REQUIRED PRACTICALS

• MICROSCOPES

  1. peel offa thin layer of tissue using forceps and add water to slide
  2. add a drop of stain with a pipette
  3. lower coverslip at an angle without trapping air bubbles
  4. clip slide onto stage and turn on light
  5. move stage closer to lense and focus
  6. swap to higher power objective lens and refocus
• Investigate the effects of antiseptics on bacterial growth

  1. Prepare an uncontaminated culture of bacteria using aseptic technique on an agar gel plate

  ● Spread bacteria evenly over plate

  1. Place paper discs soaked in different antibiotics on agar plate
  2. Include a control disc - soaked in sterile water
  3. Incubate plate at 25 C for 48 hours
  4. Use a ruler to measure diameter of zones ofinhibition (area where bacteria are killed or growth is prevented) around each disc and calculate their areas using πr2
• Investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue.

  1. Use a scalpel / cork borer to cut up a potato (remove peel) into 6 identical size cylinders
  2. Blot dry then measure initial mass of each
  3. Place each in a different concentration of sugar solution for 24 hours
  4. Blot potato dry with paper towel then measure final mass of each
  5. Repeat and calculate a mean for each concentration
  6. On a graph, plot % change in mass (y axis) against concentration of sugar solution (xaxis)
• describe the test for sugars

  1. Grind up food and add Benedict’s reagent
  2. Boil / heat in a water bath
  3. Sugar turns solution (from blue to) brick red
• describe test for starch

  1. Grind up food and add iodine solution
  2. Starch turns solution blue-black
• describe test for lipids

  1. Grind up food and add ethanol, then add water
  2. Fat turns solution milky / cloudy white
• describe tests for proteins

  • ●  Grind up food and add Biuret reagent
  • ●  Protein turns solution (from blue to) purple / lilac
• Investigate the effect of pH on the rate of reaction of amylase enzyme.

  1. Set up test tubes with different pH solutions and a set volume of starch solution
  2. Put in a water bath at 30C, leave for 10 mins
  3. Set up spotting tiles with 1 drop of iodine solution in each well
  4. Add a set volume & concentration of amylase to one of test tubes, start stopwatch / timer
  5. Remove a drop of amylase-starch mixture every30 seconds and place into a spotting tile to testfor starch (blue-black)
  6. Record time when no starch is detected (nolonger turns blue-black)
  7. Repeat steps 4 - 6 for each pH buffer solution
• Method to investigate the effect of light intensity on rate of photosynthesis

  1. Vary light intensity

  2. Control other variables

  3. Measure photosynthesis rate
• Vary light intensity

  1. Change distance of white light source from pondweed eg. 10, 20, 30, 40 cm

  2. Leave for 5 mins for pondweed to acclimatise to new light intensity
• Control other variables

  • Pondweed - use same length of pondweed or same pondweed
  • Temperature - put tube in a (thermostatically controlled) water bath OR put beaker of water between lamp / tube to absorb heat produced by light
  • CO2 conc. - use set conc. of sodium hydrogen carbonate solution
• Measure photosynthesis rate

  1. Count number bubbles of oxygen released OR collect gas in a syringe

  2. In a set period of time eg. one minute (divide volume by time to get rate)