2.1.1 - Cell Structure Flashcards
What does a microscope allow us to do
Magnify an object many times
Eyepiece graticule
Circular disk that fits onto the eyepiece and contains a tiny ruler with equal divisions on it
Stage micrometer
Usually 1-100nm long with 100 divisions on it. This sits on the stage of the microscope and is used to calibrate the eyepiece graticule
Why do we need a stage micrometer to calibrate the eyepiece graticule
The eyepiece graticule remains constant no matter what magnification the cells are used at
What are the two types of objective lens in a compound light microscope
High power
Low power
What instrument was used before the first microscope
Magnifying glasses
What type of microscope did Robert Hooke invent
A compound light microscope
What is the main feature of compound microscopes
They have 2 types of lenses, the eyepiece and objective lenses
In what year was the electron microscope invented in
1931
What is an advantage of an electron microscope
Capable for far greater resolution and magnification of 1 mil.
What is a disadvantage of electron microscope
Living specimens are destroyed by high dose of radiation
Metric equivalent of decimetre, dm
1 x 10^-1 m
Metric equivalent of millimetre, mm
1 x 10^-3 m
Metric equivalent of micro metre
1 x 10^-6 m
Metric equivalent of nanometre, nm
1 x 10^-9 m
What does the amount of detail seen through a microscope depend on
The resolving power of the microscope
Resolving power
The smallest separation at which two separate objects can be distinguished (or resolved)
What is the resolving power of a microscope ultimately limited by
The wavelength of light
What is the wavelength of light
400-600nm
Why do some microscopes have blue filters
Blue has the shortest wavelength of visible light and to improve the resolving power a shorter wavelength of light is needed
Definition of magnification
How much bigger a sample appears to be under the microscope than it’s in real life
Definition of resolution
Ability to distinguish between two points on an image i.e. the amount of detail
What is the resolution of an image limited by and why
The wavelength of radiation used to view the sample
When objects in the specimen are smaller than half the wavelength of the radiation being used, they don’t interrupt the waves, and so aren’t detected
What is the wavelength of light much larger than
The wavelength of electrons, so the resolution of the light microscope is a lot lower
How does using a microscope with a more powerful magnification affect the resolution
It does not
It will increase the size of the image but objects closer than 200nm will still only be seen as one point
Compound microscopes
Use several lenses to obtain high magnification
Resolution of light microscopy
About 200nm, which is good enough to see cells, but not details of cell organelles
Examples of procedures undertaken to prepare slide samples
Fixation Dehydration Embedding Sectioning Staining Mounting
Light microscopy
Specimens are illuminated with light, which is focussed using glass lenses and viewed with the eye or photographic film.
Specimens can be living or dead, but often need to be stained with a coloured dye to make them visible
What is the wavelength of electrons
Less than 1nm, so can be used to resolve small sub-cellular ultra-structure
How did the electron microscope revolutionise biology
Allows organelles such as mitochondria, ER and membranes to be seen in detail for the first time
Problems with an electron microscope
Specimens must be fixed in plastic and viewed in a vacuum, and must therefore be dead
Specimens can be damaged by the electron beam
Specimens must be stained with an electron-dense chemical (usually heavy metals like osmium, lead or gold)
What are the two types of electron microscope
Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)
TEM
Works much like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film
Most common form of electron microscope and has best resolution
SEM
Scans a fine beam of electron onto a specimen and collects the electrons scattered by the surface
Has poorer resolution but gives excellent 3D images
Laser scanning confocal microscope
Used to observe an object at a certain depth within a cell
Why do we stain samples
To ensure contrast between structures
Identification of cells
Magnification of light microscope
X1500
Magnification of TEM
X500,000
Resolution of TEM
0.2 nm
Magnification of SEM
X100,000
Resolution of SEM
10nm
Method of laser scanning confocal microscopy
Using a laser light to scan an object point by point and a computer assembles the image
Pros of laser scanning confocal microscopy
Can be used to study whole, live specimens and can be used to obtain images at different depths in thick sections
Main stains
Haemoxylin
Eosin
Haemoxylin
Blue colour
Stains DNA and RNA in all nuclei
Often used together (differential staining)
Eosin
Pink or red colour
Stains connective tissue and substances in cytoplasm
IAM Equation
I
A M
I - image size
A - actual size
M - magnification
Eukaryotic Cells
Have a nucleus containing genetic info
Prokaryotic cells
Don’t have a nucleus
No membrane bound organelles