CP01 - Looking At Cells

Question 1

Describe how you would prepare a microscope slide using onion tissue

Answer 1

● Peel off epidermal layer using forceps
● Place sample on drop of water on microscope slide
● Add drops of iodine solution to sample
● Lower cover slip onto sample using mounting needle

Question 2

Why is a thin sample of tissue required?

Answer 2

Allows light to pass through so internal structures can be observed

Question 3

Why is water added to the slide before the sample is mounted?

Answer 3

Allows the sample to be suspended between the slide and the cover slip, and ensures the cover slip stays in place

Question 4

Why is iodine solution added to stain the cells?

Answer 4

Iodine solution adds contrast - reacts with starch in plant cells and turns blue-black; allows internal structures (e.g. nucleus) to become more visible

Question 5

Why is the cover slip lowered using a mounting needle?

Answer 5

Ensures that no air bubbles are trapped

Question 6

How would you measure the length of a cell viewed under the microscope?

Answer 6

Measure using eyepiece graticule and calibrate with stage micrometer

Question 7

How would you calculate the magnification of an image?

Answer 7

Magnification = observed cell length / actual cell length

Question 8

What safety precautions should be taken during this experiment?

Answer 8

Wear safety goggles when handling iodine solution