Life Continuing, and Life's Variety
Reproduction: how life continues
Tell asexual reproduction from sexual, name the parts of a flower and follow pollen through to a seed, and describe fertilisation and the reproductive cycle in animals and humans.
There are two ways for a living thing to make more of itself. One parent can simply grow a copy: a potato sprouts from its underground stem, a Bryophyllum leaf grows plantlets along its edge. The offspring are genetically identical, because the cell division behind it is mitosis. Or two parents can each contribute, and then the offspring resemble both without matching either.
Why meiosis has to exist
A human body cell holds 23 pairs of chromosomes, 46 altogether. If each parent handed on a full set, the offspring would have 92, and the next generation 184. Meiosis solves it: it halves the number, so a gamete carries 23. Two gametes fuse at fertilisation and the count comes back to 46, generation after generation.
Have a play
The parts of a flower, each one named.
Tap any part of the picture.
Worked example
A farmer has one mango tree whose fruit is unusually sweet. He wants a whole orchard of trees just like it. Why does he graft cuttings from that tree rather than sow its seeds?
Ask what a seed is: the product of fertilisation, so it carries genetic material from two parents.
Sexual reproduction mixes. The seedlings would resemble the parent tree without matching it, and the sweetness might not carry over.
Try it together
Now follow the chromosomes through one human generation.
Answer with a bare number each time.
1.A human body cell holds 23 pairs of chromosomes. How many chromosomes is that altogether?
Have a go
Have a go on your own. A plant's body cell holds 24 chromosomes. How many will each gamete have after meiosis? Answer with a number.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.