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
• 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
• 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 different sub-cellular structures
• In animals, most cells differentiate early and lose the ability, but some like red blood cells are replaced by adult stem cells
• In plants, many cell types retain the ability to differentiate throughout life
• Light microscope


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


  Uses electrons instead of light, can achieve magnification up to x2,000,000 and 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


  Used to represent very large or small numbers by multiplying a number between 1 and 10 by a power of 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
• To be able to compare the size of numbers while using standard form, the 'number' which being multiplied by a power of 10 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
  • 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. Leave to cool and set

  3. Dip inoculating loops in microorganism solution and spread over agar

  4. Tape lid on and incubate for a few days
• 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 degrees to prevent growth of harmful bacteria
• Inhibition zone


  The clear area left around antibiotic discs when bacteria die
• Testing effectiveness of antibiotics

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

  2. Leave plate at 25 degrees for 2 days

  3. Measure size of inhibition zone - bigger zone means more bacteria killed, so more effective antibiotic
• To calculate cross-sectional areas (of colonies or inhibition zones) use the formula πr^2, where r is the radius of the circle
• Chromosomes


  Contain coils of DNA and carry genes
• There are 23 pairs of chromosomes in each body cell, resulting in 46 chromosomes in total
• Sex cells (gametes) have half the number of chromosomes, 23 in total
• Cell cycle and mitosis

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

  2. Mitosis: chromosomes line up at equator, cell fibres pull chromosomes to each side

  3. Cytokinesis: cytoplasm and cell membranes divide to form two identical 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 will differentiate