Methods of studying cells

Question 1

Magnification

Answer 1

The degree to which the size of an image is larger than the object itself

Question 2

Resolution

Answer 2

The ability to distinguish between 2 points.
- the minimum distance apart two objects can be to be seen as separate items

Question 3

Conditions for electron microscopes

Answer 3

-Specimen must be dead and viewed in a vacuum
- staining using metal dyes is always necessary
-Images are black and white

Question 4

Transmission electron microscope

Answer 4

Consists of electron gun that produces a beam that is focused onto the specimen by a condenser electromagnet

Question 5

Scanning electron microscope

Answer 5

Directs a beam of electrons on to the surface of the specimen in regular patterns and the electrons are scattered by the specimen building up a 3-D image

Question 6

Give one advantage of using a TEM compared with a SEM

Answer 6

-Higher resolution
-view internal structures

Question 7

What is the equation for magnification

Answer 7

Magnification= size of image/ size of real object

Question 8

Why do light microscopes have poor resolution

Answer 8

long wavelengths of light

Question 9

What are the advantages to using an electron microscope

Answer 9

-the electron beam has a very short wavelength and therefore can resolve objects well
- electrons are negatively charged so the beam can be focused using electromagnets

Question 10

What are the two types of electron microscope

Answer 10

Transmission electron microscope
Scanning electron microscope

Question 11

What type of images do TEM microscopes produce

Answer 11

2-D

Question 12

What type of images do SEM microscopes produce

Answer 12

3-D

Question 13

What are the limitations of a TEM microscope

Answer 13

-specimen must be extremely thin
-complex staining process is required
-whole system must be in a vacuum

Question 14

What is the resolving power of a light microscope

Answer 14

0.2Um

Question 15

What is the resolving power of an electron microscope

Answer 15

0.1nm

Question 16

How do you measure the size of an object using a light microscope

Answer 16

eyepiece graticule

Question 17

How do you calibrate an eyepiece graticule

Answer 17

using a stage micrometer.
when the eyepiece graticule and stage micrometer are lined up it’s possible to calculate the length of divisions on the eyepiece graticule

Question 18

Homogenisation

Answer 18

cells are broken up by a homogeniser to release the organelles from the cell. The homogenate is filtered out to remove large debris

Question 19

What is cell fractionation

Answer 19

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

Question 20

What are the two stages of cell fractionation

Answer 20

• Homogenation
  -ultracentrifugation

Question 21

What is Ultracentrifugation

Answer 21

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

Question 22

Why is the solution cold

Answer 22

to reduce enzyme activity

Question 23

Why is the solution buffered

Answer 23

to reduce pH change that might damage organelles or affect the functioning of enzymes

Question 24

Why is the solution isotonic

Answer 24

To prevent osmotic changes that may cause the cells to shrink or burst

Question 25

What is the process of Ultracentrifugation

Answer 25

spin filtrate from homogenisation at slow speed in centrifuge, heavy organelles (nuclei) fall to the bottom - fluid from the top (supernatant) removed leaving nuclei as a pellet - spin supernatant at higher speed, next heaviest organelles (mitochondria) fall to the bottom - repeat, spin supernatant at higher speed, next heaviest organelle falls to the bottom etc

Question 26

Describe how a sample of chloroplasts could be isolated from leaves.

Answer 26

1. Break open cells/tissue and filter
2. In cold, same water potential/concentration, pH controlled solution;
3. Centrifuge/spin and remove nuclei/cell debris;
4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out;