cells/ microscopes Flashcards
(30 cards)
outline how a student could prepare a temporary mount of tissue for a light microscope
1 obtain thin section of tissue
2 place plant tissue in a drop of water
3 stain tissue on a slide to make structures visible
4 add coverslip using mounted needle at 45 degrees to avoid trapping bubbles
describe how a light microscope works
1 lenses focus rays of light and magnify the view of a thin slice of specimen
2 different structures absorb different amounts and wavelengths of light
3 reflected light is transmitted to the observer via the objective lens and eyepiece
describe how a TEM works
1 pass a high energy beam of electrons through a thin slice of specimen
2 more dense structures appear darker since they absorb more electrons
3 focus image onto fluorescent screen or photographic plate using magnetic lenses
describe how a SEM works
1 focus a beam of electrons onto a specimens surface using electromagnetic lenses
2 reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate
describe how a laser scanning confocal microscope works
1 focus a laser beam onto a small area on a samples surface using objective lenses
2 fluorophores in the sample emit photons
3 photomultiplier tube amplifies the signal onto a detector. an image is produced pixel by pixel in the correct order
define magnification and resolution
magnification: factor by which the image is larger than the actual specimen
resolution: smallest separation distance at which 2 separate structures can be distinguished from one another
why do samples need to be stained for light microscopes
coloured dye binds to the structures
facilitates absorption of wavelengths of light to produce image
magnification and resolution of a compound optical microscope
magnification x2000
resolution 200nm
magnification and resolution of TEM
magnification x500000
resolution 0.5nm
magnification and resolution of SEM
magnification x500000
resolution 3-10nm
explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure
1 place micrometer on the stage to calibrate eyepiece graticule
2 line up scales on graticule and micrometer
3 length of 1 eyepiece division = 100um/ number of divisions
4 use calibrated values to calculate actual length of structures
describe the function of the nucleus
~contains DNA coiled around chromatin into chromosomes
~controls cellular processes
describe function and structure of ER
cisternae : network of tubules and flattered sacs extends from cell membrane and connects to nuclear envelope
~RER many ribosomes attached for protein synthesis and transport
~SER lipid synthesis
describe the structure and function of the gogli body
flattered disc shaped sacs called cisternae which are stacked together
~vesicles bud off trans face via exocytosis
- modifies and packages proteins for export
-synthesises glycoproteins
describe structure and function of ribosomes
fromed of protein and rRNA
~have large subunit which joins amino acids and small subunit with mRNA binding site
describe the relationship between the organelles involved in the production and secretion of proteins
the ribosomes that synthesise proteins are attached to the rER
~the gogli body which modifies proteins for secretion aligns with the rER
describe the structure of a mitochondrion
~surrounded by double membrane
~folded inner membrane forms cristae; site of electron transport chain
~fluid matrix : contains mitochondrial DNA, repitory enzymes, lipids , protiens
describe the structure of chloroplast
~vesicular plastid with double membrane
~thylakoids: flattened discs stack to form grana: contain photosystems with chlorophyll
~intergranal lamellae tubes attach thylakoids in adjacent grana
~stroma fluid filled matrix
state the function of mitochondria and chloroplasts
mitochondria ; site of aerobic respiration to produce ATP
chloroplasts ; site of photosynthesis to convert solar energy to chemical energy
describe the structure and function of a lysosome
sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes, glycoprotein coat protects cell interior;
- digests contents of phagosome
- exocytosis of digestive enzymes
describe structure and function of a plant cell wall
~made of cellulose microfibrils for mechanical support
~plasmodesmata from part of apoplast pathway to allow molecules to pass between cells
~ middle lamella separates adjacent cell walls
what are bacterial and fungal cell walls made of
bacteria; peptidoglycan
fungi: chitin
describe the structure and function of centrioles
~spherical group of 9 microtubules arranged in triples
~located in centrosomes
~migrate to opposite poles of cell during prophase and spindle fibres form between them
describe the structure and function of the cell surface plasma membrane
fluid mosiac phospholipid bilayer with extrinsic and intrinsic proteins embedded
- isolates cytoplasm from extracellular environment
- selectively permeable to regulate transport of substances
- involved in cell signalling / cell recognition
