2.5 Sexual reproduction in plants

Question 1

Define hermaphrodite

Answer 1

A multicellular organism that possesses both male and female reproductive structures. Most flowering plants are hermaphrodites. Fewer animals are hermaphrodites, but this condition is common in organism such as slugs, snails and is seen in some fish.

Question 2

What are the female structures called?

Answer 2

Carpels
- - each carpel consists of a stigma- a platform on which pollen grains may land
- a syte that supports the stigma and an ovary
- inside the ovary you can see an ovule that contains the female gametes

Question 3

What are the male structures called?

Answer 3

Stamens
-consits of an anther and a filament
-anther produces pollen grains that contain the male gametes

Question 4

Pollen formation:

Answer 4

1. Diploid microspore mother cells in the anther undergo meiosis. They form four haploid microspores.
2. Haploid microspores undergo mitosis to mature into pollen grains. Pollen grains consists of two nuclei- the generative nucleus and the pollen tube nucelus - and a protective coating.

Question 5

Ovum formation

Answer 5

1. Diploid megaspore mother cells in the ovule undergo meiosis, forming an ootid and three polar bodies which degenerate and are reabsorbed.
2. The ootid undergoes three mitotic divisions to form an embryo sac. The embryo sac contains two polar nuclei (form the endosperm), an egg cell (forms the zygote), two synergids (help the generative nucleus reach the egg cell) and three antipodal cells (no established function) with a protective coating.

Question 6

Fertilisation in plants

Answer 6

• pollen grain composed of pollen tube nucelus and the generative nucleus adheres to the stigma, where it subsequently germinates.
• the pollen tube grows the style via the secretion of digestive enzymes which digest the surrounding tissue and use it as a source of nutrients
• the pollen tube grows through the micropyle into the embryo sac
• the generative nucleus of the pollen divides by mitosis to produce two sperm cells which enter the embryo sac
• double fertilisation occurs: one of the male gametes fuses with the female nucelus to form a diploid zygote and the other male gamete duses with two polar nuceli to form a triploid endosperm nucleus which serves as a source of nutrients for the embryo.