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 specialised cells
• In animals, most cells differentiate early and lose ability to differentiate, but some stem cells retain this ability
• 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 view deep inside sub-cellular structures, max magnification x2,000,000, resolving power 10nm (SEM) and 0.2nm (TEM)
• Magnification calculation


  Magnification of eyepiece lens x magnification of objective lens
• Size calculation


  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
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• Growing microorganisms on agar plates

  1. Pour sterile agar into petri dish

  2. Allow to set

  3. Spread bacteria suspension on surface

  4. Incubate at optimum temperature
• 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 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. Tape lid on and incubate
• Reasons for sterilisation steps

  • Prevents contamination with other microorganisms
  • Prevents competition for nutrients and space
  • Prevents introduction of harmful microorganisms
• Reasons for other culturing steps

  • Inoculating loops sterilised to kill unwanted microorganisms
  • Petri dish lid sealed but not completely to allow oxygen
  • Petri dish stored upside down to prevent condensation
  • Incubated at 25°C to prevent growth of harmful bacteria
• Binary fission


  One bacterial cell splitting into two
• Calculating bacterial population growth

  1. Bacteria at beginning x 2^(number of divisions) = bacteria at end

  2. Number of divisions = time left / mean division time
• Inhibition zone


  Clear area around antibiotic disc where bacteria have died
• Testing antibiotic effectiveness


  1. Soak paper discs in different antibiotics

  2. Place discs on agar plate with bacteria

  3. Leave plate to incubate

  4. Measure size of inhibition zones
• Bigger inhibition zone indicates more effective antibiotic
• Chromosomes


  Contain coils of DNA and carry genes
• Humans have 23 pairs of chromosomes (46 total) in body cells, and 23 chromosomes in sex cells
• Cell cycle and mitosis

  1. Interphase: cell grows, organelles increase, DNA replicates

  2. Mitosis: chromosomes line up and are pulled to opposite sides

  3. Cytokinesis: cytoplasm and cell membrane divide to form two daughter cells
• Functions of mitosis


  • Growth and development
  • Replacing damaged cells
  • Asexual reproduction
• Stem cells


  Undifferentiated cells that can divide to produce more similar cells, some of which can differentiate
• Types of stem cells

  • Embryonic
  • Adult (e.g. in bone marrow)
  • Meristems in plants