Methods of studying cells

Question 1

How does an optical microscope work

Answer 1

Use light to form a 2D image

Visible light has a longer wavelength, so lower resolution ~200nm

Low magnification x1500

Question 2

Optical microscopes, advantages and disadvantages

Answer 2

Advantages: Can see living organisms

Disadvantages: 2D image, only used on thin specimens, low resolution so cannot see internal structures of organelles and low magnification

Question 3

How does a scanning electron microscope (SEM) work

Answer 3

Use electrons to form a 3D image

Beams of electrons scan surface, knocking off electrons from the specimen, which are gathered in a cathode ray tube to form an image.

Electrons shorter wavelength (so higher resolution 0.2nm)

High magnification x1500000

Question 4

Scanning electron microscope (SEM), advantages and disadvantages

Answer 4

Disadvantages: Vacuum so cannot observe living specimens, lower resolution than TEM

Advantages: 3D image, high resolution (can see internal structures of organelles), high magnification, used on thick specimens

Question 5

How does a transmission electron microscope (TEM) work

Answer 5

Use electrons to form a 2D image

Electromagnets focus beam of electrons onto specimen, transmitted.

More dense = more absorbed = darker appearance

Electrons shorter wavelength (so higher resolution 0.2nm)

High magnification x1500000

Question 6

Transmission electron microscope (TEM), advantages and disadvantages

Answer 6

Disadvantages: 2D image, only used on thin specimens, vacuum so cannot observe living specimens

Advantages: High resolution (can see internal structures of organelles) and high magnification

Question 7

Magnification vs resolution

Answer 7

Magnification - how much bigger the image of the sample is compared to the real size

Resolution - how well distinguished an image is between 2 points; shows amount of detail; limited by wavelength of radiation used eg light

Question 8

Cell fractionation

Answer 8

Homogenise tissue using a blender to disrupt cell membrane/break open the cell and release the organelles.

Place in a cold, isotonic buffered solution

Filter homogenate and remove large, unwanted debris eg connective tissue

Question 9

Why use a cold, isotonic buffered solution

Answer 9

Cold reduces enzyme activity so organelles aren’t broken down

Isotonic so water does not move in/out of organelles by osmosis so they do not burst/shrivel

Buffered keeps pH constant so enzymes don’t denature