Page 13 24. The statements below describe events that occur following the engulfing of a pathogen by a phagocyte of the mammalian immune system. P long term survival of lymphocytes Q antigen presentation to lymphocytes R antibody production by lymphocytes S clonal selection of B lymphocytes The correct sequence in which these events occur is A Q, R, S, P B R, Q, P, S C S, Q, P, R D Q, S, R, P. 25. Florida scrubjays have evolved a co-operative breeding system in which helper birds assist breeding pairs in raising young. The table below compares the effect of helpers on the breeding success of birds that are either experienced or inexperienced breeders. Breeding experience of breeding pairs Average number of offspring reared Without helpers With helpers inexperienced 1·24 2·20 experienced 1·80 2·38 Helpers increase the average number of offspring reared by inexperienced breeding pairs compared to experienced breeding pairs by A 19% B 23% C 45% D 60%. [END OF SECTION 1. NOW ATTEMPT THE QUESTIONS IN SECTION 2 OF YOUR QUESTION AND ANSWER BOOKLET] Page 14 [BLANK PAGE] do not write on this page Page 15 [BLANK PAGE] do not write on this page Page 16 [BLANK PAGE] do not write on this page AH FOR OFFICIAL USE Fill in these boxes and read what is printed below. Number of seat Town © Mark Full name of centre Forename(s) Surname Scottish candidate number Date of birth Year Day Month National Qualications 2016 Total marks — 90 SECTION 1 — 25 marks Attempt ALL questions. Instructions for completion of Section 1 are given on Page 02. SECTION 2 — 65 marks Attempt ALL questions. A Supplementary Sheet for Question 1 is enclosed inside the front cover of this question paper. Write your answers clearly in the spaces provided in this booklet. Additional space for answers and rough work is provided at the end of this booklet. If you use this space you must clearly identify the question number you are attempting. Any rough work must be written in this booklet. You should score through your rough work when you have written your final copy. Use blue or black ink. Before leaving the examination room you must give this booklet to the Invigilator; if you do not you may lose all the marks for this paper. X707/77/01 MONDAY, 9 MAY 9:00 AM – 11:30 AM A/HTP Biology Section 1 — Answer Grid and Section 2 Page 02 SECTION 1 — 25 marks The questions for Section 1 are contained in the question paper X707/77/02. Read these and record your answers on the answer grid on Page 03 opposite. Use blue or black ink. Do NOT use gel pens or pencil. 1. The answer to each question is either A, B, C or D. Decide what your answer is, then fill in the appropriate bubble (see sample question below). 2. There is only one correct answer to each question. 3. Any rough working should be done on the additional space for answers and rough work at the end of this booklet. Sample Question The thigh bone is called the A humerus B femur C tibia D fibula. The correct answer is B — femur. The answer B bubble has been clearly filled in (see below). A B C D Changing an answer If you decide to change your answer, cancel your first answer by putting a cross through it (see below) and fill in the answer you want. The answer below has been changed to D. A B C D If you then decide to change back to an answer you have already scored out, put a tick (3) to the right of the answer you want, as shown below: A B C D or A B C D Page 03 A B C D 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 SECTION 1 — Answer Grid [Turn over Page 04 [BLANK PAGE] do not write on this page Page 05 [Turn over for next question do not write on this page Page 06 MARKS DO NOT WRITE IN THIS MARGIN SECTION 2 — 65 marks Attempt ALL questions It should be noted that question 11 contains a choice. 1. Read through the Supplementary Sheet for Question 1 before attempting this question. (a) Refer to Figure 2 in the Supplementary Sheet for Question 1. (i) Use the data to describe the egg-laying of uninfected mosquitoes. (ii) If the box plots were perfectly symmetrical, mean values for egg-laying would be very close to median values. State what can be deduced about the mean number of eggs laid by infected mosquitoes in relation to the median value. (iii) Describe the effect that Plasmodium infection has on the fecundity of mosquitoes used in the study. (b) Refer to Figure 3 in the Supplementary Sheet for Question 1. (i) The data shows that infection by Plasmodium appears to increase the longevity of female mosquitoes. Explain why the difference between the two groups can be regarded as significant. (ii) Suggest a benefit to the parasite of its vector living longer. 2 1 1 1 1 Page 07 MARKS DO NOT WRITE IN THIS MARGIN 1. (continued) (c) Refer to Figure 4 in the Supplementary Sheet for Question 1. (i) Explain what the lines of best fit indicate about the relationship between longevity and fecundity in both infected and uninfected mosquitoes. (ii) State, with justification, whether or not this data is reliable. [Turn over 2 1 Page 08 MArKS DO NOT WRITE IN THIS MARGIN 2. Scientists have reported that neurons produced in cell culture from human stem cells have the potential to function when grafted into the site of a spinal injury in rats. (a) State why the cell culture medium in which the neurons were cultured should contain serum. (b) Scientists used a haemocytometer to perform a cell count to calculate the number of stem cells that developed into neurons. The diagram below represents a sample from a culture placed in a haemocytometer and viewed under a microscope. The grid is 0·1 mm in depth. Key: 1 mm Neuron Stem cell 1 mm (i) Calculate the number of neurons in 1 cm3 of the culture. Space for calculation neurons (ii) Suggest one disadvantage of cell counts performed using the haemocytometer. 