Plant Reproductive System Flashcards
What is the Corolla of a flower?
Petals of the flower
- Usually bright and colourful -> attract pollinators
- Petals serve as landing pad for insects
What is the stamen of a flower?
- Consists of Filament, Anther and Pollen sacs
- Filament supports anther
- Anther splits to release pollen grains -> contains male gametes
What is the Carpel of a flower?
Consists of Ovary with Ovules, Style and Stigma
- Stigma is sticky or hairy to receive pollen
- Ovary contains ovules which develop into seeds
What is pollination?
Transfer of pollen grains from the anther to stigma
- Self-pollination or cross pollination
Features of self-pollination
Transfer of pollen to stigma from the anther of the same flower or flowers from the same plant
Features of cross-pollination
Transfer of pollen to the stigma of a flower by male gametes produced by the flower of a different plant
Why cross-fertilisation over self-fertilisation?
- Gametes from different parents -> increase in genetic diversity
- More advantegous to produce offspring that could be better adapted to environment
How is pollination by wind done?
Releases large amounts of pollen to compensate for randomness of dispersal
How is pollination by animal/insect done?
- Relies on birds, insects to transfer pollen
- Attractive cues such as visual (bright, coloured petals), olfactory (sweet scent) and rewards (nectar, food, mating advantages)
Features of Insect Pollinated flowers
- Large brightly coloured, scented
- Nectar present
- Heavy and sticky pollen
- Sticky stigmas
- Nectar guides on petal -> guide insect to stigma
Features of Wind Pollinated Flowers
- Small, dull scentless
- Small, dry pollen that is abundant
- Stigmas protrude and are large & feathry -> catch pollen
- Long slender filaments that disperse pollen easily
What is double fertilisation?
Union of two sperm gamete with the egg gamete and polar nuclei of the embryo sac
What does the pollen grain and ovule contain for double fertilisation?
Mature ovule -> two genetically identical polar nuclei and haploid egg gamete
Mature Pollen grain -> tube cell and generative cell
- Generative cell divides by mitosis to form two haploid male gametes
- Tube cell nucleus controls pollen tube gtowth
What is the pollen tube growth process of double fertilisation?
- Pollen grain absorbs water and sugars produced by stigma
- Germinates by producing pollen tube -> grows between the cells of style towards ovary
- Growth controlled by tube cell nucleus
- Grows towards micropyle in response to chemical attractant secreted by ovule
- Pollen tube secretes hydrolyctic enzymes -> digests tissues of style to provide nutrients
- Generative cell divides by mitosis to form two male gametes
- Pollen tube reaches micropyle -> penetrates and grows into the ovule
What is the fertilisation process in double fertilisation?
- Tip of pollen tube ruptures -> releases two haploid male gametes
- One fuses with egg gamete forming a diploid zygote
- One fuses with two polar nuclei forming the triploid nutritive endosperm -> provides energy for embryo development
