Cell Structure Flashcards
how do optical microscopes work
-light is directed through a thin layer of specimen that is supported on a glass slide.
-light is focused through several lenses
-use visible light having a wavelength of between 400nm and 700nm. therefore structures closer together than 200nm will appear as one object
what is the magnification on a light microscope
x1500
what is the resolution on a light microscope
limited, 200nm
what image does a light microscope produce
-photomicrograph
-2D
-coloured image
disadvantages of using a light microscope
small organelles e.g ribosomes cannot be seen.
2D
ribosome
very small, non membrane-bound organelles 20nm diameter, cannot be observed by light microscope
how does a laser scanning microscope work
-use laser light to scan an object point by point at different depths and assemble on a computer
-have depth selectivity
-specimen must be stained with fluorescent dyes.
-thick section of tissue is scanned
-laser beam is reflected by fluorescent dyes.
advantages of laser scanning microscope
-can be used on thick or 3D specimens
-allow external 3D structure to be observes
-very clear, high resolution images produced (even see structure of cytoskeleton in cells)
how does a TEM work
-use electromagnets to focus a beam of electrons
-beam of electrons is transmitted/passed through the specimen
-denser parts absorb more electrons (these parts appear darker on the final image)
advantages of TEMs
-high resolution images
-allows the internal structures within cells to be observed
disadvantages of TEMs
-thin sections only
-dead specimens only (due to vacuum)
-lengthly preparation treatment for specimens
-no colour
how does a SEM work
-send a beam of electrons across a specimen
-beam bounces off the surface of a specimen and electrons are detected
-produce 3D images that show surface of specimens
advantages of SEMs
-can view thick or 3D specimens
-allow the external, 3D structure to be observed
-colour can be added
how do optical microscopes work
-light is directed through a thin layer of specimen that is supported on a glass slide.
-light is focused through several lenses
-use visible light having a wavelength of between 400nm and 700nm. therefore structures closer together than 200nm will appear as one object
disadvantages of laser scanning microscopes
-slow process, takes time and expertise
-expensive
-can cause photodamage to cells.
disadvantages of SEMs
-lower resolution than TEM
-dead specimens only
-no colour naturally
magnification of TEM
x500,000
resolution of TEM
0.5nm
magnification of SEM
x500,000
resolution of SEM
3-10 nm
structure of nucleus
-surrounded by a double membrane (nuclear envelope)
-are pores in nuclear envelope
-contains chromatin (DNA wound around histone proteins)
function of nuclear envelope
separates contents of nucleus from rest of cell
function of nucleus
-control centre/ controls activities of cell
-stores genome
-transmits genetic info
-provides instructions for protein synthesis
function of nuclear pore
enable larger substances e.g messenger proteins to leave nucleus