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  • (a) Draw the embryo sac of a flowering plant and label the following : (i) Central cell (ii) Chalazal end (iii) Synergids (b) Name the cell and explain the process it undergoes to develop into an embryo sac.

(a) Draw the embryo sac of a flowering plant and label the following :
(i) Central cell
(ii) Chalazal end
(iii) Synergids

(b) Name the cell and explain the process it undergoes to develop into
an embryo sac.

(c) Explain the development of endosperm in coconut.

 

 

 

 
 
 
 
 

Answers (1)

a)
 
b) The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. These mitotic divisions are strictly free nuclear, that is, nuclear divisions are not followed immediately by cell wall formation. After the 8-nucleate stage, cell walls are laid down leading to the organization of the typical female gametophyte or embryo sac.
Six of the eight nuclei are surrounded by cell walls and organized into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.

c) The coconut water from tender coconut is nothing but free-nuclear endosperm (made up of thousands of nuclei) and the surrounding white kernel is the cellular endosperm.

The development of endosperm in coconut takes place by the following steps:
1. The nucleus of the primary endosperm gets divided by free nuclear division.
2. The nucleus first divides into 2 and so on till 128 nuclei are formed.
3. By the process of cytokinesis (the process of physical cell division into daughter cells), it finally converts into the cellular endosperm.

The function of endosperm:
It provides nutrition to the growing embryo.

Posted by

Priyanka Kumari

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