3.13

Question 1

explain how the pollen tube grow through the style of the flower?

Answer 1

1) enzymes being released
2) these enzymes digest surrounding cells (tissues of style)
3) forming a pathway

Question 2

explain and describe the fertilisation in plants?

Answer 2

1) a pollen grain lands on a stigma of a flower. the grain absorbs water and splits open.
2) a pollen tube tube grows out of the pollen grain down the style. There are three nuclei in the pollen tube, one pollen tube nucleus at the tip and two male gamete nuclei behind it. the tube nucleus makes enzymes that digest surrounding cells, making a way through for the pollen tube.
3) when the tube reaches the ovary, it grows through the micropyle and into the embryo sac within the ovule.
4) in the embryo sac, the tube nucleus disintegrates and the tip of the pollen tube bursts, releasing the two male nuclei.
5) one male nucleus fuses with one egg nucleus to make a zygote, this divides by mitosis to become the embryo of the seed.
6) the second male nucleus fuses with two polar nuclei at the centre of the embryo sac. this produces a cell with a large nucleus, which divides to become food storage (endosperm) for the mature seed.
7) so double fertilisation has occurred.