Prokaryotic cells and virusesAQA A-Level Biology: Subtopic test

1. 1
   A student compares the bacterium Escherichia coli, which is about 2 μm long, with a human liver cell, which is about 25 μm across.

   (a)

   Which statement about the DNA of the E. coli cell is correct?

   [1 mark]

   • AIt is a single circular molecule, free in the cytoplasm and not associated with protein
   • BIt is linear and bound to protein inside a nucleus
   • CIt is circular and enclosed by a nuclear envelope
   • DIt is made of several linear chromosomes free in the cytoplasm

   (b)

   Which structure of E. coli contains murein?

   [1 mark]

   • AThe capsule
   • BThe cell wall
   • CA plasmid
   • DThe flagellum

   (c)

   State two differences between the DNA of E. coli and the DNA of the human liver cell.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Some antibiotics work by binding to bacterial ribosomes and stopping protein synthesis, but they do not affect protein synthesis in the cells of the person taking them. A scientist is investigating why.

   (a)

   Which difference between bacterial and human cells best explains why the antibiotic affects only the bacterial ribosomes?

   [1 mark]

   • ABacterial ribosomes are found inside a nucleus
   • BBacterial ribosomes are attached to endoplasmic reticulum
   • CBacterial ribosomes are smaller than those of human cells
   • DBacterial ribosomes are made of murein

   (b)

   Which statement about murein is correct?

   [1 mark]

   • AIt is a lipid found in the cell-surface membrane of bacteria
   • BIt is a polysaccharide found in plant cell walls
   • CIt is a protein found in the capsid of viruses
   • DIt is a glycoprotein found in the cell wall of bacteria

   (c)

   Suggest why an antibiotic that binds to bacterial ribosomes is unlikely to harm human cells, and why it stops the bacteria from growing.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Pseudomonas aeruginosa is a bacterium that infects the lungs of patients with cystic fibrosis. Each cell has a capsule, flagella and several plasmids, and one plasmid carries a gene for antibiotic resistance. The bacteria live alongside human lung epithelial cells.

   (a)

   Suggest how the capsule, the flagella and the plasmids help Pseudomonas aeruginosa to survive and spread in the lungs.

   [3 marks]

   (b)

   Compare the structure of a Pseudomonas aeruginosa cell with that of a human lung epithelial cell.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Influenza is caused by a virus. A patient with influenza asks a doctor for the antibiotic penicillin, which prevents bacteria from forming murein in their cell walls. The influenza virus particle consists of RNA surrounded by a protein coat, with attachment proteins projecting from its surface.

   (a)

   Describe the structure of a virus particle and explain why viruses are described as acellular and non-living.

   [6 marks]

   (b)

   Explain why penicillin kills bacteria but has no effect on the influenza virus.

   [6 marks]

   Total for question 4: 12 marks

End of questions