the onus is on the candidate to ensure that what is written in the answer can be interpreted easily. Candidates should be advised to follow the rubric on the front of the question paper and write in black ink or black ball point pen only. The scanning process involved in online marking does not pick up pale colours well. Furthermore, candidates should be advised to ensure that they keep their answers within the writing frame ruled around each page; otherwise part of the answer may be removed when pages are cut during the scanning process. 3 of 12

4 44151F Foundation Tier Question 1 Question 2 This question was about health professionals and their role in health and medical care. It proved to be a straightforward opening question. Most candidates were able to select what the different health professionals do. A few did not know that a cytologist studies cells. This question was about the male reproductive system. Around three-quarters of candidates gained 2 marks for this question. Where a mark was lost it was usually because they named the testis as the scrotal sac. Well over three-quarters of the entry correctly identified the testis as the site of sperm production but only a third correctly identified the prostate as an organ that produces a fluid for sperm to swim in, with only slightly fewer selecting the bladder. The vast majority of candidates identified the penis as the organ which becomes erect during intercourse. Just over half the candidates correctly identified the urethra on the diagram. Three-quarters of candidates gained 2 marks, usually for saying that a sperm cell is adapted for its function by having a tail in order to swim. Question 3 This question was about the protective functions of the skeleton and movement at the elbow joint. Most candidates stated correctly that the skull protects the brain and the rib cage protects the heart or the lungs. They had more difficulty in deciding what the vertebral column protects. Common incorrect organs were the liver, kidney or intestines rather than the spinal cord. In part (ii), the majority of candidates correctly gave some reference to women having a wider pelvic girdle than men for pregnancy or for birth of a baby. A few thought it was to push the baby out, which was not credited. Others referred to women having different organs compared to a man, but this was insufficient to gain a mark. Most candidates studied the diagram and identified the correct structure, C (the ligament), that was shown to connect bone to bone. Slightly fewer than half the candidates identified the tendon, B, on the diagram, with a similar proportion correctly identifying the muscle that would straighten the arm as structure E (the triceps). Reassuringly, most of the others did select the only other muscle shown on the diagram, the biceps. Three-quarters of candidates selected the correct structure from the diagram, D (cartilage) that reduced friction in the joint. 4 of 12

5 Question 4 This question was based on nutritional information on the label of a can of baked beans. Most candidates correctly calculated that a 200 g serving of baked beans would contain 9 g of protein. Common errors were to either multiply 200 by 4.5 giving an answer of 900 g, or to divide 200 by 4.5 giving 44.4 g. In part (ii), most candidates linked the use of protein in the body to muscles. If they stated protein was needed for growth, repair or to build muscle they were awarded a mark. Vague statements such as protein helps muscle or strengthens muscle were ignored. A reference to growth or repair of cells, tissues or a named tissue was required. In part (i), the correct answer of 10% for the proportion of the daily iron requirement provided by 100 g of baked beans was calculated by just under half of the candidates. Common incorrect answers were 0.14, where they had divided 14 mg by 100, and 7.14, where they had divided 100 by 14. In part (ii), almost half of the candidates gained full marks. Most identified anaemia as being caused by a shortage of iron. The most common error was to mix up scurvy and rickets. Although the correct answer (1200 kj) for the extra energy needed each day by a breastfeeding woman compared to a pregnant woman was successfully calculated by two-thirds of candidates, many others gained at least 1 mark for either giving two correct readings from the bar chart, or correctly subtracting incorrect readings. In part (ii), the question asked why a breast-feeding woman needs more energy than a pregnant woman, so just stating that she is breast feeding, or she is feeding her baby was insufficient. Some value had to be added by either saying she had to produce milk, or that she would be more active as she had to look after her baby. In part (iii), many responses just repeated information given in the bar chart without clearly stating the factor that would affect the amount of energy a person needs. Others referred to pregnancy and breast-feeding even though the question said to give other factors. Correct answers included exercise, gender and age. Question 5 This question was about microorganisms, disease and antibiotic resistance in some bacteria. Over three-quarters of candidates correctly named the microorganisms that cause disease as pathogens. The question was well answered. Most candidates gained at least 1 mark for knowing that athlete s foot is caused by a fungus and almost two thirds of candidates gained all 3 marks. 5 of 12

