Monday 12 June 2017

Question 1

Give the two types of molecule from which a ribosome is made.

Answer 1

• One of RNA

- One of proteins

Question 2

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

Answer 2

1. mRNA binds to ribosome;
2. Idea of two codons/binding sites;
3. (Allows) tRNA with anticodons to bind/associate;
4. (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules);
5. Moves along (mRNA to the next codon)/translocation described;

Question 3

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA.
Explain why.

Answer 3

1. Introns (in pre-mRNA);

2. Removal of sections of (pre-mRNA)/splicing;

Question 4

Describe the structure of glycogen.

Answer 4

1. Polysaccharide of α-glucose;

2. (Joined by) glycosidic bonds

Question 5

Suggest how glycogen acts as a source of energy.

Do not include transport across membranes in your answer.

Answer 5

1. Hydrolysed (to glucose);

2. Glucose used in respiration;

Question 6

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

Answer 6

1. 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;
4. Large number of protein (channels/carriers in membrane) for co-transport;

Question 7

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.

Answer 7

1. Co-transport;
2. Uses (hydrolysis of) ATP;
3. Sodium ion and proton bind to the protein;
4. Protein changes shape (to move sodium ion and/or proton across the membrane);

Question 8

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.

Answer 8

1. There is a significant difference with Tenapanor/drug/between A and B;
2. There is a less than 0.05 probability that the difference is due to chance;
3. (More salt in gut) reduces water potential in gut (contents);
4. Water moves into the gut (contents) by osmosis.

Question 9

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.

Answer 9

1. Co-transport;
2. Uses (hydrolysis of) ATP;
3. Sodium ion and proton bind to the protein;
4. Protein changes shape (to move sodium ion and/or proton across the membrane);