2.1.1 Studying Cells

Question 1

Microscopes are used to…

Answer 1

Analyse cell components and observe organelles

Question 2

Magnification

Answer 2

How many times bigger the image produced by the microscope is than the real-life object you are viewing

Question 3

Resolution

Answer 3

The ability to distinguish between objects that are close together (the ability to see two structures that are very close together as two separate structures)

Question 4

Optical Microscopes

Answer 4

• Use light to form an image

Question 5

What does this mean the about the resolution of a light microscope

Answer 5

• limits it because using light it is impossible to resolve two objects that are closer than half the wave length of light
  -the wave length of visible light is between 500-650 nm so it can’t distinguish between objects closer that half this

Question 6

The maximum resolution is

Answer 6

• around 0.2 micrometres or 200nm
• this means it can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts
• they can’t be used to observe smaller organelles like ribosomes, the endoplasmic reticulum or lysosomes

Question 7

The maximum useful magnification is

Answer 7

Around x1500

Question 8

Electron Microscopes…

Answer 8

• use electrons to form an image

Question 9

This means…

Answer 9

• the resolution is greatly increased compared to optical microscopes, giving a more detailed image
• this is because a beam of electrons has a much smaller wavelength than light, so can resolve two objects that are extremely close together

Question 10

The max resolution

Answer 10

• is around 0.0002 micrometres or 0.2 nm
• this is 1000 times greater than a light microscopes
• this means they can observe small organelles such as ribosomes, the er and lysosomes

Question 11

The max magnification

Answer 11

• is around x1,500,000

Question 12

Transmission Electron Microscopes (TEMs)

Answer 12

• use electromagnets to focus a beam of electrons
• this beam is then transmitted through the specimen
• denser parts of the specimen absorb more electrons making them appear darker on the final image, giving contrast between different parts of the object being observed

Question 13

Advantages

Answer 13

• give high-resolution images (more detail)
• allows internal structures within the cell (or even within organelles) to be seen

Question 14

Disadvantages

Answer 14

• only can be used with very thin specimens
• cannot observe live specimens as there is a vacuum inside TEMs so all water must be removed so must be dead and cannot observe like specimens like light microscopes
• the lengthy treatments required to prepare specimens means that artefacts can be introduced (look like real structures but are actually the result of preserving or staining)
• they do not produce a colour image, unlike light microscopes

Question 15

Scanning Electron Microscopes (SEMs)

Answer 15

Scan a beam of electrons across the specimen, which then bounces off the surface and electrons are detected, forming an image of the specimen
This means SEMs can produce 3-D images that show the surface of the specimen

Question 16

SEM Advantages

Answer 16

They can be used on thick or 3-D specimens
They allow the external, 3-D structure of the specimen to be observed

Question 17

SEM Disadvantages

Answer 17

They give lower resolution images than TEMs
They cannot be used to observe live specimens (unlike light microscopes)
They do not produce a col,lured image (also unlike a light microscope)

Question 18

Laser Scanning Confocal Microscopes

Answer 18

Relatively new technology
The cells being viewed must stained with fluorescent dyes
A thick section of tissue or small living organisms are scanned it’s a laser beam, which is then reflected by the fluorescent dyes
Multiple depths of tissues/organism are scanned to produce an image (aka the laser beam is building up the image layer by layer)

Question 19

Laser Scanning Confocal Microscopes Advantages

Answer 19

They can be used on thick or 3-D specimens
They allow the external, 3-D structure of the specimens to be observed
Very clear images are produced
The high resolution is due to the fact that the laser beam can be focused at a very specific depth (you can even se the structure of the cytoskeleton in cells)

Question 20

Laser Scanning Confocal Microscopes Disadvantages

Answer 20

It is a slow process and takes a long time to obtain an image
The laser has their potential to cause photodamage to the cells