* Producers: Plants are the foundation of a food chain. They capture energy from the sun through photosynthesis and use it to make their own food.

* Consumers: Animals eat plants (herbivores) or other animals (carnivores) to obtain energy.

* Decomposers: Organisms like bacteria and fungi break down dead plants and animals, returning nutrients to the soil.

Important points about energy transfer:

* Not all energy is transferred: Only about 10% of the energy from one trophic level (e.g., plants) is transferred to the next trophic level (e.g., herbivores). This is because some energy is lost as heat during metabolism and some is used for things like growth and reproduction.

* Energy flow is unidirectional: Energy flows in one direction, from the sun to producers and then to consumers. It is not recycled.

* Food webs are complex: In reality, food chains are interconnected to form complex food webs, with organisms often eating multiple types of food.

So, while food chains involve the transfer of matter (like carbon, nitrogen, and phosphorus), the primary thing passed along is energy.