cell biology

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes

  Cells that lack a nucleus and membrane-bound organelles typically bacteria cell
• Components of animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Organelles


  Structures in a cell that have different functions
• Orders of magnitude


  Used to understand how much bigger or smaller one object is from another
• Prefixes


  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Structures only in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells

  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• Cell specialisation


  The process where cells gain new sub-cellular structures to be suited to their role
• Sperm cells


  • Streamlined head and long tail to aid swimming
  • Many mitochondria to supply energy
  • Acrosome with digestive enzymes to break down egg cell membrane
• Nerve cells


  • Long axon to transmit signals
  • Many dendrites to form branched connections
  • Many mitochondria to supply energy for neurotransmitter production
• Muscle cells


  • Special proteins (myosin and actin) to cause contraction
  • Many mitochondria to provide energy
  • Can store glycogen for respiration
• Root hair cells


  • Large surface area for water and mineral uptake
  • Large vacuole to affect water movement
  • Mitochondria to provide energy for active transport
• Xylem cells


  • Lignin deposition to form hollow tubes for water transport
  • Lignin spirals to withstand water pressure
• Phloem cells


  • Sieve plates to allow movement of substances
  • Rely on mitochondria in companion cells for energy
• Cell differentiation


  The process where stem cells switch on/off genes to become specialised cells
• In animals, most cells differentiate early and lose ability to differentiate further
• In plants, many cells retain ability to differentiate throughout life
• Light microscope


  • Has two lenses (objective and eyepiece) to magnify and direct image to eye
  • Illuminated from underneath
  • Maximum magnification x2000, resolving power 200nm
• Electron microscope


  • Uses electrons instead of light to form image
  • Scanning electron microscope creates 3D images, transmission electron microscope creates 2D images
  • Magnification up to x2,000,000, resolving power 10nm (SEM) and 0.2nm (TEM)
• Calculating magnification of light microscope

  Magnification of eyepiece lens x magnification of objective lens
• Calculating size of object

  Size of image / magnification = size of object
• Standard form


  Multiplying a number by a power of 10 to represent very large or small numbers
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• Growing microorganisms in nutrient broth

  Make suspension of bacteria and mix with sterile nutrient broth, stopper with cotton wool, shake regularly
• Growing microorganisms on agar plates

  Spread bacteria suspension on agar plate, seal and incubate
• Standard form


  Multiplying a certain number by a power of 10 to make it bigger or smaller, with the 'number' being between 1 and 10
• Standard form examples


  • 1.5 x 10^-5 = 0.000015
  • 3.4 x 10^3 = 3400
• Culturing microorganisms


  Growing many microorganisms in the lab using nutrients
• Components of culture medium

  • Carbohydrates
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in nutrient broth

  1. Make suspension of bacteria

  2. Mix with sterile nutrient broth

  3. Stopper flask with cotton wool

  4. Shake regularly to provide oxygen
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar jelly into sterilised Petri dish

  2. Allow to cool and set

  3. Inoculate with microorganism using sterilised loop

  4. Seal plate and incubate
• Reasons for sterilisation


  • Prevents contamination with other microorganisms
  • Prevents competition for nutrients and space
  • Prevents introduction of harmful microorganisms
• Reasons for sealing plate

  • Stops airborne microorganisms from contaminating
  • Allows oxygen to enter but prevents anaerobic bacteria
• Reasons for incubating at 25°C


  • Prevents growth of bacteria harmful to humans
• Bacteria can multiply by binary fission every 20 minutes
• Formula to calculate bacterial population growth

  Bacteria at beginning x 2^(number of divisions) = bacteria at end
• Testing antibiotic effectiveness


  1. Soak paper discs in antibiotics and place on agar plate with bacteria

  2. Leave plate to incubate

  3. Measure size of inhibition zone around discs