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Fig. 1.1 shows a cell of a female fruit fly, \textit{Drosophila melanogaster}, during a stage of mitosis.
(a) (i) Name the stage of mitosis shown in Fig. 1.1.
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(ii) Shade a pair of homologous chromosomes. [1]
(iii) Name the structure labelled W and state its function.
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(b) State what happens to structure X and to structure Y between the stage shown in Fig. 1.1 and the end of cell division.
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(a) Table 2.1 shows eight ions that are biologically important.
[Table_1: Image of Table 2.1]
Choose one ion to match each of the following statements. In each case write one letter from Table 2.1. You may use each letter (A to H) once, more than once or not at all.
(i) A component of polynucleotides.
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(ii) Ion produced by enzyme activity inside red blood cells.
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(iii) Ion used in the production of all amino acids in chloroplasts.
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(iv) Ion that diffuses through carrier proteins with sucrose into companion cells in phloem tissue.
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(v) Component of haem group in haemoglobin that binds oxygen.
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(b) The enzyme nitrogenase is found in free-living and symbiotic nitrogen-fixing bacteria. Nitrogenase catalyses the reaction:
$$\text{N}_2^{(g)} + 6\,e^- + 8\,\text{H}^{+}_{(aq)} \rightarrow 2\,\text{NH}_4^{+}_{(aq)}$$
Some nitrogenase enzymes have vanadium ions in their active sites; others have molybdenum ions.
Explain how the enzyme nitrogenase functions in the fixation of nitrogen.
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(c) Some pea plants were grown with their roots in a solution of mineral ions. The solution was kept aerated for three days. The concentrations of five ions in the solution and in the root tissue were determined after the three days. The results are shown in Table 2.2.
[Table_2: Image of Table 2.2]
With reference to Table 2.2, suggest how cell surface membranes of root cells are responsible for the concentrations of ions in the roots compared to the surrounding solution.
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(a) Tuberculosis (TB) and chronic obstructive pulmonary disease (COPD) are diseases that affect the lungs.
With reference to TB and COPD, explain how infectious diseases differ from non-infectious diseases.
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Macrophages are large phagocytic cells that are found in many tissues including alveolar tissue in the lungs. They provide the main means of defence against pathogens in this tissue.
Fig. 3.1 is a drawing made from an electron micrograph showing part of a capillary and two alveoli, with a macrophage.
[Image_1: Drawing of a macrophage]
(b) With reference to Fig. 3.1, explain:
(i) how alveoli are adapted for gaseous exchange
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(ii) how macrophages function to protect the lungs from becoming infected.
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(c) Phagocytes release enzymes that digest proteins. In smokers, this may lead to the large-scale destruction of alveolar walls.
Outline the effects of this destruction on a person’s health.
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(a) Name structure T in Fig. 4.1 and state its role in liver cells.
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(b) (i) Suggest why cholesterol is packaged into lipoproteins before release from liver cells into the blood.
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(ii) Explain why cells of the body need to be supplied with cholesterol.
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(c) Cholesterol is also packaged into vesicles by the SER and then secreted from the cell into small fluid-filled spaces between the liver cells. These spaces form ducts that drain into the gall bladder to form bile.
Suggest how cholesterol is secreted into ducts, such as the duct in Fig. 4.1.
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(d) State one function of the Golgi apparatus other than the packaging of substances into vesicles for transport.
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(a) (i) Use Table 5.1 to complete Fig. 5.1. [3]
(ii) State the term used to describe the sequence of amino acids in a polypeptide. [1]
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(b) In sickle cell anaemia, the amino acid at position 6 in the β chain is valine and not glutamic acid.
Explain how a single change in the DNA triplet for the sixth amino acid of the gene coding for the β chain leads to the production of a different amino acid sequence. [5]
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(a) Explain the meaning of the terms extit{niche} and extit{community}.
\textit{niche} ..........................................................................................................
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(b) With reference to the food web in Fig. 6.1, suggest why sea otters are considered to be a keystone species.
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(c) Suggest how the efficiency of energy transfer from kelp to sea urchins could be determined.
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