CAIE A-Level Biology AS 4 Cell Membranes and Transport Topic Practice

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Question 1

[Maximum number: 5]

In thale cress, Arabidopsis thaliana, most of the stomata are on the lower surface of the leaves.
Fig. 4.1 is a diagram of an open stoma and two guard cells. Some of the cellulose fibres in the cell wall of the guard cells are shown.

Fig. 4.1

Fig. 4.1

Question (a)

(a)

The width of stomatal openings in A. thaliana is regulated by movement of ions. These ions move through channel proteins in the cell surface membranes of the guard cells.

[ 5 ]

Question (i)

(i)

Draw a diagram to show part of a cell surface membrane with a channel protein.

Label your diagram.

[ 3 ]

Question (ii)

(ii)

Explain why channel proteins are needed for the movement of ions into and out of cells.

[ 2 ]

Question 2

[Maximum number: 8]

Question (a)

(a)

Fig. 1.1 is a diagram representing part of the phospholipid bilayer of a cell surface membrane.

Fig. 1.1

Fig. 1.1

[ 2 ]

Question (i)

(i)

Cholesterol is an important lipid component of many cell surface membranes. Fig. 1.2 shows the structure of a cholesterol molecule.

Fig. 1.2

Fig. 1.2

Using the information in Fig. 1.2, explain the orientation (positioning) of cholesterol molecules in the phospholipid bilayer, as shown in Fig. 1.1.

[ 1 ]

Question (ii)

(ii)

State one role of cholesterol in phospholipid bilayers.

[ 1 ]

Question (b)

(b)

Explain why sodium ions cannot cross phospholipid bilayers by simple diffusion.

[ 1 ]

Question (c)

(c)

Ions and some molecules move across cell surface membranes by facilitated diffusion and active transport.

Compare facilitated diffusion and active transport by stating one way in which they are similar and two ways in which facilitated diffusion is different from active transport.
similarity
difference 1
difference 2

[ 3 ]

Question (d)

(d)

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

[ 2 ]

Question (i)

(i)

Prostaglandins are examples of cell-signalling molecules.

Outline the process of cell signalling that leads to a response by the cells involved in inflammation.

[ 2 ]
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