A consumer is an organism that generally feeds on other organisms or organic matter, since they cannot manufacture their own food from inorganic sources. Consumers take in oxygen from the air and return carbon dioxide. Their wastes return other chemicals to the environment. Another name for consumers is heterotrophs. There are three levels of consumers: primary consumers (herbivores that feed on producers), secondary consumers (consumers that feed on primary consumers and/or producers), and tertiary consumers (consumers that feed on producers, primary, and/or secondary consumers).