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In This Part :
Any system in a living organism's body is buildup of tiny structures called "the cell".
The cell
It is the main building unit of the living organism's body that carries out all its own vital activities.
Cells are found only in the bodies of living organisms, and they are not found
in non-living things.
Cells are tiny particles that cannot be seen by naked eye,
but we need a special device called "microscope"
to see cells and their structures.
Cells as building blocks:
▌As a brick is the building unit of a wall or a building,
the cell is the main building unit of life, structure,
and function of all living organisms on Earth.
▌As you can see in opposite figures that the animal cells differ from plant cells
in shape and structure.
Plant cell Animal cell
Cells are usually tiny:
The length of most of cells are tiny, where:
- The length of common animal cells and plant cells ranges between 0.1 mm and 0.005 mm, so we need a microscope to see them.
Characteristics of cells
Let's see some similarities and differences between cells.
1. All cells have a cell membrane
2. Not all cells have a cell wall
- Animal cell doesn't have a cell wall
- Plant cell has a cell wall
3. Not all cells have a nucleus
4. The cells of one living organism are not identical
Human muscle cell Human bone cell
Cell Needs
During the growth of a living organism, the new cells are formed from cells that were already existed in its body.
What are the needs of the cell?
- The cell needs energy to carry out all its own life activities to survive and get rid of waste materials.
The cell needs some materials such as:
- Food (nutrients) and oxygen to get energy.
- Water to stay alive.
How does the cell get its need of water ?
- Water enters the cell through a membrane that surrounds the cell known as
"The cell membrane".
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