3.2.1.3 Methods of studying cells

Question 1

what is magnification?

Answer 1

how much the image can be increased in size

Question 2

what is resolution?

Answer 2

the ability to determine between two separate points

Question 3

what is the equation for magnification?

Answer 3

magnification = image / object

Question 4

what is another name for an optical microscope?

Answer 4

a light microscope

Question 5

what are the principles of an optical microscope?

Answer 5

directs light waves through a sample (or reflects light off the surface of a live sample) into the eye of the observer

Question 6

what is the purpose of staining a specimen?

Answer 6

it is used to colour cell structures so that they can be seen as most cells are transparent / don’t contain pigment

Question 7

what is the maximum magnification of an optical microscope?

Answer 7

1500 x

Question 8

what is the maximum resolution of an optical microscope?

Answer 8

0.2 µm

Question 9

why is the resolution of an optical microscope low?

Answer 9

because light rays have a longer wavelength

Question 10

optical microscopes can view ____ specimens?

Answer 10

live

Question 11

why does the specimen need to be extremely thin for an optical microscope?

Answer 11

so that the light rays can pass through

Question 12

what is the resolution of an electron microscope?

Answer 12

upto 0.1 nm

Question 13

why is the resolution of an electron microscope better than that of an optical microscope?

Answer 13

the electron beam has a shorter wavelength than light

Question 14

what are the two types of electron microscopes?

Answer 14

• transmission
• scanning

Question 15

what are the principles of a TEM?

Answer 15

• electrons fired at the specimen
• denser parts absorb more electrons and so appear darker

Question 16

what are the principles of a SEM?

Answer 16

uses a focused beam of high-energy electrons which reflect off the surface of structures

Question 17

what are the advantages of using a TEM over a SEM?

Answer 17

• can view internal structures
• higher resolution

Question 18

what are the limitations of electron microscopes?

Answer 18

• the whole system must be in a vacuum so living specimens cannot be observed
• a complex staining process is required which may introduce artefacts (e.g. dust or air bubbles) into the image
• specimens have to be very thin, especially for the TEM so that electrons can pass through
• SEM has a lower resolving power than TEM

Question 19

what is cell fractionation?

Answer 19

the process by which cells are broken up and the different organelles are separated out based on their mass using gravity

Question 20

what are the three main stages of cell fractionation?

Answer 20

• homogenisation
• filtration
• centrifugation

Question 21

what type of solution does the tissue need to be placed in before cell fractionation and why?

Answer 21

• ice-cold - reduces enzyme activity to prevent digestion of organelles
• isotonic - prevents osmosis so no lysis / shrinkage of organelles
• buffer - maintains pH so that enzymes / proteins are not denatured

Question 22

what happens during homogenisation?

Answer 22

breaking up the tissue to break open cell membranes and release organelles

Question 23

what happens during filtration?

Answer 23

homogenate is filtered to remove large debris as this will be heavy and will sink to the bottom of the test tube

Question 24

what happens during centrifugation?

Answer 24

• faster spinning = a greater force
• at a slower speed, large fragments collect at the bottom forming a pellet whilst, at the top, smaller fragments remain suspended in a liquid called the supernatant
• the supernatant is transferred to another test tube and re-spun at higher speeds
• smaller organelles collect at the bottom forming a new pellet

Question 25

what is the heaviest organelle?

Answer 25

the nucleus

Question 26

what does it mean if a pellet is closer to the bottom of the centrifuge tube?

Answer 26

the organelle it consists of is denser