biology f211measuring cells

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  • Created by: Cheryl
  • Created on: 08-04-11 09:27

cell size & maginification

magnification - does NOT increase the level of detail seen

resolution - the ability to see two distinct points seperately

  • light microscope use # lenses to produce a clear image
  • light passes from a bulb under the stage, through condenser, through specimen
  • light is the focused through object lenese and then eye peice
  • # of objective lense that can be rotated to see different magnifications(4 - X4 X10 X40) (X100 - OIL IMMERSION LENSE)
  • advantages
  • most light micro. can x1500
  • wide range of specimen can be viewed - (living)
  • used widely in education, labs, research
  • weaknesses
  • not high resolution so cant give detail about internal cell structure
  • max resolution power is 200nm objects closer than 200nm look like 1 object
  • preparing for light microscope
  • staining - allows them to be seen, dark red DNA indentify it :)
  • sectioning - embedded in wax then cut without distorting the structure of them, useful for making sections of soft tissue - brain
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                         (MAGNIFICATION) = 1200

50MM/1200 = 0.0414MM =41.6 UM


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  • use of electrons:
  • beam of electrons 100,000 x shorter than light wavelength
  • tell objects 0.2nm apart
  • use magnets to focus beam
  • projects image onto a screen and 'greyscale'  image is seen (electron micrographs)
  • resolution 500,000x greater than human eye :O


  • beam passes through thin sample, passing through denser parts easier
  • final image 2 dimensional (mag. possible 500,000x)
  • beam directed onto sample, not through it and bounced off
  • final image is 3D view of surface of sample mag.possible (x100,000)
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  • 2000x more resolution than light microscope
  • so detailed images can be seen
  • the SEM produces 3D images revealing contourus, tissues or cellular arrangement (cant do that in a light microscope)
  • weaknesses
  • electron beams are deflected by particles of air so samples have to be in a vacuum
  • very expensive
  • preparing samples and using electron microscopes require high skill & training
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cells & living processes

  • actin filaments -move against eachother cam move organelles around inside the cell
  • microtubles - cylinders 25nm in diametre made of protein called tublin, move microorgans movements through liqiud or waft liquid past a cell (use ATP)
  • eukaryotes/flagella/cilia - hair like extensions from surface of cells, contain nine microtubules in a circle, 2 microtubules in a central bundle
  • ATP through microtubules allows these cells to create movement so cilia can waft and undulipodium forms tail of sperm
  • vesicles & vaculous
  • vesicles - memebrane bound sacs in a cell carry substances
  • plants -vacuole maintains cell stability filled with water/solutes =turgid pushes against cytoplasm
  • plant cells wall made of cellulose carbohydate polymer =glucose subunits
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organelles - structure & function

  • THE NUCLEUS - structure: surrounded by a nulear envelope, 2 membranes with fluid between them contains a nucleolus. function: houses cells gentic information. chromatin consitis of DNA/proteins - can make proteins. the nucleolus makes RNA/robosomes pass into cytoplasm proteins assemble there.
  • ENDOPLASMIC RETICULUM - structure:flatterned membrane bound sacs called cisternae, ROUGH er - studded with ribosomes. SMOOTH - no ribosomes. function:transports proteins, somes can be secreted/place on cell surface membrane. SMOOTH - makes lipids the cell needs.
  • GOLGI APPARATUS:structure:membrane bound fatterned sacs. function: recieves proteins and modifys them adds sugar. then packs them into vesicles to be transported
  • MITOCHONDRIA:structure:spherical shaped two membranes seperated by fluid highly folded from cristae. function: ATP is produced during respiration.
  • CHLOROPLASTS:structure:two membranes seperated by fluid. inner - continuous network of flattened membrane sacs - thylakoids. function:make carbohydrates 
  • LYSOSOMES:structure: spherical sacs surrounded by a single membrane. function: powerful digestive enzymes that break down materials.
  • RIBOSOMES:structure:some in cytoplasm bound to ER consists of 2 sununits. function:protein synesis.mRNA from nucleus assembles proteins from amino acids.
  • CENTRIOLES:structure: tubes of protein fibres pair of them next to nucleus. functions: cell divisionform spindle move chromosomes in nuclear divsion.
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roles of membranes

  • membranes = seperate cell contents from the environement/cytoplasm
  • cell recognition and signalling
  • holding compents of some metabolic pathways
  • regulating transort materials in/out of cell
  • the plasma membranes of a growing shoot contain receptors that allow them to detect the molecules that relate to growth
  • muscle cells membranes contain a large number of channels that allow rapid uptake of glucose to provide energy for mucle contraction
  • internal membranes of chloroplasts contain chlorrophyll and other molecules needed for photosynesis
  • the plasma membranes of white blood cells contain special proteins that enable the cells to recognise foreign cells and particles
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FLUID MOSAIC = the molecular arrangements in membranes. the main features are: phospholipid molecules from basic structure, various proteins either freely floating or attached to structures. some extrinsic proteins embedded in the bilayer.

  • chlesterol gave membranes stability
  • channel proteins allow movement of some substances across membrane
  • carrier proteins actively move substances across the membrane
  • receptor sites some allow hormones to bind to the cell so cell respenses can be carried out can only respond if it has a receptor for that hormone
  • glycoproteins may be invloved in cell signalling to allow recognition by immune system can also bind cells together in tissues.
  • enzymes/coenzymes may be bound to membranes of chkoroplast/mitochondria help reactions photosynesis/respiration.
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