What do light microscopes use to form an image?
Light
What do electron microscopes use to form an image?
Electrons
What is the maximum resolution of light microscopes?
0.2 micrometres
What organelles can’t you view with a light microscope?
- Ribosomes
- Endoplasmic reticulum
- Lysosomes
What is the maximum useful magnification of a light microscope
x1,500
What is the maximum resolution of electron microscopes?
0.0002 micrometres
What is the maximum useful magnification of an electron microscope?
x1,500,000
What are the two types of electron microscope?
- Transmission
- Scanning
How do transmission electron microscopes - TEMs - work?
- Electromagnets to focus on a beam of electrons
- Transmitted through a specimen
- Denser parts absorb more electrons - look darker on the image
How do scanning electron microscopes - SEMs - work?
- Scan a beam of electrons across the specimen
- Knocks off electrons from specimen
- Gathered in cathode ray tube to form image
- Shows surface of specimen and can be 3D
What is the advantage of using TEMs?
Higher resolution, can see internal structure of organelles e.g mitochondria
What is the advantage of using SEMs?
Can be used on thick specimens
What is the disadvantage of using TEMs?
Can only be used on thin specimens
What is the disadvantage of using SEMs?
Lower resolution than TEMs
Describe how to carry out the root tip mitosis experiment 14
- Cut 1cm from the tip of a growing root
- Prepare boiling tube with 1M of hydrochloric acid
- Put in water bath at 60c
- Transfer root tip to boiling tube
- Incubate for 5 minutes
- Use pipette to rinse root tip well with cold water
- Leave to dry on paper towel
- Place root tip on microscopic slide
- Cut 2mm from very tip, remove the rest
- Use a mounting needle to break tip open and spread cells thinly
- Add a drop of toluidine blue O stain
- Leave for a few minutes
- Push down cover slip firmly over cells to squash tissue - makes tissue thinner for light to pass through
- Observe stages of mitosis under light microscope
What stain can you use to stain the root tip cells with?
Toluidine blue O
Why is the root tip used to observe mitosis?
This is where growth occurs in the plant and so where mitosis takes place
