+

Preparing an onion cell slide

+Aim of this practical

To be able to prepare a slide of an onion cell to be viewed under a microscope.

To accurately draw observations

+What you will need…

• Glass microscope slides• Plastic cover slips• Paper towels or tissue• Iodine solution • Plastic pipette or dropper• Onion• Tweezers

+

1. Carefully peel back a layer of onion with the tweezers – thinner the better.

2. Place the onion on the slide as flat as possible.

3. Put two drops of iodine on top of the onion (IODINE STAINS).

4. Place the coverslip over the top without bubbles being trapped underneath.

5. Look through microscope at cells.

Method

+ Drawing Microscope Slides / Specimens:

Use a pencil Draw only the lines you see. No shading or colouring Each circular diagram (field of view) should be about

a 3rd of a page in size If the cells you are viewing are similar/repetitive it’s

useful to draw about 4-5 onlyAlways record the:

magnification name of specimen and the date of the

observation

+

+Conclusion: What do you see?

The iodine solution stains starch in the cells blue-black, making the cell features easier to see.

+

Preparing a cheek cell slide

+Aim of this practical

To be able to prepare a slide of a cheek cell to be viewed under a microscope.

To accurately draw observations

+What you will need…

• Glass microscope slides• Plastic cover slips• Paper towels or tissue• Methylene Blue solution • Plastic pipette or dropper• Cotton swabs

+Method1. Take a clean cotton swab and gently scrape the

inside of your mouth.2. Smear the cotton swab on the centre of the

microscope slide for 2 to 3 seconds.3. Add a drop of methylene blue solution and

place a coverslip on top. 4. Remove any excess solution by allowing a

paper towel to touch one side of the coverslip.5. Place the slide on the microscope, with 4x or

10x objective in position and find a cell. Then view at higher magnification

+ Drawing Microscope Slides / Specimens:

Use a pencil Draw only the lines you see. No shading or colouring Each circular diagram (field of view) should be about

a 3rd of a page in size If the cells you are viewing are similar/repetitive it’s

useful to draw about 4-5 onlyAlways record the:

magnification name of specimen and the date of the

observation

+

+Conclusion: What do you see?

Methylene blue stains negatively charged molecules in the cell, including DNA and RNA.

The cells seen are squamous epithelial cells from the outer epithelial layer of the mouth. The small blue dots are bacteria from our teeth and mouth.