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

  A way to understand how much bigger or smaller one object is compared to another
• Prefixes to show multiples of units

  • 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
• Cell specialisation

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

  • Sperm cells
  • Nerve cells
  • Muscle cells
• Specialised plant cells

  • Root hair cells
  • Xylem cells
  • Phloem cells
• Cell differentiation

  The process where stem cells switch on/off genes to produce different proteins and acquire new sub-cellular structures
• In animals, most cells differentiate early and lose ability to differentiate, but some like red blood cells are replaced by adult stem cells
• 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, two types (scanning and transmission), 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


  A way to represent very large or small numbers by multiplying by a power of 10, with the 'number' between 1 and 10
• Culture medium


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

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


  • Microorganisms are very small, so scientists need to grow many of them in the lab using nutrients
• Components of culture medium

  • Carbohydrates for energy
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in the lab

  1. In nutrient broth solution

  2. On an agar gel plate
• Steps for making an agar gel plate
• Autoclave


  An oven used to sterilise Petri dishes and culture media before use
• If Petri dishes and culture media are not sterilised

  They are likely to be contaminated with other microorganisms
• Inoculating loops are sterilised by passing through a flame

  This kills unwanted microorganisms
• The lid of the Petri dish is sealed but not completely

  This stops airborne microorganisms from contaminating the culture, but allows oxygen to enter
• The Petri dish is stored upside down

  This prevents condensation from the lid landing on the agar surface and disrupting growth
• The culture is incubated at 25 degrees

  This prevents bacteria that could be harmful to humans from growing, as their optimum temperature is nearer 37 degrees
• Bacteria can multiply by binary fission as fast as every 20 minutes
• Formula to calculate number of bacteria

  Bacteria at beginning x 2^(number of divisions) = bacteria at end
• The number of bacteria at the end of the growth period can be very large, so it is common to leave it in standard form
• Testing the effects of antibiotics on bacteria

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

  2. Leave the plate at 25 degrees for 2 days

  3. Measure the zone of inhibition around each disc
• The bigger the zone of inhibition, the more bacteria are killed and the more effective the antibiotic is
• To calculate cross-sectional areas (of colonies or inhibition zones), the formula is πr^2 where r is the radius
• Chromosome

  Contains coils of DNA, with each chromosome carrying many genes