1 1 1 Page 09 MARKS DO NOT WRITE IN THIS MARGIN 2. (continued) (c) Bright field microscopy was used to view the cells grafted into the site of spinal injury. State another type of biological material that can be viewed using bright field microscopy. (d) In studies involving animals, state one way in which harm to the animals can be minimised. [Turn over 1 1 Page 10 MARKS DO NOT WRITE IN THIS MARGIN 3. Multiple sclerosis (MS) is a neurological condition in which the body’s immune system destroys the myelin sheath that surrounds and insulates nerve axons. A clinical study was carried out into the effects of a new drug interferon beta-1b for this condition. A randomised trial, with a negative control group (placebo), was carried out across four different health centres. During the study patients were given one of three treatments: 0·00 mg (placebo), 0·05 mg or 0·25 mg interferon. The patients administered the drug themselves at home. The study measured how effective the drug was by asking patients to record any worsening of symptoms after 2 years of treatment. The study involved 372 patients aged 18-50 years. Fourteen patients dropped out before completing the trial. Patients’ results are shown in Table 1. Table 1 Level of interferon beta-1b in treatment (mg) Proportion of patients reporting no worsening of symptoms after 2 years of treatment (%) 0·00 16 0·05 18 0·25 25 At one health centre 52 patients were MRI scanned every 6 weeks to monitor any new damage to nerve tissue. The results are shown in Table 2. Table 2 Level of interferon beta-1b in treatment (mg) Proportion of patients showing new nerve damage (%) 0·00 29 0·05 no data recorded 0·25 6 (a) Identify the independent variable in this trial. (b) This trial was carried out in vivo. State one advantage of this type of trial. 1 1 Page 11 MARKS DO NOT WRITE IN THIS MARGIN 3. (continued) (c) Explain why a placebo group was included in this trial. (d) Suggest one way in which the results of the trial may not be reliable. (e) Describe an ethical issue that the researchers would need to consider before this trial. (f) Suggest two conclusions that can be drawn from the results of this trial. Conclusion 1 Conclusion 2 [Turn over 1 1 1 2 Page 12 MARKS DO NOT WRITE IN THIS MARGIN 4. Sickle cell anaemia is an inherited blood disorder that reduces the ability of red blood cells to transport oxygen round the body by changing the structure of haemoglobin. In sickle cell anaemia, the primary structure of a haemoglobin subunit is altered; the amino acid glutamic acid is substituted by the amino acid valine. The structures of glutamic acid and valine are shown below. COOH C H H2N C H H C H H C O O COOH C C CH3 H2N H H3C H Glutamic acid Valine R group (a) State the class of amino acids to which valine belongs. (b) Identify one type of secondary structure shown in the haemoglobin molecule in the figure below. Haem Haem Haem Haem 1 1 Page 13 MARKS DO NOT WRITE IN THIS MARGIN 4. (continued) (c) Explain the term cooperativity in relation to oxygen binding to haemoglobin. (d) The graph below shows the oxygen saturation of haemoglobin at different oxygen pressures for an individual with normal haemoglobin and for another individual with sickle cell haemoglobin. Normal haemoglobin Sickle cell haemoglobin 0 10 20 30 40 50 60 70 80 90 100 Oxygen pressure (units) 100 90 80 70 60 50 40 30 20 10 0 Oxygen saturation (%) Key: Use the graph to compare the oxygen saturation of normal and sickle cell haemoglobin as oxygen pressure increases. (e) Molecules of sickle cell haemoglobin clump together preventing access to oxygen binding sites. Suggest why this is a result of the substitution of glutamic acid by valine. 1 2 1 [Turn over Page 14 MARKS DO NOT WRITE IN THIS MARGIN 5. Describe the structure of spindle fibres and explain their role in the movement of chromosomes during cell division. 4 Page 15 MArKS DO NOT WRITE IN THIS MARGIN 6. The sodium potassium pump (Na/KATPase) is a membrane protein found in animal cells. (a) Give one function of sodium potassium pumps. (b) Describe the role of ATP in altering the affinity of the pump for sodium ions (Na+). (c) Digoxin is a chemical that inhibits the sodium potassium pump by binding to the potassium ion (K+) binding site as shown in the diagram below. Outside cell Inside cell K+ and digoxin binding site Cell membrane 2 K+ Na+ binding site 3 Na+ Explain why binding by digoxin prevents further binding of sodium (Na+) ions by the pump. 1 2 2 [Turn over Page 16 MArKS DO NOT WRITE IN THIS MARGIN 7. Binding of antidiuretic hormone (ADH) to its receptor on the plasma membrane of kidney collecting duct cells triggers the recruitment of water channel proteins as shown below. ADH Activated G proteins recruit water channel proteins Extracellular Intracellular Plasma membrane } (a) (i) Name the water channel protein involved in this process. (ii) Name the process by which a response within the cell is triggered by the binding of ADH to its cell surface receptor. 