Fig. 1 shows stages used by a clinic offering IVF treatment to a couple who have not achieved pregnancy after two years. Eggs are collected from the woman a...
Question 1 Report
Fig. 1 shows stages used by a clinic offering IVF treatment to a couple who have not achieved pregnancy after two years. Eggs are collected from the woman after hormone treatment. Sperm cells are added in a laboratory dish. Early embryos are observed before one is placed into the uterus. The cells in the embryo divide by mitosis.
(a) Name the process in the dish in which a sperm nucleus joins an egg nucleus. [2]
(b) Describe why the early embryo increases in number of cells before transfer to the uterus. [3]
(c) Suggest two reasons why a clinic may transfer only one embryo, rather than several embryos, to the uterus. [4]
Answer Details
(a) The process is fertilisation: fusion of the male and female nuclei, or gametes. [2 marks]
(b) The embryo cells divide by mitosis. Mitosis produces genetically identical cells, increasing the number of cells so the embryo can grow and develop after implantation. [3 marks]
(c) Transferring one embryo lowers the chance of a multiple pregnancy. Multiple pregnancy increases health risks to the mother and the risk of premature or low-mass babies. It can also avoid having more children than intended and reduce emotional or financial pressure. Any two developed reasons are credited. [4 marks]
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