mr Allsop- cell structure Flashcards
how do electron microscopes work
electron beams have shorter wavelengths than light resulting in higher resolution.
what is resolution
the smallest distance between two points where they both look like two separate points.
what is magnification
making an image appear larger.
what is calibration
how many lines on the eyepiece graticule (small ruler) can fit into large ruler (stage micrometer)
what is a transmission electron magnification (TEM)
beam of electrons fired through specimen
magnification-1,000,000 image-2D
resolution-0.5nm cost-expensive
colour-none sample-dead
have to be installed, take up a lot of space, training to use, slide and sample prep
what is scanning electron magnification
beam of electrons sent across surface of specimen. reflected electrons collected.
3D image mag- 150,000 expensive only dead sample
resolution is 3-10nm
no colour
light microscope (mag, resolution, image etc)
magnification- x2000 natural colour/stain
resolution-200nm no vacuum living/dead
2D image cheaper
accessible, less training, slide prep easy, no vacuum- living/dead
laser scanning confocal microscopy
marked with fluorescence: absorbs and re-radiates light which has a longer wavelength and lower energy- filtered through a pinhole aperture.
very high resolution images.
non-invasive, currently used to diagnose eye disease and development of drugs.
dry mount
solid specimen viewed not with water.
can be viewed whole or in slices.
eg. pollen ,hair ,dust.
wet mount
specimen suspended in water.
cover slip added at angles (prevent bubbles)
allows viewing of small aquatic organisms.
squash slides
wet mount prepared then blotted dry and gently applied pressure to squash sample, thin enough to transmit light.
smear slides
apply thin ,even coat using edge of slide and add cover slip. eg. blood cells
what is staining ?
increases contrast because components take up the stain so is easier to identify.
+VE dyes
attracted to -ve dye ,staining them blue
-VE dye
repelled by -ve dye so dye stays outside of cell and remains unstained and stands out against stained background.
differential staining and gram p/N
distinguishes between two types of organisms.
gram positive-thick cell wall- dye is retained gram negative- thin wall so dye leaves and is a less visible image.
steps to differential dye
1) crystal violet applied to specimen
2)iodine added, fixing dye
3)slide washed positive: blue/purple
negative: red
what do membranes do ?
surround organelle keeping components inside.
allows selected molecules to move in and out.
allows cellular processes to occur separately
allow cell to change shape
what is chromatin?
inside nuclear membrane.
spread out DNA before becoming chromosomes.
what and where the nucleolus ?
where ribosomes are made and synthesised into proteins.