Producers are always the lowest level of a trophic hierarchy, and consist of the autotrophs in the system. Organisms that feed off of producers are considered primary consumers.

In this example, the grasses are the producers. Both the rabbits and the turtles will be primary consumers.

An organism that feeds on primary consumers is considered a secondary consumer.

Autotrophs are organisms that are capable of generating biological energy from inorganic sources, such as sunlight in the case of photoautotrophs. Cyanobacteria are thought to be the prokaryotic precursor to chloroplasts through the endosymbiotic theory because they are able to perform photosynthesis. Cyanobacteria are, thus, photoautotrophs. Green algae are another type of photoautotroph.

Heterotrophs use organic materials from the environment to general energy. Animals are heterotrophs, including cows.

Saprotrophs, many of which are fungi, gain nutrients from decaying organic material. Mushrooms are saprotrophs.

Ecology is essentially the study of all the living things on the planet and their relationships with each other. Ecology can be organized into levels: population, community, ecosystem, and biosphere. A population is a group of organisms that belong to the same species, share an area, and can reproduce with each other. A community is composed of the different species that can be found in a geographical location. An ecosystem encompasses all abiotic and biotic factors in an area. The biosphere refers to those parts of the earth that are able to support and sustain life.

Within ecosystems, there is always a transfer of energy, usually from one organism to another. There is also energy transfer between abiotic and biotic factors. The caterpillar and lion are examples of consumers because they are unable to make their own food and must rely on other living organisms for energy. Consumers are subdivided into herbivores, omnivores, and carnivores. Producers are those living things in the ecosystem that generally produce energy using photosynthesis or light. Organisms that break down dead or decaying matter for energy are called decomposers. These are most likely bacteria, fungi (such as mushrooms), and some worms.

A flower in this example is a producer, which means it will make its own energy through photosynthesis. As a result, the flower must be the first element of our chain; food chains will always start with a producer. The caterpillar, frog, and snake are consumers, meaning they will need other organisms for energy.

A producer is an organism that makes its own food from the energy of the sun via photosynthesis. Green algae is a producer; it has chlorophyll pigments and can make glucose via photosynthesis. A frog is a consumer; a worm is a decomposer; a fungus is a saprophyte; a bear is a consumer.

An omnivore eats both plants and animals. Humans are an example of omnivores.

Herbivores only eat plants. Carnivores only eat animals. Detritivores eat decaying matter.

Organisms that eat producers are known as primary consumers. Organisms that eat primary consumers are secondary consumers, and organisms that eat secondary consumers are tertiary consumers and so on. Autotrophs are able to fix their own carbon from the air, converting it into food e.g., glucose, and need not eat other organisms. Predators are animals that eat prey animals, thus they are a type of secondary (or higher) consumer.

Biomagnification is described as the concentration of a pollutant increasing as it moves through the tropic levels of an ecosystem. For example, if a pollutant has a low concentration in a plant, that concentration will be much higher in the animal that eats that plant. This occurs because organisms do not have enzymes that can break down these chemicals. This process does not occur with minerals. 

Plants make up the bottom trophic level: the producers. This is because plants produce energy through photosynthesis. They do not have to eat other organisms to obtain energy, they make their own using carbon dioxide, water and sunlight.