Topic 3

Question 1

What do light microscopes use to form an image?

Answer 1

Light

Question 2

What do electron microscopes use to form an image?

Answer 2

Electrons

Question 3

What is the maximum resolution of light microscopes?

Answer 3

0.2 micrometres

Question 4

What organelles can’t you view with a light microscope?

Answer 4

• Ribosomes
• Endoplasmic reticulum
• Lysosomes

Question 5

What is the maximum useful magnification of a light microscope

Answer 5

x1,500

Question 6

What is the maximum resolution of electron microscopes?

Answer 6

0.0002 micrometres

Question 7

What is the maximum useful magnification of an electron microscope?

Answer 7

x1,500,000

Question 8

What are the two types of electron microscope?

Answer 8

• Transmission

- Scanning

Question 9

How do transmission electron microscopes - TEMs - work?

Answer 9

• Electromagnets to focus on a beam of electrons
• Transmitted through a specimen
• Denser parts absorb more electrons - look darker on the image

Question 10

How do scanning electron microscopes - SEMs - work?

Answer 10

• 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

Question 11

What is the advantage of using TEMs?

Answer 11

Higher resolution, can see internal structure of organelles e.g mitochondria

Question 12

What is the advantage of using SEMs?

Answer 12

Can be used on thick specimens

Question 13

What is the disadvantage of using TEMs?

Answer 13

Can only be used on thin specimens

Question 14

What is the disadvantage of using SEMs?

Answer 14

Lower resolution than TEMs

Question 15

Describe how to carry out the root tip mitosis experiment 14

Answer 15

• 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

Question 16

What stain can you use to stain the root tip cells with?

Answer 16

Toluidine blue O

Question 17

Why is the root tip used to observe mitosis?

Answer 17

This is where growth occurs in the plant and so where mitosis takes place