Paper 1: Microscope Slide

Question 1

Describe how you prepare a microscope slide using onion tissue?

Answer 1

Peel of 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 slowly using mounting needle to avoid air bubble

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 coverslip and ensures the coverslip 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 (nucleus e,g) to become more visible.

Question 5

Why is cover slip lowered using a mounting needle

Answer 5

Ensures that no air bubbles are trapped

Question 6

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

Answer 6

Measuring using eyepiece graticule and calibrate with stage micrometers

Question 7

How would you calculate magnification of an image?

Answer 7

Observes cell length / actual cell length

Question 8

What safety precautions are needed?

Answer 8

Wear safety goggles or gloves when handling iodine solution as it is irritant