GCSE Science A / Biology

Transcription

1 GCSE Science A / Biology BL1HP Report on the Examination 4405 / 4401 June 2014 Version: 1.0

2 Further copies of this Report are available from aqa.org.uk Copyright 2014 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 was evidence that a minority of students had been entered for the Higher tier examination, when they may have benefitted from taking the Foundation tier paper. Marks appreciably below 15 out of 60 indicate a poor depth of factual knowledge and a weakness of understanding and application such that these students may be more confident sitting the Foundation tier examination. Students should be encouraged to arrive at the examination properly equipped; the lack of the correct writing equipment (a black ball-point pen or black ink and a pencil) or the lack of a calculator may have consequences on performance. The quality of writing, and consequent legibility of scanned scripts, compromises students work and possibly affects the outcome of their efforts. Students may also disadvantage themselves by poor examination practice. Previous advice regarding the extension of answers around white space within the paper appears to have been acted upon. Large numbers of students continued their answers on additional pages. This often meant that single words for several answers were written on an additional page. The paper revealed a number of misconceptions, these were particularly evident in questions 7(a) and 8(b) but appeared elsewhere too, as will be referred to in the report on specific questions, below. Question 1 (Standard Demand) (a) This question appeared to be fairly straightforward for the large majority of students. Most students drew block-shaped pyramids, rather than an equally acceptable triangle with three layers. Those who did not gain both marks commonly drew a correct pyramid shape, but labelled it in the reverse order, showing humans as having the largest biomass and grass the smallest. Some, often more able, students felt the need to include additional information such as producer and herbivore. These were not required and were ignored by examiners whether correct or incorrect. (b) (i) A very large proportion of students realised that food chain C would provide the greatest proportion of biomass and energy to humans. As might have been expected, food chain B was the more attractive alternative to those who did not give the correct answer. (b) (ii) Those students who had not identified C in part (b)(i) were at a considerable disadvantage here, although some of those who suggested either of the other food chains would be most efficient could still gain two of the marks. The first mark was for identifying that a shorter food chain would be most efficient; this could be expressed in a number of ways, such as fewer steps or fewer trophic levels but also in a simpler way such as food being passed directly from the plant to humans. Some students chose to only go down one route, referring to either energy losses or to biomass losses, whilst more able students gave both of these. Those students who gained all three marks, tended to get the second and third marking points by giving what seemed like a well learned list such as energy and biomass being lost by intermediate organisms in respiration, keeping warm, movement and faeces. The examiners were pleased that relatively few students referred to energy being used for respiration or to energy being made by respiration, most correctly quoting energy being released by 3of 10

4 respiration. Where either of the two errors was given, the mark for energy losses was not given. Students who had given food chain B as their answer to part (b)(i) were generally under the misconception that biomass builds up along the food chain, so that the humans would be eating not only the biomass of the trout, but also that of the frogs, grasshoppers and plants, which would be accumulated en route. Alternatively those who chose food chain A often suggested that humans would get more biomass from sheep than from trout or plants because sheep are bigger, so contain more biomass, clearly not understanding that biomass refers to the population rather than to the individual. Question 2 (Standard Demand) This question tested students knowledge of adaptations to dry conditions, however the strong reference to desert habitats in the question meant that examiners could also credit descriptions of adaptations to these habitats; thus for example, descriptions of camels having long eyelashes to protect themselves from wind-blown sand were accepted. Most students also referred to both animal and plant adaptations, with descriptions of the latter usually being better. Very many students knew a large number of adaptations and were often keen to write about every one, paying little heed to the space available. A large number of students who wrote well over twice as much as was required and this must have impacted on the completion of the paper. Students are advised to plan their time carefully in order to ensure they complete the paper. Despite there being many acceptable adaptations for both plants and animals, it was evident that misconceptions are common. It appears to be almost universally believed that the hump in camels contains water and it was very rare for students to clearly express the idea that the fat stores in the hump can be metabolised to release water. A second common misconception was that the spikes on cacti increase surface area for light absorption, rather than reduce the surface area from which water may be lost. Others believed that the whole purpose of the spikes is to stop animals getting at water in the plant. Students who expressed ideas about large ears in terms of keeping cool rather than increasing heat loss were not given full credit. However, as relatively few examples were required to gain access to Level 3, many students still wrote about enough examples to achieve this. Examiners were looking for clear examples of adaptation to dry / desert habitats and not examples which could apply to any habitat, therefore descriptions about camouflage were not credited. Similarly, the idea that plants in dry habitats may have wax coatings on their aerial parts was insufficient as again this is true of any terrestrial plant; here examiners were looking for the idea of thicker wax. A Level 1 answer was matched by at least one simple description of a suitable adaptation without any attempt to correctly describe how these adaptations helped the organism(s) to survive. A simple statement such as camels have long eyelashes sufficed. Students were awarded Level 2 if they gave more than one suitable adaptation and then attempted to describe how at least one of these helped the animal or plant to survive. An answer such as cacti have long roots. Camels have wide feet so they do not sink into the sand fell into this 4of 10

