b. When does a pollen grain germinate?
c. How many nuclei are present in pollen grain and what are
their functions?
Answers
Answer:
Pollen germination starts with the pollen grain landing on stigma. The cell of the pollen grain divides into two cells- one of these is smaller in size and called generative cell and bigger one is called tube cell. The intine grows out through the germ pore and form pollen tube. It grows into the tissue of the style towards the ovary. By this time the tube nucleus degenerates and the generative nucleus divides to form two male gametes. The pollen tube bursts open and the male gametes are released –one of which then fuse with the egg cell and other nuclei with two polar nuclei.
In non-flowering seed plants, pollen generates in the pollen chamber, located beneath the micropyle, underneath the instruments of the ovule. A pollen tube is produced, which grows into the nucleus to provide nutrients for the developing sperm cells.
