A trophic level describes an organism's position in a pathway of energy and matter transfer through feeding.

Primary producers form the first trophic level by building organic matter from inorganic carbon. Primary consumers eat producers. Secondary consumers eat primary consumers, and higher-level consumers feed farther along the chain.

A food chain is one linear pathway of transfer:

algae → zooplankton → small fish → larger fish

Real ecosystems contain many overlapping pathways. A food web represents this network of feeding relationships.

An organism need not occupy exactly one trophic level. An omnivore can feed on both producers and consumers, so its effective trophic position depends on diet.

Arrows in a food web are best interpreted as the direction in which energy and consumed matter move: from resource to consumer.

Food webs also include a detrital pathway. Dead organisms, shed tissues and wastes become detritus that can be consumed or decomposed rather than passing only through living prey-consumer links.

The important distinction is that food webs describe who transfers organic matter and energy to whom. They do not by themselves tell us how much energy is transferred, how efficiently it is converted into new biomass, or how chemical elements are recycled. Those are separate ecosystem properties built on top of trophic structure.