6 In part (i), only about a quarter of candidates correctly identified the dependent variable from the three given options. Candidates usually confuse the dependent and independent variables, but in this question an equal proportion chose the control variable. Some candidates gave more than one answer, so could not gain the mark. If they change their mind, they should clearly cross out anything that they do not want marked. In part (ii), the vast majority realised that the antibiotic which had the largest clear area around it was most effective at killing the bacteria. In part (iii), the question told candidates that antibiotic C did not kill the bacteria, so restating this was not creditworthy. The question asked for evidence from the diagram to support the statement. The evidence was that there was no clear area around antibiotic C. A little over half the candidates correctly described this. In (iv), just over half of the candidates knew that bacteria that cannot be killed by antibiotics are said to be resistant. The most common incorrect choice was immune. Question 6 This question was about excretion, and the relative costs of dialysis and a kidney transplant in the treatment of kidney disease. (d) Most candidates scored the mark for stating that the lungs excrete carbon dioxide, but found the other two organs more difficult to name. A common error was to give the name of the substance excreted, rather than the name of an organ. For example, many gave sweat as an organ that excretes mineral ions, and urine as an organ that excretes urea. Part (i) was very well answered with most candidates correctly calculating that 13% of the water excreted was in the form of sweat. Errors were made in adding the three figures given on the pie chart. In part (ii), most responses contained a correct statement about sweat cooling the body. Some candidates referred to control of water in the body or excretion of urine which were not creditworthy. In (iii), approximately three-quarters of candidates selected the option that less water would be lost in the urine if more water was being lost in sweat on a hot day. There was almost an equal split between the three options for the chemical found in the urine that would indicate kidney damage. Thus only a third correctly selected protein. In the calculation of the cost of a kidney transplant operation plus immunosuppressant drugs for ten years, some candidates added and together and multiplied the total by 10, to give an answer of , which was incorrect. Others correctly multiplied by 10 and added this to the cost of the operation, giving the correct total cost of , to gain 1 mark. In part (ii), most candidates who gave the correct answer in (i) went on to gain the mark here. When an incorrect value was calculated in part (i), examiners made allowance for this if that answer was correctly subtracted from the given cost of dialysis treatment over 10 years. In (iii), some candidates did not read the question carefully and stated that people did not have kidney transplants because it would cost too much. Others thought it was because people were afraid of having an operation or because there was a high failure rate. Just under half stated that there was a shortage of suitable kidneys. 6 of 12