5 category. An attempt to describe how wide feet help the camel had been made but an appreciation of them increasing the surface area so being able to reduce pressure had not. To achieve Level 3, students needed to give examples of adaptations shown by both plants and animals (as stated in the question) and to clearly describe how at least one of these helped survival in dry conditions. An answer such as cacti have spikes for leaves to reduce the surface area for water loss. Some animals are nocturnal to avoid the heat of the day was just enough to match Level 3. Both animals and plants were correctly referred to and the spiky leaves of a cactus were described in terms of how they allowed survival. Students should always give careful consideration to the descriptive words they choose to use in answers. Large, for example, does not adequately convey the idea of long or wide-spreading in relation to roots; whilst big does not necessarily imply wide with reference to feet. They should also use comparative words like more or less where necessary. A minority of students wrote about adaptations per se and discussed animals such as polar bears. The Quality of Written Communication element of this question rarely caused any problem for students. For the most part, students appeared to have made particular efforts with punctuation and paragraphing along with organising their answer adequately, to match the level of biological knowledge expressed. Question 3 (Standard Demand) (a) Considering that the stem of the question referred twice to decay many students failed to link this process to microorganisms. Those who did often referred to respiration by these microorganisms in their explanation. However how this respiration was able to keep the eggs warm for many weeks was less well understood. The misconception that heat or energy is somehow created or produced (rather than being released ) by respiration was common, although the examiners were pleased to note that this was less common than in previous years. A further misconception, also common, was that the carbon dioxide released by respiration would keep the eggs warm. How this might be achieved was often not clear, although some extended their explanation to the idea that carbon dioxide, as a greenhouse gas would help to retain heat. The examiners were also pleased by the increased use of energy, rather than heat in students responses. Furthermore this appeared in answers for students at all levels of achievement. (b) (i) Many students realised that letting oxygen in enabled the (embryos in the) eggs or the microorganisms to respire. Others realised the need to let heat in or out depending on the temperature outside. There were many vague, unscientific responses - with the vents letting in light to allow photosynthesis of the (dead) plants, letting in warmth, and being closed to keep out seawater at high tide. As in part (a), not letting carbon dioxide (often just carbon) out would, according to some, have caused the nest to overheat. Despite the information provided, some students appeared to believe that the parent megapode sits on the eggs, under the layer of sand. Other unacceptable suggestions included exclusion of predators and the reduction of odours from the decay process in the environment. A misunderstanding of energy transfer was shown by a significant minority of students referring to cold getting in. 5of 10

6 (b) (ii) Roughly half the students realised the importance of maintaining a sex balance, described in one way or another or of ensuring that the population contained both male and female birds. Some went on to describe the importance of this in terms of survival of the species. Those who failed to get the mark often discussed the wishes of the parent bird in terms such as she might want a boy / girl or missed the point about gender balance completely, by suggesting that they need females to lay eggs, apparently being unaware that males might also be necessary for the reproductive process. Question 4 (Standard and High Demand) (a) Identification of both diseases was required here for one mark. Most students were able to do this. Those who did not, often gave one correct answer along with another from a long list of diseases they might have heard of. (b) (i) Most students showed their working. The most common error was dividing 630 by 504; it did not occur to these students that there was something wrong with a percentage above 100 in this case, although some possibly recognising this, converted their answer to 1.25% or 12.5%. Another common error was subtracting the two numbers. Mis-copying the numbers, 540 instead of 504, resulted in no marks being awarded. Some, possibly misread the question, and arrived at 20 %, i.e. those who had been vaccinated, rather than those who had not, although depending on the working shown, examiners may have been able to award some credit. (b) (ii) Those students who did not recognise the importance of to the population as a whole in the question often answered in terms of children being less likely to catch any of the diseases. There was evidence of misunderstanding here, in that some described children being less likely to catch MMR. However, roughly half the students did recognise that as a result of improved protection the diseases would be less likely to spread or there would be less chance of an epidemic. (c) (i) Students appear to be well versed in the composition of vaccines and a large proportion gained the mark here, referring to dead or weakened pathogens. Dead disease was a not infrequent, unacceptable response. (c) (ii) The majority of students explained that white blood cells produce antibodies. Beyond this, there were often vague ideas about armies of antibodies lying in wait for future invading pathogens. There was only infrequent understanding that on re-infection the white blood cells will produce the same type of antibodies more quickly and it is these antibodies that kill the pathogen. There was, however, much vague reference to antibodies fighting the pathogen, fighting the infection or killing the disease. (d) (i) There were a few good, detailed answers here, clearly identifying the ideas shown in the mark scheme. Many students got part way, explaining that viruses live inside cells. Students often showed poor understanding of technical terminology here, referring to antibiotics treating, curing or fighting, rather than killing the pathogen. (d) (ii) The idea of antibiotic resistance appears to be fairly well known, although once more, poor use of technical terminology often resulted in no mark being awarded. Those students who referred to the bacteria becoming immune were not given credit, nor were those who suggested that the infection develops resistance. Others appeared to believe 6of 10

