Microscopy RPA

Question 1

What part of the microscope is responsible for changing the magnification

Answer 1

Objective lens

Question 2

2 types of focussing dial

Answer 2

Coarse (on top)
Fine (on bottom)

Question 3

How to prepare microscope slide for onion cell

Answer 3

Peel off thin layer of onion cells from onion using forceps (tweezers)
Use pipette to add drop of water on microscope slide
Add a few drops of iodine solution to sample
Lower cover slip onto sample using mounting needle

Question 4

What are forceps

Answer 4

Tweezers (used to peel off thin layer of onion cells from onion)

Question 5

Why only use a thin sample of tissue to examine cells

Answer 5

Allows light to pass through so sub-cellular structures can be observed

Question 6

Why is iodine solution used to stain the cells

Answer 6

Adds contrast to make the internal structures (e.g nucleus) more visible

Question 7

Why lower cover slip onto slide using mounting needle (not hands)

Answer 7

So no air bubbles are trapped

Question 8

How to measure length of cell viewed under microscope

Answer 8

Count number of cells across width of field view (circle) when looking through microscope
Place clear ruler on stage and look through microscope to see width of field view
Divide width by number of cells to get width of one cell (in m)
Convert to micrometers

Question 9

If we use a 4x magnification in the objective lens why is the total magnification x40

Answer 9

The eyepiece lens has a magnification of 10x (we times them together)

Question 10

Safety precautions for investigation

Answer 10

Wear safety goggles when handling iodine

Question 11

Steps for using microscope to examine onion cell

Answer 11

1) To prepare slide use forceps to peel off one thin layer of onion cells from onion
2) Add a drop of water to the slide with a pipette then place the layer onion cells on it
3) Add a few drops of iodine solution to the cell sample (use paper towel to remove any excess stain)
4) Use mounting needle to place cover slip over the top

To examine onion cells:
1) Place slide onto stage and use clips to secure in place
2) Make sure eyepiece lens is on lowest power
3) Looking at the microscope side on, turn the coarse focus dial so the objective lens is as close to the slide as possible
4) Look into the eyepiece lens and turn the coarse focus dial until the cells come into focus
5) Use the fine focusing dial to bring the cells into a clear focus
6) Use a pencil to make a labelled drawing of the cells views under the microscope and include the magnification