REPRODUCTION IN PLANTS Flashcards
Define asexual reproduction.
Process whereby one parent produces genetically identical offspring.
Define sexual reproduction.
Process whereby two gametes fuse together to form an entirely new organism that is genetically different from its parents.
What is the reproductive organ of flowering plants?
Flower
What are the main parts of the flower?
- Petal
- Stamen
- Receptacle
- Sepal
- Nectary
- Carpel/Pistil
- Pedicel
Describe the petal in animal-pollinated and wing-pollinated plants.
AP
- brightly-coloured, sometimes scented to attract animals to bring about pollination
WP
- dull, unscented
What are the parts of the stamen?
Anther and filament
Describe the filament and its function.
Long stem-like structure that positions the anther so that pollen grains can be pollinated by agents.
Describe the anther and its function.
Made up of two or four pollen lobes, each containing two pollen sacs where pollen grains are formed
Describe the receptacle and its function.
Expanded end of the pedicel that holds the flower
Describe the sepal and its function.
Modified leaves that are green in colour. They protect the flower when it is in the bud shape.
Describe the nectary and its function.
Found in insect-pollinated flowers only and produces sugary nectar to attract insects/birds.
What are the parts of the carpel/pistil?
Style, stigma, ovary
Describe the stigma and its function.
Sticky (AP) or feather-like (WP) surface for pollen grains to attach to.
It secretes a sugary fluid that stimulates the germination of pollen grains after pollination.
Describe the style and its function.
Connects the stigma to the ovary, and holds it in position to trap pollen grains. Made up of soft tissues that allow the pollen tube to grow down.
Describe the ovary and its function.
Contains and protects the ovules
Describe the ovule.
Contains female gametes
Define pollination.
Transfer of pollen grains from the anther to the stigma
What is the difference between cross and self-pollination?
In cross-pollination, pollen grains are transferred to the stigma of a flower on another plant of the same kind. In self pollination, pollen grains are transferred to the stigma of the same or different flower of the same plant.
What factors promote self-pollination?
- Bisexual flowers with anthers and stigma maturing at the same time
- Stigma located directly below the anthers
What factors promote cross-pollination?
- Plants bearing only male or female flowers (dioecious plants)
- Anthers and stigmas of bisexual flowers maturing at different times
- Biochemical block when pollen of a flower lands on the stigma of a flower on the same plant, preventing flower from germinating
What are the advantages of self-pollination?
- Not dependent on external pollinators (e.g. insects, wind)
- Less wastage of pollen and energy
- Only one parent plant is required
What are the disadvantages of self-pollination?
- Produces offspring genetically identical to the parent -> loss of genetic diversity + less adapted to environmental changes
What are the advantages of cross-pollination?
- Greater genetic variation -> higher chance of surviving environmental changes
- Offspring can inherit favourable traits from both parents
What are the disadvantages of cross-pollination?
- Relies on pollinators -> energy consuming, and wastage of pollen grains
- Two parent plants required
What are the differences between insect-pollinated and wind-pollinated flowers in terms of petals, scent, nectary guide and pollen?
PETALS
AP: Large, brightly-coloured
WP: Small, dull (flower parts protected by bracts)
SCENT
AP: Scented
WP: Unscented
NECTARY GUIDE
AP: Present
WP: Absent
POLLEN
AP: Smaller quantities; large, sticky and heavy pollen with rough surface
WP: Large quantities; small, dry and light pollen with smooth surface
What are the differences between insect-pollinated and wind-pollinated flowers in terms of reproductive parts?
STAMEN
AP: Small, firmly attached to filament inside the flower
WP: Large, loosely attached to filament and hanging out of the flower
STIGMA
AP: Small and sticky, inside the flower
WP: Large and feathery, protrudes out of the flower
Describe fertilisation in plants (after a pollen grain from an anther lands on a stigma).
- Pollen grain absorbs sugary liquid from the stigma and germinates
- Pollen tube cell grows into a pollen tube, growing through the cells of the style by secreting enzymes to digest them
- Pollen tube enters the ovary and then the ovule through the micropyle in the ovule
- Generative nucleus divides to form two male gametes
- The male gametes travel down the pollen tube into the ovule
- One of the male gametes fuse with the ovum to form the zygote
- The zygote undergoes cell division to develop into the embryo
- The ovule will develop into a seed and the ovary will develop into a fruit
