Microscope History and Types

• A microscope is an instrument used to see objects that are too small for the naked eye

History of Microscopes

• 1590: The first compound microscope was invented by Zacharias Janssen.
• 1655: Robert Hooke used a compound microscope to observe pores in cork, naming them "cells".
• Antoine van Leeuwenhoek was the first to observe single-celled organisms in pond water.

Types of Microscopes

• Compound Light Microscope:

  • It is the first type of microscope
  • It is the most widely used microscope
  • Light passes through lenses
  • Capable of magnifying up to 2,000x

• Electron Microscope:

  • Uses beams of electrons
  • It is needed to observe very small objects, such as viruses, DNA, and parts of cells

• Transmission Electron Microscope:

  • Uses transmitted electrons to create an image
  • Used to study the internal structures of a cell

• Scanning Electron Microscope:

  • Creates an image by detecting reflected or knocked-off electrons
  • Used to study the detailed surface of a specimen

• Compound Light Microscope uses multiple lenses and visible light to magnify small objects

• Electron Microscope uses a beam of electrons to magnify specimens

• Transmission Electron Microscope passes electrons through a thin specimen to study internal structures

• Scanning Electron Microscope scans a sample's surface to produce detailed 3D images

• Simple Light Microscopes use a single lens

• Compound Light Microscopes use a set of lenses or a lens system

Compound Microscope Parts

• The Mechanical Parts:

  • Base: The bottommost portion that supports the microscope
  • Pillar: Part above the base that supports the other parts
  • Inclination Joint: Allows tilting of the microscope for user convenience
  • Arm/Neck: The curved/slanted part held while carrying the microscope
  • Stage: The platform where objects are examined
  • Stage Clips: Secures the specimen to the stage
  • Body Tube: Attached to the arm and supports the lenses
  • Draw Tube: Cylindrical structure on top of the body tube that holds the ocular lenses
  • Revolving/Rotating Nose Piece: The rotating disc where objectives are attached
  • Dust Shield: Sits atop the nose piece, keeping dust from settling on the objectives
  • Coarse Adjustment Knob: Geared to the body tube, elevating or lowering when rotated to bring the object into approximate focus
  • Fine Adjustment Knob: A smaller knob for delicate focusing, bringing the object into perfect focus
  • Condenser Adjustment Knob: Elevates and lowers the condenser to regulate light intensity
  • Iris Diaphragm Lever: Controls the diaphragm, moving horizontally to open/close it

• Illuminating Parts:

  • Mirror: Located beneath the stage with concave and plane surfaces, gathers and directs light to illuminate the object
  • Electric Lamp: A built-in illuminator beneath the stage, used if sunlight is unavailable or not preferred

• Magnifying Parts:

  • Ocular/Eyepiece: Lens on top of the body tube, further magnifying the image produced by objective lenses, it usually ranges from magnifications of 5x to 20%.
  • Objectives: Metal cylinders attached below the nosepiece, containing specially ground and polished lenses
    • Scanning Lens: Provides the lowest magnification, usually 4x
    • LPO (Low Power Objective): Higher than the scanning lens, typically 10x
    • HPO (High Power Objective): Generally provides a higher magnification, usually 40x
    • OIO (Oil Immersion Objective): Gives the highest magnification, usually 100x

• As magnification increases, detail increases but less of the cell is seen.

Caring for the Microscope

• Do not let any liquids come in contact with the microscope
• Always store the microscope inside a box after use
• Return the objective lens onto low power after use
• Carry the microscope by the arm
• Use a soft, clean tissue to wipe the lenses

Cover Slips and Microscope Slides

Preparing a Slide as a Wet Mount

• Add a drop of water to a slide
• Place the specimen in the water
• Position the edge of a coverslip on the slide so that it touches the water's edge
• Slowly lower the coverslip to prevent forming and trapping air bubbles

Use of Stains

• Some parts of a plant cell can be clearly seen when the cell is mounted in water, examples include Stomata and Guard Cells
• Other cell structures not so obvious are often shown more clearly by the addition of dyes called stains
• Iodine solution is used to stain plant cells
• Methylene blue is used to stain animal cells

Microscopic Adaptations

• Adaptation is how living organisms cope with environmental stresses and pressures
• Organisms adapted to their environment can get air, water, food, and nutrients
• They can cope with physical conditions (temperature, light, and heat) and defend themselves against natural enemies
• Reproduction and responding to environmental changes are also key for survival

Types of Adaptations

• Physiological Adaptations jobs of body parts controlling the life processes to aid survival, example snake making venom
• Structural Adaptations body part/coloring that aids survival, example mimicry
• Behavioral Adaptations actions that aid survival, example hibernation/migration
• Microscopic Adaptations structure not seen with naked eye but impacting survival, example trichomes
• Other examples include setae, flagella, stigma, and spores