Temperature is a major physical environmental factor which profoundly influences the vital activities of living organisms like, metabolism, growth and reproduction. The primary effect of temperature is on the stability and activities of enzymes which carry out and regulate the biochemical reactions in the cells. Temperature also affects the properties of biomembranes.
We know that there are large temperature differences over the earth to which organisms must adapt. Temperature and availability of water in an area largely determine the types of plants and animals that can grow, survive and reprduce there. Every organism has a certain range of tolerance for temperature delineated by an upper and lower lethal temperature, which vary from species to species. Thus, temperature is one of the factors that limit the geographical distributions of plants and animals. Temperature also indirectly influences the availability of water which itself is an important ecological factor. Before we describe the adaptations in organisms due to temperature stress let us discuss the temperature variation at different latitudes and altitudes and examine the global picture of temperature.