(a) A - Stigma. The top part of carpel is called stigma. Stigma is for receiving the pollen grains from the anther of stamen during pollination.
B - Pollen tube. When a pollen grain falls on the stigma, it bursts open and grows a pollen tube downward through the style towards the female gamete in the ovary. A male gamete moves down the pollen tube.
C- Female gamete (ovum). It is a special reproductive female sex cell which combines with male gamete to form zygote.
(b) Sexual reproduction takes place by the combination of special reproductive cells called sex cells. These cells are of two types - male sex cells and female sex cells, which are coming from two different parents-a male and a female. The cells involved in sexual reproduction are called gametes. In sexual reproduction, a male gamete fuses with a female gamete to form a new cell called zygote. This zygote then grows and develops into a new organism in due course of time.