7 that repeated use of antibiotics would make people resistant to them, so the antibiotic became ineffective. Question 5 (Standard and High Demand) (a) (b) (c) The link to the relay neurone and the arrow showing the direction of the impulse resulted in a high proportion of students correctly identifying the motor (neurone). The small percentage of students who did not give the correct answer usually offered sensory. Although another relay neurone would have been accepted, the examiners were not aware of any student giving this response. Students are expected to know that information crosses the synapse in the form of chemicals. It was hoped that students would interpret the diagrams in the figure and so gain further marks. Neither the release of the chemical from the relay neurone, nor its attachment to neurone X are expected specification knowledge, however the diagrams clearly showed both of these stages in transmission. Better students recognised that the chemical started off in the relay neurone, some referred to vesicles, exocytosis and to neurotransmitters released. Only the best students went further to describe the chemical attaching to neurone X, again some using terms such as receptors in their answer, showing that they had revised this area of the specification far beyond the requirements. A minority of students had the chemical and electrical parts of the process reversed, describing chemicals passing down the neurones and turning into an electrical impulse to cross the synapse. Students are expected to know that muscles respond by contraction. Relatively few students offered this term in either part of their answer, thus limiting themselves to just one of the two marks for describing a weaker or no response (for curare) and a stronger response (for strychnine). Students are not expected to have any knowledge of ideas about how these responses are created, so the examiners accepted a wide range of possible alternative terms, such as slower / faster or decreased / increased response. However a number of students denied themselves any opportunity of the marks by not answering the question. Instead of referring to responses by the muscles, they discussed the decreased or increased impulse in neurone X. Question 6 (Standard and High Demand) Those students who had learned the specification details about thalidomide did well in part (a). Others displayed a vague knowledge, mixed up different ideas or invented possible answers. (a) (i) That thalidomide was originally developed to treat sleeping problems (often quoted as insomnia ) or as a sleeping pill was generally well known. (a) (ii) Slightly more students gained this mark for morning sickness than gained the mark in (a)(i). The examiners did not accept weaker, indeterminate diseases, such as sickness or illness during pregnancy. (a) (iii) The most common omission was to refer simply to deformity in babies, rather than to provide the extra information that it was the limbs that were deformed. There were a number of acceptable descriptions such as short although a few students incorrectly suggested that the drug caused extra limbs to grow. 7of 10

