Answer:
1) pollen grain (A), stigma (B), pollen tube (C), Ovary (D)
The pollen grain is a male reproductive part while ovary is the female reproductive part.
2) When a pollen grain lands on the stigma of a flower, a pollen tube begins to grow. It grows through the style until it reaches an ovule inside the ovary.
3) The pollen tube is a tube that transports the male gamete cells from the pollen grains to the ovule (female gamete) inside the ovary.
The nucleus of the pollen passes along the pollen tube and fuses with the nucleus of the ovule. This process is called fertilisation.
4) After the fertilisation, female parts of the flower develop into fruit and ovules become seeds.
