Marine biology, study of the flora and fauna of the sea, from the smallest plankton to massive whales. It includes the study of the complex interrelationship between different marine organisms and between the organisms and their environment. Through experiments with marine organisms, marine biologists can increase our knowledge of human reproduction and development and the nervous system. Scientists have also discovered substances in certain marine animals, such as sponges and seaweeds, that may be used in treating cancer, infections, and pneumonia. These substances might possibly be used as commercial drugs in the future.