Living off others
Organisms that use the food produced by plants, or any other organic food of living origin, belong to the heterotrophic group.
All animals are heterotrophic. They have no chlorophyll, so they cannot make food — what they do is obtain food that has already been made.
Saprophytes
Organisms that obtain their nutrition from dead organisms or decaying organic matter are saprophytes. Most fungi and many bacteria belong here. They are heterotrophic too.
Figure to be added
Reading a food web
An arrow in a food web does not mean "this eats that" — it means the direction energy flows. So the arrow always runs from the one eaten towards the one eating.
The web starts at an autotroph — always. That is the one door through which energy from sunlight enters the living world. It ends at the saprophytes; they release the materials back into the environment.
Plants respire too
Photosynthesis is nutrition, not respiration. Once a plant has made its food, it still has to respire in order to get energy out of that food — which is what the next section is about.