6.2 Meiosis
6 exam questions worth 13 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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How many chromosomes are in (a) a human body cell and (b) a human sperm cell?
Mark scheme
- (a) 46 / 23 pairs (1)
- (b) 23 (1)
Model answer
A body cell has 46 chromosomes and a sperm cell has 23.
Explain why gametes must have half the number of chromosomes of a body cell.
Mark scheme
- at fertilisation two gametes fuse (1)
- so the full / normal number of chromosomes is restored (and not doubled) (1)
Model answer
When two gametes fuse at fertilisation, their chromosomes combine, so the fertilised egg gets the normal number of 46 instead of double.
Give two differences between meiosis and mitosis.
Mark scheme
Any two from:
- meiosis makes four cells, mitosis two (1)
- meiosis cells have half the chromosomes / haploid; mitosis same number (1)
- meiosis cells are genetically different; mitosis identical (1)
- meiosis has two divisions, mitosis one (1)
Model answer
Meiosis makes four cells but mitosis makes two, and the cells from meiosis are genetically different while those from mitosis are identical.
Where does meiosis take place in a flowering plant?
Choose one answer.
Correct Not quite: the answer is Anthers and ovaries
Mark scheme
C: anthers and ovaries
Model answer
C: in the anthers and ovaries.
Describe what happens during meiosis.
Mark scheme
- copies of the genetic information / chromosomes are made (1)
- the cell divides twice (1)
- four gametes are formed (1)
- each with a single set of chromosomes / half the number (1)
- all genetically different (1)
Maximum 4 marks
Model answer
First the chromosomes are copied. Then the cell divides twice, forming four gametes. Each gamete has a single set of chromosomes, and they are all genetically different from each other.
What happens to a fertilised egg cell after fertilisation?
Mark scheme
- divides by mitosis (1)
- (forming an embryo whose) cells differentiate (1)
Model answer
It divides by mitosis to form an embryo, and as the embryo develops its cells differentiate.
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