Living things make up the world as we know it. Living things are involved in our life constantly, seeing that we are alive. There are five characteristics that are common to all living things. Living things are made up of one or more cells. Each cell is made up of living matter and is separated by a barrier that encloses the cell from its surroundings. However, there are many different kinds of cells that make up living things. A single cell can be one organism. These organisms are known as unicellular. Most of the organisms that we know best such as people, trees, and dogs are all made up of more than one cell. Organisms made of more than one cell are said to be multicellular. Another characteristic that living things share is that they reproduce. They reproduce, or make new organisms of the same sort. In order for a species to survive, it is a necessity for them to reproduce because all organisms die eventually. There are two ways living things reproduce, sexually and asexually. Sexual reproduction needs two cells from two different organisms to merge and form the first cell of a new organism. Asexual reproduction is when only one organism can reproduce without the assistance of another. The third characteristic of living things, is that all living things need to grow and develop. When an organism is growing, most go through a cycle called development. The single cell that starts the cell divides over and over again to make all the cells that the organism has when in adulthood. As the cycle continues the organism ages. Aging is when the organism becomes less efficient in the process of life. The organism will not be able to reproduce, and death comes as finally too. The fourth characteristic of a living thing is the ability to obtain and use energy. Living things obtain energy from their environment or their surroundings. All living things require energy to live and build their cells. This process is anabolism.