1 1 Page 17 MArKS DO NOT WRITE IN THIS MARGIN 7. (continued) (b) A urine output of greater than 0·05 litres per kg body mass per day is considered diagnostic of diabetes insipidus. The bar chart below shows the urine output over 6 days of a 70 kg individual being investigated for diabetes insipidus. During days 3 and 4 the individual was treated with the drug desmopressin, a synthetic form of ADH. 12 10 8 6 4 2 0 1 2 3 4 5 6 Day Total daily urine output (litres) (i) Use the data to confirm that a diagnosis of diabetes insipidus is correct for this individual. Space for calculation (ii) Give evidence from the graph that supports the conclusion that desmopressin is an effective treatment. (iii) Diabetes insipidus results from failure to recruit water channel proteins to the cell membrane. Identify the cause of recruitment failure in this individual. 1 1 1 [Turn over Page 18 MARKS DO NOT WRITE IN THIS MARGIN 8. The diagram below shows the pairing of homologous chromosomes in a cell undergoing meiosis. chiasma formation (a) Name the type of cell that undergoes meiosis. (b) (i) Explain how the chiasma formation between the paired homologous chromosomes shown in the diagram leads to variation. (ii) Name the process that ensures haploid gametes produced by meiosis contain a mixture of chromosomes of maternal and paternal origin. 1 2 1 Page 19 [Turn over for next question do not write on this page Page 20 MARKS DO NOT WRITE IN THIS MARGIN 9. In 1971, biologists moved five adult pairs of Italian wall lizards (Podarcis sicula) from their small home island of Kopiste to the neighbouring small island of Mrcaru, which did not have a lizard population. On their return in 2005 Mrcaru was found to have a large population of P. sicula (confirmed by genetic analysis) with significantly larger heads and a greater bite force than the lizards from Kopiste. Their digestive systems were also found to contain microorganisms that assist in the breakdown of plant cell walls. The summer diets of the two lizard populations are shown below. Key: plant matter arthropods other Kopiste Mrcaru Island 1·0 0·8 0·6 0·4 0·2 0·0 Proportion of total food mass (a) Describe the most significant change in the summer diet of the lizards on Mrcaru. 1 Page 21 MARKS DO NOT WRITE IN THIS MARGIN 9. (continued) (b) (i) Explain how the information supports the conclusion that the changes to the lizard population on Mrcaru were the result of natural selection. (ii) Evolution of the lizards on Mrcaru occurred very rapidly. State one factor that can increase the rate of evolution. (c) This study involved taking representative samples of the lizard populations on the two islands. State one feature of a representative sample. [Turn over 2 1 1 Page 22 MARKS DO NOT WRITE IN THIS MARGIN 10. The Figures below show male and female capercaillies (Tetrao urogallus) which are found in some Scottish pine forests. Males are much larger and darker than females and the breast feathers of the male have a metallic green sheen. female capercaillie male capercaillie (a) State the term used to indicate the different body forms of males and females belonging to this species. (b) Capercaillies are a lekking species. Males perform displays during which they fan their tails, hold their wings down and make a variety of sounds. These features, which are attractive to females, are thought to serve as honest signals. (i) Explain what is meant by a lekking species. (ii) Explain why this display is often given as an example of sexual selection. (iii) If the display provides honest signals, state the benefit that may be obtained by females receiving these signals. 1 1 1 1 Page 23 MARKS DO NOT WRITE IN THIS MARGIN 10. (continued) (c) Peacocks are the males of another lekking bird species, Pavo cristatus, whose natural habitat is the dense forests of South-East Asia. As well as the visual stimulus of a tail-feather display, peacocks, during mating, can emit a distinctive “hoot”. These hoots are loud enough to be heard by other females, out of sight of the lek, who may be attracted by the calls and provide the dominant males at the lek with additional mating partners. (i) Suggest why auditory stimuli are advantageous to species inhabiting forest ecosystems. (ii) Recent research has found that some peacocks emit hoots in the complete absence of females at the lek. Females are still attracted to the lek by these sounds. Such “solo” hoots have been described as “dishonest signals”. Explain what is meant by a “dishonest signal” in this behaviour. [Turn over for next question 1 1 Page 24 MARKS DO NOT WRITE IN THIS MARGIN 11. Answer either A or B in the space below and on Page 25. A Discuss reproduction under the following headings: (i) costs and benefits of sexual reproduction; (ii) asexual reproduction as a successful reproductive strategy. OR B Discuss endoparasitic infections under the following headings: (i) difficulties involved in their treatment and control; (ii) benefits of improved parasite control to human populations. Labelled diagrams may be used where appropriate. 4 5 7 2 Page 25 MARKS DO NOT WRITE IN THIS MARGIN SPACE FOR ANSWER FOR QUESTION 11 [END OF QUESTION PAPER] Page 26 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK Page 27 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK