Cell theory and Microscopy Flashcards
What are cells?
The basic building blocks of all living organisms and tissues.
HISTORY: First observed by Hooke in 1665 in a cut surface of cork where he observed (using an early compound microscope with 30X magnification and a flame) spaces which he termed ‘cells’ because they resembled rooms monks lived in within monasteries.
How many cells are present in the human body?
Between 5 and 10 x10^13 cells
At least 200 different types present with the same DNA.
What is the largest organism in the world?
The ‘Honey Fungus’ known as Armillaria ostoyae.
Found in Oregon growing underground, only seen in the Autumn when it sexually reproduces to produce toadstools growing through thread-like structures called mycelium.
What is the purpose of microscopy?
To produce enlarged images through magnification to see more detailed specimens (invisible to the human eye)
Provides a better resolution (ability to distinguish between two points on an image)
What is light microscopy?
A broad beam of illuminating light focused on a specimen by a condenser lens and passed through to get a differential absorption of light
Limited magnification due to the wavelength of a photon of light being quite large.
What is classic light microscopy?
An image is illuminated with white light and collected on various lens.
Does require staining and often results in cell death
What is phase-contrast microscopy?
Relies on light slightly refracting to generate a contrast through differences in the refractive index of the sample
What is differential interference contrast microscopy?
Relies on the refractive index of the sample and the observed rates of change in the refractive index production of apparent 3D images
What is fluorescence microscopy?
The specimen is stained with fluorescent dye or protein and then UV light is used to excite the specimen producing a bright high contrast image against a dark background
Green protein from Jellyfish
Red, Blue and Yellow protein from sea anemone.
What is laser scanning confocal light microscopy?
Allows the image of a thin plane within a thicker specimen to be magnified
Laser beam if focused to excite fluorescent molecules in cells and tissues
Sections are stored and pooled to form a 3D image.
What is the process for microscope slide preparation?
Fixation - stops the tissue from falling apart and immobilizes the cell material (formaldehyde/alcohol/acetic acid)
Embed - mechanical support (wax/resin)
Section - cut thin section using a microtome with metal, glass or a diamond blade
Staining - improve visibility of thin sections
What is electron microscopy?
Uses a beam of electrons to produce the image. Has a much higher resolution and magnification, as it is not limited by the wavelength of light (photon much shorter)
What is transmission electron microscopy?
Electrons pass through a thin specimen and allows magnification up to 1,000,00X
Specimens must be fixed, dehydrated, sectioned and stained with electron-dense heavy metal (Osmium) and must be done in a vacuum so electrons are not absorbed by air molecules.
Focused by magnets
What is freeze-fracture microscopy?
Samples were rapidly frozen (cryofixation) to reveal cell internal structure by cleaving the cell with a knife
Coat surfaces with platinum to form replica
What is scanning electron microscopy?
electron beam is scanned over the specimen = they bounce off and strike detectors
Produces a 3D image with a magnification between 15-150,000X
Must be fixed, dehydrated and stained with gold
