CAIE A-Level Biology AS 1 Cell Structure Topic Practice

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Question 1

[Maximum number: 1]

Prostaglandins are small lipids produced in many tissues of the body. One role of prostaglandins is to cause inflammation at the site of an injury or infection. Inflammation is the normal first response of the immune system to injury or infection.

Cyclooxygenase (COX) is an enzyme that catalyses one of the steps in the reaction pathway for the formation of prostaglandins from phospholipids. The reaction pathway occurs in the smooth endoplasmic reticulum (SER) of cells. Part of the reaction pathway is shown in Fig. 1.3.

Fig. 1.3

Fig. 1.3

Suggest an advantage for this reaction pathway occurring in the smooth endoplasmic reticulum of a cell rather than in the cytoplasm.

Question 2

[Maximum number: 1]

Some students were asked to look at the photomicrograph of a cross-section of unfamiliar material and describe what they could see.

Figure for Question 2 — CAIE A-Level Biology AS

The students described the cross-section of F as:
1 circular
2 a hollow tube
3 spherical.
Which descriptions of the cross-section of F correctly state what the students could actually see?

A

1, 2 and 3

B

1 and 2 only

C

1 only

D

3 only

Question 3

[Maximum number: 4]

Saccharomyces cerevisiae is a unicellular fungus that is important in the brewing and baking industries.

Fig. 4.1 is a diagram of a transmission electron micrograph of S. cerevisiae.

Fig. 4.1

Fig. 4.1

Question (a)

(a)

A student was asked to calculate the magnification of the image shown in Fig. 4.1.

The student began by measuring the length of the scale bar in millimetres using a millimetre ruler.

State what the student should do next to obtain the correct answer.

[ 1 ]

Question (b)

(b)

The lysosomes and vacuole of S. cerevisiae contain acid hydrolases (hydrolytic enzymes) that function in an acid pH .

Explain why lysosomes need hydrolases to carry out their function.

[ 1 ]

Question (c)

(c)

The hydrolysis of trehalose is catalysed by two different enzymes produced by S.cerevisiae, regulatory trehalase and non-regulatory trehalase.

A study was carried out to compare regulatory trehalase and non-regulatory trehalase extracted from S. cerevisiae.

The results of the study showed that:
- regulatory trehalase had a higher Km\mathrm{K}_{\mathrm{m}} value (Michaelis-Menten constant) than non-regulatory trehalase
- the optimum pH of regulatory trehalase was pH 7.0-7.8
- the optimum pH of non-regulatory trehalase was pH 4.5-5.0.

[ 2 ]

Question (i)

(i)

Regulatory trehalase is found only in the cytosol, the fluid part of the cytoplasm.

Non-regulatory trehalase has been found on the external surface of the cell surface membrane and inside the cell.

State the location inside the cell where non-regulatory trehalase is likely to be found and explain the reason for your answer.

[ 2 ]

Question 4

[Maximum number: 1]

Fig. 3.1 is a transmission electron micrograph showing two adjacent cells in a leaf.

Fig. 3.1

Fig. 3.1

State one feature visible in Fig. 3.1, other than the cell wall, that identifies the cells as plant cells.

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