Cell Structure Flashcards
Describe light microscopes
Poor resolution due to long wavelength of light
Living samples can be examined and a colour image obtained
Describe transmission electron microscope
High magnification and resolution
Electrons pass through the specimen to create an image
Describe scanning electron microscopes
High magnification and resolution
Electrons bounce off the surface of the specimen to create an image
Describe laser scanning confocal microscopes
High resolution and 3D imaging
Laser light used to create an image
What is resolution
Minimum distance between two objects in which they can still be viewed as separate
Optical microscope determined by wavelength of light
Electron microscope determined by the wavelength of the beams of electrons
What is magnification
Refers to how many times larger the image is compared to the object
What are the 4 main types of sample preparations?
Dry mount
Wet mount
Squash slide
Smear slide
Describe dry mount
When thin slices of whole specimens are viewed, with just the coverslip placed on top e.g. plant tissue or hair
Describe wet mounts
When water is added to the specimen before lowering the coverslip with a mounted needle to prevent air bubbles from forming. Aquatic organisms could be viewed this way
What are squash slides
Wet mounts which you then push down on the coverslip to squash the sample to ensure you have a thin layer to enable light to pass through. This is used when creating a root tip squash sample to view the chromosomes in mitosis
What are smear slides?
Created using the edge of another slide to smear the sample across another slide to create a smooth, thin even coated specimen. A cover slip is placed on top after smearing. This is used when examining blood cells in a blood sample
What is an eye piece graticule?
Scale on a glass disc which is called eyepiece graticule.
Used to measure the size of objects you are viewing under a microscope
Each time you change the objective lens and the magnification you have to calibrate the eyepiece
How to calibrate an eyepiece graticule
1) Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece
2) count how many divisions on he eyepiece graticule fit into one division on the micrometer scale
3) each division on the micrometer is 10μm so this can be used to calculate what one division on the eyepiece graticule is at the current magnification
What formula do we use for viewing structures under a microscope?
Magnification = size of image/ size of real object
What is differential staining?
Technique which involves many chemical stains being used to stain different parts of a cell in different colours
How do crystal violet and methylene blue stain?
They are positively charged so they are attracted to and stain negatively charged material
How does nigrosin and Congo red stain?
Negatively charged so cannot enter cells as cytosol repels them. Creates a stained background, so unstained cells stand out
How is crystal violet used in gram staining
Crystal violet added, then iodine to fix the stain, alcohol is used to wash away any unbound stain. Gram positive bacteria appear blue/purple as the stain is retained to the thicker peptidoglycan cell wall later absorbing the dye.
How is safranin used in gram staining?
Gram negative bacteria cannot absorb methylene value as their peptidoglycan walls are too thin so they do not retain the stain. Safranin is used as a counterstain, turning them red
How does gram staining help medics?
Distinguishing between two different types of bacteria helps antibiotic diagnosis
What are electron microscopes
A beam of electrons have a very short wavelength = a high resolution so small organelles and internal structures can be visualised.
Image is created using an electromagnet to focus the beam of negatively charged electrons
Electrons are absorbed by air = EM must be in a vacuum
Only non living specimens can be examined
Image is black and white so samples must be stained
Outline process of transmission electron microscopes
Extremely thin specimens are stained and placed in a vacuum
Electron gun produces beam of electron that passes through the specimen
Some parts of the specimen absorb the electrons and this makes them appear darker
2D image produced and shows detailed images of internal structure of cells
Outline scanning electron microscopes
Specimens do not need to be thin as electrons are not transmitting through
Electrons are beamed onto the surface and the electrons are scattered in different ways
Produces a 3D image
Outline laser scanning confocal microscope
Fluorescent microscope
Image created using high light intensity to illuminate the specimen stained with a fluorescent dye
Enables scientists to view sections of tiny structures that is challenging to physically section off and creates a 3D image
Microscope scan specimen point by point using a focused laser beam to create a 2D image of a 3D image in different focal planes is used,
