3A

• actual size = image size/magnification
• total magnification = magnification of objective lens x magnification of eyepiece lens
• stains:

  • haematoxylin - nucleus
  • methylene blue - nucleus (animal)
  • acetocarmine - chromosomes
  • iodine - starch containing material
• light microscope


  tool that uses a beam of light and optical lenses to magnify specimen up to 1500 times actual size
• magnification


  measure of how much bigger the image is than the real object
• electron microscope


  tool that uses a beam of electrons and magnetic lenses to magnify specimen up to 500 000 times actual size
• resolution


  measure of how close together 2 objects must be before they are seen as 1
• artefacts


  things observed in a scientific investigation that are not actually present, which occur as a result of the preparation or investigation
• graticule


  series of lines in the eyepiece of a microscope which help to measure specimen accurately
• transmission electron microscope (TEM)


  micrographs that give 2D images, but more magnified than a light microscope
• scanning electron microscope (SEM)


  micrographs that give 3D images, but have a lower magnification than TEMs
• cytoplasm 


  jelly-like liquid that makes up the bulk of the cell and contains organelles
• nucleus


  organelle containing DNA and RNA, as well as proteins, surrounded by a double membrane with pores
• protoplasm


  cytoplasm and nucleus combined
• ultrastructure


  detailed organisation of the cell, which is only visible with an electron microscope
• membrane function:

  • control movement of substances
  • localise enzymes in reaction pathways
  • keep biological molecules separate
• nucleolus


  extra-dense region of almost pure DNA and protein found in the nucleus, which is involved in the synthesis of ribosomes and control of growth and division
• chromatin


  granular combination of DNA bonded to protein found in the nucleus when the cell is not dividing
• mitochondria


  rod-like structure that are the site of aerobic respiration
• mitochondria:

  • outer and inner membrane
  • contains its own genetic material (mitochondrial DNA)
  • folded to form cristae, which give a larger surface area for sites of attachments for enzymes to carry out respiration
  • filled with fluid, called matrix
• centrioles


  bundles of tubules found near the nucleus, which are involved in cell division by the production of spindle fibres that move chromosomes during cell division
• spindle fibres


  sets of overlapping protein microtubules that run the length of the cell, that are used during cell division
• ribosome


  site of protein synthesis
• 80S ribosome:

  • site of protein synthesis
  • main type in eukaryotic cells
  • 1 RNA : 1 protein
  • 60S and 40S subunit
• 70S ribosome:

  • site of protein synthesis
  • found in mitochondria and chloroplast
  • main type in prokaryotic cells
  • 2 RNA : 1 protein
  • 50S and 30S subunit
• endosymbiotic theory


  theory that suggests that mitochondria and chloroplasts originates as independent prokaryotic organisms that began living symbiotically inside other cells as endosymbionts
• lysosome


  organelle full of digestive enzymes used to break down cells and organelles, or to digest food in simple organisms
• lysosome functions:

  • break down food into chemicals in unicellular organsisms
  • destroy organelles
  • release extracellular enzymes
  • self-destruction to kill the cell, if the cell has a mutation, disease, or stress
• apoptosis


  breakdown of worn-out, damaged, or diseased cells by the lysosomes
• endoplasmic reticulum


  a 3D network of membrane bound cavities in the cytoplasm that links to the nuclear membrane, and makes up a large part of the cellular transport system, and plays a role in the synthesis of chemical substances
• rough endoplasmic reticulum (RER)

  endoplasmic reticulum covered in 80S ribosomes which is involved in the production and transport of proteins
• smooth endoplasmic reticulum


  smooth tubular endoplasmic reticulum which is involved in the synthesis and transport of steroids and lipids
• exocytosis


  movement of large molecules out of cells by the fusing of chemical containing vesicles to the cell membrane
• Golgi apparatus


  stacks of membranes that modify proteins made elsewhere in the cell, and package them into vesicles for transport
• peptidoglycan


  large, net-like molecule found in all bacterial cell walls, made up of many parallel polysaccharide chains with short peptide cross-linkages
• capsule (slime layer)


  layer formed from starch, glycolipid, gelatin or protein found around the outside of some bacteria to protect from phagocytosis and dry conditions
• The bacteria cell wall shapes the bacterium, and prevents the cell from bursting due to contents being hypertonic
• pili


  thread like projections found on the surface of some bacteria, used to attach to host cells and for sexual reproduction
• flagella


  many-stranded helices of flagellin protein found on some bacteria, used for movement by rapid rotations
• mesosomes


  infoldings of the cell membrane of bacteria