Plant Reproduction Flashcards
What are the adaptations of insect pollinated flowers?
- Brightly coloured petals, nectar and a scent
- Sticky pollen
- Anthers and stigma are inside the flower
What are the adaptations of wind pollinated flowers?
- Small flowers, no scent and dull petals
- Anthers hand outside the flower
- Large feathery stigma
- Large volumes of pollen produced
Explain self-pollination
When pollen lands on the stigma from the same flower or plant
Why is self-pollination not favourable?
- Reduces genetic variation
* Increases interbreeding depression (negative recessive alleles being expressed)
What is a benefit of self-pollination?
Lack of variation to preserve successful phenotypes
Explain cross-pollination
Where pollen is transferred from the anther to the stigma of another plant of the same species
Why is cross-pollination favourable?
Increases genetic variation due to meiosis forming gametes and random fertilisation of the gametes
Name three ways of reducing the chances of self-pollination
- male and female parts mature at different times (dichogamy)
- stigma higher than the anther
- have male flowers or female flowers
How are pollen grains developed?
- first, mitosis occurs to produce pollen mother cell
- meiosis occurs and produces tetrad haploid cells
- the tapetum provides the cells with pollen
- pollen grains contain a non reproductive cell and a generative cell
- generative cell contains a generative nucleus and a tube nucleus
- generative nucleus divided to form male gametes
- tube nucleus forms the pollen tube
What is a pollen grain composed of?
- inner layer (intine), made of cellulose
* outer later (exine) tough layer to prevent dessication (drying out)
What is dehiscence?
When pollen grains are mature, the anther dries out and splits along lines of weakness
Explain the development of an ovule
•meiosis of a megaspore mother cell in the nucellus to give 4 haploid megaspores
•three megaspores disintegrate
•one megaspore develops and undergoes 3 mitotic divisions
•produces 8 haploid nuclei within the embryo sac
-3 antipodals
-2 synergids
-2 polar nuclei
-1 egg cell
Explain the process of pollination and double fertilisation
- Pollen grain takes in water and germinates in the sucrose solution secreted by the style
- The tube nucleus begins to form the pollen tube
- Hydrolase enzymes in the pollen tube digest through the style. In the pollen tube, the male generative nucleus divides by mitosis to produce two haploid gametes
- Pollen tube enters the embryo sac through the micropyle
- Male nuclei enters the ovule ( 1 haploid nucleus fuses with haploid female nucleus to for a diploid zygote)
- Other male nucleus fuses with both polar nuclei to form a triploid primary endosperm nucleus
- Seed and fruit develop
Explain the development of the seed and fruit ( what makes what )
- zygote becomes embryo
- integuments form testa / seed coat
- ovule forms the seed
- surrounding ovary forms the fruit
- ovary wall becomes the wall of the fruit
- triploid endosperm cell forms endosperm tissue
What is the endosperm useful for?
Food storage tissue in cereal grains
