Summative Practice 15 – Question 1 – 4 (Form 4 Biology Textbook Exercise and Answer)

Question 1:
What causes the premenstrual syndrome in some women?

Imbalance of the oestrogen and progesterone levels

Question 2:
State the differences between the formation of identical and fraternal twins.

Identical twins are formed when a fertilised ovum divides to form two zygotes whereas fraternal twins are produced when two simultaneously released ova are fertilised by two separate sperms to form two zygotes.

Question 3:
The foetus has its own blood circulation system, separate from its mother.
Explain why.

• To protect the fine blood vessels of the foetus from bursting due to the high blood pressure of the mother

• To prevent the mother’s and foetus blood from mixing which may cause agglutination.

Question 4:
(a) A pair of identical twins were separated at birth. Once they reached adulthood, they found out that they both have different body sizes. Explain the factors that would cause this.

(b) Explain why pregnant mothers must stop smoking.

Both grew up in different conditions. Therefore, their food intake was different and both carried out different daily activities.

• Chemicals such as nicotine and carbon monoxide diffuse across the placenta into the foetus.
• Nicotine may affect foetus growth.
• Carbon monoxide competes with oxygen to combine with haemoglobin.
• This reduces the oxygen content received by the foetus and may cause miscarriage.

Leave a Comment