Topic 1 : 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


  Multiplying a number by a power of 10 to represent very large or small numbers, 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
• 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 with 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
• Formula to calculate cross-sectional area of colonies or inhibition zones is πr^2
• Chromosomes


  Contain coils of DNA, with each chromosome carrying many genes
• Number of chromosomes


  46 in body cells, 23 in gamete cells
• Stages of the cell cycle and mitosis

  1. Interphase: cell growth, organelle increase, DNA replication

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

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


  • Growth and development, replacing damaged cells, asexual reproduction