Define cell and name the one who discovered it.

Cell is the basic structural, functional unit of life. 

Discovery of cell : Cell was discovered by Robert Hooke in 1665. 

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What are the characteristics of a semipermeable membrane ?

A semi-permeable membrane is one which allows only a few substances to pass through it while preventing the others. The cell membrane found in the cell is a semi-permeable membrane which allows only certain substances to pass throught it.  
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What is cell theory ? 

Cell theory was given by Schleiden, Schwann and Rudolf Virchow. The cell theory states that  

(i) all living organisms are composed of cells and products of cells.

(ii) all cells arise from pre-existing cells.

 

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What is plasma membrane?


Plasma membrane is the outer membrane of the cell. It is composed of lipids bilayer which is quasi fluid in nature. The plasma membrane is semi permable in nature. Besides, the lipid content it also has protein and carbohydrates. It provides protection and structural support to the cell. The plasma membrane helps in the transport of material in and out of the cell. The fluid nature of the membrane helps in the formation of cell wall, secretion, cell growth etc. 

 

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 “The function of an organism is the sum result of the sum total of activities and interactions of constituent cells”. Comment.

An oganisms has billions or trillions of cells. Cells performing similar functions are grouped together to form tissue. The different tissue perform different functions. These different activities work together to sustain lie in a multicellualr organisms. Since, the main constituent of the any organism is a cell that is capable of all activities of life, we can say that the functions of an organism are sum total of functions performed by constituent cells.
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