AS & A Level Biology - 9700 Paper 2 2017 Summer Zone 1

(a) Each of the statements A to D describes a structure found in eukaryotic cells. Identify the structure that is described in each statement.
A An organelle that contains 70S ribosomes. ................................................................................................................................................
B A thread-like structure composed of DNA and histone proteins. ................................................................................................................................................
C The organelle that modifies and packages proteins for secretion. ................................................................................................................................................
D The structure that synthesises rRNA and combines it with proteins. ................................................................................................................................................ [4]
(b) Prokaryotes and plant cells have cell walls.
Outline the composition of the cell wall of a prokaryote and the composition of the cell wall of a plant cell to show how they differ.
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(a) The students used Fig. 2.1 to derive the Michaelis-Menten constant ($K_m$) for enzyme A as 0.3 mmol dm$^{-3}$.

Explain how they derived $K_m$.
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(b) The students investigated a different phosphatase enzyme (enzyme B) and found the value of $K_m$ to be higher than 0.3 mmol dm$^{-3}$.

Explain the difference between the values of $K_m$ for these two phosphatase enzymes.
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[2]

(c) The students repeated their investigation on enzyme A with a competitive inhibitor.

They used the same concentrations of substrate as before, but added a competitive inhibitor to each reaction mixture.
They used the same concentration of the inhibitor in each reaction mixture.
The students found that $V_{max}$ was the same as before, but $K_m$ was higher than 0.3 mmol dm$^{-3}$.

Explain how the addition of the competitive inhibitor results in the same value for $V_{max}$ but a higher value for $K_m$.
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[4]

Fig. 3.1 is a diagram that shows the structure of an antibody molecule.

(a) State why the antibody molecule shown in Fig. 3.1 has quaternary structure.
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(b) (i) Use Fig. 3.1 to explain how the structure of the variable region of an antibody molecule is related to its function.
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(ii) State the role of the constant region of an antibody.
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(c) Monoclonal antibodies are used both in diagnosis and in treatment of disease.
(i) Outline how monoclonal antibodies are produced.
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(ii) Suggest the advantages of using monoclonal antibodies in diagnosis of disease.
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(a) Fig. 4.1 shows part of a DNA molecule.

Use Fig. 4.1 to explain how the structure of mRNA differs from the structure of DNA.

(b) Fig. 4.2 shows:
• the first seven amino acids of the $\beta$ chain of haemoglobin
• the first amino acid in the sequence is valine (Val)
• the 21 base pairs in the sequence of DNA that code for these seven amino acids.
[Table_1]
Table 4.1 shows the triplets of bases that code for seven amino acids.
Using Fig. 4.2 and Table 4.1, state what will happen to the sequence of amino acids in the first part of the $\beta$ chain of haemoglobin:
(i) if the base pair at position 6 is deleted
[1]
(ii) if the three base pairs at positions 7, 8, and 9 are deleted.
[1]

(c) DNA is involved in the processes of replication and transcription.
Complete Table 4.2 by using a tick (✓) to indicate which features apply to each of the processes. Use a cross (✗) for features that do not apply.
The first row has been completed for you.
[Table_2]

(d) Telomeres are parts of chromosomes. Describe the function of telomeres.

(e) Describe the function of ribosomes in protein synthesis.

Sugar molecules enter cells through transport proteins.
(a) Explain why transport proteins are required for the movement of sugar molecules, such as glucose and fructose, into cells.
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Some plant cells convert fructose and glucose into sucrose for transport from sources to sinks. Sucrose is moved into phloem sieve tubes as shown in Fig. 5.1.

(b) Use the information in Fig. 5.1 to explain how sucrose:
• moves into the companion cell
• moves from the companion cell into the sieve tube element.
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(c) Sucrose travels in phloem sieve tubes to sinks.
State two examples of sinks.
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Cholera bacteria release the toxin, choleragen, when they are in the intestine.

(a) (i) Name the bacterium that is the pathogen of cholera.
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(a) (ii) Describe the way in which cholera is transmitted from an infected person to an uninfected person.
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(b) Suggest how choleragen interacts with gangliosides on intestinal epithelial cells.
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(c) Name the process by which choleragen enters the intestinal epithelial cell as shown in Fig. 6.1.
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(d) Suggest and explain the likely consequences on the intestinal epithelial cells of the loss of chloride ions through the channel proteins.
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(e) Health authorities recommend that antibiotics, such as tetracycline, are only to be used for treating people with severe cases of cholera.

Explain why it is recommended that antibiotics should not be given to people with mild cases of cholera or to protect people from cholera.
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