Name Subject Class Class Candidate Number

2BIX

ANGLO-CHINESE JUNIOR COLLEGE Preliminary Examination 2009

BIOLOGY 8875/02 19 AUGUST 2009

HIGHER 1 2 hours Paper 2

Additional Material: Writing Paper

For Examiner's Use

Section A

1

2

3

4

Section B

5 / 6

Total

60

READ THESE INSTRUCTIONS FIRST Write your name, index number and class on this answer booklet. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Section A Answer all questions. Section B Answer any one question.

At the end of the examination, circle the number of the Section B question you have answered in the grid opposite. Fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question.

This question paper consists of 10 printed pages.

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Use1 (a) Fig. 1.1 shows the electron micrograph of part of a plant cell.

F

E

D G

A

B

C

Fig. 1.1

(i) Name structures A F. [3]

A

D

B

E

C

F

(ii) Structure G is the cellulose cell wall. Describe how the structure of cellulose is adapted to give rise to its fibrous nature.

[2]

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Use(b) Mitochondria and chloroplasts are two eukaryotic organelles which are thought to have originated as prokaryotic cells that have been engulfed by a host cell and become endosymbionts.

(i) Name and describe the process that results in the engulfing of the prokaryotic cell by a host cell.

[2]

(ii) The structures of a mitochondrion and a chloroplast share similar adaptations for ATP synthesis. Describe and explain two of them.

@ m [2]

(c) Fig. 1.2 shows two worn-out mitochondria in a lysosome.

Fig. 1.2

(i) State one similarity in the interior of a lysosome and the intermembrane space of a

mitochondrion.

[1] (ii) The membrane of a lysosome in a cell is accidentally ruptured. Suggest what will be

the effect of this on the cytoplasmic enzymes.

[2][Total: 12]

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Use2 mRNAs in a bacterial cell are very unstable, having half-lives of less than a couple of minutes. mRNAs in eukaryotes are relatively more stable, having longer half-lives of not more than 30 minutes. Different mechanisms exist for destroying the eukaryotic mRNAs. One of these is decay by exonucleases.

(a) Explain why eukaryotic mRNAs are more stable than bacterial mRNAs.

[3] (b) Describe how exonucleases are able to carry out their role in breaking down mRNAs .

[2]

Transferrin is the protein that transports iron in the blood stream. It is transported into the cell by the membrane-bound transferrin receptor (TfR). At low intracellular iron concentrations, there are higher amounts of TfR to increase iron intake into the cell. The expression of the TfR gene is mediated by aconitase which is an iron-sensitive RNA-binding protein. This protein binds to the 3-untranslated region (3 UTR) of the TfR mRNA, as shown in Fig. 2.1.

Fig. 2.1 (c) State the level at which the expression of TfR gene is controlled. [1]

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Use(d) Describe briefly how TfR levels are increased in low intracellular iron concentration.

[3]

[Total: 9]

3 (a) Fungi can make their own amino acids and are able to grow on a substance called minimal media (contain the minimum nutrients possible for growth of bacteria).

An abnormal strain of fungus that could not grow on minimal media was discovered. The abnormal fungus was able to grow on minimal media to which all of the twenty amino acids were added. These observations can be summarised as follows.

Fig. 3.1

It was assumed that the deficiency in the abnormal fungus was because of a fault in the genetic material coding for the production of one of the amino acids.

An experiment was designed to investigate which amino acid was involved. The experimental set up, involving 22 tubes, is outlined in the following diagram and the results are shown.

Fig. 3.2

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Use (i) Explain why tubes 1 and 2 were included in the experiment.

[1]

Fig. 3.2 shows that the fungus grew in tube 12. The amino acid histidine had been added to this tube.

(ii) From the above experiment, state two conclusions that can be made about the ability

of the abnormal fungus to produce amino acids.

[2]

Consider the following genetic code table and three DNA sequences.

sequence 1 AACGCCTCGGTGCCA sequence 2 CAAGTAGGTACACTC sequence 3 TAATGGACCCCCGGT

Fig. 3.3

Premature termination of polypeptide synthesis occurs when a required amino acid is missing.

(iii) State and explain which of the above DNA sequences could lead to the production of

an uninterrupted chain of amino acids in the abnormal fungus.

[2]

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Use(b) There were three suspects in an assault case. A forensic scientist found blood, other than the victims, at the site. DNA was extracted from five blood samples.

the victim the blood at the assault site (not the victims) the three suspects

Polymerase Chain Reaction (PCR) was used on the extracted DNA.

(i) A DNA polymerase enzyme is involved in the PCR process. Explain the role of the

polymerase enzyme in PCR.

[2]

One of the regions used in the forensic analysis was a short tandem repeat sequence of 4 bases, AATG located on chromosome 11. The number of repeats of this sequence varies from individual to individual. The samples were loaded onto a gel and electrophoresis was performed.

A diagram of the gel is shown below.

1 = standard 2 = victim 3 = other blood found on victim 4, 5, 6 = suspects

(ii) Explain why there is only one band in lane 2.

[1] (iii) State and explain which piece of DNA, A or B, has the greater number of the 4 base

repeat sequence.

[1]

(iv) Identify and explain which of the suspects appears to have committed the assault.

[2]

[Total: 11]

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Use4 One population of rats, found on a remote island off the coast of South Australia, have had no genetic contact with mainland rats since they were isolated by rising sea levels at the end of the last glacial period, around 10 000 years ago.

Scientists have taken blood samples from the rats and compared the distribution of unique DNA sequences called microsatellites, which are scattered across the rats' chromosomes. These microsatellites give a measure of the population's genetic diversity, or lack of it. In this case the microsatellite data showed that the island population has low genetic diversity.

Despite the island rats lack of genetic diversity, the population size has been maintained over many generations. In fact, the rats appear to be thriving. (a) Explain the scientists' choice of using microsatellites over genes for the analysis of genetic

diversity of the rat population on the island.

[2] (b) Suggest one reason for the rats' success despite the lack of genetic diversity within the

population.

[1] Warfarin is a poison used to control rat populations. Fig. 4.1 shows changes in the proportion of rats resistant to warfarin in a particular population over a period of about 4 years. High levels of warfarin were used on this population during Year 2 but poisoning stopped at the end of this period. Rats are reproductively mature at an age of three months and can breed about every three weeks.

Fig. 4.1

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Use(c) Explain the process which led to the increase in the percentage of resistant rats during Year 2.

[3] (d) Using the data Fig. 4.1, explain what can be concluded about the selective advantage to a

rat of being warfarin-resistant compared to being non-resistant in an environment without warfarin.

[2]

[Total: 8]

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UseSection B

Answer one question. Write your answers in the lined pages provided. Your answers should be illustrated by large, clearly labelled diagrams, where appropriate. Your answers must be in continuous prose, where appropriate. Your answers must be set out in sections (a), (b) etc., as indicated in the question. 5 (a) Describe the structural differences between starch and collagen. [5]

(b) Describe the roles of proteins in the synthesis of proteins in eukaryotic cells. [10]

(c) Explain the molecular adaptations of the cell membrane of an organism found in cold environments that enables it to survive in its habitat. [5]

6 (a) Compare and contrast the processes of the Polymerase Chain Reaction and DNA

replication. [5]

(b) Outline the procedures for cloning an eukaryotic gene in a bacterial plasmid. [10]

(c) Describe, with named examples, how genetic engineering has improved the quality and yield of crop plants and animals. [5]

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ANGLO-CHINESE JUNIOR COLLEGE