Reproduction: How Life Continues

How living things make more of their kind: asexual methods, sexual reproduction in flowering plants and humans, and why gametes have half the chromosomes.

Key ideas

Asexual reproduction needs one parent and gives offspring nearly identical to it; sexual reproduction needs two parents and gives variation.
Asexual methods: binary fission (Amoeba), multiple fission (Plasmodium), budding (yeast, Hydra), fragmentation (Spirogyra), regeneration (Planaria), spores (Rhizopus).
Vegetative propagation grows new plants from stems, roots or leaves (potato tubers, rose cuttings, Bryophyllum leaves).
Pollination carries pollen from the anther to the stigma; fertilisation is the fusion of the male and female gametes in the ovule.
After fertilisation the ovule becomes the seed and the ovary becomes the fruit.
Gametes have half the chromosome number, so the zygote gets the full number back.

Remember

Chromosomes	gamete = body cell ÷ 2; zygote = gamete + gamete
Binary fission	cells after k divisions = start × 2ᵏ
Germination rate	seeds germinated ÷ seeds sown × 100%
Seeds and ovules	one seed for each fertilised ovule

Watch out

Mixing up pollination (transfer of pollen) and fertilisation (fusion of gametes).
Saying the ovary becomes the seed (it becomes the fruit).
Multiplying by the number of divisions instead of doubling each time.

Worked example

A brinjal has 83 seeds. How many ovules were fertilised, and at least how many pollen grains must have grown pollen tubes?

Working: each seed comes from one fertilised ovule, and each ovule is reached by its own pollen tube

Answer: 83; 83