7 Question 7 This question was about coordination and the handling of data about the measurement of reaction times by different methods. A sense organ was required for each stimulus in part (i), but many candidates gave part of an organ, or used words that were given on the next question effectors or receptors. Quite a lot gave fingers or hands for the organ that detects touch. These were ignored as skin was the required answer. Just over one-third scored all 3 marks. In (ii), most candidates correctly selected receptors as the cells that detect stimuli. Candidates are generally very good at identifying anomalies, as were over two-thirds in part (i). Some incorrectly circled 0.27 in the light column, or the mean of 0.17 calculated for touch, rather than the correct value of 0.35 for the third test relating to touch. In part (ii), two-thirds of candidates correctly said the anomalous results should be discarded or the test repeated. And three-quarters of candidates correctly calculated the mean value in (iii). Part (iv) involved completion of the bar graph. Some very neat and accurate bars were drawn. Candidates that had miscalculated the mean in part (iii) were still able to gain this mark if they had plotted their value correctly. Those candidates whose calculated mean would not fit on the bar chart should have gone back and checked their calculation. Oneeighth of candidates did not attempt this question, possibly because they missed it as it involved drawing the answer on a graph rather than answering on a dotted answer line. Part (v), on drawing a conclusion from the data, was answered rather poorly. A response about the reaction time was required. Sound had the shortest reaction time would have been preferred, but examiners did allow sound had the fastest reaction time. Many candidates did not understand the bar chart. They thought that light had the fastest reaction time, rather than the slowest. Other types of response also highlighted a misunderstanding, for example stating that light had the best reaction or light had the highest reaction. Question 8 This question was about the roles of cilia and mucus in the trachea and the effects of cystic fibrosis and smoking on the lungs. A lung disorder caused by smoking was asked for; therefore heart disease was incorrect. Some candidates gave descriptions of effects caused by smoking, for example smoker s cough, rather than a named disorder. The most common correct answer was lung cancer. Over three-quarters of candidates gave a correct example. Most responses included some reference to the mucus trapping dirt or particles. Candidates found it more difficult to explain what the cilia do. They had to relate movement of the cilia to moving the mucus out of the trachea. References to filtering and brushing were ignored. Some thought the cilia, rather than the mucus, trapped dirt. Fewer than half of the candidates had any success in this question. Less than one-third of candidates successfully gained the mark for stating that, in cystic fibrosis, the mucus made it harder to breathe, caused shortness of breath or caused more coughing. A few stated that the risk of infection would be higher, or that there would be a reduced gas exchange in the alveoli. References to drowning and stopping breathing were ignored. 7 of 12

8 (d) Most candidates stated correctly that if a smoker were allowed a lung transplant, continuing to smoke would damage the new lungs. Acceptable comments, such as wastage of a lung, or wastage of money, were also seen, but were less common. A few gave confused responses about cystic fibrosis, rather than smoking. Over three-quarters of candidates scored at least one mark. Question 9 This question was about phenylketonuria and its inheritance. In part (i), only one-third of candidates knew that amino acids were released by the digestion of protein. Many candidates did not give the name of a food molecule, but either gave the name of an enzyme or a type of food, for example meat. Similarly, in (ii), a third of candidates said that the diet of a child with PKU should not contain protein, which was allowed. In (i), capital N and lower case n, as symbols for the alleles, were not always clearly written. Most candidates gave the correct gametes for the mother. Only occasional errors were seen in generating the correct genotypes of the offspring in the Punnett square. Over twothirds of candidates scored full marks. In part (ii), when more than one genotype was circled, both had to be nn to gain the mark. Some candidates did not write nn in the Punnett square, so they could not gain this mark unless they had written nn near the question, and not circled any genotypes in the square. Over one-eighth of candidates did not answer this question, although nearly two-thirds did so successfully. In (iii), just over two-thirds of candidates gained the mark for correctly selecting 1 in 4 as the chance of the parents producing another child with PKU. Question 10 This question was about components of the blood and blood transfusion. In part (i), as is always the case, many candidates thought the cell membrane was the cell wall. Most candidates correctly labelled the nucleus, but some thought the cell membrane was the cytoplasm. Nearly two-thirds of candidates selected the correct names for all three structures. In (ii), candidates had to use a ruler and the scale bar on the diagram to find the diameter of the cell in micrometres. Although the question instructed candidates to give the answer to the nearest micrometre, many did not give a whole number. Many gave an answer of 4, where they had presumably measured the correct length in centimetres, but then not used the scale to convert this value to 8 micrometres. 8 of 12

