2.5 - Sexual Reproduction in Plants Flashcards
1
Q
Male Gametes of the plant
A
- male gametes are contained within pollen grains which are released from the anthers
- the anthers contain pollen sacs
- each pollen sac contains a diploid mother cell which undergoes meiosis to form four haploid microspores (gametes)
- mitosis occurs to mature the haploid microspores into mature pollen grains
- pollen grains consist of two nuclei (generative nucleus and pollen tube nucleus)
2
Q
Describe the structure of pollen grains
A
- generative cell with haploid nucleus produces 2 male gametes via mitosis
- pollen tube cell (also has its nucleus) elongates to penetrate ovule
- outer protective coating
3
Q
Female Gametes of the Plant
A
- female gametes are made in the ovules
- a single diploid cell within the ovule undergoes meiosis to produce 1 ootid + 3 polar bodies
- only one of the cells survives which undergoes mitosis to produce a female gamete ( embryo sac)
- the polar bodies degenerate and are reabsorbed
4
Q
Describe the structure of the embryo sac
A
- 2 polar nuclei form endosperm
- ovum forms a zygote
- 2 synergids help the generative nucleus of pollen grain to reach the ovum
- 3 antipodal cells
- outer protective coating
5
Q
How do male nuclei reach the embryo sac?
A
- pollen grain composed of pollen tube nucleus and the generative nucleus adheres to the stigma, where it subsequently germinates
- The pollen tube grows down 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 haploid male nuclei which enter the embryo sac
6
Q
What is the process of double fertilisation?
A
One of the male gametes fuses with the female nucleus to form a diploid zygote and the other male gamete fuses with two polar nuclei to form a triploid endosperm nucleus which serves as a source of nutrients for the embryo
