Final answer:
Herbicides are substances used to control unwanted plants. Some herbicides contain highly toxic substances known as pesticides. Defoliants are herbicidal chemicals that cause leaves to fall off plants.
Step-by-step explanation:
Herbicides are substances used to control unwanted plants, also known as weedkillers. Some herbicides contain highly toxic substances, known as pesticides, which are intended to protect plants from weeds, fungi, or insects. Defoliants are a type of herbicidal chemical sprayed on plants to cause their leaves to fall off.