Notes of class ix 

Topic : Cell

• Meaning of term cell is the small compartment. Robert Hooke observed bee hives like small compartments in the thin slice of cork with the help of self invented microscope. These small chambers were considered as "cell".
• Antony van Leeuwenhoek was credited to observe the first living cell in pond water, sputum, blood  etc.
• The branch of science which deals with study of cell is called "Cytology".

The cell is a microscopic structure so for better understanding of a cell, at first we should have some idea about evolution of microscope which is very first requirement of cytology.

• Antony Van Leeuwenhoek designed first simple microscope having power of magnification 200 times. There was single biconvex lens in this microscope.
• Robert Hooke developed the microscope by using two lenses. It was compound microscope having power of magnification 2000 times.
• Knoll and Ruska designed electron microscope which is having power of magnification 200,000 times.

Cell Theory :- Cell theory was proposed by J.M. Schleiden and Theodor Schwann in 1838/39. Later on in 1858 Rudolf Virchow added one more point in the cell theory.

1. J.M.Schleiden a botanist in 1838 proposed that "Every plant is made up of large number of cells and each cell performs various life processes".
2. Theodor Schwann a zoologist in 1839 proposed that "All animals and plants are composed of cells which serves as a unit of structure and function".
3. Rudolf Virchow said - "Omnis cellula e cellula" that is all cells originate from preexisting cells.

Some important points about cell :-

• Bacterial cell and RBC of human body is considered as smallest cell.
• Nerve cells ( Neuron ) is the longest cell of the body.
• Ostrich egg is the largest cell.
• Small size of cell is facilitating better diffusion of materials through it, so efficiency increases.

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That's all for this session. We will meet in our next session with the notes on topic "Structure of Cell".