In this topic you will learn about how living things play an important role in their surroundings.

Living things and nonliving things are made of elements such as carbon, hydrogen, and oxygen. However, in living things these elements are organized into units or parts that make up the living things. All living things need food because they need raw materials and energy to live and grow. They need the right temperatures in their surroundings. They meet their needs by carrying out certain activities.

Life activities are carried out even in the smallest unit of a living thing. This basic unit of life is called a cell. Robert Hooke was the first person to see cells in 1665. All living things are made up of cells. Some living things are made of only one cell. Many-celled living things, such as complex plants and animals, are made of different kinds of cells, each with its own special function.

In many-celled living things, cells do not work alone. They work in groups called tissues. A tissue is a group of similar cells working together at the same job. Groups of different tissues working together to do certain jobs are called organs. Your heart, which is made of muscle, nerve, and blood tissue, is an example of an organ. Different organs of your body are organized into organ systems. An organ system is made up of different organs working together to do a certain job. All the organ systems together make up an organism. An organism is any living thing that can carry out its life activities on its own.

In any environment there are many kinds of organisms using the same space and raw materials. All the organisms of the same kind living in a particular place make up a population. The size of the population and its location may be large or small.

The members of a population often live and interact with each other. Different populations also interact with each other. All the populations living together in the same place make up a community.

Many populations can live in the same area because each kind of living thing has a certain function in the community. What a living thing eats, when it eats, and where it eats are part of its function. No two kinds of organisms in a community meet their needs in exactly the same way.

Living things interact with nonliving things in their environment. Nonliving things include soil, water, and air. These relationships form an ecosystem. An ecosystem is made up of the living and nonliving things in an area interacting with each other.

Living things are organized internally from cell to tissues to organs to organ systems. They are also organized into populations and communities, based on the way they get along or interact in their environment.