2.1.1- Microscopes Flashcards
Define the term ‘magnification’.
The number of times larger an image appears, compared to the size of the original object.
Define the term ‘organelles’.
Small structures that are within cells- each of which has a specific function.
Define ‘photomicrograph’.
Photograph of an image seen using an optical microscope.
What is ‘resolution’?
The ability to be able to distinguish between two points clearly.
Microscopes produce what kind of magnification?
Linear magnification.
List four reasons as to why optical (aka light) microscopes are still used in schools, colleges and labs.
- relatively cheap
- relatively easy to use
- can be used to study WHOLE AND LIVING SPECIMENS
- portable- can be used in the field and lab
Explain simply how optical microscopes work.
They rely on lenses to focus a beam of light.
What is the maximum magnification of an optical microscope?
X1500
Explain why light microscopes can not magnify any higher than around x1500 effectively.
As their resolution is limited- they cannot magnify any higher whilst also producing clear images.
What is the maximum resolution of optical microscopes?
200 nanometers.
What are the four types of microscopes?
- Optical microscope
- Laser scanning microscope
- Scanning electron microscope
- Transmission electron microscope
Explain why ribosomes cannot be seen using an optical microscope.
They are about 20nm diameter so are smaller than the resolution of the optical microscope (200nm)
What is the formula for calculating the total magnifying power of an optical microscope?
Total magnification= objective lens magnifying power ‘X’ magnifying power of eyepiece lens
Define the term ‘electron micrograph’.
Photograph of an image that is seen using an electron microscope.
How do modern digital microscopes display their image?
On computer screen.
What is the alternative name for laser scanning microscopes?
Confocal microscopes.
Explain how laser scanning microscopes work.
They use laser light to scan an object point by point and assemble the pixel information by computer, on a computer screen.
The images produced by laser scanning microscopes are high _________ and show high __________.
High resolution.
High contrast.
Laser scanning microscopes have a special feature. What is that?
Depth selectivity.
Explain what depth selectivity is- a feature of laser scanning microscopes.
It means they can focus on structures at different depths within a specimen. It makes it useful to observe full and living specimens, as well as cells.
What are the two main places where laser scanning microscopes are used?
The medical profession and biological research.
Describe an example of how laser scanning microscopes are used in the medical profession.
They’re used to observe fungal filaments in the cornea of the eye of a patient with a fungal corneal infection. This gives a swift diagnosis- therefore, giving a more effective treatment.
What are the two different types of electron microscopes.
- Transmission electron microscopes.
* Scanning electron microscopes.
What is the maximum resolution of a laser scanning microscope?
x2000
Explain how electron microscopes work.
They use a beam of fast travelling electrons (wavelength about 0.004nm) that are fired from a cathode and focused, by magnets.
Explain the types of images produced by electron microscopes.
They give clear and highly magnified images, especially compared to optical microscopes.
In preparation for use by a TEM microscope, explain what has to happen to the specimen in preparation.
The specimen has to be chemically fixed by being dehydrated and stained.
Explain how transmission electron microscopes work.
The beam of electrons shot by the cathode pass through the specimen (that’s stained with metal salts) and some of the electrons pass through and are focused onto the screen/ photographic plate.
Explain the electron micrograph that TEM’s produce.
They form 2D black and white images.
What is the maximum magnification formed by TEM’s.
x2million.
Explain how the specimen for SEM microscopes must be prepared.
The electrons shot by the cathode don’t pass through the specimen (which is whole) as the electrons bounce off and are focused on the screen.
Explain the image that SEM’s give.
The images produced are black and white and are 3D. Computer software programmes can also add false colour.
List three disadvantages that are with both types of electron microscopes.
> very large.
very expensive.
need a great deal of skill and training to use.
Specimens used for electron microscopes have to be _____ when used in the microscopes.
Dead.
What are the effects the metallic salt stains used for staining can have on humans?
They can be potentially hazardous for humans.
