2.1.1 - observing cells

Question 1

Who was Robert Hooke?

Answer 1

• designed one of the first working microscopes
• in 1665
• examined thin sections of cork
• then called the compartments cells
• this is because it reminded him of the monk’s cells

Question 2

What is the cell theory?

Answer 2

1. cells are a fundamental unit of structure, function and organisation in living organisms
2. cells are formed by cell division
3. cells contain genes used as instructions
4. all chemical reactions take place in cells

Question 3

Define resolution?

Answer 3

measure of how close together two objects can be before they are seen as one
resolution of naked eye = 0.1 mm

Question 4

what is the resolution and magnification of a light microscope ?

Answer 4

0.2 micrometers (um)

x1500

Question 5

What is the equation for magnification? (using lenses)

Answer 5

Magnification = magnification of object lens x magnification of eyepiece lens

Question 6

How do you calculate image size?

Answer 6

image size = actual size x magnification

Question 7

Why is staining used?

Answer 7

because it makes it easier to see and identify particular parts of the cell

Question 8

Name some staining examples.

Answer 8

haematoxylin –> stains nuclei in plants + animal cells blue/brown/purple
Methylene blue –> stains nuclei in animal cells blue
acetocarmine –> stains chromosomes in dividing nuclei in plant + animal cells
iodine –> stains starch in plant cells blue-black

Question 9

How does a light microscope work?

Answer 9

1. sunlight is reflected by mirror or a built-in light source in turned on
2. this illuminates the stage with the specimen from underneath
3. objective lens produces a magnified and inverted image
4. eyepiece lens then focuses this so an image is created

Question 10

What are the advantages of a light microscope?

Answer 10

1. can see and compare living tissue
2. relatively cheap (so increases accessibility as can be put in schools, hospitals and labs)
3. relatively light and portable (so can be used almost everywhere)

Question 11

What are the disadvantages of a light microscope?

Answer 11

1. limited powers of resolution and magnification
2. preservation and staining can produce artefacts in the tissue (what we see might not be a true representation of the living tissue)

Question 12

What is the resolution and magnification of an electron microscope?

Answer 12

x500 000

0.1-1 nm

Question 13

How does an electron microscope work?

Answer 13

• beam of electrons towards the cell
• electromagnetic lens focuses this beam
• image is formed
  The resolving power increases as wavelengths gets smaller (the electrons behave like light waves)

Question 14

What are the advantages of an electron microscope?

Answer 14

1. huge powers of magnification and resolution

2. huge detail of cell structure can be seen

Question 15

What are the disadvantages of an electron microscope?

Answer 15

1. can’t look at living material as the specimen has to be dead due to it being in a vacuum
2. extremely expensive
3. limited accessibility
4. has to be kept at a certain temperature/ pressure
5. severe treatment results in artefacts

Question 16

What can be used in staining to give a clearer image?

when using an electron microscope

Answer 16

metal ions such as lead

it gives a clearer image as there is a greater contrast

Question 17

What are TEMs?

Answer 17

Transmission electron micrographs

• 2D images
• in black and white
• transmits through the specimen rather than across the surface

Question 18

What are SEMs?

Answer 18

Scanning electron micrographs

• 3D images
• lower magnification
• scanned across the surface of the specimen rather than through