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# Cell Structure And Organization ## Can You Recall? 1. Who observed cells under the microscope for the first time? 2. Who made the first microscope? 3. How do onion peel cells and our body cells differ? 4. Why is bacterial nucleus said to be primitive? ## 5.1 Cell - The unit of life is called a...

# Cell Structure And Organization ## Can You Recall? 1. Who observed cells under the microscope for the first time? 2. Who made the first microscope? 3. How do onion peel cells and our body cells differ? 4. Why is bacterial nucleus said to be primitive? ## 5.1 Cell - The unit of life is called a structural and functional unit of life. - A cell is an independent existence and can perform all functions of life. - To see cells clearly we need a microscope. - Larger cells can be seen through a simple microscope, while smaller cells require a compound microscope. - A simple microscope can magnify the image 50 to 100 times, while a compound microscope can do so 1000 times or more. - In the lab, a beam of light is used to make things visible. - This is a light microscope. - To see the interior of a cell we need an electron microscope. - An electron microscope can magnify the image 500000 times. ### Fig 5.1 - Microscope ### Fig 5.2 - Cell Size - There is no typical shape of a cell. - Cells may be spherical, rectangular, flattened, polygonal, oval, triangular, conical, columnar etc. - Cell size varies greatly in various plants and animals. - Some of them are not visible to the naked eye. - Some are barely visible, and some are macroscopic. - The smallest cell size can be seen in mycoplasma (0.3 µm in length). - Bacterial cell size is 3 to 5,μm. - The largest cell size can be seen in an ostrich egg (nearly 15cms). - Longest cells are nerve cells. - You already know that cell theory was proposed by Schwann and Schleiden. - However, there was no explanation about the formation of new cells in this theory. - It was Rudolf Virchow (1855) who explained for the first time that new cells are formed by cell division from preexisting cells (Omnis cellula-e-cellulla). - In later years, advanced research in cytology led to modifications in cell theory, which is now known as Modern Cell Theory. ## Find Out 1. How does a combination of lenses help in higher magnification? 2. When do we use plane and concave mirror and diaphragm? 3. What is the difference between magnification and resolution?