9 There were some very comprehensive responses which included all components of the blood with correct functions. Those who added an incorrect function could only gain a maximum of 4 marks out of the 5 available. Most candidates wrote about red blood cells and stated that they carried oxygen around the body. Functions given for white blood cells were sometimes too vague. For example, to kill pathogens was only credited if no other points had been made. References to white blood cells eating, fighting or attacking pathogens were ignored. Plasma and platelets were often named, but the functions of these tended to be less well understood. This question had a maximum of 5 marks, which was scored by one-fifth of candidates; the question differentiated very well across the ability range. In (i), candidates had to describe what would happen if blood of the wrong blood group were transfused into a person. Vague answers such as it would kill the patient were not credited. A reference to the blood cells agglutinating, or clotting, or small blood vessels becoming blocked was required. Responses which did not gain credit included it would cause an infection, make the person ill or cause a heart attack. In (ii), it had to be clear in the response that universal donor meant that blood group O could be given to any blood group. Some responses suggested that blood group O could receive any blood group, which was incorrect. Many candidates correctly stated that blood group O is the most common, but this did not answer the question. In (iii), the required answer was that donated blood is tested for pathogens, or an example of a pathogen. Other responses that were given credit included testing for HIV, STDs and infections. Disease was ignored. Question 11 This was the first of three questions common to both the Foundation and Higher Tier papers. It was about the effect of temperature on the rate of digestion of fat by lipase. Only a quarter of Foundation Tier candidates knew that lipase was the enzyme that digested fat, and even fewer knew that the reaction took place in the small intestine the stomach being a common incorrect answer and even the pancreas. Details were given in the question about how some students carried out an investigation into the effect of temperature on the activity of the enzyme. In part (i), candidates could have chosen any two from the seven control variables mentioned in the account of the investigation. Five of these were given in the labels on the diagram of the apparatus, but most candidates attempted to find the answer in the bulleted list of procedural points, choosing the 5 drops of indicator solution and the equilibration time for the two test tubes in the water bath before mixing (the latter often being expressed inadequately). Many thought that the temperature, or time, was a control variable and some even cited the volume of water in the water bath. In (ii), less than a third of candidates were able to suggest why the two test tubes were kept in the water bath for 10 minutes before mixing a common error was that this allowed the tube contents to warm up or to reach the optimum temperature rather than to reach the temperature being investigated. In (iii), the simple explanation of why the indicator changed from pink to colourless was that fatty acids were produced in the reaction. Despite this having been shown in the equation describing the reaction on the facing page, only a tiny minority of candidates gave this answer, although about a fifth at least understood that acid was produced. Some thought that the undigested fat itself was alkaline, others that it was acidic; some did not understand the ph scale and thought that 9 of 12

10 the mixture had become more alkaline. Many had no idea that the ph change related to the digestion of fat. (d) Candidates were provided with a table of results showing the time taken to digest the fat at six different temperatures. In part (i), many thought that the fat was digested more quickly at 20 o C than at 10 o C because 20 o was nearer to body temperature. Hardly any understood that the molecules in the mixture had more energy at 20 o C. In (ii), around one-sixth of candidates knew that the enzyme would have been denatured at 60 o C, resulting in no reaction at this temperature. Some, unfortunately, believed that the enzyme was killed and many weak candidates just described 60 o C as being too hot. Almost two-thirds of candidates scored 1 mark in this question for stating that no test had been performed at 35 o C, so the claim that this was the temperature at which the enzyme worked best was unjustified. Some went on to state that the enzyme was only tested at 30 o C and 40 o C, which was regarded by examiners as being the same point. Only a very small proportion of candidates were able to suggest a second reason why it was not valid to claim that 35 o C was the best temperature such as it possibly being difficult to tell when the end point had been reached, or the times being reported only to an accuracy of one minute, or there being no mention of any repetition of the measurements. Question 12 This was the second of the three common questions. It was about the structure and functioning of the heart and the effect of exercise on heart rate. In part (i), less than one-fifth of candidates correctly related the three given functions to the correct chambers of the heart. There was marginally more success in part (ii) for identifying valve C (the mitral valve) as the one that would close when the blood pressure in the left ventricle is greater than that in the left atrium. However, in (iii), just over a quarter of candidates knew that the function of valves was to prevent the backflow of blood weaker candidates described the function as to control blood flow, which lacked sufficient detail, or to help pump the blood or to separate oxygenated blood from deoxygenated blood, which were simply incorrect. Correct explanations of why a pulse could be detected in an artery but not in a vein usually referred to the higher pressure in the artery, sometimes accompanied by the fact that arteries carried blood away from the heart, but hardly any candidates related the pulsations to the rhythmic beating of the heart. Less than one-third of candidates scored even 1 mark out of 3 in this section. There was more success in part (ii), for relating a higher heart rate to an increased rate of exercise. Candidates who gained marks in this section related the higher heart rate to the need for more oxygen, but few mentioned that more glucose would also be needed. Respiration, and the need for more energy were mentioned by some, but a fair proportion lost the energy mark as they stated that more energy would be produced or made which, of course, contradicts the physical law of conservation of energy. Some realised that more of the waste products, carbon dioxide and/or lactic acid, would need to be removed by the blood. Many forgot to relate the situation to the increased heart rate by stating that more blood would need to be pumped around the body (or pumped at a faster rate). Three-quarters of candidates scored at least 1 mark, but very few scored all of the 4 marks available. 10 of 12

