Course 1.1Lesson 2 of 3
Reproduction is the making of new individuals like the parents. It can be sexual, or asexual by binary fission, budding, fragmentation, spores and regeneration. A mule or a worker bee does not reproduce, so reproduction is not the defining feature. Metabolism, the sum of all the chemical reactions in the body, is found in every living organism and in no non-living object, so it is a defining feature of life.
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A dog has puppies. A mango tree gives a fruit with a seed, and the seed grows into a new tree. Reproduction is the making of new individuals that are more or less like their parents.
When we say "reproduction", we usually think of two parents. This is sexual reproduction. But many organisms reproduce with one parent. This is asexual reproduction, common in single-celled organisms and in simpler plants and animals.
If every living thing reproduced, we could say that reproduction defines life. But it does not hold.
All of these are alive. So reproduction is a common feature of living things, not a defining one. Yet it is a good clue: no non-living thing can make a copy of itself.
Your body is made of chemicals. Every minute, some of them are broken down, and new ones are built. Food is digested, proteins are made, and energy is released. A plant takes in carbon dioxide and water and makes sugar. In a living body these chemical reactions are called metabolic reactions.
Metabolism is the sum of all the chemical reactions in the body of an organism.
So metabolism is a defining feature of life, with no exception.
Even at rest, metabolism releases energy, and the rate depends on the size of the body.
You should find that a human at rest uses about kcal a day, but only about kcal for each kilogram. A mouse uses about kcal a day for each kilogram of its tiny body.
Take a cell and break it. Take one enzyme out of it, and put it in a test tube with its substance. The reaction goes on, outside the body. Is the test tube alive?
No. The reaction is a living reaction, because it is the same reaction as the one in the cell. But the test tube is neither living nor non-living. A living thing is the whole organism, with its thousands of reactions working together.
This program lists eight organisms with their way of reproducing, and it groups them by the way.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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