3.2.1.3 Methods of Studying Cells

Question 1

How can specimens be observed under a light microscope?

Answer 1

Living or dead

Question 2

Specimens are living or dead, illuminated by _____________, focused using a __________ _________ and viewed using the eye

Answer 2

1. Light
2. Glass lens

Question 3

Resolution

Answer 3

The ability to distinguish between objects that are close together

Question 4

What is needed to be done with specimens before viewing?

Answer 4

Staining

Question 5

By using more _______, light microscopes can magnify a larger amount, but lose ___________________

Answer 5

1. Lenses
2. Resolution

Question 6

How does a small wavelength affect resolution

Answer 6

Makes it worse

Question 7

How do electron microscopes use electrons to view specimens

Answer 7

Use beams of electrons

Question 8

Why do electron microscopes have a good resolving power

Answer 8

Electron beams has a short wavelength

Question 9

When using electro in microscopes, why does a vacuum need to be created?

Answer 9

Electrons are absorbed or deflected by molecules in the air

Question 10

Images in an electron microscope are always in which colour

Answer 10

Black and white

Question 11

In TEM, in which dimension are images observed

Answer 11

2D

Question 12

When using electron microscopes, why must specimens be dead?

Answer 12

Specimens are fixed in resin and sliced thin, also, it would be unethical to place them in a vacuum

Question 13

Why are parts of an image in electron microscopy darker than others?

Answer 13

Thicker parts absorb more electrons so appear darker

Question 14

State the limitations to electron microscopy (4)

Answer 14

Any four from
- Live specimens cannot be used
- Complex staining process required
- Specimen must be held in resin and sliced very thin (not in SEM)
- Image may contain artefacts

Question 15

Describe the similarities and differences between SEM and TEM (5)

Answer 15

Similarities
- Both use magnets to ficus
- Samples must be dead
- Black and white images produced
- Denser parts absorb more electrons
- High resolution

Differences
- SEM always forms a 3D image unlike TEM
- In SEM, specimens aren’t sliced, electrons bounce of them

Question 16

How are electrons involved in producing an image in SEM

Answer 16

Bounce off

Question 17

Describe how a light microscopes is different to an electrons microscope (6)

Answer 17

• Illuminated by light rays not beams of electrons/light has a longer wavelength compared to electron
• Focused by lens not electromagnets
• Maximum magnification is x1500, electron microscopes can magnify x500000
• Resolution is lower
• Larger organelles can be observed not smaller organelles
• Specimens are living and don’t have a complex staining process

Question 18

m —> mm

Answer 18

x1000

Question 19

mm —> micrometers

Answer 19

x1000

Question 20

nm —> micrometers

Answer 20

Divide by 1000

Question 21

Magnification equation

Answer 21

Size of image/Size of real object

Question 22

Which process separates organelles from a cell

Answer 22

Cell fractionation and ultracentrifugion

Question 23

Why does the solution during cell fractionation have to be ice cold?

Answer 23

Reduces kinetic energy, and action of enzymes preventing damage to organelles

Question 24

Why does the solution during cell fractionation have to be isotonic?

Answer 24

Maintains osmosis, so no movement of water, same water potential in and out of the cell, organelles won’t burst or shrivel

Question 25

Why does the solution during cell fractionation have to be buffered?

Answer 25

Maintains a constant pH as changes could alter/denature proteins and enzymes

Question 26

Explain the process of cell fractionation and ultracentrifugion (5)

Answer 26

1. Tissue homogenised (cell wall is broken) in a blender, ice cold, isotonic and buffered solution
2. Mixture is filtered to remove large tissue/debris producing a solution of organelles (supernatant)
3. Differential centrifugation - centrifuged at a low initial speed, densest organelles forced to the bottom of the tube forming a pellet, the pellet is removed and the solution above is the supernatant
4. Supernatant is centrifuged at higher speed to remove next densest organelles forced, this is repeated
5. Microscope detects the organelle harvested in pellet

Question 27

When the pellet is removed, the solution left is the ______________________

Answer 27

Supernatant

Question 28

Order of density of organelles

Answer 28

1. Nucleus
2. Mitochondria
   3, Chloroplasts
3. Golgi apparatus
4. sER
5. rER
6. Ribosomes