11 Question 13 This was the third of the three common questions. It was about the exchange of materials across the placenta and the effects of a mother smoking during pregnancy on the growth of her unborn child. Not many candidates knew the properties of an ideal exchange surface, i.e. a large surface area, thin, and a good blood supply, all of which were evident in the diagram. Many just described the blood vessels and there was a misconception among some candidates that blood flowed from the mother into the fetus. The large surface area was mentioned by some, but very few described the surface as being thin, or just a few cells thick, or that the mother s and fetus s blood vessels were close together. Almost half the candidates scored no marks in this section, while just 1% scored all 3 marks. In part (ii), almost three-quarters of the candidates knew at least one correct substance that passed from the mother to the fetus across the placenta, but very few were able to give two. Oxygen and glucose were the most common correct answers, but food or nutrients was considered too vague, although the latter were common answers. In this section, candidates were presented with data, in the form of two bar graphs, showing the effect of mothers smoking cigarettes during pregnancy on the birth weights of their babies. In part (i), many candidates were unable to give the correct range of birth weights of babies from mothers who smoked some gave the full range of weights on the x-axis, others read just the lower figures labelling each column (1.50 to 4.80) instead of the correct 1.50 to 5.09 and, inevitably, some read the figures from the wrong graph. Part (ii) was answered much more successfully, with almost three-quarters correctly reading the value 3.60 to 3.89 from the correct graph for the most common birth weights of babies from nonsmoking mothers. In part (iii), candidates were told the number and percentage of babies that were underweight for mothers who smoked and asked to calculate the percentage for non-smoking mothers. Even with these clues, only one sixth of the candidates were able to calculate the correct value of 1.6 per cent. Errors included miss-reading the value from the graph and rounding the answer incorrectly (e.g. to 1.64 or 1.7) Given that carbon monoxide from cigarette smoke combined with haemoglobin in the mother s blood and prevented it from carrying out its normal function, most candidates were able to interpret this as meaning that less oxygen would be carried in the mother s blood. Only a few candidates related this to reduced respiration (or energy release) in the fetus and/or to less growth. Answers ending...which would affect growth lacked sufficient specificity. Some candidates thought that the carbon monoxide was transferred to the fetus, others expressed their answers poorly by referring to no oxygen / no respiration / no growth, and some even thought the baby would suffer from some type of deformity. At Foundation Tier, quite a lot of the candidates thought the carbon monoxide would affect the lungs of the fetus or cause cancer. 11 of 12

12 Mark Ranges and Award of Grades Grade boundaries and cumulative percentage grades are available on the Results Statistics page of the AQA Website. Converting Marks into UMS marks Convert raw marks into Uniform Mark Scale (UMS) marks by using the link below. UMS conversion calculator 12 of 12