9700_w05_qp_2
A paper of Biology, 9700
Questions:
6
Year:
2005
Paper:
2
Variant:
0
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1
is a drawing made from an electron micrograph of a goblet cell from the epithelium of the gas exchange system. Name A to C. A B C State two places in the gas exchange system where goblet cells are found. 1. 2. A mucus 'plug' vesicle containing mucus B C [T Mucus contains a number of different glycoproteins, called mucins. These have a protein ‘core’ that is formed by repeated sequences of amino acids, some of which have carbohydrates attached to their side chains (R groups). A part of one of these repeated units is shown diagrammatically in . Use label lines and the letters P and G to indicate on the positions of: P – a peptide bond; G – a glycosidic bond. Describe the role of mucus in the gas exchange system. Glycoproteins are found in cell surface membranes. State one function of these glycoproteins. carbohydrate chains protein 'core' Examiner s Use
9. Gas exchange  →  9.1. The gas exchange system
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2
Phospholipids are components of cell surface membranes. Describe how phospholipid molecules are arranged in a cell surface membrane. You may use the space below for a simple annotated diagram if you wish. shows the structure of the lipids: • tristearin, which is a triglyceride; • phosphatidylcholine, which is a phospholipid. H H H C O C = O C = O C = O H O H O C C H H H C O C = O C = O H O O H C C P O C H C O – O = H H N + CH3 CH3 CH3 H tristearin phosphatidylcholine Use [T State two ways, visible in , in which phosphatidylcholine differs from tristearin. 1. 2. Explain how the structure of triglycerides, such as tristearin, makes them more suitable for energy storage than carbohydrates, such as glycogen. Examiner s Use The enzyme lipase catalyses the hydrolysis of ester bonds in triglycerides. As the reaction proceeds there is a decrease in pH. The progress of the reaction may be followed by using a pH meter. A solution containing tristearin was placed in a water bath at 25 °C. When the solution had reached this temperature, lipase was added and the mixture stirred. The pH of the reaction mixture was recorded every minute for 20 minutes. The results are shown in . Using the data in , state the time when lipase was added; the reaction ended. Explain why the pH decreases during this reaction. A similar solution was placed in a water bath at 35 °C and left for the same length of time to reach this temperature. Lipase was added as before. Sketch on the results that you would expect. pH time / min Examiner s Use
2. Biological molecules  →  2.2. Carbohydrates and lipids
4. Cell membranes and transport  →  4.1. Fluid mosaic membranes
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3
[T is an electron micrograph of HIV particles leaving a T lymphocyte. Magnification × 100 000 HIV instructs the cell to reproduce more viruses. During this process the cell makes viral DNA and viral proteins that assemble to make new viral particles. These particles bud away from the cell membrane to infect other T lymphocytes. This process of viral budding kills T lymphocytes. A decrease in the number of T lymphocytes in the blood results in the destruction of a person’s immune system and leads to the onset of AIDS. Calculate the actual size of a viral particle shown in . Show your working and express your answer to the nearest nanometer. Answer nm State the property of the electron microscope that makes it possible to view clearly very small objects, such as viral particles. Suggest why an infected T lymphocyte that is producing HIV particles has a higher demand for amino acids than an uninfected cell. Use State three ways in which HIV is transmitted. 1. 2. 3. Outline the problems involved in controlling the spread of HIV. Examiner s Use
1. Cell structure  →  1.1. The microscope in cell studies
10. Infectious diseases  →  10.1. Infectious diseases
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4
[T Explain why the mammalian circulatory system is described as a closed double circulation. Mature mammalian red blood cells have no nuclei. State one advantage and one disadvantage of this. advantage disadvantage Use shows the origin and development of a B lymphocyte and its subsequent role in an immune response following an infection with the measles virus. Examiner s Use Z V X Y measles infection in lymph node in tissue W B lymphocyte matures stem cell [T Name the type of nuclear division that occurs at V. Name the tissue W. State the term given to foreign molecules, such as those on the surface of the measles virus, that stimulate an immune response. Name cell X and molecule Y. X Y Cell Z is responsible for long-term immunity to measles. Name cell Z and outline its role. name role Examiner s Use
11. Immunity  →  11.2. Antibodies and vaccination
11. Immunity  →  11.1. The immune system
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5
An experiment was performed to find the effect of surface area:volume ratio on the rate of osmosis. Pieces of yam were cut into cubes of the following sizes: • 2 cm × 2 cm × 2 cm (surface area = 24 cm2, volume = 8 cm3) • 1 cm × 1 cm × 1 cm (surface area = 6 cm2, volume = 1 cm3) The cubes were carefully blotted dry, weighed and their fresh masses recorded. One cube, 2 cm × 2 cm × 2 cm, was put into a beaker and covered with distilled water. Eight cubes each measuring 1 cm × 1 cm × 1 cm were put into another beaker of distilled water, making sure that they were all covered with distilled water. At intervals for a period of 45 hours, the cubes were removed from the beakers, blotted dry, reweighed and then replaced into fresh distilled water. The percentage increase in mass was calculated for the eight cubes of side 1 cm and the one cube of side 2 cm. The results are shown in . key time / hours percentage increase in mass 8 cubes of side 1 cm x 1 cm x 1 cm 1 cube of side 2 cm x 2 cm x 2 cm 1 cm 2 cm Use [T Explain why eight cubes of side 1 cm × 1 cm × 1 cm were used in this experiment. Describe the results shown in . Explain, in terms of water potential, why all the cubes of yam gained in mass. Explain why the percentage increase in mass for the eight cubes of side 1 cm was faster than that of the cube of sides 2 cm. Examiner s Use
4. Cell membranes and transport  →  4.2. Movement into and out of cells
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6
Haemoglobin is a globular protein that shows quaternary structure. It is composed of two types of polypeptide, known as α and β globin. Explain how a globular protein differs from a fibrous protein, such as collagen. shows part of the base sequence of the mRNA that codes for the first ten amino acids of β globin. Table 6.1 shows some of the codons and the amino acids for which they code. Table 6.1 Use the information in Table 6.1 to complete the sequence of amino acids at the beginning of β globin using the first three letters of each amino acid. Some of them have been done for you. Use GUG CAC CUG ACU CCU GAG GAG AAG UCU GCC amino acid abbreviation codons alanine ala GCA GCC GCG GCU glutamic acid glu GAA GAG histidine his CAC CAU leucine leu UUA UUG CUA CUC CUG CUU lysine lys AAA AAG proline pro CCA CCC CCG CCU serine ser UCA UCC UCG UCU AGC AGU threonine thr ACA ACC ACG ACU valine val GUA GUC GUG GUU val his glu ala β globin has a tertiary structure that consists of eight helices arranged to give a precise three-dimensional shape. Describe how the precise three-dimensional shape of a polypeptide is maintained. Examiner s Use
2. Biological molecules  →  2.3. Proteins
6. Nucleic acids and protein synthesis  →  6.2. Protein synthesis
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