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Which one of the following is surrounded by a callose wall?
A
male gamete
B
egg
C
pollen grain
D
microspore mother cell
Detailed Solution
Callose is a polysaccharide, a $\beta$-1,3-glucan.
Each microspore mother cell (pollen mother cell) of the sporogenous tissue becomes surrounded by a thick wall of callose before it undergoes meiosis.
This callose wall isolates the meiotic cells from each other and from the surrounding tissue; the four microspores of the tetrad are also held within callose.
Later the enzyme callase, secreted by the tapetum, dissolves the callose wall and the microspores are set free to develop into pollen grains.
The mature pollen grain is covered by the exine made of sporopollenin and the intine made of cellulose and pectin, not by callose.
The male gametes and the egg are not enclosed in callose walls.
So the structure surrounded by a callose wall is the microspore mother cell.
Each microspore mother cell (pollen mother cell) of the sporogenous tissue becomes surrounded by a thick wall of callose before it undergoes meiosis.
This callose wall isolates the meiotic cells from each other and from the surrounding tissue; the four microspores of the tetrad are also held within callose.
Later the enzyme callase, secreted by the tapetum, dissolves the callose wall and the microspores are set free to develop into pollen grains.
The mature pollen grain is covered by the exine made of sporopollenin and the intine made of cellulose and pectin, not by callose.
The male gametes and the egg are not enclosed in callose walls.
So the structure surrounded by a callose wall is the microspore mother cell.