8 (a) (iv) Many students realised that the lack of testing on pregnant animals / women had resulted in the failure to detect the harmful effects of thalidomide. Weaker students could only suggest that the drug had been insufficiently tested, without explaining the details of how the testing had been inadequate. (b) (i) Students generally appear to have a very weak understanding of what dependence involves. There were many suggestions of addiction and reference to withdrawal symptoms along with suggestions that the body cannot function without the drug. However relatively few students knew that drugs change chemical processes in the body. (b) (ii) Again, many students wrote well beyond the available space in this question. A large proportion gained one mark for quoting one example of an unclassified drug that caused greater, or equal dependence than a named classified drug. Many then went on to give a second different example and collected a second mark. An alternative route to one of these marks was to generalise that some of the unclassified drugs caused greater dependence than some of the classified drugs. Many weaker students ignored the introduction to the question, believing that the data was about numbers of users who were dependent or the increased chance of becoming dependent. Either of these misunderstandings made it difficult to gain marks here. Other students only quoted numbers from the graph, nicotine has a dependence of 2.3 and LSD has a dependence of Many students gave the impression that they were surprised by the data in Figure 4, not realising that dependence is only a small part of drug classification. Some even suggested that the data provided strong evidence for de-classification of all drugs. (b) (iii) Weak answers included effects on, rather than possible harm to, the body. Many got no further than restating dependency despite the request in the question for other information. Many others referred to the impact on tax revenue of making nicotine or alcohol classified drugs. It is of interest to the examiners that within three weeks of the examination having been taken, khat was reclassified as a Class C drug hence teachers using this question for future revision may wish to amend the information. Question 7 (Standard and High Demand) (a) (i) There was common confusion between the two theories of Darwin and Lamarck, in particular in terms of longer noses being needed, environmental change causing the changes and characteristics or noses being passed on. However, examiners believed that the similarity between this example and the often quoted example concerning the evolution of longer necks of giraffes, helped many students to formulate their responses. Indeed some students discussed giraffes only, whilst others described the elephant s neck evolving. There was some confusion amongst students who described competition for limited food between Phiomia and African elephants, which the elephant won or they alternatively went down the speciation route, describing isolation and its effects. There were many answers that appeared to lack understanding of the timescale involved in evolution, implying that this evolution might be completed within one generation. Those students who only repeated the standard story about natural selection could not access all the marks; there needed to be reference to this particular example. However good students, who had carefully revised this topic did well and there was a good proportion of students scoring at least three marks. 8of 10

9 (a) (ii) Again examiners were looking for responses that were linked to this particular example. Thus those who discussed Phiomia stretching its trunk without reference to food, could not access the first mark, whilst those who referred to genes being passed on, rather than the long nose being passed on, could not access the second mark; in addition, those who simply suggested that the long nose was passed on, without informing the examiner as to what it was passed on to, offspring, were also not awarded the second mark. (b) (i) Those students who did not read the information and question carefully often went down the route of opposition to religious views. However, the question had specifically excluded this from the possibilities by asking why scientists were unable to decide which of the two theories was right, rather than why neither were fully accepted at the time. Students should realise that in the mid eighteenth century there was some knowledge of fossils and there was also other evidence for evolution theories, although it was rather disjointed, and so answers which stated that no evidence existed could not be credited. (b) (ii) Many students gained the mark here for stating that people believed God made all living things, or words to that effect. Phrases such as against God or religious views were considered to be insufficient. Other quite common misconceptions included The Big Bang Theory, and meteors from outer space, neither of which had been proposed in the 1800s. Question 8 (High Demand) (a) (b) A number of students showed excellent knowledge of the process of genetic engineering and, had five marks been available would have gained all five. Most students were able to invoke enzymes at some relevant point and students often went on to describe the cutting out of genes, although many were imprecise as to what these were cut from, often suggesting the bacterium or the nucleus rather than the bacterial chromosome. Descriptions of the process thus far would have been sufficient to gain full marks. Where students more often fell down was in describing to where and when the excised gene should be transferred. Many stopped at the maize plant, a maize cell whilst others again got as far as the nucleus, rather than going all the way to a maize chromosome. Relatively few students realised that this transfer would need to be done at an early stage of development or that it might be done at the embryonic stage. There is considerable misunderstanding about the use of and problems associated with genetically engineered plants. Many students appeared to believe that individual farmers would need to go around to every maize plant and genetically engineer it, suggesting the disadvantage that this would take a long time. There was further confusion about what the GM maize plants would contain, with many believing it was the Bacillus itself and that people might catch diseases from it, or that the bacteria might mutate. Other students suggested that the GM plants would lack genetic variety leading to the potential for all such maize crops to be wiped out by a new strain of pathogen. These students were clearly unaware that non-gm crop plants also have no genetic variety and so the same problem exists for these crops. A number of students also discussed a wider variety of genetic modifications, referring to drought resistance, increased shelf-life and herbicide resistance, some went as far as to suggest that the Bt gene could confer these advantages; however examiners ignored these examples which were not specific to the question about growing this particular GM maize. 9of 10

10 Previous reports on this type of question have always explained that marks are not awarded for simply repeating or paraphrasing the information provided. Thus answers which expressed opposition to genetic engineering because bees are needed to pollinate some crops could not gain credit; instead these students needed to add just a little value to the information, bees may be killed, so there would be less pollination could gain two marks. There were many acceptable responses referring to greater crop yield, but not just more maize plants. Also seen were damage to food chains and reduced biodiversity. Students were not as good when it came to the effect of GM crops on humans, often suggesting only that allergies could be caused or people may be harmed, failing to refer to the specification statement referring to when the crop is eaten. 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 10 of 10