4.2 Plant reproduction Flashcards
What is the male gamete (plant)?
Pollen grain
What is the female gamete (plant)?
Ovum
What is pollenation?
The transfer of pollen from the anther of one flower to the stigma of the other
What are the traits of a wind-pollinated flower?
-Feathery stigma
-Anther and stigma hang out of plant
-No petals/green petals
-No scent/nectar
-Large volume of small, smooth, light pollen grains
What are the traits of an insect-pollinated flower?
-Colourful petals with nectar guides
-Scented and nectar (sucrose)
-Anther and stigma in plant
-Small amount of large, sculpted, sticky pollen
What part of the anther provides nutrients to male gametes?
Tapetum
How many times do pollen mother cells undergo meiosis?
twice
What are the characteristics of the pollen cell wall?
-Blocks UV light to prevent mutation
-Tough and resistant to desiccation
-Sculpted/smooth
What are the nuclei found in a pollen grain, and what is their function?
-pollen tube nucleus: guides pollen tube to micropyle
-Generative nucleus x2: fertilises ovum/polar bodies
What is dehiscence?
The opening of an anther, releasing pollen grains via stomium
What are the integuments in the ovary?
2 walls of the ovule
What provides nutrition for the megaspore?
Nucellus
How many times does a mother megaspore cell undergo meiosis?
1
How many times does a megaspore undergo mitosis?
3
What are the different nuclei called in an embryo sac?
- 2x polar nuclei
-3x antipodals
-2x synergids
-1x ovum
What is the function of the fertilised polar bodies?
They become triploid endosperm, used for nutrition of the ovum
What is the function of the synergids?
To guide pollen tube to ovum
What is the function of the antipodals?
Nothing, they disintegrate
What are the advantages of self-pollination?
-Reliable
-Successful in harsh environments where pollinators are scarce
-Good for preserving successful genotypes in stable environment
What are the disadvantages of self-pollination?
-Inbreeding reduces genetic variation
-Relies upon crossing over, mutations, and random assortment for genetic variation
-Greater chance of homozygous recessive individuals
What are the advantages of cross-pollination?
-Maintain genetic variation
-Reduced chance of homozygous recessive individuals
What are the disadvantages of cross-pollination?
-Relies on the successful transfer of pollen
What are the 4 cross-pollination mechanisms?
-Monoecious/Dioecious
-Protandry/Protogyny
-Self-incompatIbility
-Structural-incompatibility
What does Monoecious mean?
Separate male and female flowers on the same plant
What does dioecious mean?
Separate male and female plants
What is genetic self-incompatibility?
Pollen cannot germinate on the stigma of the same flower
What is structural incompatibility?
Anther is below stigma so pollen cannot drop onto the stigma
How does fertilisation occur?
1) Pollen grain lands on stigma, germinates in sucrose solution secreted by stigma, and produces pollen tube
2) Pollen tube grows down into style and generative nucleus undergoes mitosis
3) Pollen tube enters embryo sac via micropyle
What part of the seed do the polar bodies become?
Endosperm
What part of the seed does the ovule become?
The seed
What part of the seed does the ovary become?
The fruit
What part of the seed do the integuments become?
Testa
What happens when a seed is monocotyledon?
-Endosperm remains
-Testa fuses with ovary wall
What happens when the seed is a dicotyledon?
-Plumule will become shoot
-Radicle will become root
-Endosperm absorbed into cotyledon
-Non-Endospermic
What are the seed dispersal mechanisms?
-Wind
-Animals
-Water
-Rolling
-Bursting
What is dormancy?
When a seed’s growth is suspended?
What can break dormancy?
-Heat
-Cold
-Scarification
-Soaking
What are the benefits of dormancy?
-Low metaboli rate (survive cold weather)
-Testa is chemcially resistant
-Endosperm/Cotyledon provides nourishment
-Dispersal away from parent reduces competition
-Inhibitors prevent germination
What are the conditions for germination?
-Water to soften testa
-Oxygen for aerobic respiration
-Suitable temperature for enzymes
How does germination occur in Non-Endospermic seeds?
1) Water absorbed through micropyle
2)Testa ruptures and radicle pushes downward
3)Amylase hydrolyses Starch into Maltose, which goes to plumule and radicle
4)Plumule bends over into a hook to protect tip against soil abrasion, unfurls once above soil and starts photosynthesizing
How does germination occur in Endospermic seeds?
1) Water absorbed by seed
2) Gibberellic acid synthesised by embryo, initiating germination
3) GA diffuses into Aleurone layer surrounding endosperm & stimulates Amylase synthesis
4) Amylase hydrolyses Starch into Maltose
5) Maltose converted to glucose for respiration
6) Glucose transported to embryo, providing energy for growth
