3.2.1.3 Methods of studying cells

Define resolution

The ability to distinguish two objects.

Define magnification

How much times larger the image produced is

Principle of optical microscope?

Uses light as source

Gives 2d And true colour

Limitations of optical microscope?

High wavelength

Low resolution and magnification

Principle of scanning electron microscope

Uses electron as source

Electron scan across specimen and bounces off

3d image

Thick external structure viewed

Limitations of scanning electron microscope

Specimen must be dead

Black and white image formed

Lower resolution

Principle of transmission electron microscope

Uses electron as source

Electron sent through specimen

High resolution

Internal structure can be viewed

Limitations of transmission electron microsocope?

Requires thin specimens

Artefacts may appear

Specimens must be dead

Black and white image formed

Formula for magnification?

Size of image = actual size of object x magnification

Formula for overall magnification?

Objective lens x eyepiece lens

Define cell fractionation?

When cells are broken and organelles are sepearted

Conditions for cell fractionation to take place

Cold - reduces enzyme activity

Buffered - maintains pH

Isotonic - prevents gain or loss of water by osmosis

Principle of homogenation

Cells broken up by homogeniser(blender)

Fluid created is homogenate and must be filtered to remove debris and complete cells

Filtrate is then centrifuged slowly

Leaves pellet(solid) at bottom and supernatant(liquid) at top

Principles of ultracentrifugation

Nuclei is in first pellet

The supernatant is the ultracentrifuged

Centrifuge at a higher speed

Pellet and supernatant separate each time

Organelles can be selected from different pellets