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 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, with the 'number' between 1 and 10
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• 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 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


  • 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 in making an agar gel plate
• Reasons for sterilisation


  To prevent contamination from other microorganisms that could compete for nutrients and space, or be harmful
• Reasons for other steps in culturing microorganisms
• Binary fission


  One bacterium splitting into two, which can happen as fast as every 20 minutes
• Formula to calculate number of bacteria

  Bacteria at beginning x 2^(number of divisions) = bacteria at end
• Antibiotics can be tested on bacteria to see their effectiveness
• Steps in testing antibiotic effectiveness

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

  2. Leave plate to incubate

  3. Measure size of inhibition zone around discs
• Inhibition zone


  The clear area around antibiotic discs where bacteria have died
• Formula to calculate cross-sectional area is πr^2
• Chromosomes


  Contain coils of DNA, with each chromosome carrying many 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