Life in a Biologist's View

This is probably one of the deepest questions man can ask and one of the greatest mysteries facing him.
Scientists have discovered that all living things are made of a material called protoplasm. They can make a chemical formula for protoplasm, and they can take molecules of various elements and compounds to put them together and make materials like protoplasm. But the materials they make are not alive!
All man can do is examine the living creatures on earth, in all sizes and shapes and wherever they live, and find what it is they have in common. Then we can say that these common qualities make up life.
Let's see what these qualities are.

Growth

All living things must be able to grow. They grow to a fairly definite size and shape. A kitten becomes a cat; an acorn becomes an oak tree and so on. For some living things, it takes a short time to grow to full size but this is not the case for every living organism; a redwood tree may take thousands of years.

Repairers

All living things, being alive, can repair and replace parts of themselves. A lobster can grow a new claw; human beings can grow new skin or bones; trees grow new leaves and branches.

Reproduction

Another characteristic shared by living things is the ability to reproduce. If this ability didn't exist, living things would have disappeared from the earth as they grew old and died. Animals, fish, birds, insects, plants-all produce offsprings.

Do you know?
     Viruses have all the qualities of non-living things, but they can reproduce. For this reason they are considered to be a link between living and non-living things.

Environmental Behaviour

Living things are capable of adapting the environment they live in. Man can do this better than any other creature because of his brainpower. But plants can do this only to a limited extent.

Response

Living things can also respond to stimuli which means if something outside of them affects them, they react. When we smell food, we respond; flowers grow towards the light.
This doesn't tell you what is life, but it does describe the qualities that things must have to be considered alive.

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