b,c (D pag) preparing microscopes,

Why are stains used in light microscopes?

• Some specimens are transparent → light passes through → image appears white
• Staining uses dyes to increase contrast between parts of the specimen
• Some parts absorb more stain → appear darker
• Makes different parts of cells visible

What are common stains and what do they stain?

• Methylene blue → stains DNA
• Giemsa stain → differentiates types of blood cells

How does staining help produce an image?

• Image appears because parts of the specimen absorb stain differently
• Creates contrast between structures
• Tip: Staining makes some parts appear darker or a different colour

How can multiple stains be used together?

• Haematoxylin and eosin often used together (H&E staining)
• Eosin → dyes cytoplasm pink
• Haematoxylin → stains RNA/DNA purple/blue
• Highlights structures like nucleus and ribosomes

What is a microscope slide and why is it used?

• Clear glass or plastic strip
• Flat or with a small dip/well for large or liquid specimens
• Holds the specimen for observation under a microscope

What is a dry mount?

• Simplest slide preparation
• Useful for hairs, insect parts, pollen, flower parts
• Thin slice needed if specimen is thick
• Specimen placed on slide using tweezers
• Cover slip placed on top
• Tip: Handle slides carefully → glass can break; do risk assessment

What is a wet mount?

• Specimen placed in a liquid (usually water)
• Produces clear view → can be used for living specimens
• Pipette a drop of water onto the slide
• Place specimen in water
• Cover slip placed upright, then tilted down carefully
• Avoid air bubbles → obstruct view
• Stain can be added by placing next to one edge of cover slip → paper towel draws stain across specimen
• Tip: Used for liquid specimens (e.g., pond water) → no extra water needed if sample provides liquid

What is a smear slide?

• Special type of wet mount
• Often used for blood samples
• Spread liquid thinly over slide, cover slip applied
• Excess liquid wiped off

How do you use a light microscope to view a specimen?

1. Clip slide onto stage
2. Select lowest-powered objective lens
3. Use coarse adjustment knob → move stage close to objective lens
4. Look through eyepiece → adjust coarse knob to roughly focus
5. Fine adjustment knob → clear image
6. Swap to higher-powered lens if greater magnification needed → refocus

What are the main features of a light microscope?

• Eyepiece (ocular lens)
• Objective lenses (low/high power)
• Stage (holds slide)
• Clips or slide holder
• Coarse adjustment knob
• Fine adjustment knob
• Light source
• Tip: Eyepiece graticule → transparent disc with scale, can be inside eyepiece

How should microscope drawings be done?

• Use sharp pencil, not pen
• Take up at least half the space
• Outlines neat, not sketched
• Labels straight, not crossing
• Include magnification and title
• Do not colour in or shade
• Tip: Drawing should accurately show relative sizes of objects

What is an eyepiece graticule and stage micrometer used for?

• Measure specimen size
• Eyepiece graticule → scale without units, fits in eyepiece
• Stage micrometer → slide with accurate scale (has units)
• Calibrate eyepiece graticule with stage micrometer → know size of divisions

How do you calibrate an eyepiece graticule using a stage micrometer?

1. Line up eyepiece graticule and stage micrometer
2. Each stage micrometer division = 0.1 mm
3. Count how many eyepiece divisions match stage division (e.g., 1 stage = 4.5 eyepiece)
4. Division on eyepiece = 0.1 ÷ 4.5 = 0.02 mm
5. Measure specimen: e.g., 20 eyepiece divisions → 20 × 0.02 = 0.4 mm

• Tip: Change in magnification → re-calibrate eyepiece graticule
• Tip: Each eyepiece division = 1 eyepiece unit (epu)