Cell Structure, Reproduction and DevelopmentEdexcel International A Level Biology: Topic test

1. 1
   A light microscope can distinguish two points only if they are at least 0.2 µm apart. A student wants to see the internal membrane folds (cristae) of mitochondria. A mitochondrion is about 1.5 µm long, and its membrane folds are about 20 nm apart.

   (a)

   Why can the student not see the membrane folds using a light microscope?

   [1 mark]

   • AThe magnification of a light microscope cannot be increased enough
   • BThe wavelength of light is too long, so the resolution is too low to distinguish structures 20 nm apart
   • CMitochondria are too thick for light to pass through
   • DStains cannot be used with a light microscope

   (b)

   In an electron micrograph, the image of one mitochondrion is 30 mm long. What is the magnification of the micrograph?

   [1 mark]

   • A× 200
   • B× 2,000
   • C× 20,000
   • D× 45,000

   (c)

   Explain why specimens are stained before they are viewed under a microscope.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student compares a bacterial cell with a cell of yeast, which is a eukaryote. Both types of cell have a cell wall.

   (a)

   Which structure is found in a yeast cell but not in a bacterial cell?

   [1 mark]

   • AA nucleus surrounded by a nuclear envelope
   • BA plasmid
   • CA cell wall
   • DRibosomes

   (b)

   What is the function of pili on a bacterial cell?

   [1 mark]

   • AMovement of the cell through liquid
   • BProtection against the cells of the immune system
   • CStorage of genes for resistance to antibiotics
   • DAttachment to surfaces and to other bacterial cells

   (c)

   Describe the functions of the flagellum and of the cell wall in a bacterial cell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A diploid animal has a body cell with 6 chromosomes (2n = 6), made of three pairs of homologous chromosomes. Cells in its gonads divide by meiosis to make gametes.

   (a)

   Calculate the number of different combinations of chromosomes that can be found in the gametes as a result of independent assortment alone, and explain how independent assortment produces genetic variation.

   [3 marks]

   (b)

   Explain how crossing over during meiosis produces genetic variation in the gametes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A plasma cell is a type of white blood cell that makes large quantities of antibody proteins and releases them from the cell. A plasma cell contains the same genes as the other nucleated cells of the body.

   (a)

   Describe how the organelles of a plasma cell are involved in making an antibody and releasing it from the cell.

   [6 marks]

   (b)

   Explain how the plasma cell can contain the same genes as other cells of the body but make a different set of proteins.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A pathologist examines a stained section of tissue from a tumour. In one field of view she counts 250 cells, of which 40 are in mitosis. In a section of normal tissue from the same organ, the mitotic index is 0.03.

   (a)

   What is the mitotic index of the tumour tissue?

   [1 mark]

   • A0.040
   • B6.25
   • C0.16
   • D0.19

   (b)

   Which statement describes anaphase of mitosis?

   [1 mark]

   • AChromosomes line up at the equator of the cell
   • BChromosomes condense and become visible
   • CThe nuclear envelope reforms around each set of chromosomes
   • DCentromeres divide and sister chromatids are pulled to opposite poles

   (c)

   Suggest why the mitotic index of the tumour tissue is higher than that of the normal tissue.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Fertilisation in humans takes place in the oviduct. A sperm cell must reach the secondary oocyte, which is surrounded by a protective layer called the zona pellucida.

   (a)

   What is the function of the acrosome of a sperm cell?

   [1 mark]

   • AIt contains enzymes that digest the zona pellucida
   • BIt contains mitochondria that supply ATP for swimming
   • CIt contains the sperm cell's DNA
   • DIt forms the flagellum used for movement

   (b)

   After the nuclei of the sperm and the secondary oocyte fuse, which cell is formed?

   [1 mark]

   • AA haploid cell with 23 chromosomes
   • BA diploid zygote with 46 chromosomes
   • CA haploid zygote with 46 chromosomes
   • DA diploid cell with 23 chromosomes

   (c)

   Describe the roles of the zona pellucida in fertilisation.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A fertilised human egg divides to form a solid ball of cells, the morula, and then a hollow ball called the blastocyst. Researchers want to use stem cells from early embryos to repair damaged tissue, but some people object to the use of human embryos in this way.

   (a)

   Compare totipotent stem cells with pluripotent stem cells.

   [3 marks]

   (b)

   Evaluate the use of embryonic stem cells to treat damaged tissue.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   In a mammal, a fertilised egg develops into an adult made of millions of cells. The cells of the adult divide for growth and repair, and the adult also makes gametes, which fuse to form the next generation.

   (a)

   Compare the processes of mitosis and meiosis.

   [6 marks]

   (b)

   Describe the events of fertilisation in a mammal from the arrival of the sperm cell at the secondary oocyte, and explain why meiosis is necessary for the chromosome number to stay constant between generations.

   [6 marks]

   Total for question 8: 12 marks

End of questions