What type of organism is specifically defined as a consumer?

A consumer is defined as an organism that obtains energy by consuming other living organisms or organic matter. This definition encompasses a variety of organisms, such as animals and some fungi, that rely on external sources of energy rather than producing it themselves.

Option D accurately captures this concept, emphasizing the dependence of consumers on other organisms for their energy and nutrients. Consumers play a crucial role in ecosystems by transferring energy through the food web, making them essential for biological processes and the maintenance of ecological balance.

The other options illustrate different types of organisms and their functions: the first describes producers, which are capable of photosynthesis and making their own food, while the second refers to decomposers that break down dead material. The third option is misleading as it specifies that consumers eat only living organisms, which does not fully encompass the behavior of all consumers, as many consumers may also feed on decaying organic matter.