9781422283349

Chapter

LIFE FORMS

The study of life is called biology . The word comes from the Greek bios , meaning life, and logos , meaning word or study.

Life is all around us. As living beings ourselves we are part of a complex web of life and we depend for our survival on a huge range of other living things that supply us with the food we eat and the oxygen we breathe. If sometimes seems that there is no end to the variety of forms life can take—from giant redwood trees 330 feet (100 meters) tall to microscopic bacteria ; from huge whales swimming in the depths of the ocean to high-flying vultures. These living things, or organisms , seem to be quite unrelated. Yet at a deep level all life on Earth shares common characteristics. In this book we shall concentrate on finding out just what these

characteristics are. The story that will unfold is of the way life changes and adapts. We shall look at some of the discoveries that have been made on the way to understanding how these changes work.

The smallest life forms are bacteria. There are many different kinds. The bacteria shown here are of a harmless type commonly found in human intestines.

5.