Microscopes: Parts and Functions

Microscopes: Copy & Cells

• Microscopes are used to view tiny specimens that are not visible to the naked eye.
• The course will cover parts of microscope, magnification, specimen size, and biological drawing techniques.

What Will Be Learned

• Parts and functions of a microscope
• Total magnification and actual size of specimens
• Biological drawing techniques (magnification)

Parts & Table of Contents

• Parts of a Microscope:

  • Objective lens
  • Ocular lens (eyepiece)

• Biological Drawings:

  • Learning to accurately draw the specimen
  • Labeling the parts of the specimen

• Functions of the microscope parts:

  • Eyepiece (ocular) lens: Magnifies the image. Typically 10x.
  • Objective lens: Different magnification lenses (e.g., 4x, 10x, 40x)
  • Stage: Area where the slide is placed
  • Diaphragm: Controls light
  • Light: Illuminates the specimen
  • Base: Keeps the microscope steady
  • Arm: Supports the eyepiece
  • Coarse focus knob: Used for initial focusing
  • Fine focus knob: Used for precise focusing

How a Microscope Works

• The lens is convex.
• Light is bent and converges at a focal point.
• Beyond the focal point, the rays spread out again (magnifying the image).
• An inverted image is formed.

Looking Through a Microscope

• The specimen is placed on the stage.
• The image is viewed through the eyepiece.
• The objective lens magnifies the image.
• Different objective lenses provide varying magnifications (e.g., 4x, 10x, 40x).

Calculations

• The total magnification is the product of eyepiece magnification and objective lens magnification.

Conversions

• 10.5 cm is equal to 10,500 micrometers (µm).

Total Magnification

• Formula: Total magnification = magnification of eyepiece lens × magnification of objective lens

Magnification of Objective Lens

• To find the magnification of objective lens: use the formula Total magnification = Eyepiece magnification × Objective magnification

Actual Size Calculation

• Calculation: Actual size of specimen = Image size / magnification

Practicing

• Calculate specimens of known sizes (e.g., 1.5 mm long image magnified 100x).

Ocular Scale (Graticule)

• For precise measurements
• Scale printed onto the eyepiece of the microscope.
• Units are typically in millimeters (mm).
• Ocular scale is used with calculation: Actual size = number of divisions on graticule × graticule scale interval

Specimen Measurements

• A table of magnification and intervals and the relationship to the specimen (e.g., 4x, 40X, and 25μm)
• 1000μm = 1mm

Practice – Image Measurement

• Measure the size of a specimen in micrometers (µm).

Biological Drawings

• Use blank paper. Drawings should be large (greater than 5cm)

• Use only pencil

• Label lines horizontally, and to right of diagram

• No arrowheads

• Underlined title below diagram

• Calculations go below diagram area

• Stippling to indicate shading if required

• Examples of correct and incorrect biological drawing techniques.

Identifying Microscope Parts for Drawing

• Correct labeling of microscope parts for accurate drawings.

Preparing Specimens

• How to prepare a wet mount:
  • Place the specimen on a slide.
  • Add a drop of water or another liquid.
  • Carefully place a cover slip on top.

Specimen Parts

• Cell membrane: outer edge/layer
• Cytoplasm: inside the cell, fluid-like substance
• Nucleus: dense structure within the cell
• Cell wall: outer layer of plant cells (typically seen in an onion or leaf cell)
• Chloroplast: green parts in a plant cell

Microscope Rules and Procedures

• Using the microscope safely
• Powering on and off the microscope
• Finding the specimen
• Using the coarse and fine focus
• Preparation and storage