Microscopy Flashcards
Many of the cell contents are…
colourless so they need to be stained to be seen.
The deeply staining material in the nucleus is…
chromatin, which is a mass of loosely coiled threads.
Chromatin collects together…
to form visible separate chromosomes during nuclear division.
The nucleolus is made of…
loops of DNA from several chromosomes. It is even more deeply staining area than chromatin.
The number of nucleoli is…
variable, one to five being common in mammals.
Organelle
Functionally and structurally distinct part of a cell. Often surrounded by membranes.
Why are many organelles surrounded by membranes?
So that their activities can be separated from the surrounding cytoplasm. This is called compartmentalisation.
Compartmentalisation is essential for a strucutre…
as complex as an animal or plant cell to work efficiently.
Division of labour means that…
work is shared between differently specialised organelles.
The most numerous organelles seen with a light microscope are usually…
mitochondria. They can move, change shape and divide.
Golgi apparatus is a part…
of complex internal sorting and distribution system within the cell.
Plasmodesmata
Fine strands of cytoplasm which pass through pore-like structures in their walls.
Phagocytic vacuoles
Small temporary vacuoles that can be found in animal cells.
The plant vacuole is surrounded by a membrane called…
tonoplast, which controls exchange between cytoplasm and the vacuole.
The fluid in the plant vacuole is…
a solution of pigments, enzymes, sugars, waste products, mineral salts, oxygen and CO2.
The plant vacuole helps to…
regulate the osmotic properties of cells as well as having a wide range of other functions. E.g. red pigment of beetroot, may be located in vacuoles.
Granum
Located in the chloroplast. They contain chlorophyll. Can be seen with a light microscope.
Cell walls are…
freely permeable, unlike the cell surface membrane.
Smallest structure visible with a human eye is…
50-100 micro meters.
Magnification
The number of times larger an image is than in the real size of the object.
Magnification formula
Observed size/actual size
Resolution
The ability to distinguish between two separate points. If the two points cannot be resolved, they will be seen as one point.
The maximum resolution of a light microscope is…
200 nm.
The length of visible light waves is…
from 400nm (violet light) to 700nm (red light).
The greater the energy…
the shorter the wavelength.
The limit of resolution is about…
one half the wavelength of the radiation used to view the spiecemen.
Maximum useful magnification of a light microscope is…
1500x
If the object is transparent…
it must be stained, otherwise, the waves would pass through it.
Why are electrons used as a source of radiation?
- wavelength is extremely short
- because they are negatively charged they can be focused easily using electromagnets
Resolution of an electron microscope is…
0.5 nm.
TEM
Transmission electron microscope. Only electrons that pass through the specimen are seen. Allowing us to see internal structures.
SEM
Scanning electron microscope. Only the reflected beam is observed. This allows us to see the surfaces. 3D appearance is achieved.
Resolution of SEM
3nm-20nm
To see the beam of electrons…
the fluorescent screen must be used(very expensive).
