exp-1.pptx genetics praticle for first semester
- 1. Experiment -1 Objective: To study about microscope
- 2. Principle: • Microscope is a delicate precision instrument, which resolves the details of a micro-object that cannot be seen by the human eye. • Human eye can clearly see object of only 0.1 mm (100 μ) or larger size under optical viewing condition. • Thus if two objects are separated by distance less than 0.1 mm, they will appear as one object to the human eye. • They are very small to be seen by the necked unaided human eye, which makes the use of microscope unavoidable. The light microscope can magnify objects as much as 2000-fold and its limit of resolution is about 0.2 μ. • The limit of resolution of a microscope is approximately ½ the wave length of the light used. • One way to increase the resolution is to increase the numerical aperture. The maximum numerical aperture in air is 1.0, but can be increased to 1.6 by using oil immersion object. • Another way to increase the resolution is to decrease the wave length of the light used (that is, as in the Ultraviolet microscope).
- 3. Type of Microscope • SIMPLE MICROSCOPE • This is the simplest type of microscope having a single lens. • It has a doubled convex piece of glass (lens) mounted on a handle. • It magnifies things up to 4-5 times. • It is ordinarily called ‘hand lens’ or ‘reading glass’ and is generally used for a closer examination of small objects, e.g. flower buds, anthers etc. • It is not useful for the study of cells. An example of a simple microscope is the ordinary dissecting microscope described below.
- 4. SIMPLE DISSECTING MICROSCOPE • It consists of a single lens mounted on to the folded arm of a vertical stand. • The arm is fitted into the stand with a focusing screw, which allows the up and down movement of the arm needed for focusing. • The microscope has a basal foot to keep it stable, a reflecting mirror to provide light for observation and a glass stage on which the objects being studied are kept. • This microscope magnifies objects from 4 to 40 times depending upon type of the lens used. • It is commonly used for magnifying the small objects like flower buds, young ovules etc. during dissection.
- 5. COMPOUND MICROSCOPE • Such microscopes have a system of two or more lenses, which together magnify objects up to several hundred times. The lenses are placed in a vertical tube one above the other at such a distance that the image formed by one lens is magnified again by the second lens and so on.
- 6. Parts of the compound Microscope 1. Optical parts • The different lenses an the mirror constitute the optical parts of a compound microscope a. Lenses • Usually there are two types of lenses termed as: (i) objective, and (ii) ocular or eye piece. i. Objective • The objective lens is mounted on a revolving nose-piece of the lower end of the body tube. The revolving nose-piece supports both a lower power (10x) and high power (40x and 100x) objective lenses. They are called objective since the object to be viewed is placed just below them. ii. Eye piece • It is fitted at the top of body tube and contains lenses to enhance the magnification achieved by the objectives. The eye-piece can be readily replaced with another lens of suitable magnification. The usual magnifications are 5x, 7.5x, 10x and 15x. b. Mirror • It is attached to the lower end of the arm or the pillar. There are two or three mirrors- a plane and a convex mirror. It is used for reflecting light rays into the microscope to aid the viewing the objects.
- 7. 2. Mechanical parts a. Base • It is usually similar to a horse shoe in shape. It provides a stable support to the microscope. b. Pillar • It is small vertical projection form the base. c. Arm • It is usually curved and supports the body tube. d. Inclination joint • At this joint, the arm is joined to the pillar. The microscope can be tilted at this point. e. Stage • Usually it is a rectangular flat plate attached to the lower end of the arm. The object to be viewed is placed on the stage. The stage has a hole in the center for the light rays to travel form the mirror to the object. f. Clips • There are two clips attached to the stage, they hold the slide firmly on to the stage to facilitate its study. g. Diaphragm • It is attached to the base of the stage and is located directly below the hole in the stage. It regulates the amount of light passing rom the mirror to the object being studied. h. Sub- stage condenser • It is associated with the diaphragm. It concentrates the light reaching the specimen or the object being studied. i. Body tube • It is a tubular hollow part attached to the upper part of the arm. It can be moved up and down with the help of focusing screws. The lenses (both the eye piece and objective) are attached to the body tube. j. Nose-piece • It is a circular metallic structure attached to the lower end of the body tube. Generally, three different objective lenses are fitted into it. k. Coarse adjustment screw • It is the bigger size screw. It is used to move the body tube up and down to bring the specimen in sharp focus. l. Fine- adjustment screw • It is a smaller size screw. It is used fine adjustment in focus.