tranport

Question 1

A student investigated the effect of pH on the activity of the enzyme amylase.
She set up the apparatus shown in the diagram.

The tubes were made from Visking tubing. Visking tubing is partially permeable.
She added an equal volume of amylase solution and starch to each tube.

• She added a buffer solution at pH2 to tube A.
• She added an equal volume of buffer solution at pH8 to tube B.

After 30 minutes, she measured the height of the solutions in both tubes.
She then tested the solutions in tubes A and B for the presence of reducing sugars.

(3)

(b) After 30 minutes, the solution in tube B was higher than the solution in tube A.

(i) Explain why the solution in tube B was higher.

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(3)

(ii) The student concluded from her investigation that the optimum pH of amylase was pH8. Is this conclusion valid? Explain your answer.

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Answer 1

Starch hydrolysed / broken down / glucose / maltose produced;

Neutral: Sugar produced

2. Lower water potential;
3. Water enters by osmosis;

3

(ii) Only 2 pHs studied / more pHs need to be tested;

Question 1

Suggest one way in which the scientist could have ensured the solutions she used for curve X contained no oxygen.

Answer 1

She could have used) boiled (and cooled) water

OR

Layer of oil in top of solution;

Question 2

During early pregnancy, the glycogen in the cells lining the uterus is an important energy source for the embryo.

Suggest how glycogen acts as a source of energy.

Do not include transport across membranes in your answer.

Answer 2

Membrane folded so increased / large surface area;

OR

Membrane has increased / large surface area for (fast) diffusion / facilitated diffusion / active transport / co-transport;

2. Large number of protein channels / carriers (in membrane) for facilitated diffusion;
3. Large number of protein carriers (in membrane) for active transport;

Question 3

A dialysis machine contains artificial membranes which enable urea to be removed from the blood of a person with kidney failure. The diagram shows a dialysis machine.

Suggest two reasons for keeping the fluid in the dialysis machine at 40 °C rather than room temperature.

1. ____________________________________________________________

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2. ____________________________________________________________

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(2)

(iii) The blood and the dialysis fluid flow in opposite directions in the dialysis machine. Explain the advantage of this.

Answer 3

higher rate of exchange / diffusion;
prevents cooling of the blood / prevents increase in viscosity;

2

(iii) concentration gradient maintained / equilibrium never achieved;
blood always meets fluid with lower concentration of urea;
diffusion / exchange along the whole length of surface;