Biology can be studied at different levels, from sub-atomic particles to entire ecosystems. At the smallest level of study are molecules like water, DNA, proteins, carbohydrates, lipids, and nucleotides. The largest system studied is the biosphere, which contains all ecosystems and can be viewed from satellites. Autotrophs are organisms that produce their own food using sunlight, while heterotrophs obtain energy from food. Adaptations are inherited traits that increase an organism's chances of survival, such as long legs, eyelashes, and fat storage.