MeiosisAQA A-Level Biology: Subtopic test

1. 1
   A grasshopper has 24 chromosomes in each of its body cells. Sperm cells are produced in the testes by meiosis, starting from diploid cells that have already replicated their DNA.

   (a)

   How many chromosomes are present in each cell at the end of the first meiotic division in the grasshopper?

   [1 mark]

   • A6
   • B12
   • C24
   • D48

   (b)

   What is the usual outcome of meiosis in the testes of the grasshopper, starting from one diploid cell?

   [1 mark]

   • ATwo cells, each with 12 chromosomes
   • BTwo cells, each with 24 chromosomes
   • CFour cells, each with 24 chromosomes
   • DFour cells, each with 12 chromosomes

   (c)

   Explain why the first division of meiosis is known as a reduction division.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a species of seaweed, the main plant body is haploid. It releases gametes, and two gametes fuse to form a diploid zygote. The zygote grows by mitosis into a diploid plant body, which releases spores. Each spore grows by mitosis into a new haploid plant body. Cells of the diploid plant body contain 18 chromosomes.

   (a)

   At which stage of the seaweed life cycle does meiosis occur?

   [1 mark]

   • AWhen the haploid plant body releases gametes
   • BWhen two gametes fuse to form a zygote
   • CWhen the diploid plant body forms spores
   • DWhen a spore grows into a haploid plant body

   (b)

   The haploid seaweed plant body makes gametes by mitosis rather than meiosis. Which statement explains this?

   [1 mark]

   • AMitosis halves the chromosome number, which is needed for gametes
   • BThe cells are already haploid, and mitosis keeps the chromosome number the same
   • CMitosis produces genetically different cells, which gametes require
   • DMeiosis can only occur in animals

   (c)

   State the number of chromosomes in a spore of this seaweed and explain how this number is produced from the diploid plant body.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A biologist studies cells in the testis of a mouse, where each body cell has 40 chromosomes. Some testis cells divide by mitosis to produce more of the same cell type, while others divide by meiosis to form sperm.

   (a)

   Describe what happens to the chromosomes in the first division of meiosis and how this differs from what happens in the second division.

   [3 marks]

   (b)

   Compare the outcomes of mitosis and meiosis when each starts with one mouse testis cell containing 40 chromosomes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A researcher studies a species of fly in which each body cell has six chromosomes, arranged as three homologous pairs: one long pair, one medium pair and one short pair. In one testis cell undergoing meiosis, DNA replication has already taken place, so every chromosome consists of two sister chromatids.

   (a)

   Describe the chromosome content of the cells produced from this testis cell at the end of the first meiotic division and at the end of the second meiotic division.

   [6 marks]

   (b)

   Explain the different outcomes of mitosis and meiosis in this fly, and suggest why the difference is essential for sexual reproduction.

   [6 marks]

   Total for question 4: 12 marks

End of questions