1. Producers: These organisms, primarily plants and algae, are the foundation of the food web. They capture energy from the sun through photosynthesis and convert it into chemical energy stored in organic molecules (like sugars).

2. Consumers: These organisms obtain their energy by eating other organisms. They can be herbivores (eating plants), carnivores (eating animals), or omnivores (eating both plants and animals).

3. Decomposers: These organisms break down dead organisms and waste products, returning nutrients to the ecosystem. They are essential for recycling matter and making it available for producers again. Examples include bacteria and fungi.