Cell Biology

• Eukaryotes


  Cells that have 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 found in animal and plant cells

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

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


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


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


  • Sperm cells
  • Nerve cells
  • Muscle cells
• Specialized plant cells


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


  The process where stem cells switch on/off genes to produce specialized cells
• In animals, most cells differentiate early and lose ability to differentiate, but some retain ability as adult stem cells
• In plants, many cell types retain ability to differentiate throughout life
• Light microscope


  Has two lenses (objective and eyepiece), magnification up to x2000, resolving power of 200nm
• Electron microscope


  Uses electrons instead of light, magnification up to x2,000,000, resolving power of 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
• Culture medium


  Nutrients (carbohydrates, minerals, proteins, vitamins) used to grow microorganisms in the lab
• 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
• 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
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar jelly into sterilised Petri dish

  2. Allow to cool and set

  3. Spread bacteria using inoculating loop

  4. Tape lid on and incubate
• Reasons for steps in culturing microorganisms

  • Sterilise Petri dishes and culture media to prevent contamination
  • Sterilise inoculating loops to kill unwanted microorganisms
  • Seal Petri dish lid but not completely to allow oxygen
  • Store Petri dish upside down to prevent condensation
  • Incubate at 25°C to prevent growth of harmful bacteria
• 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
• Testing effectiveness of antibiotics


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

  2. Leave plate for 2 days at 25°C

  3. Measure size of inhibition zone around each disc
• Inhibition zone


  Clear area around antibiotic disc where bacteria have died
• To calculate cross-sectional areas, use the formula πr^2 where r is the radius
• Chromosomes


  Contain coils of DNA and carry genes
• There are 23 pairs of chromosomes in each body cell, and 23 chromosomes in each sex cell
• Cell cycle and mitosis

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

  2. Mitosis: chromosomes line up at equator, cell fibres pull them apart

  3. Cytokinesis: cytoplasm and cell membrane divide to form two daughter cells
• Importance 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 stem cells
  • Adult stem cells
  • Meristems in plants
• Therapeutic cloning


  Producing an embryo with the same genes as the patient, to obtain stem cells that won't be rejected