These are Biology, Chemistry and Physics.
Biology is generally a study of life on earth. It looks at all things that lie, including animals, humans and of course plants. It is an absolutely essential study as it allows us to understand precisely how the world works in terms of creating life and providing for that life. It also allows us to see how species have changed over thousands of years, and how they have adapted to different climates. Biology is also incredibly important as it allows us to understand the human body and know precisely what we need to do to ensure that it is working properly and that it remains healthy. Biology intertwines with Chemistry in that some things produced in that other field of science can be used in Biology to help people remain healthy.
Chemistry is the study of different chemicals and their properties. Chemicals can be either man made or natural, and it can overlap quite a lot with biology. Chemicals can provide ill patients in hospital with a new lease of life. The drug industry is absolutely huge, and would not exist without the study of Chemistry. Chemistry is also incredibly important for the field of petroleum engineering. Chemists are required in many fields these days and it's becoming an increasingly popular subject to study at university.
Physics is another popular scientific study, too. It looks at the way things move, energy, and matter. It's also massively involved with outer space. Physics can look at energy within the earth and outside of the earth, as well as how planets move and cause one another to change direction. It overlaps with other areas of science, too, and is incredibly popular to study at university.
For more information on these sciences, make sure you look at the detailed pages available on Wikipedia.
