Units of Measurement
One mm= 10^-3m
micrometre= 10^-6m
nanometre= 10^-9m
What features do animal and plant cells have in common
- Cell surface membrane
- Nucleus
- Cytoplasm
- Mitochondria
- Golgi apparatus
- ER’s
Differences between animal and plant cells
- Centrioles (A)
- Cell walls and plasmodesmata (P)
-Permanent vacuoles- only in plants cells (animal cells have phagocytic vacuoles)
-Chloroplasts (P)
Equation for magnification
Observed size of image/ actual size
How to read the eyepiece graticule
First calibrate it using the stage micrometre. Place them alongside each other and look for coinciding lines. Figure out the length of 1 egu and then apply the formula.
Formula to find the length of a specimen
number of egu * calibration of one egu
Define resolution
The ability to distinguish two points that are very close together as separate
How do you find the limit of resolution
The limit of resolution is half the wavelength of the radiation used to view the sepcimen
How does the Transmission electron microscope (TEM) work?
Electrons are passed through the specimen and thus internl structures can be seen.
Only electrons that have managed to pass through the specimen are used to create the image of the specimen.
How does a Scanning electron microscope (SEM) work?
A beam of electrons is projected onto the specimen.
The image is created by the electrons that have been reflected of the surface of the specimen and so the image apears 3D
This allows fro surace sturctures to be seen
How are electron slides prepared? Both light and electron.
Light microscope specimen are coated in stains and must be alive.
Electron microscope specimen are coated in heavy metals and must be dehydrated as they are viewed in a vacuum.
Resolution and wavelength of radiation in a light microscope
Radiation used: Beams of visible light- usually violet
Wavelength 400nm
Maximum resolution: 200nm
Uses glass lenses
Resolution and wavelength of radiation in an electron microscope
Radiation used: beam of electrons
Wavelength: 0.005nm
Resolution in practice: 0.5nm
Uses electromagnetic lenses
What is ultrastructure?
The fine (detailed) structure of a cell as revealed by the
electron microscope
What are “False-colour” images?
standard black and white electron micrographs which have been altered and coloured by computers
Width of the cell surface membrane
7 nm
Width of the mitochondria
1 micrometre
Width of a ribosome
25 nm
what is compartmentalisation and why is it useful?
- to ensure reactions do not interfere with each other
- all organelles therefore have their own membranes ast they have their own distinct functions
what is ultrastructure?
- detailed structures of the cell that can only be seen via an electron microscope
- not necessarily surrounded by membranes
Plasmodesmata
- a section in a plant cell where there is no cell wall.
Functions- allows substances to pass - allows rapid transport of substance
cell wall
- made of cellulose
- fully permeable
- only found in plant cells
- provides structural support - prevents bursting and thus limits cell size
Vacuole
- permanent vacuoles only found in plant cells
- animal vacuoles can be phagocytic
- surrounded by a partially permeable mebrane called tonoplast
- stores water, ions, minerals, salts, sugars
- also seperates waste products
- helps maintain turgor pressure- gives turgidity
centrioles
- they are cylindrical
made of 9 groups of 3 microtubules
not found in plant cells - involved in cell division
- are at right angles and moves to opposite poles of the nucleus -
- found in flagella and cilia, act as microtuble organising centres at the basal body
- prganises microtubules
