CBSE Class 8 Biology Notes for Chapter 4 Cell

                         CHAPTER 4 CELL
 
The basic structural unit of a living organism is called a cell.
 
VARIETY OF CELLS
There are a number of varieties when it comes to cells. Some of them are:

• Number of cells: Some organisms are unicellular and contain only one cell. Some organisms are multicellular and contain more than one cell.

 

• Shape of the cells: Some cells are spherical. Some cells are spindle shaped i.e. they are long and pointed at both ends. Some cells are branched like the nerve cells.

 

• Size of cells: Most cells are microscopic and can be as small as micrometres or as large as a few centimetres.

 
 
CELL STRUCTURE AND FUNCTION
Similar cells performing similar functions form a tissue.
Tissues combine to form an organ.
And every organism is made up of organs.
This goes out to show the cell is the basic structure of every living organism.
 
PARTS OF A CELL

• Cell membrane: The cell membrane encloses the cytoplasm and the nucleus.

 

• Cell wall: The outer thick layer is called the cell wall. This is present in plant cells only.

 

• Cytoplasm: The jelly like substance between the cell membrane and the nucleus is called cytoplasm. Various other components of the cell (called organelles) are also present in the cytoplasm.

 

• Nucleus: It is generally located in the centre of the cell. There is a smaller spherical body inside the nucleus called nucleolus. The nucleus also contains thread-like structures called chromosomes. The chromosomes carry the genes. The cells which have nuclear material without a nuclear membrane are called prokaryotic cells. The cells which have a well- defined nuclear membrane are called eukaryotic cells.

 

• Vacuole: The blank structure in the cytoplasm is called a vacuole. Plant cells have larger vacuoles and animal cells have smaller vacuoles.

 

• Plastids: The small coloured bodies found in the cytoplasm of the plant cell are called plastids. The plastids that contain green pigment in them are called chloroplasts and the green coloured pigment is called chlorophyll.