The study of all living things called Biology. Men and women who study living things are called Biologists . Biologists often use the word organism to mean anything that is alive today or was once alive . An organism can be a flower or a tree, a goldfish, a chicken or a kangaroo, or even a man. Things which are not alive ; rocks, water or air are not organisms. For hundreds of years, men have tried to answer the question: what makes a living thing live? Men tried to discover which came first, the chicken or the egg. The answer, they thought, would give them the secret of life . Today scientists are getting closer and closer to the answer. Soon, we will know what life is.


scientists experiment to discover the real secret of what makes a living thing live.But, meanwhile, we know how to tell whether or not an object is a living thing.There are seven signs to look for in a living thing . These signs of life are called characteristics.Each living organism has a characteristics of life.If a thing is a living being, whether it is a a small as an amoeba ( a little bit of living jelly) or as large as an elephant, it has the characteristics of life. All living thing can move . That is the first characteristics of life.All living things feed (and drink). They all must breathe, or take in oxygen from the air. Then they all grow feeding and breathing help things to grow. Living things must excrete . They must get rid of waste materials in their bodies. Things that are alive are sensitive . This means that living things notice changes around them . A chick coming out of it’s shell feels air blow on it’s wet feathers. The last characteristics of life is very important. All living things reproduce their own kind. Because the bodies of living organisms wear out, they die. So they must make sure other living things like themselves will live. All living things bear babies, or seeds, or eggs. The minutes a chick hatches of it’s egg, it shows all the sign of being a living thing. To stay alive, a chick must move towards food. It must grow up into a chicken it must get rid of waste from food. It must seek shelter and warmth. When it is an adult chicken, it must lay eggs so that other chicks will take it’s place when it dies.


Long timeago, when men were just beginning to study living things, they thought that perhaps dead things could sometimes spring into life . This was called spontaneous generation. Men thought this happened because they could not understand why mould or maggots ( tiny insects) appeared in rotting food. Until 1668 people believed the idea that small organisms could suddenly come to life. In that year and Italian proved that when meat decays and goes rotten, no maggots will appear if the is kept free from flies. But if flies lay their eggs on the meat, then maggots will hatch from the flies’ eggs and eat the meat. Broth kept in a corked bottle will stay fresh. But if the bottle is uncorked , then mould will appear. Mouly spores are carried in the air.

mould spores are tiny living organisms . Once the bottle is open, mould spores can get in to grow in the broth. Scientists now know that some things which do not have all seven signs of life can act like living things. The virus, a tiny disease organisms, acts as if it were alive, but is not really a living thing.


The cell can be called the life building bricks . Both animals and plant are made up of tiny cells which cannot be seen without a microscope. The cells in our bodies, or in plants or animals, have different jobs to do . The cells have different shapes too. There are skin cells, nerve cells, bone and muscle cell animals. Plant have cell that make food or carry water. Just as house can be built of small bricks, all fitting together, So plants and animals are built of living cells. Living cells were only discovered in 1665 , when Robert Hooke , an Englishman , looked through a microscope at a piece of cork . So we have known for only 300 years that life building bricks exist. Some living things are made up of only one cell . These are called protozoa. Protozoa are unicellular organisms. Uni means one . Unicellular means one-celled . The amoeba , one of the simplest of all living things, is a protozoon . Most living things are multicellular . Multi means many. A sponge is a simple multicellular organisms. Plant and animals are built of many more cell than a sponge . They are said to be more complex than a sponge. But a sponge is more complex than a tiny one- celled protozoon.


We tend to think that it is only worms that eat apples . They sometimes do. But more often it’s the germ that eat the apple . Bacteria germs are parasites . A parasites lives on another living organisms . Bacteria eat red juicy apples , onces they are no longer fresh. A microscope will show bacteria on an apple . We think of harmful bacteria causing disease in man and animals, but bacteria are helpful too. They eat all the dead and decaying plants and animals on the Earth . If bacteria did not do their work, the Earth would be covered with rotten corpses.


Bacteria reproduce themselves by dividing in half . This takes place very quickly. One form of bacteria can divide every twenty minutes. In Eight hours, this bacteria can reproduce itself sixteen million times. There are literally billion of bacteria on the Earth . These germs are rod shaped or spherical. They exist as single cell, as long chains of cells, or as masses of cell. Bacteria help to make yoghurts, vinegar and wine. They also makes soil fertile by breaking down dead plants. This produce heat. A badly made compost heap can grow hot enough to burst into flame. This is called spontaneous combustion.


Nitrogen is a colourless , tasteless gas , which is part of the air. To grow, plants must have it. Sometimes lighting helps plants to take up Nitrogen from air . But most of their nitrogen is provided by the action of bacteria. Dead plants and animals are broken Down by the bacteria. This releases nitrogen into the soil. Growing plants Take up the nitrogen. Animals eat the plants. When the animals (and other plants) dies, bacteria return the nitrogen to the soil. This round and round movement of nitrogen, from soil back to soil, is called the nitrogen cycle.




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