How are leaves and weeds similar?

Weeds is not a scientific classification. Weeds are simply plants that annoy us, becuase we do not intend to grow them and they grow faster than our crops, smothering them and taking the lion's share of nutrients. Weeds come from many different families of plants. Therefore herbicides affect the plants we intend to grow and the weeds in the same way. Some herbicides are particularly designed to affect particular weeds so they do not affect the plants you intended to grow. Different herbicides act in different ways. Many herbicides inhibit plant enzymes or other proteins so that they can not carry out the important functions they need to survive