2.5 Sexual reprod in plants (brief)

Question 1

Describe how a pollen grain forms

Answer 1

-Microspore mother cells divide by meiosis to produce 4 haploid microspores
- Microspores go under one meiotic division to form a pollen grain containing one generative nucleus and tube nucleus

Question 2

Describe the formation of egg cells in a plant

Answer 2

• Diploid megaspore goes under one meiotic division to produce 4 haploid cells however three degenerate
• The remaining haploid cell goes under three mitotic divisions to form embryo sac
• 2 polar nuclei fuse together
• Other 6 move to each side

Question 3

Describe the process of pollen tube formation

Answer 3

• Protease enzymes are made via the tube nucleus
• The enzymes digest through the stigma into the style
• This forms a hollow tube
• This acts as a pathway for the generative nucleus to get to the ovary
• Pollen tube eventually fuses with the embryo sac

Question 4

How is tube growth achieved of the pollen grain

Answer 4

• Via protease enzymes using the pollen tube nucleus and digesting the tissue of the style to make a hollow tube

Question 5

Explain fertilisation of plants

Answer 5

• Generative nucleus divides into two in the pollen tube to form two male gametes
• Pollen tube fuses with the embryo sac
• One male nucleus fuses with the egg cell nucleus to form a diploid zygote
• The other male nucleus fuses with the two polar nuclei to form a triploid endosperm