2.1.1 Cell Structure Flashcards
What are the 4 stages of preparing a sample for a light microscope?
- Fixation
- Dehydration and clearing
- Embedding and sectioning
- Staining
Def of resolution and magnification
Magnification - the enlargement of something in appearance not physical size
Resolution- The shortest distance between two points that can be distinguished by the microscope as two separate entities
Describe Fixation
Tissue samples are placed in a fixative solution
which penetrates the tissue
to strengthen the tissue and inactivate enzymes that could degrade the tissue
Describe dehydration and clearing
The sample must be embedded in wax but first all water must be removed by using alcohols (dehydration)
And replaced with the solvent xylene (clearing)
Describe embedding and sectioning
Cleared tissue samples are embedded in wax
then they are cooled and cut into thin sections
Describe staining
The wax is removed with xylene
and are rehydrated with alcohols and water
What are the two types of mounts?
Dry mounts - dry specimen cut into slices
wet mounts - the specimen is suspended in liquid
why is staining used?
Due to cells lacking colour, are transparent, and there is little difference between cells of different tissues
Also to identify where different metabolic processes take place
what are the 4 different types of microscopes?
Light microscope
Transmission electron microscope
scanning electron microscope
laser scanning confocal microscope
What is gram staining used for?
To detect between gram positive and gram negative bacteria
Describe how a gram test is done ?
A bacterial smear is flooded with crystal violet and is taken up by the bacterial cells
It is then treated with iodide to fix the stain so the cells remain purple
It is then rinsed with either alcohol or water which rinses out some of the cells
However gram positive will retain the dye
And a counter dye such as safarain which will dye the bacteria red
Describe how a gram test is done ?
A bacterial smear is flooded with crystal violet and is taken up by the bacterial cells
It is then treated with iodide to fix the stain so the cells remain purple
It is then rinsed with either alcohol or water which rinses out some of the cells
However gram positive will retain the dye
And a counter dye such as safarain which will dye the bacteria red
The equation for magnification ?
Image size / actual size is the magnification
Both must be in millimetres or micrometers
Describe light microscopes
They use light rays to observe objects
they observe living specimens and
is very cheap and portable to set up
However max magnification of x2000 and low resolution
describe transmission and scanning electron microscopes
Both use focused beams of electrons ( which are at a shorter wavelength then light microscopes) through sections of tissues
With a magnification of x 500,000 times and see details of cell surfaces
can only use dead samples and harsh chemicals to prepare samples
describe laser scanning confocal microscope
Uses a laser beam of light to illuminate chemical stains which then fluoresce
can see living cells and track and observe cell processes
More expensive and complex than a light microscope several dyes can be used to help increase the contrast in different sub cell organelles
what is the cytoskeleton of the cell?
a network of protein fibres that gives the cell shape and structure to allow organelles to be moved and organised
What are the 2 fibres that make up the cytoskeleton?
Actin- can contract and relax to allow the movement of WBCs and organelles
Tubulin- uses ATP to drive these movements, used to move chromosomes in mitosis and to move vesicles from the endoplasmic reticulum to the Golgi apparatus
The difference between flagella and undulipodium
bacteria have flagella used as motors that spins like a propeller
undulipodium is made up of microtubules in a circle structure and are much longer
How are amoeba’s different to animal cells?
It is an animal cell with a contractive vacuole that is used to squeeze water out of the amoeba
Define the plant cell wall
Made of cellulose (an isomer of glucose) to create strong strands supported by turgor pressure
define the Golgi apparatus
Is an organelle that processes and packages lipids and protein molecules
Vesicles bring the Golgi molecules and under go remodelling in the cisternae to be transported out of the cell or to another organelle
what is a vesicle
are membrane bound sacs found in the cells that carry substances around the cell
what is the endosymbiotic theory?
the theory that cells engulfed mitochondrion like bacteria as they have there own DNA and ribosomes to increase ATP production
