Practise explaining mammalian fertilisation from sperm binding to nucleus fusion, including acrosome and cortical reactions.
Fertilisation in mammals, such as the African northern white rhino, results in the fusion of gamete nuclei.
The photograph shows the last two remaining northern white rhinos.
Both of these rhinos are female.
Sperm and tissue samples were taken from the last few male northern white rhinos before they died. The sperm samples were frozen.
Sperm cells contain a digestive enzyme called acrosin.
The effect of acrosin activity of samples of sperm cells on the percentage of egg cells fertilised was investigated.
The graph shows the results of this investigation.
> acrosin activity of the sperm cell/a.u. sample
Explain why a higher activity of the digestive enzyme acrosin resulted in a higher percentage of egg cells being fertilised.
In vitro fertilisation (IVF) has been used to fertilise northern white rhino egg cells using the frozen sperm samples.
The zona pellucida of some egg cells were damaged when they were removed from the ovaries of the females.
The drawing shows a fertilised egg cell with three nuclei.
magnification \(\times 200\)
Suggest why this fertilised egg cell has three nuclei.