Biological organisms are made of chemicals. Some branches of biology study how the chemicals in organisms do their jobs. The scientists who study the molecules of life are called biochemists.
There are many biologists who study aspects of living things that are not directly related to the molecules that make up the animal or plant. But since animals and plants are made up of molecules, even people who study animal behavior, or classify plants will eventually find some chemistry is useful.
Suppose you were studying the behavior of butterflies. You might want to know how they find their food, or how they find their mates. Both of these behaviors involve sensing molecules in the air using their antennae. That’s chemistry.
Or maybe you want to study human nutrition. To understand why some foods are essential, you might want to learn about vitamins, minerals, proteins, fats, carbohydrates, and other chemicals that make up our food.
Charles Darwin studied biology, and came up with the theory of evolution. But it was chemists who figured out how evolution works, many years after Charles Darwin was no longer around.
Doctors used to give their patients mixtures of plant material or other things in attempts to cure or alleviate symptoms of disease. But it was chemists who discovered how drugs work, and how to find, extract, or make new ones.
As we learn more and more about life and about chemistry, the sciences of biology and chemistry have more and more to do with each other.