Energy flow, food chains and food webs — Cambridge IGCSE Combined Science

Revision notes

3 short notes, in the order of the specification. Each one in short:

1. Energy flow

   The Sun is the principal source of energy input to biological systems. Plants and algae transfer light energy into chemical energy in organic nutrients by photosynthesis. This chemical energy passes to animals by feeding and to decomposers. Energy flows in one direction, not a cycle, and at every stage much of it is transferred to the environment as heat.

2. Food chains and food webs

   A food chain shows the transfer of energy from one organism to the next, beginning with a producer, and a food web is a network of interconnected food chains. Each arrow points from the organism that is eaten to the one that eats it. Overharvesting and introducing foreign species change food webs and affect other populations.

3. Producers, consumers and decomposers

   A producer is an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis. A consumer gets its energy by feeding on other organisms: herbivores eat plants and carnivores eat other animals. Consumers are primary, secondary, tertiary or quaternary. Decomposers, such as bacteria and fungi, get energy from dead or waste organic material.