Topic 1:Cell structure Flashcards
A common method of examining material with light microscope is
To cut thin slices of material called section
The advantage of cutting sections
Thin enough to allow light to pass through
Light passing through the sections produces an image which can then be magnified using
Objective lens and eyepiece lens
Prepared slide contain material that has been
Killed and preserved in a life like state
Temporary slides are ____ and _____ to prepare and are often used to examine ______
Quicker; easier; fresh material containing living cells
Sections are typically stained because
Structures in cell are transparent hence difficult to distinguish
Sometimes macerated(chopped up) material can be used as when examining
The structure of wood(xylem)
Some temporary stains commonly used
Iodine in Pottasium Iodide is useful for plant specimens- will colour starch blue black and nuclei and cell walls pale yellow.
Dilute methylene blue solution used to stain animal cells such as cheek cells.
Procedure of making temporary slides(2 steps)
1.Place the biological specimen on a clean glass slide and add one or two drops of stains.
2.Carefully lower a cover over the specimen.
Advantages of placing a coverslip on the specimen
Protects the microscope lens and prevents the specimen from drying out.
How to prevent drying out of a specimen
Adding a drop of glycerine and mixing it with the stain.
Suitable animal material
Human cheek cells obtained by gently scraping the lining of the cheek with a finger nail.
Suitable plant material
Onion epidermal cells, lettuce epidermal cells, chlorella cells, Moss slip leaves
Define Magnification
Is the number of times larger an image of an object is than the real size of the object.
Magnification formula
Magnification= observed size of the image/actual size
Micrographs
A picture taken with the aid of a microscope
Define eyepiece graticule
Small scale that is placed in a microscope eyepiece
The eyepiece graticule is placed in the microscope eyepiece so that
It can be seen at the same time as the iobject to be measured
The eyepiece graticule can be calibrated using
Stage micrometer
Define stage micrometer
Very small, accurately drawn scale of known dimensions, engraved on a microscope slide
mm to micrometer
x10^-3
micrometer to nanometer
x10^-3
mm to nm
x10^-6
Define resolution
The ability to distinguish between the objects very close together
The higher the resolution the greater
The detail that can be seen
The maximum resolution of a light microscope is
200nm
A resolution of 200nm means that
If two points or object are closer than 200nm, they cannot be distinguished as separate
The longer the waves
The lower the frequency
Wavelength changes with energy
The greater the energy, the shorter the wavelength
Why is a mitochondrion seen using a light microscope but not ribosomes
Because the mitochondrion is large enough to interfere with the light waves, however the ribosomes are far too small to have any effect on the light waves
The limit of resolution is
Half the wavelength of the radiation used to view it
When metals becomes very hot
Some of its electrons gain so much energy that they escape from their orbits.
Free electrons behave like
electromagnetic radiation
Electrons are suitable for microscopy for two reasons
1.They have extremely short wavelengths(as short as X-rays
2.They are negatively charged so they can be focused using electromagnets
A magnet can be made to alter the path if a beam
The equivalent of glass lens bending light
How does Transmission electron microscope work
1.The beam of electrons is passed through the specimen before being viewed.
2.Only the electrons that are transmitted are seen.
3.This allows us to see thin sections of specimen and thus see inside the cells.
How does a scanning electron microscope work
The electron beam is used to scan surface of the structures and only the reflected beam is observed.
The advantage of SEM
Surface structure can be seen
How is a 3d appearance achieved in SEM
It is because much of the specimen is in focus at the same time
Disadvantage of SEM
It cannot achieve the same resolution as TEM
Resolution of SEM
3nm to 20nm
It is not possible to see electron beams. How is this problem resolved
To make the image visible the electron beam is projected on a fluorescent screen. The areas hit by electron shine brightly giving an overall black and white image
The stains used in electron microscopy contain
Heavy metal atoms which stop the passage of electrons. The more densely stained
