Question

In a 7 celled and 8 nucleate embryo sac:
(a) The polar nuclei are situated below the egg apparatus in central cell
(b) Egg apparatus has two synergids and one egg cell at micropylar end
(c) filiform apparatus in synergids direct the pollen tube to enter into egg cell
(d) Antipodal cells are haploid but have different genetic composition to that of egg cell

How many above statements are true for the statement given in the question?
A. Two
B. Three
C. One
D. Four

Answer 1

Hint: A single functional Megaspore forms the female gametophyte. It receives three mitotic divisions successively to form an eight nucleate embryo sac. The micropylar end has two synergids and one egg cell. This forms the egg apparatus.
The chalazal end has three antipodal cells.

Complete answer:
- A functional megastore forms the female gametophyte i.e embryo sac. It undergoes three mitotic divisions successively to form an 8 nucleated embryo sac which on maturation appears as 7 celled 8 nucleated embryo sac.
- When the first mitotic division occurs, the nucleus divides into two nuclei (one moving to the micropylar end and the other moving to the chalazal end). These nuclei further divide and re-divide on the respective ends to form 8 nucleated cells.
- On the chalaza end, out of four nuclei three differentiate as antipodal cells.
- On the micropylar end, out of four nuclei three differentiate and form one egg cell and two synergids. This forms the egg apparatus.
- The remaining one on both the ends move toward the centre forming a large cell known as the central cell.
- The combined Female gametophyte is a 7-celled and 8 nucleated embryo sacs.
- Therefore, all the statements except (a) i.e the polar nuclei are situated below the egg apparatus in central cell are true for the given question as the plate nuclei are situated above not below the egg apparatus

Hence, the correct answer is option (B).

Note: The female gametophyte has two ends I.e. micropylar end and chalazal end. The micropylar end has two synergids and one egg cell. This forms the egg apparatus.
The chalazal end has three antipodal cells. In the centre lies a large central cell.