with these points in mind ,the effect of pollutants will be considered at several differ- ent levels of organization from organelles to whole organisms figure 8.1). In this chapter, we are concerned mainly with physiological effects above the biochemical level (covered in Chapter 7). Physiology is defined as the branch of science concerned with the functioning of organisms and the processes and functions of all or part of an organism. Thus, in ecoto ogy, we are concerned with describing the dis- ruptive effects of pollutants on 'normal' physiology, normal referring to the state of the organism when not exposed to pollution though subject to other forms of stress. Abnormal stresses may be completely novel and occur in response to man-made chemicals that have appeared in the environment recently (on the geological time-scale), or they may simply be an increase in a response to a substance to which the organism has evolved natural protection mechanisms.