4.2 - A - Food Chains
In most ecosystems, the primary source of initial energy is sunlight. Chloroplasts in producers absorb this light energy and synthesize glucose through photosynthesis. The chemical energy in glucose is then consumed by heterotrophs who release the energy via cell respiration.
The amount of sunlight that is available and the amount that is absorbed varies between habitats on Earth. As a result the amount of energy that is available for consumption also varies. This in turn affects potential population sizes in ecosystems.
For example, much of the sunlight in tropical rainforests is absorbed as there is a high population of autotrophs. In contrast, deserts are exposed to much sunlight, but very little is absorbed and autotroph populations are small.
As mentioned above, after photosynthesis, chemical energy flows to primary consumers through feeding. These consumers are then eaten by secondary consumers, which are then eaten by tertiary consumers. This continues until the apex predator is reached. Food chains are a graphical way of representing this flow of energy in an ecosystem.
Food chains use arrows to represent the flow of energy. Since producers absorb energy from the sun, they are always at the beginning of the chain.
The arrow then points to the primary consumer, and then to the secondary consumer, etc. When constructing food chains, ALWAYS make sure that your arrows are pointing in the appropriate direction.