3.1 Methods of studying cells

Question 1

Define magnification

Answer 1

The number of times greater an image is than the size of the real(actual) object

Question 2

What is the formula for Magnification

Answer 2

Size of image/ Size of real object=Magnification

Question 3

Define resolution

Answer 3

The minimum distance 2 objects can be to be distinguished as separate objects

Question 4

What are the characteristics of the optical microscope
(10)

Answer 4

• Light is focused using glass lenses
• Light passes through specimen differnet structures absorb different amounts of light and wavelengths
• Generates a 2D image of a cross section
• Low resolution due to long wavelength of light
• Cant see internal structures of organelles or ribosomes
• The specimen is thin
• Low magnification (x1500)
• Can View living organisms
• Simple preparations
• Can show colour

Question 5

What are the characteristics of the Transmission electron microscope
(10)

Answer 5

• Electrons focused using electromagnets
• Electrons pass through specimen, Denser parts absorb more and appear darker
• Generates a 2D image of a cross section
• Very high resolution due to short wavelength of electrons
• Can see internal strctures of organelles and ribosomes
• Specimen= very thin
• High magnification (1,000,000)
• Can onlu view dead/dehydrated specimens as a vacuum
• Complex preparations so artefact often present
• Does not show colour

Question 6

What are the characteristics of the scanning electron microscope
(10)

Answer 6

• Electrons focused using electromagnets
• Electrons deflected/ bounce off specimen surface
• Generates a 3D image
• High resolution due to short wavelength of electrons
• Cant see internal strcutres
• Specimen does not need to be thin
• High magnification (x1,000,000)
• Can only view dead/dehydrated specimens as it uses a vacuum
• Complex preparations so artefacts are present
• Does not show colour

Question 7

What is an artefact

Answer 7

Artefacts are visible details that aren’t part of the specimen being observed, such as air bubbles or fingerprints

Question 8

Describe how the size of an object viewed with an optical microscope can be measured

Answer 8

1. Line up eyepiece granule with stage micrometre
2. Calibrate eyepiece graticule- use stage micrometre to calculate size of divisions on eyepiece graticule
3. Take micrometre away and use graticule to measure how many divisions make up the object
4. Calculate the size of object by multiplying numbers of divisions by size of divison
5. Recalibrate eyepiece graticule at different magnifications

Question 9

What is cell fractionation

Answer 9

The process where cells are broken up and the different organelles they contain are separated out

Question 10

What are the conditions required for Cell fractionation to take place

Answer 10

The tissue must be in a cold, buffered and isotonic solution

Question 11

Why must the cell fractionation require the solution to be cold

Answer 11

To reduce enzyme activity that might break down the organelles

Question 12

Why must the cell fractionation require the solution to be isotonic

Isotonic-Any external solution that has the same solute concentration and water concentration compared to body fluids. In an isotonic solution, no net movement of water will take place

Answer 12

So water does not move in or out of organelles by osmosis
also so they do not burst

Question 13

Why must the cell fractionation require the solution to be Buffered

A buffer solution is one which resists changes in pH

Answer 13

To keep the pH constant–>so enzymes dont denature

Question 14

What are the two stages to cell fractionation

Answer 14

Homogenation and ultracentrifugation

Question 15

What is a homogeniser

Answer 15

A blender

Question 16

Why is a homogeniser needed

Answer 16

It disrupts the cell membrane, breaking open cells and releasing organelles

Question 17

What happens to the resultant fluid in the homogeniser

Answer 17

It is filtered to remove an ocmplete cells and large pieces of debris

Homogenate= reslutalnt fluid from the homogneiuser

Question 18

What is ultracentrifugation

Answer 18

The process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge

Question 19

What is the process of ultracentrifugation
(6)

Answer 19

• The filtrate is placed (ina tube) in the centrifuge and spun at low speeds
• The heaviest organelles,nuclei, are forced to the bottom (of the tube) where they form a thin sediment or pellet
• The fluid at the top of the test tube (supernatant) is removed
• The supernatant is transferred to another tube and spun in the centrifuge at a faster speed
• The next heaviest organelle is forced to the bottom of the tube
• Repeat this process and the speed is increased every time