Answer any two of the following :
(i) Draw a longitudinal section of the pistil of an angiosperm showing the growth of pollen tube up to the micropyle of ovule, Label (a) stigma, (b) embryo sac, (c) pollen tube, (d) micropyle,
(ii) Explain the events that occurs, up to fertilisation, when the compatible pollen grain lands on the stigma.

Explanation

(i)
(ii) The sequence of events that occur when a compatible pollen grain lands on stigma are as follows:
(a) Pollen-pistil interactions Once the compatible pollen grain lands on stigma which is receptive, it recognises and accepts the pollen with the aid of chemical components, interacting with pollen.
(b) Germination of pollen grain Once the pollen is recognised, it germinates on the stigma. of flower. The tube cell of pollen grain protrudes out through germ pores to form a .pollen tube. The generative cell divides to form two male gametes and are released into the tube.
(c) Growth of pollen tube The pollen tube grows down through the tissues of stigma and style and enters ovule, usually through micropyle end of ovule. Inside ovule, the filiform apparatus guides the pollen tube, carrying gametes to the egg.
(d) Double fertilisation After releasing the two male gametes into the synergids, one of them fuses with egg to form a diPloid zygote (syngamy) and other male gamete fuses with diploid polar nuclei to form triploid primary endosperm cell (triple fusion). Because of occurrence of these two types of fusions, this event is called double fertilisation.