required practicals

• Optical microscope

  A microscope that uses lenses and light to magnify small objects
• Using an optical microscope to view a prepared microscope slide

  1. Place slide on stage

  2. Select lowest power objective lens

  3. Position objective lens close to slide

  4. Look through eyepiece

  5. Adjust course focusing dial to bring cells into focus

  6. Adjust fine focusing dial for clear focus

  7. Calculate total magnification
• Optical microscope parts

  • Stage
  • Lamp or mirror below stage
  • Objective lenses
  • Eyepiece
  • Course focusing dial
  • Fine focusing dial
• Total magnification

  Magnification of eyepiece lens x magnification of objective lens
• Optical microscopes have limited detail compared to electron microscopes
• A magnification scale should be included on drawings made from an optical microscope</b>
• Preparing uncontaminated bacterial culture using aseptic technique

  1. Sterilize petri dishes, bacterial nutrient broth, and agar to kill unwanted microorganisms

  2. Transfer bacteria using a sterilized inoculating loop

  3. Seal plate with adhesive tape to prevent contamination

  4. Incubate plate upside down at 25°C to prevent moisture disrupting colonies
• Investigating effect of antibiotics on bacterial growth

  1. Clean bench with disinfectant

  2. Sterilize inoculating loop

  3. Spread chosen bacteria evenly on sterile agar plate near Bunsen burner flame

  4. Place sterile filter paper discs containing antibiotics on plate

  5. Incubate plate at 25°C

  6. Measure zone of inhibition around antibiotic discs to calculate area using formula: Area = π x r^2
• Bacteria can double in number every 20 minutes with enough nutrients and suitable temperature
• Nutrient broth

  Solution containing all the nutrients bacteria need to grow and divide
• Agar gel plate

  Nutrient broth gelled using a chemical called agar, allows bacteria to grow into visible colonies
• Contamination by other microorganisms must be avoided when culturing bacteria
• Incubating bacteria at 25°C reduces chances of harmful bacteria growing
• The zone of inhibition around antibiotic discs indicates the effect of the antibiotic on bacterial growth
• Osmosis

  Diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Plant cells placed in water


  Water moves into the cell by osmosis, causing the cell to expand
• Plant cells placed in concentrated solution


  Water moves out of the plant cell by osmosis, causing the cell to shrink
• Investigating the effect of osmosis on plant tissue

  1. Peel potato

  2. Use cork board to produce cylinders of equal diameter

  3. Trim cylinders to equal length

  4. Measure length and mass of cylinders

  5. Place cylinders in test tubes with different solutions (0.5M sugar, 2.5M sugar, distilled water)

  6. Leave overnight

  7. Remove cylinders, gently roll on paper towel to remove surface moisture

  8. Measure length and mass of cylinders again
• Percentage change

  Calculated as: (Change in value / Original value) x 100
• Concentration of sugar solution

  Affects percentage change in mass/length of potato cylinder