Each stage in a food chain is called a trophic level. The levels are numbered, starting at level 1 with plants and algae. Each further level is numbered according to how far along the food chain the organism is.
Level 1 is made up of plants and algae. They make their own food by photosynthesis, so they are called producers. Level 2 is made up of herbivores, which eat plants or algae. They are called primary consumers. Level 3 is made up of carnivores that eat herbivores, called secondary consumers. Level 4 is made up of carnivores that eat other carnivores, called tertiary consumers.
An apex predator is a carnivore with no predators of its own. It sits at the top of the food chain.
Decomposers break down dead plant and animal matter. They secrete enzymes into their surroundings, and the small soluble food molecules this produces then diffuse into the microorganism.
