Class 12th Biology 2017 Set1 Outside Delhi Board Paper Solution
A pollen grain in angiosperm at the time of dehiscence from an anther could be 2-celled or 3-celled. Explain. How are the cell placed withing the pollen grain when shed at a 2-celled stage?
A pollen grain is partly germinated microspore representing the male gametophyte. It divides by unequal mitotic division and forms two cells. Thus, each mature pollen grain in angiosperms have a generative cell and a vegetative cell. In about 60% of angiosperms, pollen grains are shed at this 2-celled stage.
However, in about 40% flowering plants, the generative cell may further divide mitotically to give rise to two male gametes and pollen grains are shed at this 3-celled stage. The placement of cells within the pollen grain when shed at 2-celled stage can be visualised as :
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