Explanation

(a) Formation of zygote in a flower takes place in the following ways:

• The pollen grain absorbs water, sugary fluid and glucose from sticky stigma.
• It swells and germinates.
• Pollen tube emerges, carrying a tube nucleus and a generative nucleus.
• The generative nucleus divides into two male nuclei; it grows down the style and ovary wall.
• It derives energy and food from the tissues, to reach the ovule; It enters ovule through the micropyle; to enter embryo sac;
• Pollen tube releases male nuclei into embryo sac; as tube nucleus degenerates.
• Nucleus of one male gamete fuses with the egg cell in order to achieve fertilization which resulted to the formation of zygote.

(b) Importance of Amniotic sac are as follows:

(i) Amniotic fluid contains the embryos.

(ii) This provides a constant warm temperature for the foetus.

(iii) It provides a sterile environment for development.

(iv) It provides hydrostatic protection against mechanical injury and shock

(v) It allows movement of the foetus. 

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