2015 HCI H1 Biology Prelims P2 Questions

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3 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 (b) Discuss the advantages of having four subunits in haemoglobin. [3] The Greylag goose and the Andean goose have different haemoglobin structures. Possession of a haemoglobin with high oxygen affinity helps the A ndean goose to adapt to high altitudes. Greylag goose lives in the Indian plains, whereas t he Andean goose lives in the High Andes. The haemoglobin of the Andean goose differs from that of the Greylag goose by nine replacements in the -chain and seven in the -chain. (c) Explain how the differences in haemoglobin structure of the Greylag and Andean geese contribute to their different oxygen affinities. [4] [Total: 9]

4 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 QUESTION 2 Studies were carried out on soil-dwelling aerobic and anaerobic bacteria. Samples were taken from different depths at intervals of one month and six months after the soil was put into a large heap for storage. Table 2.1 shows the numbers of aerobic and anaerobic bacteria at different depths in the stored soil. Table 2.1 depth in soil store / m mean number of bacteria per gram of stored soil 10 7 aerobic bacteria anaerobic bacteria after one month after six months after one month after six months 0.0 12.4 12.5 0.4 0.6 0.5 10.1 8.3 0.6 1.0 1.0 9.8 5.9 0.8 3.8 1.5 9.7 3.1 0.8 7.6 2.0 10.5 0.8 0.7 8.1 2.5 10.8 0.7 0.8 8.5 3.0 10.2 0.9 0.6 8.8 (a) (i) Account for the trends shown by the distribution of the two types of bacteria after six m o n t h s . [ 3 ] (ii) Describe how aerobic bacteria are structurally adapted for cellular respiration. [2]

5 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 In a further study, soil samples were taken at two depths, A and B, in the soil store. The samples were taken at intervals over six years. Soil samples of equal mass were used to determine the activity of dehydrogenases in the Krebs cycle of the aerobic bacteria. Fig. 2.1 shows the mean dehydrogenase activity of the bacteria in these samples. Fig. 2.1 (b) (i) State with evidence from Fig. 2.1 which depth, A or B, were samples taken from a greater depth. [2] (ii) Explain the roles of dehydrogenases in the Krebs cycle of aerobic bacteria. [2] [Total: 9]                                                                         0 1 1 2 2 3 3 4 4 5 5 6 6 mean dehydrogenase activity / arbitrary unit time / year A B

6 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 QUESTION 3 (a) State the structural features of DNA that make it a stable molecule. [2] 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 Fig. 3.1. Fig. 3.1

7 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 (b) Explain, in terms of mode of action of enzymes, the results of the investigation shown in F i g . 3 . 1 . [ 3 ] Colour blindness is a genetic condition characterised by the inability of the brain to perceive certain colours accurately.  The most common form is termed red-green colour blindness (RGC).  RGC results from a recessive allele.  0.6% of females worldwide have RGC.  8.0% of males worldwide have RGC. The results of the investigation are shown in Fig. 3.2. Fig. 3.2

8 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 (c) Define the term recessive. [1] (d) Explain why females are less likely than males to have RGC. [2] (e) With reference to Fig. 3.2, and using the symbols R for the dominant allele and r for the recessive allele, state the genotypes of the individuals 1 and 6. [2] 1 6 [Total: 10]

9 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 QUESTION 4 Genes can be transferred from one species to another using plasmids, which are circular pieces of DNA found in some bacteria. Fig. 4.1 shows how a plasmid is cut and a piece of foreign DNA inserted. The foreign piece of DNA usually contains more than one gene. Fig. 4.1 Many copies of the new recombinant plasmid DNA are then incubated with bacteria. (a) Explain what is meant by recombinant plasmid DNA. [2] (b) Outline the roles of the enzymes used in the formation of the recombinant plasmid DNA. [2] foreign DNA cut point gene 1 gene 2 gene 3 plasmid plasmid is cut piece of foreign DNA inserted into cut plasmid recombinant plasmid DNA with three inserted genes

10 © Hwa Chong Institution 2015 8875 H1 Biology / Preliminary Exam / Paper 2 (c) One of the foreign genes inserted into the plasmid, codes for resistance to a particular antibiotic. Explain why it is important to include a gene for antibiotic resistance in the plasmid produced. [2] Recombinant