Human Body
Just like your computer, human body is also made up of matter. The smallest particles of all matter are atoms. Two or more atoms joined together form larger particles called molecules.
There are many different kinds of atoms. An element is a substance that contains only one type of atom. Although there are over 100 different elements, only some of them are found in your body. Other elements make up the remaining portion of a human's mass. For example, there are several grams of phosphorus and more than 1000 g of calcium in the body of a typical adult. Elements such as iron and iodine occur in even smaller amounts. Although these and other elements are present in very small amounts, they are still important. Without them, body cannot work properly.
Most of the elements found in the human body are not present in pure form, but are joined together with other elements to form molecules called compounds. For example, most of the oxygen atoms and hydrogen atoms in your body are joined together to form molecules of water. Water is a compound made up of these two elements.
Some of the elements and compounds found in body are used to build or repair body cells. Other elements and compounds supply energy to the cells in your body. Cells are the tiny subunits that make up all living things. Inside cells, many chemical reactions occur. It is these chemical reactions that keep your body alive and active. For the reactions to occur, cells need energy. This energy as well as the substances cells need for growth and repair comes from the food.
