2.1: Introduction
By the end of this section, you will be able to do the following:
- Describe the role of cells in organisms
- Compare and contrast light microscopy and electron microscopy
- Summarize cell theory
Close your eyes and picture a brick wall. What is the wall's basic building block? It is a single brick. Like a brick wall, cells are the building blocks that make up your body.
Your body has many kinds of cells, each specialized for a specific purpose. Just as we use a variety of materials to build a home, the human body is constructed from many cell types. For example, epithelial cells protect the body's surface and cover the organs and body cavities within. Bone cells help to support and protect the body. Immune system cells fight invading bacteria. Additionally, blood and blood cells carry nutrients and oxygen throughout the body while removing carbon dioxide. Each of these cell types plays a vital role during the body's growth, development, and day-to-day maintenance. In spite of their enormous variety, however, cells from all organisms—even ones as diverse as bacteria, onion, and human—share certain fundamental characteristics.
A cell is the basic unit for living organism. According to the Cell Theory, all living organisms are made of one or more cells. A bacterium or a yeast is made of one cell, and is called unicellular organism. A human being or an elephant is made of many cells, and is called a multicellular organism.
In the human body, there are more than 200 different types of cells, including muscle cells, nerve cells called neurons, bone cells and liver cells. Each cell type has specialized functions: muscle cells contract, allowing you to move your body; neurons conduct nerve impulse, allowing them to communicate with each other and other cells, etc. These mature cells that have specialized functions are called our body (somatic) cells.
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