Paper 1: 2017

Question 1

Describe the role of a ribosome in the production a polypeptide. Do not include transcription in your answer. (3)

Answer 1

mRNA binds to ribosome.
There are two codons/ binding sites available.
tRNA and anticodon can bind together.

Question 2

Suggest and explain two ways the cell-surface membranes of the cells lining the
uterus may be adapted to allow rapid transport of nutrients. (2)

Answer 2

1. Cell membrane is highly folded allowing for faster diffusion.
2. CSM has large numbers of protein carriers for facillitated diffusion.

Question 3

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some
of these cells have membranes with a carrier protein called NHE3.

NHE3 actively transports one sodium ion into the cell in exchange for one proton
(hydrogen ion) out of the cell.

Use your knowledge of transport across cell membranes to suggest how NHE3
does this. (3)

Answer 3

1. Co-transport.
2. Uses ATP.
3. Sodium ion and proton bind to the protein
4. causing the protein to change shape (moving the Na+ ion and proton across the membrane.)

Question 4

Scientists investigated the use of a drug called Tenapanor to reduce salt absorption
in the gut. Tenapanor inhibits the carrier protein, NHE3.

The scientists fed a diet containing a high concentration of salt to two groups of
rats, A and B.

• The rats in Group A were not given Tenapanor (0 mg kg–1).
• The rats in Group B were given 3 mg kg–1 Tenapanor.

One hour after treatment, the scientists removed the gut contents of the rats and
immediately weighed them.

Their results are shown in Table 2.
Table 2
Concentration of Tenapanor / mg kg–1
1. 0
2. 3
Mean mass of contents of the gut / g
1. 2.0
2. 4.1

The scientists carried out a statistical test to see whether the difference in the
means was significant. They calculated a P value of less than 0.05.

They concluded that Tenapanor did reduce salt absorption in the gut.

Use all the information provided and your knowledge of water potential to explain
how they reached this conclusion. (4)

Answer 4

1. There is a significant difference with Tenapanor between A and B
2. less than 0.05 probability shows that the significant difference is due to chance.
3. More salt in the gut reduces the water potential in the gut contents
4. Less water is absorbed out of gut by osmosis.

Question 5

High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid.

Explain how. (2)

Answer 5

High salt -> higher blood pressure so more fluid is forced out of the capillary.

Question 6

Some proteases are secreted as extracellular enzymes by bacteria.
Suggest one advantage to a bacterium of secreting an extracellular protease in its natural environment.
Explain your answer. (2)

Answer 6

To digest more protein allowing them to absorb amino acids for growth or protein sythesis.

Question 7

Mammals have some cells that produce extracellular proteases. They also have
cells with membrane-bound dipeptidases.
Describe the action of these membrane-bound dipeptidases and explain their
importance. (2)

Answer 7

1. Hydrolyse peptide bonds to release the amino acids.
2. This will allow the amino acids to cross through the membrane as dipeptidases cannot.

Question 8

The new antibiotic is safe to use in humans because it does not inhibit the ATP
synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase is inhibited. (1)

Answer 8

The structure of the active site of the human ATP synthase and the bacterial synthase are different.

Question 9

The antibiotics were given to the mice at a dose of 25 mg kg–1 per day.
Calculate how much antibiotic would be given to a 30 g mouse each day.
Show your working (2)

Answer 9

25mg kg-1 to g = 0.025mg g-1. (1)
30g to kg = /1000
30/1000 = 0.03kg (1)

0.03 X 25 = 0.75mg