Abiotic factors: temperature

The idea

Temperature is an abiotic factor that affects the rate of biological processes and the distribution of organisms. In general, enzyme-controlled reactions in plants and animals increase as temperature rises towards an optimum, then decrease if temperature becomes too high because enzymes denature. Ectothermic animals, such as reptiles, rely on external heat sources and may bask in the sun, while endothermic animals maintain a constant internal temperature using energy from respiration. Temperature also interacts with other abiotic factors, so conclusions should consider more than one factor.

What earns the marks

• Temperature is measured with a thermometer, usually in degrees Celsius, and affects the rate of enzyme-controlled reactions in living organisms.
• As temperature increases towards an optimum, the rate of photosynthesis and other metabolic reactions generally increases because particles have more kinetic energy.
• Above the optimum temperature, enzymes denature and reaction rates fall, which can reduce growth and survival.
• Ectothermic animals rely on external heat sources and may behaviourally regulate their temperature, for example by basking or seeking shade.
• Endothermic animals maintain a constant internal temperature using energy released by respiration, so they can remain active in a range of environmental temperatures.
• Temperature affects the distribution of organisms, so species adapted to particular temperature ranges are found in habitats where those temperatures occur.

Common mistakes and how to put them right

• Stating that enzymes are killed at high temperature.

  Put it right: Enzymes are denatured, meaning the active site changes shape and the substrate no longer fits.

• Confusing temperature with heat energy.

  Put it right: Temperature is a measure of the average kinetic energy of particles, while heat is a form of energy transfer.

• Assuming all organisms have the same optimum temperature.

  Put it right: Different species and enzymes have different optimum temperatures, so distribution varies.

Exam tips

• Use the idea of an optimum temperature and explain what happens both below and above it.
• When describing an investigation, state where and when temperature readings are taken and how you would control other variables.
• Link temperature to a named process, such as photosynthesis or enzyme activity, to show cause and effect rather than simply stating that temperature affects organisms.