Class 10 How do Organisms Reproduce?: cheat sheet

CBSE Science. How living things produce offspring: asexual methods, sexual reproduction in flowering plants and in humans, and why variation matters.

Key ideas

Reproduction copies DNA; small copying changes create variation, which helps a species survive changes in its surroundings.
Asexual methods: fission (Amoeba, Plasmodium), fragmentation (Spirogyra), regeneration (Planaria), budding (Hydra, yeast), spores (Rhizopus) and vegetative propagation.
In a flower, the stamen (anther and filament) is the male part and the pistil (stigma, style and ovary) the female part.
Pollination carries pollen to the stigma; fertilisation joins the male and female gametes to make a zygote.
After fertilisation the ovule becomes the seed and the ovary becomes the fruit.
In humans, the testes make sperm and the ovaries make eggs; fertilisation happens in the oviduct and the embryo grows in the uterus.

Flower: male	stamen = anther + filament
Flower: female	pistil = stigma + style + ovary
After fertilisation	zygote → embryo; ovule → seed; ovary → fruit

Mixing up pollination (pollen to stigma) and fertilisation (gametes joining).
Saying asexual reproduction gives much variation (offspring are almost identical).
Calling the anther a female part.

Each body cell of a pigeon has 80 chromosomes. How many chromosomes are there in (a) a sperm, (b) an egg, (c) the zygote?

Working: gametes have half; fertilisation restores the full number

Answer: (a) 40; (b) 40; (c) 80

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