People and animals can't use inorganic substances such as carbon dioxide and water to make organic matter like green plants. They must take food from the outside to get nutrition and energy. This kind of nutrition is called heterotrophic.

A metabolic pattern of organisms in the process of assimilation. Organic matter cannot be directly synthesized from inorganic matter, but can only absorb ready-made organic nutrients from the outside. Heterotrophs includes humans, animals, parasitic and saprophytic plants. ?

The birth of mankind

There are countless bacteria and other microorganisms in the human digestive tract. In fact, the food residue discharged by people mainly depends on the decomposition of food by bacteria. These bacteria have many functions, but their main duty is to decompose substances in the digestive tract. Without them, the human digestive tract cannot accomplish this task.

For example, a large number of undigested carbohydrates enter the intestine, and bacteria in the intestine can decompose them into various acidic substances that can be absorbed and transformed. In this way, the human body uses bacteria to digest and get more nutrients and calories from food, while the bacteria in the digestive tract (intestine) get a stable food supply through the human body.