Unlike animals, plants have neither a mouth nor a stomach. Except for a few plants such as Venus flytrap, almost all plants don't "eat". How do plants get energy and build "parts" to repair their bodies?
Plants need energy not from other creatures, but from sunlight. Chlorophyll in plants can absorb the energy of some bands of sunlight and transmit it to special protein complexes, where it decomposes the water in cells into hydrogen and oxygen. Although oxygen is extremely valuable to many organisms, it is useless "waste" to plants and is released into the air. Hydrogen is precious to plants and must not be "released", but used as "fuel" to "generate electricity", that is, synthesize ATP.
Hydrogen is also used to combine with carbon dioxide to produce sugars, the most important of which is glucose. Plants also use these compounds to further synthesize other molecules they need, such as proteins, fats and vitamins.
Therefore, plants can "make" various "parts" of the body by themselves. All they need is the elements to build these parts, and in the form of small molecules. For example, the amino acid molecules that make up proteins have an "amino group", which contains nitrogen atoms. These nitrogen atoms can come from urea or ammonium sulfate. Phosphorus is needed to synthesize genetic material DNA, and phosphate can be supplied. The small molecules that supply these elements to plants are fertilizers in the soil.
Therefore, plants only need sunlight, air, water and fertilizer to grow and reproduce. Because plants can rely on themselves and do not need other biomaterials to provide energy and "parts", they are called "autotrophs". Animals do not have this "ability" and can only obtain energy and "parts" from other creatures, which is called "heterotrophic creatures"