Required Practicals

• Culturing Microorganisms


  1. Sterilise petri dishes, agar gel plates and bacterial nutrient broth

  2. Sterilise inoculating loop by passing through bunsen burner flame

  3. Spread bacteria evenly over gel using inoculating loop

  4. Cover gel by putting lid on dish and sticking down with adhesive tape

  5. Place petri dish upside down in incubator

  6. Incubate at 25 degrees celsius
• Osmosis


  The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Investigating the effect of antibiotics on bacteria


  1. Sterilise bench using disinfectant solution

  2. Sterilise inoculating loop by passing through bunsen burner flame

  3. Open sterile agar gel plate near bunsen burner flame

  4. Spread chosen bacteria evenly on agar gel using inoculating loop

  5. Place sterile filter paper discs containing antibiotic on agar gel

  6. Incubate at 25 degrees celsius

  7. Measure area of zone of inhibition using formula: area= pi x r^2
• Parts of the microscope


  • Eyepiece lens
  • Stage
  • Lamp/mirror
  • Objective lenses (3)
  • Coarse focussing dial
  • Fine focussing dial
• Effect of osmosis on plant tissue


  1. When a plant cell is placed into a dilute solution, water moves into the cell and the cell expands

  2. When a plant cell is placed into a concentrated solution, water moves out of the cell and the cell shrinks
• Amylase


  A carbohydrate enzyme that breaks down starch molecules into simple sugars
• Eyepiece lens


  See through it, has a magnification of 10x
• Photosynthesis experiment


  1. Place boiling tube 10 cm from LED light

  2. Use beaker of water if using normal light bulb

  3. Pour sodium hydrogen carbonate solution into boiling tube

  4. Place pondweed cutting into solution

  5. Leave for 5 minutes to acclimatise

  6. Observe bubbles forming and escaping from pondweed

  7. Start stopwatch and count bubbles produced in 1 minute

  8. Repeat experiment from 20 cm, 30 cm, 40 cm
• Experiment procedure


  1. Place a drop of iodine solution into every well on a spotting tile

  2. Take three test tubes

  3. The 1st test tube should contain 2 cm3 starch solution

  4. The 2nd test tube should contain 2 cm3 of amylase solution

  5. The 3rd test tube should contain 2 cm3 of a pH 5 buffer solution

  6. Place all three test tubes into a water bath that is 30 degrees celsius and leave them for 10 minutes so that the solutions all reach the correct temperature

  7. Then pour all three solutions into the same test tube and stir with a stirring rod

  8. Immediately place the test tube back into the water bath and start a stopwatch

  9. After 30 seconds place a drop of the solution into a well on the spotting tile that contains iodine solution

  10. Every 30 seconds, place another drop of the solution into the iodine solution until the iodine no longer turns blue-black
• Zone of inhibition


  Area around antibiotic discs where bacteria have not grown
• Practical (using potatoes)


  1. Peel the potatoes

  2. Use a cork borer to create three potato cylinders

  3. Use a scalpel to cut the three cylinders to the same length (approx. 3 cm)

  4. Measure the mass and length of each cylinder

  5. Place each of the cylinders into a test tube

  6. The first tube should contain 10 cm3 of 0.5 molar sugar solution

  7. The second tube should contain 10 cm3 of 0.25 molar sugar solution

  8. The third test tube should contain 10 cm3 of distilled water

  9. Leave the test tubes overnight

  10. Take the cylinders out of the test tubes and gently roll them on a paper towel

  11. Measure the length and mass of the cylinders again and calculate the percentage change in mass
• Food Tests


  1. Take the food sample and add some distilled water to it, then grind with a mortar and pestle to create a paste

  2. Transfer the paste to a beaker and add more distilled water and stir so that the chemicals in the food dissolve into the water

  3. Filter the solution through filter paper to get rid of suspended food particles

  4. The solution is now ready to be used for food tests
• Objective lenses


  • 4x
  • 10x
  • 40x
• Measuring oxygen production


  1. Place pondweed under funnel in boiling tube

  2. Collect oxygen bubbles in measuring cylinder filled with water

  3. Measure volume of oxygen bubbles produced
• The iodine solution should turn blue-black, showing that starch is present
• The iodine no longer turns blue-black, showing that there is no more starch present and the reaction has been completed
• Stage


  Where the slide goes
• In concentrated sugar solution

  Water moves out of the cells by osmosis and the cylinder loses mass
• Carbohydrates


  • Starch
  • Sugars
• Doubling the distance


  Number of bubbles produced falls by a factor of 4
• Repeat the experiment


  Using different pH buffers e.g pH 6, pH 7 and pH 8
• In distilled water


  Water moves into the cell by osmosis and the cylinder gains mass
• Testing for starch


  1. Add 2 cm3 of the food solution into a test tube

  2. Add a few drops of orange iodine solution

  3. The iodine solution should turn blue-black if starch is present, it will remain orange if not
• Lamp/mirror


  Below stage to shine through slide
• Percentage change in mass


  change in mass / original mass x 100
• Coarse focussing dial


  Moves the stage up and down
• Testing for sugars


  1. Place 2 cm3 of the food solution into a test tube

  2. Add 10 drops of Benedict's solution (blue) into the test tube

  3. Half-fill a beaker with boiling water and place the test tube into the water

  4. After leaving it for a few minutes, the Benedict's solution should change colour based on how much sugar is present
• Fine focussing dial


  Brings the image into clear focus
• Benedict's test


  Will only work for reducing sugars e.g glucose, it will not work for non-reducing sugars e.g sucrose
• Using the microscope


  1. Place the slide onto the stage and use the slips to keep it in place

  2. Turn it to the lowest objective lens

  3. Looking at the stage from the side, turn the coarse focussing dial until the objective lens is almost touching the slide

  4. Then look through eyepiece and turn the coarse focussing dial so that the stage gets further away from the objective lens

  5. Then use fine focussing dial to bring the image into clear view
• Testing for proteins


  1. Add 2 cm3 of biuret solution (blue) to 2 cm3 of the food solution

  2. The biuret solution should turn purple or lilac if proteins are present
• Testing for lipids


  1. When preparing the food solution for the lipid test, do not filter the solution as lipid molecules stick to filter paper

  2. Add 2 cm3 of food solution into a test tube

  3. Add a few drops of distilled water and a few drops of ethanol into the solution and shake

  4. A cloudy white emulsion should form if lipids are present
• Total magnification

  Magnification of objective lens x magnification of eyepiece
• Only a limited view is given through an optical microscope
• Visible in animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
• Visible in plant cells

  • Nucleus
  • Cytoplasm
  • Cell wall
  • Vacuole
  • Chloroplasts
• There must be a magnification scale- measure the diameter of the field of vision in mm and show it on a scale bar, then write down the magnification