Staining

Question 1

Staining;

Answer 1

Many biological structures are colourless and transparent, viewed using dark backgrounds with bright light Stains are coloured chemicals that bind molecules in or on the specimen making it easy to see (e.g. Methylene-blue). Stains colour parts of the cell when they react.

Question 2

Differential staining:

Answer 2

Differential staining: Some stains bind to specific cell structures, staining each one differently so the structures can be easily identified within a single preparation.
• Acetic orcein binds to DNA and stains chromosomes dark red.
• Eosin stains cytoplasm; Sudan red stains lipids.
• Iodine in potassium iodide stains cellulose in plant cell walls yellow, and starch granules blue/black
(looks violet under microscope).

Question 3

Preparing slides:

Answer 3

• Dry mount – specimen placed in middle of slide with tweezers and cover lip placed on top.
• Wet mount – drop of water on slide with pipette, specimen placed on top. Cover slip placed on slide
  and slowly tilted to cover specimen. Once cover slip is in position, stain is dropped on one side and
  drawn with a tissue to the other.

Question 4

Prepared slides:

Answer 4

Made by dehydrating specimens, embedding them in wax to prevent distortion during slicing, and using a special instrument (cryostat) to make very thin slices called sections – these are stained and mounted in a special chemical to preserve them.