1. Write down the principle of X-ray microscope?
In X-ray microscope the electromagnetic lenses or reflecting curved mirrors focus X-ray beam and the image is formed on the film. X-ray diffraction has been used for the structural analysis of macromolecules such as lysozyme, haemoglobin and D.N.A.,etc.
2. Define Ultramicroscope?
The ultramicroscope is the improved type of compound microscope in which the object is illuminated by a strong beam of light which comes parallel to the surface of the stage or at right angles to the direction of the vision. This microscope is used in observing many smaller particles.
3. Write down the specimen preparation of electron microscope.
The specimen preparation in electron microscope are treated with chemicals or dyes to enhance the contrast. Live objects can not be observed under electron microscope because water molecules will obstruct movements of electrons. Hence, structural details will not be clear. The objects are perfectly dried, made ultrathin. Since images produced by electrons do not have the colour, the electron micrographs always have shades of black, grey and white. The colour enhanced micrographs are produced by computer aided shading.

4. What is the diameter of the majority of cells?

The diameter of majority of cells ranges from 0.1 micron to 1 millimeter.

5. What is Scanning Electron Microscope?
Scanning electron microscope was developed by Knoll in 1935. In this microscope, a very fine narrow beam (200 A0 in diameter)of electrons scans the surface of the specimen, such as a screen is scanned in a television tube. The specimens are dried properly and are coated or shaded with metals like gold, platinum and other metal, for creating a reflecting surface for incident electrons. Secondary electrons are emitted from the surface of the specimen. These are collected by the positively charged grid for transfer to television tube and fluorescent screen. The signal from the grid is transferred to a television tube which scans in synchrony with the beam of the microscope. An image of the specimen is produced on the screen. The scanning electron microscope produced an image much the same way as the image is seen with the naked eye. The eye collects light which is reflected from the solid objects some what like the grid in the scanning microscope. The image formed by this microscope, therefore, has a remarkable three-dimensional appearance.
6. What is Density Gradient Centrifugation?
In density gradient centrifugation, in a centrifuge tube, a density gradient of sucrose is established by means of a special device. In this, the denser solution is at the bottom and its density gradually decreases towards the top. Once the gradient is formed, the homogenate is layered at the top and centrifuged.
7. What is Thin –layer chromatography?
In this technique, a thin plate of cellulose powder or alumina of even thickness is prepared. When a drop or two of the mixture is poured over the plate, the various chemicals spread to different distances on the plate. This technique is used for separation of amino acids, nucleotides and other low molecular weight products.
8. Define refractive index.
Numerical aperture (NA)=n sin α, where n is the refractive index of the medium, and sin α is the sine of half angle (semiangle) of light entering the objective lens from the specimen. λ is the wave length used to illuminate the object.
9. What is Gel filtration chromatography?
A column of gel like sephadex is used. The gel is available having various pore sizes. The mixture is poured over the gel. The components of the mixture are separated according to their molecular size. They come out of the column, with larger molecules coming out first followed by progressively decreasing size molecules. This technique is used for determination of molecular weight of proteins by caliberating the column with proteins of different molecular weight.
10. What is Scanning Electron Microscope used for?
Scanning electron microscopes (SEMs) are used in the study of ultra structure of cell and its components like mitochondria, golgi apparatus, chloroplasts, endoplasmic reticulum, ribosome etc.
11. What is Ion-exchange chromatography?
A small beads of positive and negative charges are taken in a column. The beads  are commonly of cellulose. As the mixture passes through the column, the cell components get separated  according to their charges. This technique is used for insulin purification and plasma fractionation.
12. List the scientific methods of research.

There are many ways of discovering new facts about nature. Generally, the scientific method of gathering information involves same steps. They are: Observation, Formulation of Hypothesis, Testing of Hypothesis and Developing teory.
Problem: To begin with there must be a problem, and a desire on the part of worker to solve it. The worker should inform himself on all aspects of the problem. He should read articles in scientific journals dealing with the subject and learn what others have done on similar problems. This will gie him ideas on the techniques which may be used in solving his problem. The worker will probably do a few preliminary experiments to perfect his technique.
Formulation of hypothesis: At all times, the worker will be thinking about the problem. His brain will sort out all of the information which has been fed into it, somewhat like a living computer, and come up with a possible solution to the problem. Such an educated guess, backed up by the information available, is known as a hypothesis. A hypothesis often consists of a group of interconnected statements or assumptions that give a possible solution to a problem. A hypothesis can then be tested for validity. Perhaps it will be disproved and another hypothesis will have to be formulated. As evidence in favour of a hypothesis accumulates, on the other hand its validity becomes more likely.
13. What is Chromatography?
Chromatography is one of the most commonly used method of separation of molecular components of cells present in a solution or cytosol left after centrifugation. The solution or cytosol is allowed to percolate (to pass through) in an insoluble medium which has different affinity for molecules of different substances
14. Define Electrophoresis.
This is a technique in which particles of different sizes and charges diffuse to variable distances under the influence of an externally applied electric field. The macromolecules ( especially proteins, nucleotides, nucleic acid etc.) are separated by differences in their net charge in the presence of externally applied electric field according to their molecular weight after nullifying their net charge under electric field.
15. What is fine adjustment?
The fine adjustment is very essential for the perfect image of the object. It is attached with the arm on either side in the form of horizontal small heads parallel to the coarse adjustment heads.

16. Describe Electron Microscope.
The electron microscope is a derivative of compound microscope. It uses analogous components. Wave length are 1,00,000 times shorter than the wave length of visible light. Due to this, the resolving power of an electron microscope is very high.
The resolving power of light microscope is limited to objects of approximately the same dimensions as the wavelength of the light used. Objects between 2,000 A^o to 3,000 A^oin diameter can just be detected but may not be sharply resolved. Therefore, the biologists searched for some source of light which might have very short wave length and they found it in the electrons. It has been observed that when a metal filament placed in a vaccum tube heated, it emits electrons which can be accelerated by an electrical potential. These electrons can be controlled and focused by high vaccum the stream of electrons follows a straight path and has properties similar to light, it has corpuscular and vibratory characters, but unlike that the electron beam has very short wave length (i.e., the wavelength of electron beam = 0.05 Å and the wavelength of light rays = 5500(A^o). For the efficient working, the vaccum must be great so that the electrons may not collide with the atoms of oxygen or nitrogen in the air.

17. Define Transmission electron microscope.

In transmission electron microscope, the electrons pass through the object and produce an image. The specimen, therefore, is cut into ultra thin sections 100Å (= 0.1mm). These sections are then treated for enhancing contrast by staining (coating) with the salts of various heavy metals like lead, tungsten, uranium, etc. The staining or coating is necessary because most of the constituent elements in biological materials are of low mass and hence, the contrast is weak. The coating also helps the material to withstand the electron bombardment.