- Main Article: Photosynthesis
A photosynthetic organism is one that produces its own food through the biochemical process called photosynthesis'. This complex chemical synthesis allows organisms to produce carbohydrates, from carbon dioxide and water using sunlight as the source of energy and with the aid of associated pigments and protein machines (enzymes).
For most organisms on Earth, photosynthesis is the beginning of the food chain. The food that photosynthetic organisms make for themselves is then ultimately passed on to animals and microbial organisms when they are eaten. An important byproduct of photosynthesis is oxygen, which is a basic requirement of life for all higher lifeforms. Because plants make their own food, they are called producers (autotrophs), as opposed to animals which are consumers (heterotrophs). Photosynthesis is not only used in green plants, but also algae, and some forms of bacteria.
- Main Article: Herbivore
Herbivores are animals that eat only plants. They form an important link in the food chain, between carnivores and plants. Common herbivores include cattle, sheep, deer, grasshoppers, rabbits, honeybees, moose, elephants, some dinosaurs, and the pond snail. The most numerous types of herbivores are the zooplankton — tiny creatures that live in the surface waters of oceans, and feed on small photosynthetic algae.
According to the Bible, God created animals on the fifth and sixth days of the Creation Week. The Bible also clearly states that all animals were originally created as herbivores. It is believed by many that carnivorous behaviors began after God cursed the world due to the original sin that was committed by Adam and Eve in the Garden of Eden.
Genesis 1:29-30 Then God said, "I give you every seed-bearing plant on the face of the whole earth and every tree that has fruit with seed in it. They will be yours for food. 30 And to all the beasts of the earth and all the birds of the air and all the creatures that move on the ground—everything that has the breath of life in it—I give every green plant for food." And it was so. (NIV)
Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as organic fecal matter). By doing so, they contribute to decomposition and the nutrient cycles. They should be distinguished from other decomposers, such as many species of bacteria, fungi and protists, which are unable to ingest discrete lumps of matter, but instead live by absorbing and metabolizing on a molecular scale. However, the terms detritivore and decomposer are often used interchangeably.
Typical detritivorous animals include millipedes, woodlice, dung flies, slugs, many terrestrial worms, sea stars, sea cucumbers, fiddler crabs, and some sedentary polychaetes such as amphitrites (Amphitritinae, worms of the family Terebellidae) and other terebellids.