Polar bear are adapted to life in the polar region, around the North Pole. Their bodies have

special features that work particularly well in the polar seas. For instance, they have sharp and

powerful claws for catching their food, which is mainly seals. In their own environment, they are

excellent hunter; but if they had to live on the birds and squirrels in other places, they would die.

The science that studies the way that different forms of life are adapted to their particular

environment is called ecology.

The first lesson of ecology is that all life in an environment depends on other forms of life.

Polar bears depend on seals, which can live only where they do because they depend on particular

kinds of fish which are found in the Arctic seas.

There are certain important cycles in nature that show plants and animals depend on each

other: for example, the nitrogen cycles. Plants take nitrogen compounds from the soil and turn

them into protein. Animals eat these proteins and return some of them to the soil as waste products

and the rest when they die. Another cycle is the oxygen cycle. When we breathe, we take in

oxygen, and give out carbon dioxide. Plants absorb it to make sugar compounds, and in the

process oxygen is produced and released to the atmosphere.

An ideal ecological system, living things exist in balance. However, particularly where man

interferes, a species may become too successful and abundant, and the balance is destroyed. For

instance, the use of pesticides to kill a particular plan pest may also kill predatory insects and

even birds, and thus other pests are allowed to increase. Therefore, great care is needed in the use

of pesticides.

Through ecology we try to restore the balance in the ecological system, and thus save the

world from devastation.

The ecology in certain area will

be in danger if ...