9700_w12_qp_22
A paper of Biology, 9700
Questions:
6
Year:
2012
Paper:
2
Variant:
2
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1
is a labelled diagram of a leaf palisade mesophyll cell, as seen with a high quality light microscope. cytoplasm mitochondrion nucleus golgi body chloroplast cell wall vacuole tonoplast plasmodesma An electron micrograph of the same leaf mesophyll cell at the same magnification would show more detail than is shown in . Explain why, at the same magnification, an electron micrograph is able to provide more detail than a light micrograph. Describe three additional features that could be seen on an electron micrograph of the leaf mesophyll cell that are not seen in . 1. 2. 3. For Examiner’s Use The length of the labelled chloroplast in is 5.0 μm. Calculate the magnification of the cell shown in . Show your working. magnification × In , starch granules are visible within the chloroplasts. Starch is the most common storage compound of plants. It is composed of amylopectin and amylose. Describe the structural differences between amylopectin and amylose. State one role of magnesium ions within chloroplasts.
13. Photosynthesis  →  13.1. Photosynthesis as an energy transfer process
2. Biological molecules  →  2.2. Carbohydrates and lipids
1. Cell structure  →  1.2. Cells as the basic units of living organisms
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2
For Examiner’s Use The fluid mosaic model of membrane structure was first proposed in 1972 by Singer and Nicolson. The model describes in detail how the components of a membrane are organised. Some of the components of the cell surface membrane are: • phospholipid molecules • protein molecules • cholesterol molecules. In the box below, draw a labelled diagram of a section through a cell surface membrane to show how the above components are organised within the membrane. The diagram should include other named components of the membrane. Label the inner and outer surfaces of the membrane. For Examiner’s Use Suggest why ‘fluid mosaic’ is an appropriate term to use to describe membrane structure.
4. Cell membranes and transport  →  4.1. Fluid mosaic membranes
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3
For Examiner’s Use The humpback whale, Megaptera novaeangliae, is one of the world’s largest aquatic mammals. It can grow to a length of up to 15 metres and a mass of up to 36 000 kg. A large proportion of the mass of a humpback whale is a very thick layer of fat-filled cells stored under the skin, called blubber. The humpback whales are seasonal feeders. They feed in polar regions during the summer and then migrate to warmer temperate and tropical waters to mate and have their young during the polar winter. One reason that the humpback whale has managed to reach its enormous size is because it is a member of a simple food web. is an example of such a food web. humpback whale krill (small crustaceans) herring phytoplankton (very small photosynthetic organisms) not drawn to scale The humpback whale is a carnivore, feeding on krill and herring. The herring feed on krill. Add arrow heads to the lines drawn on to show the direction of energy flow in the food web. State the trophic level to which the humpback whale belongs. For Examiner’s Use In terms of energy transfer, explain how the humpback whale is able to reach such a large size. The thickness of blubber in humpback whales decreases during the non-feeding season and increases during the feeding season. Suggest explanations for this observation. Describe the roles of water as an environment for organisms, such as those shown in .
12. Energy and respiration  →  12.1. Energy
8. Transport in mammals  →  8.2. Transport of oxygen and carbon dioxide
13. Photosynthesis  →  13.1. Photosynthesis as an energy transfer process
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4
For Examiner’s Use Diseases are either infectious or non-infectious. Complete Table 4.1 to produce a summary of four important infectious diseases. Table 4.1 name of disease type of causative organism name of causative organism cholera bacterium Vibrio cholerae HIV/AIDS virus malaria tuberculosis (TB) Mycobacterium tuberculosis Typhoid is an example of an infectious disease. Some features of typhoid include: • caused by a bacterium that can only infect humans • caused by the ingestion of contaminated food and water • can be treated with drugs • can be prevented by a vaccine. State which of the diseases named in Table 4.1 is transmitted in the same way as typhoid. State which type of drug can be used in the treatment of typhoid. Give a reason for your answer. For Examiner’s Use Child vaccination programmes against typhoid in some countries have had considerable success. The numbers contracting the disease have decreased, not only in the vaccinated children, but also in other age groups that were not part of the programme. Suggest explanations for this observation. After infection, the ingested typhoid bacteria are engulfed by phagocytes. Explain why the phagocytes act only against the bacteria and not against human cells. Unlike other bacteria, the typhoid bacteria are able to survive and multiply within the phagocytes. Suggest an explanation for this observation. Explain why people with HIV/AIDS are more susceptible to infections, such as typhoid.
10. Infectious diseases  →  10.1. Infectious diseases
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5
For Examiner’s Use State the structural features of DNA that make it a stable molecule. DNA has been described as a ‘carrier of coded information’. Explain this statement. State when, during a cell cycle, DNA replication occurs. There are two alleles of the gene for the β-haemoglobin polypeptide: • HbA • HbS (sickle cell). Describe and explain the difference between the HbA and HbS alleles of this gene. For Examiner’s Use DNA polymerase is an enzyme involved in the replication of DNA. One of the substrates required by DNA polymerase is ATP. ara-ATP is a chemical that affects DNA polymerase activity. In an investigation, the effect of different concentrations of ATP on the rate of DNA synthesis was determined: • with no ara-ATP • with a low concentration of ara-ATP • with a high concentration of ara-ATP. The results of the investigation are shown in . ATP concentration / +M rate of DNA synthesis / arbitrary units 20 +M ara ATP 5 +M ara ATP no-ara ATP Explain, in terms of the mode of action of enzymes, the results of the investigation shown in .
6. Nucleic acids and protein synthesis  →  6.1. Structure of nucleic acids and replication of DNA
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6
For Examiner’s Use Coronary artery bypass grafting is the most common heart operation in the world. is a diagram of a coronary bypass. The graft is a section of a healthy blood vessel. The blood vessel used in is the internal mammary artery. It is a common choice for surgeons as it is quite resistant to arteriosclerosis. Use label lines and the following letters to label the following on : A aorta B coronary artery C internal mammary artery D pulmonary artery E right atrium F vena cava On , mark with an X, the diseased area of the coronary artery for which the surgery has been performed. For Examiner’s Use With reference to coronary heart bypass surgery, discuss the difficulties in achieving a balance between prevention and cure.
8. Transport in mammals  →  8.1. The circulatory system
8. Transport in mammals  →  8.3. The heart
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