Some animals on earth eat meat, some animals eat grass, but why do all animals eat?
The animals on earth are very different. From fleas to elephants, from mosquitoes to goldfish, from earthworms to peacocks, from spiders to boa constrictors, it seems that there is no similarity between them. In fact, they have a lot in common, one of which is that all animals have to eat.
In order to live, many animals have to look around for food every day. It can be said that this is the most important instinct of animals. Chickens will eat when they are hatched from eggs, and piglets will be born to eat milk. Once the food is cut off, all animals face death. Why is that?
We know that all life activities need to consume energy. Respiration, heartbeat and movement are realized by muscle contraction. Energy is also needed for nerve cells to send out electric pulses, digestive organs secrete digestive fluid, and cells synthesize macromolecules in the body. Just as a power plant needs to burn coal or natural gas to supply electricity, so does the energy that animals need to burn fuel.
For animals, this' fuel 'is food, and an important role of food is to provide energy. In fact, the principle of animals using food is the same as that of power plants burning fuel to generate electricity. Power plants burn coal, turn it into carbon dioxide and water, and the energy released during combustion is converted into electricity. Animals also 'burn' food, which is converted into carbon dioxide and water. The energy released is not used to generate electricity, but to synthesize ATP (adenosine triphosphate), a 'high-energy compound', to supply energy for various life activities.
In addition to providing energy, the second important role of food is to provide the 'parts' needed to replace the body. The amino acids that make up protein molecules, fatty acids and glycerin that make up fat, and vitamins necessary for maintaining normal life activities (as the protein catalyzing chemical reactions, the 'additional component' of enzymes), need to be 'extracted' from food.
Metabolism is accompanied by the whole life of organisms, and the organism needs to be constantly updated. Inanimate objects do not renew themselves. The composition of the deep ice in the Arctic remains almost unchanged for a long time. The composition of the air bubbles in it can tell the composition of the air hundreds of thousands of years ago. However, biology is highly complex and fragile, and its' components' need to be constantly repaired and updated so that life can continue.
Many animals can live for more than ten to several decades, but most of the cells in the body can't live that long. Human intestinal parietal cells change every two or three days, epithelial cells change every 28 days or so, and liver cells change about once a year. Bone cells are also renewed every 10 years or so for bones that people don't think will grow and change again in adulthood.
In this way, the 'life span' of the molecules in the cell is shorter. Some protein molecules have only a few minutes' lifespan. Some long-lived cells, such as nerve cells, are constantly being replaced by molecules. Ten years have passed, especially in adults. Although it seems that there is no earth shaking change from 10 years ago, the cells and molecules in the body have almost been replaced in these 10 years.
Food is needed to provide energy for the continuous rejuvenation of animal bodies, the repair and renewal of 'components' in animals, and the molecular replacement in cells.