cell biology

• Eukaryotes


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


  Cells that lack a nucleus and membrane-bound organelles
• 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
• 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
• Additional structures in plant cells

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

  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• 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 impulses
  • Many dendrites for branched connections
  • Mitochondria to supply energy for neurotransmitter production
• Muscle cells


  • Proteins (myosin and actin) that slide over each other to cause contraction
  • Many mitochondria to provide energy
  • Can store glycogen for respiration
• Root hair cells


  • Large surface area for water and mineral ion uptake
  • Large vacuole affects water movement speed
  • Mitochondria provide energy for active transport of mineral ions
• Xylem cells


  • Hollow tubes with lignin deposits to withstand water pressure
  • Lignin deposited in spirals for structural support
• Phloem cells


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


  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 cell types retain ability to differentiate throughout life
• Light microscope


  Has two lenses (objective and eyepiece), illuminated from underneath, max magnification x2000, resolving power 200nm
• Electron microscope


  Uses electrons instead of light, can be scanning (3D) or transmission (2D), max magnification 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


  Expressing very large or small numbers by multiplying by a power of 10, with the 'number' between 1 and 10
• Components of culture medium

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

  Make suspension of bacteria, mix with sterile nutrient broth, stopper with cotton wool, shake regularly
• Standard form


  Useful when working with very large or small numbers
• Using standard form


  1. Multiply a certain number by a power of 10 to make it bigger or smaller

  2. The 'number' being multiplied needs to be 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 for energy
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in nutrient broth

  1. Make a 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. Leave to cool and set

  3. Use inoculating loops to spread bacteria over agar

  4. Tape lid on and incubate for a few days
• Petri dishes and culture media must be sterilised before use
• Reason for sterilisation


  To prevent contamination from other microorganisms that could compete for nutrients and space, or be harmful
• Inoculating loops must be sterilised by passing through a flame
• Reason for sealing Petri dish lid

  To stop airborne microorganisms from contaminating the culture, but not completely sealed to allow oxygen entry
• Reason for storing Petri dish upside down

  To prevent condensation from the lid landing on the agar surface and disrupting growth
• Reason for incubating at 25 degrees


  To prevent growth of bacteria harmful to humans, whose optimum temperature is nearer 37 degrees
• Testing antibiotic effectiveness


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

  2. Leave control disc soaked in sterile water

  3. Measure size of inhibition zone around discs after 2 days
• Inhibition zone


  The clear area left when bacteria die, indicating antibiotic effectiveness