2.1.1 : Cell structure - Biology

Created by

Keeley Barnes

Cards (79)

What are the features of a scanning electron microscope?
Produces a 3D image.
Beam of electrons sent across specimens surface and reflected electrons are collected.
Max. resolution of 0.002um.
Max. magnification of x500,000.
What are the disadvantages of scanning electron microscopes?
Expensive.
Electron beam can damage specimen.
Artefacts can be produced.
Specimens are dead.
Produces black and white images, can be coloured digitally.
What are the features of a light microscope?
Light underneath illuminates the specimen.
Whole cells and tissues can be seen.
Max. resolution of 0.002um.
Max. magnification of x1500.
Easy sample preparation.
What does the objective lens on a light microscope do?
Magnifies the specimen.
What does the eyepiece lens on a light microscope do?
Magnifies the image.
What are the disadvantages of a light microscope?
Low magnification and resolution.
What are the features of fluorescent tags?
Tags antibodies with GFP.
More precision when using confocal microscopy.
Emits green light illuminated by UV.
Can attach to genes coding for a protein via genetic modification.
What are the disadvantages of fluorescent tags?
GFP is relatively large and can affect the function of the protein of interest.
What are the features of atomic force microscopes?
Feels the surface with a sharp mechanical probe.
3D image.
Measured with laser beam.
No fixations or staining.
Living organisms/systems.
Max. resolution of 0.1nm.
Max. magnification of x100,000,000
Used in pharmaceutical and drug targets.
What are the disadvantages of atomic force microscopes? 
Can only obtain surface level information from samples.
What are features of laser scanning confocal microscopes? 
Single spot of focused light moved across specimen, causing fluorescence of cell components via dye.
Max. resolution of 0.2um.
Max. magnification of x1500.
Thin samples used.
Used to detect eye diseases and where molecules are in cells.
What are disadvantages of laser scanning confocal microscopes?
Cannot see deep into cell tissues as the light will not penetrate.
Expensive.
Complex.
What are the features of transmission electron microscopes?
Beam of electrons illuminates the specimen.
Organelles are visible.
Max. resolution of 0.0002um
Max. magnification of x500,000
Produces black and white images, can be coloured digitally.
What are disadvantages of transmission electron microscopes?
Expensive.
Electron beam can damage specimen.
Artefacts can be produced.
Specimens must be dead.
What are the benefits of having two lens' on a light microscope?
Higher magnification produced then with just one lens.
How to prepare a solid specimen?
Using scissors, cut a small sample of tissue (sectioning).
Peel or cut a very thin layer of cells from the tissue and place on slide with a scalpel.
Apply a stain (if needed).
Gently place a coverslip and press down (removes air bubbles).
How to prepare a liquid specimen?
Add a few drops of the specimen to a slide (dimple slides) with a pipette.
Cover the specimen with a coverslip placed at an angle to push air to the sides.
What are squash slides?
Wet mount is prepared then gently pressed down with a lens tissues on the coverslip.
Good for looking at soft samples.
What are smear slides?
Edge of slides is used to smear the sample.
Creates a thin even coating on another slide.
E.G Blood cells and blood smear tests.
What is fixation? 
Adding a chemical fixture that creates a chemical bond between proteins to increase rigidity.
What chemicals are used in fixation?
Ethanol or formaldehyde (to preserve specimens).
Heat to fix the sample directly onto the slide by denaturing the proteins.
What is sectioning?
After sample is fixed, it is dehydrated using alcohols then placed in wax or resin to form a hard block.
Then sliced thinly with a microstone.
What is staining?
Different stains show different structures.
Can involve differential staining (multiple dyes).
What is mounting?
Specimens secured to slide using a mounting medium with a coverslip on top.
Why do electron microscope specimens need to be stained?
Need to be stained to absorb electrons as the have no colour
Heavy metal ions are used to stain, and show up black or grey.
What are some common stains?
Iodine
Methylene blue
Eosin Y
Safranin
Toluidene blue
Wright stain
Leishmans stain
Crystal violet
Aceto-orcein
Sudan III
What is a lower power drawing?
One that shows the distribution of main tissues within a cell but not individual cells.
What is a high power drawing? 
More accurate and detailed than a low power drawing and shows a few cells.
What is the equation for individual eyepiece graticule?
stage graticule / eyepiece graticule.
What does calibration mean?
Making sure that a scientific process/instrument will produce accurate results.
What does magnification mean?
How many times bigger the image of a specimen observed is in comparison to the actual size.
What is the equation for magnification?
Image size / object(actual) size
Conversions.
1000 micrometres in a millimetre.
1000 nanometres in a micrometre.
What does resolution mean? 
The ability to distinguish between two close points as seperate and to see finer levels of detail.
Limited by wavelength of the sample.
What is diffraction?
Interference or bending of waves around the corners of an obstacle.
Limits the resolution as light waves spread out or overlap.
What is contrast?
Difference in colour and shade between two objects.
What are the features of a lysosome?
Sphere-shaped sacs filled with hydrolytic enzymes.
Membranous organelles.
What is the function of a lysosome?
The digestive system of the cell that degrades material and digests obsolete components.
What are the features of a vacuole?
Membranous organelles.
What is the function of a vacuole?
Help maintain water balance and take in and get rid of waste products.