AS & A Level Biology - 9700 Paper 2 2011 Summer Zone 1

(a) Calculate the magnification of the electron micrograph in Fig. 1.1.
Show your working and express your answer to the nearest whole number.
magnification × = \text{.....................} [2]
(b) Explain how the cells labelled \textbf{A} and the structures labelled \textbf{B} in Fig. 1.1 protect the lining of the trachea.
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................} [4]
(c) Cells, such as \textbf{C}, at the base of the epithelium of the trachea divide by mitosis.
Describe the changes that occur within the cell between the beginning of prophase and the end of metaphase.
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................}
\text{...............................................................................................................................} [5]

(a) Carbon dioxide is transported in the blood in various forms. Describe how carbon dioxide molecules reach red blood cells from respiring cells.
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Fig. 2.1 shows part of a capillary network and some cells of the surrounding tissue.


(b) State three ways in which the blood at Y differs from the blood at X other than in the concentration of carbon dioxide.

1. ........................................................................................................................................................
2. ........................................................................................................................................................
3. ........................................................................................................................................................[3]

An enzyme in red blood cells catalyses the reaction between carbon dioxide and water as blood flows through respiring tissues.

$$\text{CO}_2 + \text{H}_2\text{O} \xrightarrow{\text{enzyme}} \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^-$$

(c) (i) Name the enzyme that catalyses this reaction.
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(ii) Explain the significance of this reaction in the transport of carbon dioxide.
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Fig. 2.2 shows the effect of increasing the carbon dioxide concentration on the oxygen haemoglobin dissociation curve.


(d) (i) State the percentage saturation of haemoglobin with oxygen at a partial pressure of 5 kPa of oxygen when the partial pressure of carbon dioxide is:

1.0 kPa ...........................................................................................................................................................
1.5 kPa ...........................................................................................................................................................[1]

(ii) The percentage saturation of haemoglobin with oxygen decreases as the partial pressure of carbon dioxide increases. Explain how this happens.
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(iii) Name the effect of increasing carbon dioxide concentration on the oxygen dissociation curve.
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(iv) Explain the importance of the effect of carbon dioxide on haemoglobin as shown in Fig. 2.2.
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A molecule of messenger RNA (mRNA) was produced during the transcription of a gene. Part of the template sequence of DNA was ATGC.

Fig. 3.1 shows the part of the molecule of messenger RNA corresponding to that sequence of four bases.



(a) Name the parts of the mRNA molecule shown in Fig. 3.1 labelled D, E, F and G.

D ........................................................................................................

E ........................................................................................................

F ........................................................................................................

G ........................................................................................................ [4]

(b) Complete the table to show three ways in which mRNA differs from DNA.

[Table_1]

1 ........................................................................................................

2 ........................................................................................................

3 ........................................................................................................ [3]

(c) Describe the role of mRNA after it leaves the nucleus and enters the cytoplasm of a eukaryotic cell.

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The enzyme sucrase catalyses the breakdown of the glycosidic bond in sucrose.
A student investigated the effect of increasing the concentration of sucrose on the rate of activity of sucrase.

Ten test-tubes were set up with each containing 5 cm³ of different concentrations of a sucrose solution. The test-tubes were placed in a water bath at 40 °C for ten minutes. A flask containing a sucrase solution was also put into the water bath.

After ten minutes, 1 cm³ of the sucrase solution was added to each test-tube. The reaction mixtures were kept at 40 °C for a further ten minutes.

After ten minutes, the temperature of the water bath was raised to boiling point. Benedict's solution was added to each test-tube. The time taken for a colour change was recorded and used to calculate rates of enzyme activity.

The results are shown in Fig. 4.1.



(a) (i) Name the type of reaction catalysed by sucrase.
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(ii) Explain why the temperature of the water was raised to boiling point.
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(b) Describe and explain the results shown in Fig. 4.1.
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Fig. 5.1 shows five different biological molecules.



Complete Table 5.1 by indicating which molecule matches each statement.
You may use each letter (H to M) once, more than once or not at all.
You should write only one letter in each box.

[Table_1]

Table 5.1
| statement | letter |
|--------------------------------------------------------------------|--------|
| contains peptide bonds | |
| part of the molecule forms the hydrophobic part of cell membranes | |
| contains 1-4 and 1-6 glycosidic bonds | |
| forms the primary structure of a protein | |
| used for energy storage in plants | |
| forms a helical structure | |
| the sub-unit molecule is β-glucose | |

Measles is a common viral infection. A vaccine has been available for measles since the 1960s. There are vaccination programmes for many diseases including measles. Babies are born with a passive immunity to measles so the vaccine is not given in the first few months after birth.
(a) Explain how active immunity differs from passive immunity.
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(b) Explain why the vaccine for measles is not given in the first few months of a child’s life.
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The World Health Organization (WHO) publishes data on the vaccination programmes for infectious diseases. The WHO recommends vaccination rates of over 90% of children.
Each health authority in a country reports its success in vaccinating children in their district. The WHO uses these figures to estimate the percentage of districts in each country that vaccinate 90% of children against measles.
The WHO also collects statistics on death rates of children under the age of 5 from all causes, including infectious diseases.
Fig. 6.1 shows these statistics for 24 countries for the year 2007.

(c) Use the information in Fig. 6.1 to explain why the WHO recommends immunisation of 90% of children.
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