9700_s10_qp_23
A paper of Biology, 9700
Questions:
6
Year:
2010
Paper:
2
Variant:
3
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1
Examiner s Use shows part of an animal cell viewed with an electron microscope. A B C 6 µm Name the structures A to C. A B C State the function of structure C. Explain why structure C cannot be seen using a light microscope. For Examiner’s Use Suggest one disadvantage of the electron microscope compared to the light microscope for the study of cells. Calculate the magnification of the image in . Show your working and give your answer to the nearest whole number. Answer =
1. Cell structure  →  1.1. The microscope in cell studies
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2
For Examiner’s Use shows a diagram of a section through a human heart. X Y Z State the name and function of the circled structure labelled X. name function Explain why the region labelled Y is thicker than the region labelled Z. For Examiner’s Use Cardiac muscle is described as myogenic as it naturally contracts and relaxes. With reference to the structures and tissues within the heart, describe how the cardiac cycle is initiated and coordinated.
8. Transport in mammals  →  8.3. The heart
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3
The amino acid sequence of the protein hormone insulin is shown in . Phe polypeptide chain B Val Asn Gln His Leu Cys S S Gly Ser His Leu Val Glu Ala Leu Tyr Leu Val Cys Gly Glu Arg Gly Phe Phe Tyr Thr Pro Lys Thr Gly polypeptide chain A Ile Val Glu Gln Cys S Cys Thr Ser Ile Cys Ser Leu Tyr Gln Leu Glu Asn Tyr Cys Asn S S S For Examiner’s Use With reference to , state which two levels of protein structure are shown 1. 2. the name of the structures responsible for holding the two polypeptide chains together. Many people with diabetes need to take regular injections of insulin. Insulin in the form shown in cannot be taken by mouth as it would be hydrolysed by proteases in the gut. In the space below, draw a diagram to show how the peptide bond between glutamine 15 and leucine 16 in polypeptide chain A could be hydrolysed and show the products of the hydrolysis. CH3 NH2 CH2 CH3 CH leucine glutamine CH2 C H H N O C rest of chain C H CH2 C H N rest of chain O O C
2. Biological molecules  →  2.3. Proteins
14. Homeostasis  →  14.1. Homeostasis in mammals
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4
For Examiner’s Use The control of malaria is one of the top priorities of the World Health Organization (WHO). At present, there is no effective vaccine for the disease, so other preventative measures must be taken to control the spread of malaria. Describe one method of controlling the spread of malaria by targeting its vector and explain its effect. Explain why it has been difficult to develop an effective vaccine for malaria. For Examiner’s Use Another method of preventing malaria is to take drugs, such as chloroquine, but resistance to these drugs among certain species of the malarial parasite is increasing. New drugs are being developed. A laboratory investigation was carried out to determine the effect of a new drug on two strains of the malarial parasite Plasmodium falciparum. The results are shown in . chloroquine-sensitive P. falciparum chloroquine-resistant P. falciparum percentage of parasites killed after 24h concentration of new drug / µmol dm–3 With reference to , compare the effect of increasing the concentration of the drug on the chloroquine-resistant and chloroquine-sensitive strains of P. falciparum. When a person becomes infected with the Human Immunodeficiency Virus (Hthey become more susceptible to infection by the malarial parasite. shows maps of Africa produced by the WHO. • a shows the percentage population of each country testing positive for HIV • b shows the percentage increase in malaria as a result of HIV infection in each country. 20.0% – 28.0% 10.0% – Suggest how HIV infection may have led to an increase in malarial infections in these countries.
10. Infectious diseases  →  10.1. Infectious diseases
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5
For Examiner’s Use Some bacteria, such as Rhizobium, carry out nitrogen fixation, which is an important process in the nitrogen cycle. Explain what is meant by the term nitrogen fixation. An important enzyme in the nitrogen cycle is urease, which catalyses the hydrolysis of urea to ammonia. This reaction is shown below: urease (NH2)2CO + H2O 2NH3 + CO2 State the name of this process in the nitrogen cycle. Explain the importance of this process in making nitrogen from animals available for uptake by plants. For Examiner’s Use The enzyme urease is known to be affected by competitive inhibitors. A student carried out an investigation to determine the percentage of urea hydrolysed by urease at various time intervals • without any inhibitor • with a competitive inhibitor. The experiment was carried out in test tubes set up as follows: Tube A – 1 cm3 of urease solution, 10 cm3 pH 7.5 buffer solution, 1 cm3 urea solution. Tube B – 1 cm3 urease solution, 9 cm3 pH 7.5 buffer solution, 1 cm3 inhibitor, 1 cm3 urea solution. Tube C – 1 cm3 water, 10 cm3 pH 7.5 buffer solution, 1 cm3 urea solution. The results are shown in the table below. time / min percentage of urea remaining Tube A Tube B Tube C State how Tube C acts as a control for this investigation. Explain the difference in results between Tube A and Tube B.
3. Enzymes  →  3.2. Factors that affect enzyme action
2. Biological molecules  →  2.1. Testing for biological molecules
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6
For Examiner’s Use Various structures in the human gas exchange system are adapted in different ways to perform their specific functions. Complete the table below using a tick ✓ or cross ✗ in each box to show whether or not the structure shows the particular feature. Two boxes have been completed for you. lined with cilia reinforced with cartilage site of gas exchange contains smooth muscle trachea ✗ bronchus bronchiole ✓ alveolus State the two ways in which the concentration gradients of oxygen and carbon dioxide are maintained for efficient gas exchange. 1. 2. The alveoli in the lungs have elastic fibres in their walls. State one function of the elastic fibres. Name the medical condition caused by breakdown of the elastic fibres. For Examiner’s Use Cigarette smoke contains tar, a substance which has several harmful effects on the cells lining the gas exchange system. Outline three of these effects. 1. 2. 3.
9. Gas exchange  →  9.1. The gas exchange system
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