Final answer:
All animals are heterotrophs because they cannot produce their own food and must rely on consuming other organisms for energy and carbon.
Step-by-step explanation:
All animals are heterotrophs.
Heterotrophs are organisms that obtain their energy and carbon from the intake of other organisms. Unlike autotrophs, which can produce their own food typically through photosynthesis, heterotrophs rely on the complex organic substances created by autotrophs. In the context of animals, they consume either plant material, animals, or both, making them dependent on other life forms for sustenance. This includes all mammals, birds, fish, and insects. For instance, a black bear, which is an omnivore, eats both plants and animals.
Another example is the heartworm Dirofilaria immitis, a parasite that derives its energy from the host it infests. In every case, the source of nutrition for these animals comes from other living beings, classifying them firmly as heterotrophs.