the smallest particle of a substance that can exist by itself or be combined with other atoms to form a molecule
the part of the Earth in which life can exist
the smallest possible amount of a particular substance that has all the characteristics of that substance.
the complex of a community of organisms and its environment functioning as an ecological unit.
any one of the very small parts that together form all living things.
a group of people who live in the same area (such as a city, town, or neighborhood)
the material that forms the parts in a plant or animal
a part of the body (such as the heart or liver) that has a particular function.
a group of people or animals of a particular kind that live in a place.
In biology, a biological system is a group of organs that work together to perform a certain task. Common systems, such as those present in mammals and other animals, seen in human anatomy, are those such as the circulatory system, the respiratory system, and the nervous system.
a system with many parts that depend on each other and work together