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Cell : The Unit of Life

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Class 10 Class 12
Who concluded, “Cells are the ultimate units forming the structure of all plant tissues”?

Mathias Schleiden.

 Describe different types of membranes.

There are three types of membranes :

1. Permeable membranes. These membranes allow diffusion of both solvent and solute molecules or ions through them e.g. cell wall. 

2. Impermeable membranes. These membranes prevent any substance to pass through it. 

3. Semipermeable membranes. These types of membranes allow diffusion of  certain substances through it while prevent the others to pass through it. e.g. cell membrane. 



 Give the functions of cell wall.

The cell wall performs the following functions.

1. It maintains shape of the cells and provides structural support to the cell.

2. It protects the cells from mechanical injury.

3. It wards off the attacks of pathogens (viruses, bacteria, fungi, protozoans) and protects from infection.

4. It allows the transport of materials in and out of the cell.

5. The cell wall helps in cell to cell interactions. 



 What are the advantages of multicellularity?

Multicellular organization increases the efficiency of the organism in the following ways follows :

1. Avoids duplication of work : Only certain cells perform a specific function. Thus, all cells do not have to perform the same function and there is no waste of energy on duplication of work.

2. Increases chances of survival : Death of a few cells does not affect a multicellular organism. The function is taken by new cells of the same lineage.

3. Makes specialized units highly effective: Diffrent cells perform different function. Cells performing similar functions are grouped into tissue which carry out specific function. 

4. Long life : Greater efficiency of the cells, because of division of labour, makes multicellular organisms to live longer.


Describe functions of cell membrane.

Functions of cell membrane.

1. It maintains the structure and form of the cell.

2. It keeps the cell contents in place and distinct from the environment materials.

3. It helps in the transport of materials in and out of the cell. By controlling flow of materials and information into the cell, the cell membrane makes metabolism possible.

4. It permits the exit of secretions and wastes materials.

5. It protects the cell from mechanical injury and other unfavourable factors.



Define the following :

1. Nucleoid

2. Eukaryotic cells

3. Cristae

4. Mitochondrial matrix.

1. Nucleoid. It is the open nuclear material of prokaryotes. It is an irregularly shaped region that contains the genetic material of the prokaryotic cell.

2. Eukaryotic cells. The cells in which the nuclear material is enclosed by a definite nuclear membrane are known as eukaryotic cells.

3. Cristae. The infoldings of the inner membrane of mitochondria which look like finger like projections are called cristae.

4. Mitochondrial matrix. It is ground substance present in the space enclosed by the inner mitochondrial membrane. It is also known as nucleoplasm.