Answer: Key points:
Producers, or autotrophs, make their own organic molecules. Consumers, or heterotrophs, get organic molecules by eating other organisms.
A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another.
In a food chain, each organism occupies a different trophic level, defined by how many energy transfers separate it from the basic input of the chain.
Food webs consist of many interconnected food chains and are more realistic representation of consumption relationships in ecosystems.
Energy transfer between trophic levels is inefficient—with a typical efficiency around 10%. This inefficiency limits the length of food chains.
Introduction
Organisms of different species can interact in many ways. They can compete, or they can be symbionts—longterm partners with a close association. Or, of course, they can do what we so often see in nature programs: one of them can eat the other—chomp! That is, they can form one of the links in a food chain.
In ecology, a food chain is a series of organisms that eat one another so that energy and nutrients flow from one to the next. For example, if you had a hamburger for lunch, you might be part of a food chain that looks like this: grass
→
→right arrow cow
→
→right arrow human. But what if you had lettuce on your hamburger? In that case, you're also part of a food chain that looks like this: lettuce
→
→right arrow human.
As this example illustrates, we can't always fully describe what an organism—such as a human—eats with one linear pathway. For situations like the one above, we may want to use a food web that consists of many intersecting food chains and represents the different things an organism can eat and be eaten by.
In this article, we'll take a closer look at food chains and food webs to see how they represent the flow of energy and nutrients through ecosystems.
Autotrophs vs. heterotrophs
What basic strategies do organisms use to get food? Some organisms, called autotrophs, also known as self-feeders, can make their own food—that is, their own organic compounds—out of simple molecules like carbon dioxide. There are two basic types of autotrophs:
Photoautotrophs, such as plants, use energy from sunlight to make organic compounds—sugars—out of carbon dioxide in photosynthesis. Other examples of photoautotrophs include algae and cyanobacteria.
Chemoautotrophs use energy from chemicals to build organic compounds out of carbon dioxide or similar molecules. This is called chemosynthesis. For instance, there are hydrogen sulfide-oxidizing chemoautotrophic bacteria found in undersea vent communities where no light can reach.
Autotrophs are the foundation of every ecosystem on the planet. That may sound dramatic, but it's no exaggeration! Autotrophs form the base of food chains and food webs, and the energy they capture from light or chemicals sustains all the other organisms in the community. When we're talking about their role in food chains, we can call autotrophs producers.