Biology - Energy Flow

The Sun is the principal source of energy input to biological systems. Energy enters the ecosystem through photosynthesis, where light energy is converted into chemical energy: $6CO_{2} + 6H_{2}O \xrightarrow{\text{light}} C_{6}H_{12}O_{6} + 6O_{2}$.

A food chain shows the transfer of energy from one organism to the next, starting with a producer. The position of an organism in a food chain is its trophic level.

Energy is transferred between trophic levels when one organism eats another. However, energy flow is non-cyclical; it moves in one direction and is eventually lost to the environment as heat.

Efficiency of energy transfer is generally low, often cited as approximately $10\%$. This means about $90\%$ of energy is lost at each level through respiration ($C_{6}H_{12}O_{6} + 6O_{2} \rightarrow 6CO_{2} + 6H_{2}O + \text{energy}$), movement, excretion, and as heat.

Pyramids of biomass represent the total dry mass of organisms at each level. Biomass typically decreases as you move up the pyramid due to the significant loss of energy and material at each stage.

Pyramids of numbers show the total count of individual organisms. These can sometimes be inverted (e.g., one large oak tree supporting thousands of insects), whereas pyramids of energy are always upright.