The Internal Organization of Living Things

What is a cell?

Living things are made up of a large number of very small units called CELLS.

A cell is the smallest living unit that makes up a living thing.

Most cells are very small, so we need a microscope to see them.

The number of cells in a living thing varies.

• Some living things are made up of a single cell. They are called UNICELLULAR: they can only be seen with a microscope. For example: a paramecium.

• Other living things are made up of many cells: they are called MULTICELLULAR. For example: an elephant.

What are cells like?

Cells are living things. This means that, like other living things, they carry out the life processes of nutrition, reproduction and sensitivity.

However, not all cells are alike. They differ in shape, in size and in the tasks they carry out. For example, skin cells are differente from bone cells.

Cells have three main parts:

• The membrane is a covering that surrounds the cell, and separates it from the exterior.
• The nucleus is the part that controls the function of the cell.
• The cytoplasm is the space between the nucleus and the membrane.

Plant cells also have a hard cell wall around the membrane.
         

             Animal Cell                                      Plant Cell

Click on the image above to learn more about each cell part.

Now, click the following image. Read the tutorial, play the game and answer the quiz questions.