Cell structure and divisionAQA A-Level Biology: Topic test

1. 1
   A cardiac muscle cell from a human heart contracts continuously. Under an electron microscope its cytoplasm is packed with mitochondria.

   (a)

   Which structure would not be found in this cell?

   [1 mark]

   • AGolgi apparatus
   • BLysosome
   • CCellulose cell wall
   • DNucleolus

   (b)

   Which row describes the DNA in the chromosomes in the nucleus of this cell?

   [1 mark]

   • ALinear and associated with proteins
   • BCircular and associated with proteins
   • CLinear and not associated with proteins
   • DCircular and free in the cytoplasm

   (c)

   Explain why the cell contains so many mitochondria.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Staphylococcus aureus is a bacterium. Each cell has a cell wall, a capsule, a single loop of DNA and a plasmid that carries a gene for antibiotic resistance.

   (a)

   Which row describes the main DNA of S. aureus?

   [1 mark]

   • ALinear, associated with proteins, inside a nucleus
   • BCircular, not associated with proteins, free in the cytoplasm
   • CCircular, associated with proteins, inside a nucleus
   • DLinear, not associated with proteins, free in the cytoplasm

   (b)

   Which substance is the main component of the cell wall of S. aureus?

   [1 mark]

   • ACellulose
   • BChitin
   • CPhospholipid
   • DMurein

   (c)

   State two ways, other than the arrangement of its DNA, in which the structure of S. aureus differs from the structure of a eukaryotic cell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A scanning electron micrograph of red blood cells has a magnification of × 2500. One red blood cell measures 17.5 mm across on the micrograph.

   (a)

   Calculate the actual diameter of the red blood cell in micrometres (μm).

   [3 marks]

   (b)

   Explain the difference between magnification and resolution, and explain why a transmission electron microscope, rather than a scanning electron microscope, would be used to view the internal structure of a cell.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A scientist is studying tumour cells growing in a culture flask.

   (a)

   Describe the behaviour of the chromosomes in these cells from interphase to cytokinesis during mitosis.

   [6 marks]

   (b)

   Explain how uncontrolled cell division leads to a tumour, and how treatments can be directed at the cell cycle.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A cell from a fruit fly has 8 chromosomes before it enters interphase. It then divides by mitosis.

   (a)

   How many chromatids are present in this cell at metaphase?

   [1 mark]

   • A4
   • B8
   • C32
   • D16

   (b)

   What causes the chromatids to be separated during anaphase?

   [1 mark]

   • AThe nuclear envelope re-forming
   • BReplication of the DNA
   • CSpindle fibres attached to centromeres shortening
   • DCytokinesis dividing the cytoplasm

   (c)

   State the stage of the cell cycle in which the DNA is replicated, and explain why this must happen before mitosis.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Before it divides by binary fission, a bacterial cell has one circular DNA molecule and three copies of a plasmid.

   (a)

   Which structures are replicated before the cell divides?

   [1 mark]

   • AThe circular DNA and the plasmids
   • BOnly the circular DNA
   • COnly the plasmids
   • DLinear chromosomes and the plasmids

   (b)

   What does each daughter cell receive?

   [1 mark]

   • AOne copy of the circular DNA and exactly three plasmids
   • BOne copy of the circular DNA and a variable number of plasmids
   • CHalf of the circular DNA and half of the plasmids
   • DTwo copies of the circular DNA and all of the plasmids

   (c)

   Viruses cannot divide by binary fission. Explain why, and state how new virus particles are produced.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Tuberculosis is caused by the bacterium Mycobacterium tuberculosis, and AIDS is caused by the virus HIV.

   (a)

   Describe the structure of a virus particle such as HIV.

   [3 marks]

   (b)

   Give four ways in which the structure of M. tuberculosis differs from the structure of HIV.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A research student is studying cells from a pea plant leaf and, for comparison, the bacterium Rhizobium that lives in nodules on pea roots.

   (a)

   Compare the structure of a Rhizobium cell with that of a pea leaf cell.

   [6 marks]

   (b)

   Describe how cell fractionation and ultracentrifugation could be used to separate the nuclei, chloroplasts and mitochondria from the leaf tissue.

   [6 marks]

   Total for question 8: 12 marks

End of questions