Introduction

Abstract

At a superficial level it is easy to separate the non-living from the living; no one is, for example, likely to confuse a horse and a rock! However, when all living things are considered from the smallest to the greatest, superficial distinctions are no longer sufficient and more precise definitions have to be made. Briefly, living things can be recognized by the following characteristics: to a greater or lesser extent all are capable of metabolism, growth, reproduction, response to stimuli and movement.