A2.2 - cell structure Flashcards
magnification
increase in an object’s image size compared to its actual size
multicellularity
having more than one cell in an organism
resolution
minimal distance between two points at which they have be distinguished as two points
cells
basic structural unit of all living organisms
deductive reasoning
used to generate predictions from theories
- based on cell theory, a newly discovered organism can be predicted to consist of one or more cells
how do you prepare a sample to be used in a microscope?
- a thin sample is taken and placed on a slide
- stains may be used to improve visibility of structures
- a cover slip is lowered gently over the sample, avoiding air bubbles and blotting excess stain
how do you use a microscope?
- lamp is switched on and the lowest power objective lens is selected, with the stage being moved to the lowest position
- place slide in middle of stage so light is shining through it
- move stage to the highest position until the lens doesn’t touch the sample
- look through eyepiece leans and use coarse focus and fine focus knob to focus the image
- move sample if needed and use a higher magnification
eyepiece graticule
located in the eyepiece and engraved with 100 equal arbitary units and doesn’t alter magnification
arbitary units
size they measure depends on the microscope, total magnification and objective lens
micrometer
slide with a ruler 1mm long divided into 0.1mm divisions used to determine graticule divisions
how do you calculate a graticule unit?
comparing the units of the graticule to the known unit size of the stage micrometer allows you to determine the size of the object being examined
scale bars
drawn proportionally to a structure of known size determined using a graticule and stage micrometer
how do you calculate magnification?
magnification = eyepiece lens x objective lens
how do you calculate image size?
image size = actual size x magnification
how do you measure the actual size and image size?
actual size - scale bar
image size - ruler
how do you convert between units?
1cm = 10mm = 10000µm = 10000000nm
light microscopy
uses light to form an image with dead or living specimens to a maximum of 2000x magnification
fluorescent stains
bind to specific cellular components, based on the combinations of dye, and light up when irradiated with UV
immunofluorescence
uses antibodies attached with fluorescent dyes to bind to a particular molecule
- different wavelengths given off can be used to fund out locations of proteins within a cell
- allows components to be targeted more precisely e.g) a specific protein or RNA molecules
electron microscopy
uses interactions with electrons to produce an image
- higher resolution and magnification
- specimen mys be dead and fixed in plastic
- structural features are produced during preparation which can hinder image accuracy
what are the 2 types of electron microscopy?
SEM - scanning electron microscope - produces image of the surface of the object
TEM - transmission electron microscopy - uses electrons passing through a thin section
freeze fracture
rapidly freezing a biological specimen before breaking it down to reveal a plane through the sample which can be examined (membranes)
cyrogenic electron miscroscopy
allows imaging of single protein molecules and interactions with other molecules
what 3 structures are common to cells in all living organisms?
DNA, cytoplasm, plasma membrane
what is the function of DNA?
stores genetic code (sequence of nucleotides) and allows this to transfer during protein synthesis and cell division
what is the function of the cytoplasm?
made of matrix and water where metabolic reactions occur
what is the function of the plasma membrane?
lipid bilayer with embedded proteins to enclose cytoplasm, control movement of substances in and out of cells and supporting cell recognition and communication
prokaryotic cells
bacterial cells (Gram positive eubacteria such as Bacillus or Staphylococcus)
what are the components of prokaryotic cells?
cell wall, plasma membrane, cytoplasm, naked DNA, 70S ribosome