Cell : The building block of human body

 

All of us have seen cells many times. When a section of an orange is opened, the whole fibres we see are cells. The juice runs out , if the cell walls are broken. Scientists define cell as the building block that makes up all living things. Every living thing that is alive is made up of one or more cells. There are five important types of cells in the human body. They are : Epithelial cells which make up the skin and glands and line the blood vessels; Muscle cells which make up the kinds of muscles; Nerve cells make up the brain, spinal cord and nerves. Blood cells are found in the blood and lymph. Connective tissue cells make up the framework tissue of the body. All life activities take place in cells. Each cell in a plant or animal lives its own life and also makes it possible for the living thing as a whole to carry on its life activities. Living cells consist of a cell wall, a mass of jelly – like colourless material called “protoplasm”, and a kernel – like part of protoplasm called “ the nucleus”. It is the protoplasm which is the living matter. It carries on all the processes necessary for life. For instance , it takes in food and oxygen, changes some of the food into living matter, gives off waste, repairs its worn-out parts, and reproduces itself. Each cell needs food and oxygen to do work. The higher forms of living things have developed a circulatory system to carry the necessary supplies to everyone of their cells. This circulates food and oxygen to the cells and removes waste products, like carbon dioxide. The individual cells combine food and oxygen slowly, thus obtaining heat and energy necessary for their life and work. It is because of this energy that muscles can contract, nerves can conduct messages , and the brain can think.

What do the cells do? Normally all living things are made up of one or more cell. The simplest plants and animals consist of only one cell. In more complicated living things cells organize themselves in groups but work together, each, performing some special work. A tissue is a group of cells of a particular kind that does one particular type of work. For example , there is bone tissue, muscle tissue, or bark tissue. When tissues co-operate to perform a special task , such a group of tissues is called an ‘organ’. An example of this is the human hand, which is composed of bone, muscle, nerve and other tissues.