Diagram shows two types of twins.
(a)(i) Name the type of twins M. [1 mark]
(ii) Explain how twins M are formed. [2 marks]
(b)(i) Name the structure W. [1 mark]
(ii) State two functions of structure W. [2 marks]
(c) State two differences between twins K and twins M. [2 marks]
(d) Twins K are brought up by two different adopted families. The twins do not have the same body size when they are adult.
Explain why. [2 marks]
(e) A woman who is a heavy smoker becomes pregnant.
Explain why she should stop smoking. [2 marks]
When two ova are released from an ovary at the same time, the ova are fertilised by two different sperms at the same time and two different zygotes are formed.
– Provides nutrients for the growth of the foetus
– Secretes oestrogen and progesterone
– Helps to remove waste/ excretory products from the foetus
- Twins K share the same placenta whereas twins M have separate placentae.
- Twins K possess identical genetic constituents whereas twins M has different genetic constituents.
- Twins K are similar in physical appearance but twins M are not.
They may have different eating habits and different daily activities.
– Chemicals such as nicotine can diffuse through the placenta to the foetus and may cause brain damage.
– Carbon monoxide can diffuse through the placenta to the foetus. This will deprive the foetal tissues for oxygen.