1 membranes

1 Membranes1. The diagram below shows the structure of the cell surface membrane.

(a)

(i)

Name the molecules A and B.

A ............................................................................................................................. B ............................................................................................................................(2)

(ii)

Give one function of the molecule labelled A. ............................................................................................................................... ...............................................................................................................................(1)

(iii)

Explain why the molecules labelled B form a bilayer. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ...............................................................................................................................(3)

AS Unit 1: Lifestyle, Transport, Genes and Health: Topic 2: Genes and Health

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(b)

The proteins in the cell surface membranes of two cells (A and B) were stained using different coloured dyes. One cells membrane proteins were stained with a green dye and the other cells membrane proteins with a red dye. The cells were then fused (merged together) to form one cell. The diagram below shows the distribution of the proteins in the cells before and after fusion.

Use your knowledge of the properties of cell surface membranes to explain these results. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ......................................................................................................................................(2) (Total 8 marks)

1 Membranes2. The diagram below shows a model of the structure of the cell surface (plasma) membrane. g l y c o p r o t e i n p r o t e i n

p (a)

h

o

s p

h

o

l i p

i d

c h

o

l e s t e r o

l

Explain why the model used to describe the structure of this cell membrane is called the fluid mosaic model. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(b)

The graph below shows how the permeability of three different membranes to substance A changes with temperature. One of the membranes contains no cholesterol, one of the membranes has a low cholesterol content and the third membrane has a high cholesterol content.

P e r m e a b i l i o f m e m b r a t o s u b s t a n c a r b i t r a r y u

t y n e e A n i t s

/

0

1

0 T e m p

0 e r a t u

2

3 r e / C

0


3

(i)

Describe the effects of the presence of cholesterol and of an increase in temperature on the permeability of the three membranes to substance A. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

(ii)

When cholesterol is present it binds weakly to the phospholipids in the membrane. Substance A moves across the membrane between the phospholipid molecules. Suggest an explanation for the effect cholesterol has on the permeability of the membranes to substance A. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2) (Total 7 marks)

3.

(a) The table below refers to three transport mechanisms. If the statement is true, put a cross in the appropriate box. Statement Movement of water Requires ATP Molecules move down their concentration gradient Carrier proteins are needed(6)

Osmosis

Facilitated diffusion

Active transport

1 Membranes(b) An experiment was carried out to measure the uptake of substance B by some red blood cells. The red blood cells were placed in a solution containing substance B and kept at 25 C. The concentration of substance B in the cytoplasm of the cells was measured every hour over a period of 10 hours. The results of this experiment are shown in the graph below. 2 1 1 1 1 0 8 6 4 2 n / S u b s t a n c e B

C o n c e n t r a t i o i n c y t o p 1 l 0a s m g c- 3 m 8 6 4 2 0 0

2

4 T i m e

6 / h o u

8 r s

1

0

(i)

Describe the changes in cytoplasm concentration of substance B shown in the graph and explain how these changes support the statement that substance B enters the cells by diffusion. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(4)


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(ii) Suggest how the shape of the graph would change if the temperature in the experiment was decreased to 10 C. Give an explanation for your answer. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2) (Total 12 marks)

4. Animals have evolved a heart and a circulation system as a mechanism which overcomes the 2+ limitations of diffusion. However, diffusion is still important in animals. For example, calcium (Ca ) ions can be absorbed by facilitated diffusion from the bloodstream into muscle cells. (a) Describe how ions such as Ca diffusion.2+

pass through the cell surface membrane by facilitated

..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(4)

1 Membranes(b) 1 The graph below shows the diffusion of Ca over a 10 minute time period. 02+

ions into a cell at two different temperatures

8 C o n c e n tra tio n o f c a 2+ io n s in th e c e ll / a rb itra ry u n its

6

K

e y a t 2 a t 3 0 0

4

2

0 0 2 4 T i m e 6 / m i n 8 u t e s 1 0

(i)

Describe the uptake of Ca

2+

ions by the cell over the 10 minute period at 30 C.

........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)


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(ii)

Use the graph to describe the effect of a 10 C temperature rise (from 20 C to 2+ 30 C) on the uptake of Ca ions into this cell. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(iii)

Suggest an explanation for the effect you have described in part (ii). ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2) (Total 11 marks)

5.

Read through the following account of the transport of molecules across a cell surface membrane, then write on the dotted lines the most appropriate word or words to complete the account. Some molecules cross a cell surface membrane by passing down a concentration gradient through the phospholipid layer. This process is called ................................................ Some polar molecules cross the membrane by combining with transport proteins which can change their shape. When this movement occurs down a concentration gradient, the process is called ............................................... and when it occurs against a concentration gradient the process is called ................................................ Most movement of molecules against a concentration gradient uses energy in the form of ................................................(Total 4 marks)

1 membranes

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