NEET Biology Organization In The Living World Cell And Cell Structures Revision Notes

eye piece system. This second image is what we see. Light is transmitted through objects. Their visibility is usually enhanced by staining.

To study the plant cells, the epidermal layer from the lower surface of the leaf of Rhoeo sp. or from the inner layer of onion bulb is removed with the help of a forceps. The tissue which is one cell thick is placed on a drop of water and stained with safranin and spread flat on a glass slide. The cells are observed under the low and high power of compound microscope to study the size, shape and structure of the cells. Similarly a very thin slice of bottle cork is obtained a using a singe edged razor blade. The cells are observed after mounting the slice n a drop of water on a glass (similar observation on cork cells was done by Robert hook in 1665)

 

To study the animal cells, epithelial cell from the inner side of the cheek is obtained using a sterile tooth pick or clean spatula. The cell scrapings are mounted on a glass slide and stained with methylene blue and covered with a slip. The mounted specimen is observed under the microscope (both under low and high power). Similarly blood cells of human being or frog is made into a smear using two glass slides and the blood smear is stained with Leishman’s stain, to study the nucleus and their details of the cells.

 

The study/observation of cells under the microscope reveal that plant cells have a prominent cell wall and inner portion of the cells appear transparent. The cells are compactly arranged without any intercellular spaces between them. The tissue tom the leaf of Rhoeo appear purple in colour and show presence of stomata. Observation of blood cells reveal that they are ovoid and cheek cells are cuboidal with prominent nuclei.

 

3. Electron Microscope: In the last few decodes our entire concept of the cell has been revolutionized by the development of the electron microscope (Figure 1.1B).

A high resolution electron microscope currently used in blological research. This Instrument has a resolving power of about 0.2 mm and a magnification of up to 2, 40,000 times.

 

This instrument uses an electron beam instead of light and electro-magnets instead of glass lenses. The electron beam has a much shorter wavelength than light, with result that a modem electron microscope has a resolving power thousand times greater than the optical microscope.This means that objects can be magnified much more without loss of clarity A good optical microscope can only magnify on object effectively about 1.500 times. The electron microscope can give clear pictures that are magnified as high as 1,00,000 times. It is important to appreciate what this means in practice: with the electron microscope an object the size of a pinhead can be enlarged to the point at which it has a diameter of well over a kilometer: a cell with a diameter of 10 micrometers finishes up with a diameter of five metres. It is impossible to exaggerate the impact which this instrument has had on biology. Materials which were formerly described as structure less have been shown to have an elaborate internal organization, and so-called homogeneous fluids are now known to contain a variety of complex structures. The electron microscope has opened up a whole new world o structure whose existence was barely realized forty years ago.

 

Stains: Cells are fixed and stained before studying it for better differentiation and observation of its various parts. The more commonly used stains are – eosin, congo red, picric acid, safranin, methylene blue, methyl green, crystal violet etc.Some stains such as Janus green B and methylene blue are used to study various parts in living cells. Such stains are called vita stains.