REPRODUCTION IN PLANTS SUMMARY

Plants reproduce both:
1. Asexually
2. Sexually

Asexual Reproduction:
1. Natural: New plants grow from buds. Either found on stems that grow from parent plant (runners), or on perennating organs (which also help to store food for the new growing plant).
2. Articifial: Man grows new plants from buds or from nodes (where there are unspecialised cells that can divide and grow).

Asexual reproduction enables survival of the species of plant as it is a "sure-fire" way of reproduction that does not require external agents. It is used by man as a method to produce plants that have the same characteristics as their parents. genetically identical.

Sexual Reproduction:
Involves a few steps:
1. Pollination: Transfer of pollen grains to stigma of flower.
2. Growth of pollen tube to bring male gametes to embryo sac which contains ovum & definitive nucleus.
3. Double fertilisation of ovum and def. nucleus.
4. Mitosis to give rise to seed which germinates into new plant. Seed is surrounded and protected by the fruit.
Also...
5. Fruits and seeds are dispersed further away from parent plants to reduce competition for resources.
6. Seeds germinate under suitable conditions to give rise to new plants.

Pollination: 2 types
I: Self pollination (tranfer of pollen to stigma on SAME plant)
II: Cross pollination (transfer of pollen to stigma of flower on DIFFERENT plant)

Pollination: Mechanisms (see notes for more points)
i: Wind: Pollen is small, light, dry, produced in large quantities to ensure a higher chance of landing onto the stigma of a flower. Stigma has high surface area and must be exposed to catch the pollen (therefore feathery and protrudes out). No use for showy petals therefore replaced in most cases by dull-coloured bracts, no nectar, no scent.
ii: Insects: Pollen is sticky and larger, produced in smaller quantities as this method usually has a higher success rate. Stigma & stamens usually enclosed and positioned to collect pollen and rub off pollen onto insect respectively. Colourful petals, nectar guides, scent and nectar serve to attract insects to visit the flower for a meal.

Post fertilisation changes: Cells divide to form various parts of the fruit and seed (See notes for Summary)

Dispersal of fruit and seeds (NO more in the syllabus but good to know for application, Not to be confused with pollination mechanisms, bees do not carry apples around to disperse them!)
a. Wind: Seeds/fruits are light (therefore cannot have high water content, so they are dry as well), and have extensions/projections to increase surface area for bouyancy. Usually wind dispersed seeds are produced in high amounts to increase probability of reaching a suitable place and germinating.
b. Water: Seeds/fruits can float in water (air spaces) and are waterproof (to prevent entry of water, which causes sinking, which means fruit lands up at the bottom of the river).
c. Animals: Either by hooking onto fur/skin/clothes (fruits must have stiff hairs or hooks, and should be small) or by attracting animals to eat them (Parts of pericarp are succulent, bright coloured pericarp, scent) and therefore carry the fruit/seed away.
d. Explosive mechanism: Fruits have lines of weaknesses (lines of dehiscence) where after the pericarp dries, the fruit splits along those lines to throw the seeds away from parent.