The document discusses different types of microscopes and how they work. It explains that a light microscope works by magnifying a tiny object placed beyond the focal point of the objective lens, forming a virtual inverted image. It then discusses lenses and how they bend light, focusing rays at a specific focal point. Different types of microscopes are described, including compound light microscopes, dark field microscopes, phase contrast microscopes, and fluorescence microscopes. Electron microscopes are also summarized as using beams of electrons rather than light. The document concludes with an overview of specimen preparation techniques like fixation and staining to increase visibility and contrast of structures.

1. MICROSCOPE

2. NEED?

3. BASIC PRINCIPLE.
A MICROSCOPE WORKS ON THE PRINCIPLE THAT WHEN A TINY
OBJECT TO BE MAGNIFIED IS PLACED JUST BEYOND THE FOCUS OF
ITS OBJECTIVE LENS, A VIRTUAL, INVERTED AND HIGHLY MAGNIFIED
IMAGE OF THE OBJECT IS FORMED AT THE LEAST DISTANCE OF
DISTINCT VISION FROM THE EYE HELD CLOSE TO THE EYE PIECE.

4. 4
LENSES AND THE BENDING OF
LIGHT
• LIGHT IS REFRACTED (BENT) WHEN
PASSING FROM ONE MEDIUM TO
ANOTHER
• REFRACTIVE INDEX
• A MEASURE OF HOW GREATLY A
SUBSTANCE SLOWS THE VELOCITY OF
LIGHT
• DIRECTION AND MAGNITUDE OF
BENDING IS DETERMINED BY THE
REFRACTIVE INDEXES OF THE TWO

5. 5
LENSES
• FOCUS LIGHT RAYS AT A SPECIFIC PLACE CALLED THE FOCAL POINT
• DISTANCE BETWEEN CENTER OF LENS AND FOCAL POINT IS THE FOCAL LENGTH
• STRENGTH OF LENS RELATED TO FOCAL LENGTH
• SHORT FOCAL LENGTH MORE MAGNIFICATION

6. 6 Figure 2.2

7. TERMINOLOGY.
• POLARIZATION.
• FLUORESCENCE.
• RESOLUTION
• CONTRAST
• MAGNIFICATION
• SENSITIVITY

8. LIGHT MICROSCOPES.
• COMPOUND LIGHT
MICROSCOPES
• INVERTED MICROSCOPES
• DARK FIELD MICROSCOPES
• PHASE CONTRAST
MICROSCOPY
• FLUORESCENCE MICROSCOPE

9. COMPOUND LIGHT
MICROSCOPE
The microscope pictured here is
referred to as a compound light
microscope. The term light refers
to the method by which light
transmits the image to your eye.
Compound deals with the
microscope having more than
one lens. Microscope is the
combination of two words;
"micro" meaning small and
"scope" meaning view.
Early microscopes, like
Leeuwenhoek's, were called
simple because they only had
one lens. Simple scopes work
like magnifying glasses that you
have seen and/or used. These
early microscopes had
limitations to the amount of

10. THE DARK-FIELD MICROSCOPE
PRODUCES A BRIGHT
IMAGE OF THE OBJECT
AGAINST A DARK
BACKGROUND
USED TO OBSERVE
LIVING, UNSTAINED
PREPARATIONS

11. THE PHASE-CONTRAST
MICROSCOPE
ENHANCES THE CONTRAST BETWEEN
INTRACELLULAR STRUCTURES HAVING
SLIGHT DIFFERENCES IN REFRACTIVE
INDEX
EXCELLENT WAY TO OBSERVE LIVING
CELLS

12. 12
THE FLUORESCENCE
MICROSCOPE
EXPOSES SPECIMEN TO ULTRAVIOLET, VIOLET,
OR BLUE LIGHT
SPECIMENS USUALLY STAINED WITH FLUORO-
CHROMES
SHOWS A BRIGHT IMAGE OF THE OBJECT
RESULTING FROM THE FLUORESCENT LIGHT
EMITTED BY THE SPECIMEN

13. ELECTRON MICROSCOPE
• USED TO OBSERVE VERY SMALL
OBJECTS: VIRUSES, DNA, PARTS
OF CELLS
• USES BEAMS OF ELECTRONS
RATHER THAN LIGHT
• MUCH MORE POWERFUL

14. TRANSMISSION ELECTRON MICROSCOPE
(TEM)

15. SCANNING ELECTRON MICROSCOPE
(SEM)

16. 16
PREPARATION AND STAINING OF SPECIMENS
• INCREASES VISIBILITY OF SPECIMEN
• ACCENTUATES SPECIFIC MORPHOLOGICAL FEATURES
• PRESERVES SPECIMENS

17. 17
FIXATIO
N
• PROCESS BY WHICH INTERNAL AND
EXTERNAL STRUCTURES ARE
PRESERVED AND FIXED IN POSITION
• PROCESS BY WHICH ORGANISM IS
KILLED AND FIRMLY ATTACHED TO
MICROSCOPE SLIDE
• HEAT FIXING
• PRESERVES OVERALL MORPHOLOGY BUT NOT
INTERNAL STRUCTURES
• CHEMICAL FIXING
• PROTECTS FINE CELLULAR SUBSTRUCTURE AND
MORPHOLOGY OF LARGER, MORE DELICATE
ORGANISMS

18. 18
DYES AND SIMPLE
STAINING
• DYES
• MAKE INTERNAL AND EXTERNAL STRUCTURES
OF CELL MORE VISIBLE BY INCREASING
CONTRAST WITH BACKGROUND
• HAVE TWO COMMON FEATURES
• CHROMOPHORE GROUPS
• CHEMICAL GROUPS WITH CONJUGATED DOUBLE
BONDS
• GIVE DYE ITS COLOR
• ABILITY TO BIND CELLS

19. 19
DYES AND SIMPLE
STAINING
• SIMPLE STAINING
• A SINGLE STAINING AGENT IS USED
• BASIC DYES ARE FREQUENTLY USED
• DYES WITH POSITIVE CHARGES
• E.G., CRYSTAL VIOLET

20. PRESENTATION BY:
AYUSHMAAN SINHA