Membranes, Proteins, DNA and Gene ExpressionEdexcel International A Level Biology: Topic test

20 questions, 54 marks

Edexcel International A Level Biology

Membranes, Proteins, DNA and Gene Expression topic test

Total 54 marks

Name

Class

Date

1
In emphysema, the walls between neighbouring alveoli break down, so each lung contains fewer, larger air spaces. Patients become breathless because less oxygen enters the blood.
(a)
According to Fick's law, which change would decrease the rate of diffusion of oxygen across the gas exchange surface?
[1 mark]
AA decrease in the surface area of the exchange surface
BA decrease in the thickness of the exchange surface
CAn increase in the concentration difference across the exchange surface
DAn increase in the number of capillaries around each alveolus
(b)
Which feature of the mammalian lung helps to maintain a steep concentration gradient for oxygen between the alveoli and the blood?
[1 mark]
AAlveolar walls that are several cells thick
BBlood flowing continuously through the capillaries around the alveoli
CA low rate of ventilation of the lungs
DBlood that stays stationary in the capillaries
(c)
Explain how the loss of the walls between alveoli reduces the amount of oxygen that enters the blood.
[2 marks]
Total for question 1: 4 marks
2
A research student adds phospholipid molecules to water and finds that they spontaneously form a bilayer. She compares this with a cell surface membrane, which is described by the fluid mosaic model.
(a)
Which statement describes the arrangement of phospholipids in the bilayer?
[1 mark]
AThe hydrophilic heads face inwards and the hydrophobic tails face the water
BThe phospholipids stay evenly dispersed in the water as separate molecules
CThe hydrophilic heads face the water and the hydrophobic tails face inwards, away from the water
DThe phospholipids form a single sheet with all heads on one side and all tails on the other
(b)
What does the word 'mosaic' mean in the fluid mosaic model?
[1 mark]
AThe phospholipids are fixed in position and cannot move
BThe proteins form a continuous layer on the outside of the membrane
CThe membrane is made of a single type of phospholipid molecule
DThe proteins are scattered through the phospholipid bilayer
(c)
Explain why a cell surface membrane is described as fluid.
[2 marks]
Total for question 2: 4 marks
3
A technician places human red blood cells in distilled water and finds that they burst. In a second experiment she measures the rate at which glucose enters red blood cells from solutions of different glucose concentrations. The rate increases as the glucose concentration rises, then levels off at a maximum rate.
(a)
Explain why red blood cells burst when they are placed in distilled water.
[3 marks]
(b)
Explain the shape of the relationship between the rate of glucose uptake and the concentration of glucose.
[4 marks]
Total for question 3: 7 marks
4
A biotechnology company has isolated a protease from a bacterium for use in a biological washing powder. The protease is a globular protein made of a single polypeptide. A mutant strain of the bacterium makes a version of the protease that has no activity. Sequencing shows that the gene for the mutant protease differs from the normal gene by a single base substitution.
(a)
Explain how a single base substitution in a gene could result in a protein that has no enzyme activity.
[6 marks]
(b)
The company needs to find the optimum temperature of the normal protease. Describe how an investigation into the effect of temperature on the initial rate of the reaction could be carried out.
[6 marks]
Total for question 4: 12 marks
5
Before a human cell divides by mitosis, all of the DNA in its nucleus is replicated. The double helix is unwound and each strand is used to make a new strand.
(a)
Which enzyme joins nucleotides together to form the new DNA strand?
[1 mark]
ARNA polymerase
BHelicase
CAmylase
DDNA polymerase
(b)
Which bonds are broken when the two strands of the DNA double helix are separated?
[1 mark]
AHydrogen bonds between complementary bases
BPhosphodiester bonds between nucleotides
CGlycosidic bonds between glucose units
DPeptide bonds between amino acids
(c)
Explain why DNA replication is described as semi-conservative.
[2 marks]
Total for question 5: 4 marks
6
Haemophilia A is a condition in which blood does not clot properly. It is caused by a recessive allele, h, of a gene on the X chromosome. The dominant allele is H. A woman who is a carrier of haemophilia has children with a man who does not have haemophilia.
(a)
What is the genotype of the carrier woman?
[1 mark]
A $X^{H}X^{H}$
B $X^{H}X^{h}$
C $X^{h}X^{h}$
D $X^{h}Y$
(b)
What is the probability that their first child is a son with haemophilia?
[1 mark]
A0
B1 in 2
C1 in 4
D3 in 4
(c)
Explain why haemophilia is more common in males than in females.
[2 marks]
Total for question 6: 4 marks
7
The start of a gene has the template (antisense) strand base sequence TACCTTGGGACT, written from its 3' end to its 5' end. It is transcribed into mRNA, and the mRNA is translated by a ribosome. The mRNA codon CCC codes for the amino acid proline, and so does the codon CCA.
(a)
Give the base sequence of the mRNA, the anticodon on the tRNA that brings the second amino acid to the ribosome, and the number of amino acids in the polypeptide made.
[3 marks]
(b)
A substitution of the third base of the CCC codon could have no effect on the polypeptide, but the insertion of one extra base after the first codon would have a large effect. Explain why.
[4 marks]
Total for question 7: 7 marks
8
A pregnant woman learns that her partner and she are both carriers of the recessive allele that causes cystic fibrosis (CF). The allele f is recessive and the normal allele is F. Her doctor offers either chorionic villus sampling (CVS) or amniocentesis to test the fetus.
(a)
Use a genetic diagram to show the probability that the child will have CF, and describe how one prenatal test could show whether the fetus has the condition.
[6 marks]
(b)
Discuss the ethical and social issues that may arise from prenatal genetic screening for CF.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).