Biology - Food Chains and Food Webs

The Sun is the principal source of energy input to biological systems, providing the energy required for photosynthesis.

Producers are organisms that make their own organic nutrients (like glucose) using energy from sunlight via photosynthesis: $6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2$

Consumers are organisms that get their energy by feeding on other organisms. They are classified as primary consumers (herbivores), secondary consumers (carnivores that eat herbivores), and tertiary consumers (carnivores that eat other carnivores).

A Trophic Level refers to the position of an organism in a food chain, food web, or ecological pyramid. Trophic level 1 is always the producer.

Food Chains show the transfer of energy from one organism to the next, starting with a producer. The arrows represent the flow of energy.

Food Webs are networks of interconnected food chains. They provide a more realistic model of ecosystem interactions because most consumers have more than one food source.

Decomposers are organisms, such as bacteria and fungi, that get their energy from dead or waste organic matter.

Energy is lost between trophic levels through processes such as respiration (heat loss), movement, excretion, and uneaten parts. Only approximately $10\%$ of energy is typically passed to the next level.

Pyramids of Numbers represent the total number of individual organisms at each trophic level. They can be 'inverted' if a single large producer (like a tree) supports many small consumers.

Pyramids of Biomass represent the total dry mass of living material at each trophic level. These are almost always pyramid-shaped because biomass is lost at each stage.