Flower Structure: reproductive parts
Female part- CARPEL
- OVARY males female ovules
- STIGMA recieves male pollen grains
- STYLE- links the two
Male part- STAMEN
- ANTHER-produces male pollen grains
- FILAMENT- thin stalk holding anther, with vascular tissue.
Flower structure: other
- SEPAL- small grene leaves which protect flower in bud
- PETALS- colourful and scented to attract insects
- The mother cell undergoes meiosis
- to make a haploid embryo sac
- with 8 haploid nuclei later made by mitosis.
- Undergoes meiosis to make haploid pollen grains
- Haploud nuclei udnergoes mitosis to make a generative nucleus and tube nucleus.
- Have a hard coat shell to avoid dessication
- Released when four pollen sacs dry out and split
- This is called dehiscence.
Fertilisation 8 POINTS
The fusion of male and female gametes to make a zygote.
- The pollen grain lands on a complemntary stigma.
- Pollen rain germinates in a sugary solution produced by the stigma.
- The tube nucelus release proteases which digests the stigma, creating a pollen tube.
- Tube nucelus leads growth of tube.
- Proteases may be used for pollen grain nutrients.
- The pollen tube grows down the stigma and up through the micropyle, past integuments.
- Tube nucelus disintegrates when reaching the ovule sac, and the pollen tube burts, releasing the 2 generative nuclei.
- DOUBLE FERTILSATION- one nuclei combines with female nucleus to ake zygote, and other nucleus combines with polar bodie sto make the triploid endosperm.
Seed and fruit development
- Integuments become seed coat or testa.
- Zygote divides by mitosis to make the seed, with a radicle and plumule, and two cotelydons (seed leaves.)
- Ovary becomes the fruit.
- Ovule sac becomes seed.
- Triploid endosperm becomes sa food source for the devloping seed.
Pollination: Cross v Self
When the pollen grain from one flower is transferred to teh stigma of a differnet flower on a different plant of the same species.
When the pollen grain is transferred to teh stigam of teh same flower on the same plant.
Pollination: Pros/Cons of self pollination
Pros and Cons of Self pollination
- preserves good genomes
- Harmful recessive alleles are expressed
- Low resistance to diseases
- Relies on crossing over and independent assortment for variation.
Pollination Insect v Wind Characteristics
- Brightly coloured and scented
- small amounts of sticky pollen
- anther inside the plant
- Small green and inconspicuous
- no nectar
- large amounts of light smooth pollen
- antehrs are large and feathery to increase surface area
- anther and stigma hang outside plant.
Insect v Wind mechanisms
- relies on isnects such as bees
- they feed on nectar at base of flower
- brush past anther, and pollen grains stick to them
- they then transfer this pollen to another plant.
- Wind picks up pollen grains from the feathery anthers.
- transfers them to a stigma of another plant.