1. 1
   A cut on a person's skin heals over several days as new cells are produced by cell division to repair the damaged tissue, all genetically identical to the original skin cells and to each other.

   (a)

   A cut on a person's skin heals over several days as new skin cells are produced to replace damaged tissue. Which type of nuclear division produces these genetically identical new cells?

   [1 mark]

   • AMeiosis
   • BMitosis
   • CFertilisation
   • DOsmosis

   (b)

   Before mitosis begins, an important process must occur inside the cell's nucleus. What is this process?

   [1 mark]

   • AThe exact replication of the chromosomes
   • BThe halving of the chromosome number
   • CThe fusion of two gametes
   • DThe random assortment of alleles

   (c)

   Describe mitosis and explain why the chromosome number stays the same in each new cell produced.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A single-celled bacterium reproduces by dividing into two identical daughter cells, and a gardener observes a strawberry plant producing new, genetically identical plants from runners; a plant biologist explains that both processes rely on the same fundamental role of mitosis.

   (a)

   Which process in more complex, multicellular organisms serves a similar role in producing new individuals from a single parent without a mate, such as in a strawberry plant spreading by runners?

   [1 mark]

   • AFertilisation
   • BSexual reproduction using meiosis
   • CAsexual reproduction using mitosis
   • DDeamination

   (b)

   Beyond growth, tissue repair and asexual reproduction, which of the following is also an important role of mitosis in multicellular organisms?

   [1 mark]

   • AHalving the chromosome number to produce gametes
   • BFusing the nuclei of two cells together
   • CProducing genetic variation between offspring
   • DReplacement of worn-out or dead cells

   (c)

   State two roles of mitosis in a multicellular organism, other than asexual reproduction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Doctors are researching the use of stem cells, which divide by mitosis and can become specialised, to treat patients with damaged liver tissue, and comparing this to how a developing human embryo relies entirely on mitosis to grow from a single fertilised egg into a fully formed body.

   (a)

   A liver contains a small number of unspecialised stem cells that can divide to help repair damaged liver tissue after injury. Describe what is meant by a stem cell, and explain how such cells contribute to the repair of damaged tissue.

   [3 marks]

   (b)

   A human embryo develops from a single fertilised egg (zygote) into a body containing trillions of cells over the course of pregnancy. Explain, in terms of mitosis, how a single zygote can give rise to the many genetically identical cells that make up the tissues and organs of the developing embryo.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A cancer researcher explains that cancer occurs when cells divide by mitosis in an uncontrolled way, forming a tumour of genetically identical cells, and is investigating a new drug designed to stop cancer cells from being able to divide.

   (a)

   A cancer researcher explains that cancer cells divide by mitosis in an uncontrolled way, producing a growing tumour, but the resulting cells remain genetically identical to each other and to the original cancerous cell. Explain, using your understanding of what mitosis normally achieves in the body, why uncontrolled mitosis leads to a mass of genetically identical cells rather than a mass of genetically varied cells, and why this uncontrolled division can be harmful to the body.

   [6 marks]

   (b)

   The researcher is testing a new drug that specifically prevents cells from replicating their chromosomes before mitosis. Explain why this drug would be expected to stop cancer cells from continuing to divide, and discuss why a drug with this mechanism might also cause side effects in healthy, normally dividing tissues of the body such as skin or the lining of the gut.

   [6 marks]

   Total for question 4: 12 marks

End of questions