Answer: This is so because plants are autotrophs.
Step-by-step explanation:
Living beings are classified into two classes on the basis of their ability to food consumption:
1. Autotrophs: These organisms have the ability to make their own food and they act as producers in the food chain. For Example: Green plants
2. Heterotrophs: These organisms does not make their own food but depend on other organisms for the food. These organisms act as consumers in the food chain. For Example: Human beings, Animals.
In the food chain, producers are the organisms which act as the beginning of the food chain. Hence, plants only begin the food chain.