How do Organisms Reproduce?Introduction
Riya forgot a bowl of dal on the kitchen counter one hot afternoon. By evening it smelled sour, and Dadi threw it away. "Bacteria," she said. "A few got in, and by now there are crores of them."
How can a few become crores in one afternoon? Every one of those bacteria came from another bacterium. In warm food, some bacteria can split into two about every 20 minutes.
Start with a single bacterium in the dal. Drag the clock forward and watch the population grow. Get past ten lakh bacteria.
Time since the bacterium landed:
One bacterium on its own is invisible. It is the huge numbers that a species makes of itself that bring it to our notice — the sour smell of the dal, the green film on a pond, the mould on old bread. And notice something else: every one of those ten lakh bacteria looks just like the first one. Organisms make new individuals that look very much like themselves, and that is how we can tell that two organisms belong to the same species.
A Process the Individual Does Not Need
Nutrition, respiration, transportation and excretion — the life processes of Chapter 5 — keep an organism alive from minute to minute. Reproduction is different.
Which of these could an organism stop doing and still stay alive?
Exactly. Reproduction is not necessary to keep an individual alive. Worse, making new individuals costs the parent a lot of energy. So why should an organism spend energy on a process it does not need to stay alive? Think about it and discuss it in class. By the end of this chapter you will have some good answers, and they have to do with keeping the species going, not the individual.
In this chapter you will find out why copies of living things are never perfect and why that matters; how single organisms make more of themselves by splitting, budding, breaking up, regrowing and making spores; how two parents make a new individual, in flowering plants and in human beings; and how people look after their reproductive health.