Topic 2.5 Sexual reproduction in plants

Question 1

How does a pollen grain form in the anther?

Answer 1

1. Meiosis of diploid cells in the anther forms 4 haploid microspores
2. Haploid microspores mature into pollen grains via mitosis

Question 2

Describe the structure of the pollen grains

Answer 2

Generative cell with haploid nucleus produces 2 male gametes via mitosis.

Pollen tube cell (also has its own nucleus) elongates to penetrate ovule.

Outer protective coating.

Question 3

How does the embryo sac form in the ovule?

Answer 3

1. Mitosis of diploid megaspore cells in ovule forms 1 ootid and 3 polar bodies. Polar bodies degenerate then are reabsorbed.
2. After 3 mitotic divisions, ootid forms embryo sac

Question 4

Describe the structure of the embryo sac

Answer 4

• 2 polar nuclei form endosperm
• Ovum forms zygote
• 2 synergids help generative nucleus of pollen grain to reach ovum
• 3 antipodal cells
• Outer protective coating

Question 5

How do male nuclei reach the embryo sac?

Answer 5

1. Pollen grain germinates on stigma
2. Enzymes digest surrounding tissue, providing nutirent source. Enables pollen tupe to grow down style then through micropyle
3. Mitosis of pollen grain generative cell produces 2 male gametes which enter embryo sac

Question 6

Where does double fertilisation occur?

Answer 6

Embryo sac of the ovule

Question 7

What happens during double fertilisation?

Answer 7

Diploid zygote forms when 1 male gamete and ovum nucleus fuse.

Triploid endosperm forms when 1 male gamete and 2 polar nuclei fuse.

Question 8

What is the purpose of the triploid endosperm?

Answer 8

Nutrient source for embryo

Question 9

At what sucrose concentration do pollen tubes grow best?

Answer 9

Near isotonic; prevent osmotic damage