شرح ساينس الصف الرابع الابتدائي لغات - الفصل الدراسي الأول
شرح ساينس رابعة ابتدائي - ترم أول

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This Lesson:
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 carry out all vital activities that living organisms need to survive such as growth, reproduction, repairing the damaged cells.

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.



Building Blocks of Living Organisms
▌Living organisms are different in shape and structure .
▌As you can see in the opposite figures that the animal cells differ from plant
cells in shape and structure.

Size of cells:
► The naked eye can see objects that are about 0.1 mm long but if the size of these objects is smaller than that, it is difficult to see them.
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.
- Bacteria is a living organism that its body consists of one cell only with length less than 0.005 mm.
- So, we need a microscope to see these tiny cells.


► Some cells may be too large and you can see them with your naked eye without using a microscope such as a bird's egg that contains only one big cell.

Living organisms grow and reproduce as a result of increasing the number of the cells that make up their bodies.
This means that new cells are formed as shown in the following figure :

The body of some living organisms are made up of :

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
What are the needs of the cell?
• The cell has needs that are completely similar to the needs of all living organisms.
- 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 ?
• The cell membrane allows water to enter and exit the cell according to its needs.
• So, the cell keeps the water balance on both sides of the cell membrane (i.e. inside and outside the cell).


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