Required Practicals

• Tips for answering practical questions


  • Identify the independent variable (the thing you change)
  • Identify the dependent variable (the thing you measure that changes as a result)
  • Identify the control variables (things you keep the same)
  • Specify the equipment used for each measurement
  • Discuss safety precautions like using goggles, gloves, etc.
  • Discuss the accuracy of measurements and how to reduce errors/uncertainties
  • Discuss taking multiple/repeat measurements to calculate a mean
• Microscopy


  1. Use a scalpel and tweezers to take a thin layer of onion skin

  2. Place it on a microscope slide and add a drop of iodine to stain the cells

  3. Place a cover slip on top

  4. Place the slide on the microscope stage

  5. Start with the shortest objective lens and use the coarse and fine focus knobs to bring the specimen into focus

  6. Change to a higher magnification objective lens and refocus if needed

  7. You could also use a graticule (tiny ruler) to measure cell size in micrometers
• Osmosis


  1. Cut equal-sized cylinders from the same vegetable using a cork borer

  2. Dab off excess water and weigh the cylinders

  3. Place the cylinders in test tubes filled with different concentrations of sugar solution

  4. After a set time, remove the cylinders, dab off excess water, and reweigh

  5. Calculate the percentage difference in mass for each cylinder

  6. Plot the percentage change in mass against solution concentration to find the concentration with no osmosis (same as the cell's internal concentration)
• Enzymes


  1. Measure out a set volume of amylase enzyme and starch solution

  2. Mix them together and start a timer

  3. Every 10 seconds, remove a sample and test it with iodine (will turn black if starch is still present)

  4. Record the time when the iodine no longer changes colour (endpoint)

  5. Repeat this process at different temperatures or pH levels

  6. Plot the time taken to reach the endpoint against temperature or pH to find the optimum conditions
• Food tests


  1. For solid foods, grind with water to make a solution

  2. Test for starch by adding iodine (turns black/purple)

  3. Test for glucose/simple sugars by adding Benedict's solution and heating (colour change indicates amount of sugar)

  4. Test for proteins by adding biuret reagent (turns purple)

  5. Test for lipids by adding ethanol then water (cloudy solution indicates lipids)
• Photosynthesis


  1. Use pondweed submerged in water in an inverted test tube or measuring cylinder

  2. Cut the stem at an angle and add sodium hydrogen carbonate to promote oxygen release

  3. Measure the distance between the light source and pondweed

  4. Count the bubbles of oxygen released or measure the volume in a set time

  5. Repeat at different distances and plot the rate of photosynthesis against distance
• Reaction times


  1. Hold a ruler between your lab partner's finger and thumb with the zero mark in line

  2. Drop the ruler without warning and have your partner catch it as quickly as possible

  3. Calculate the reaction time using the distance fallen and acceleration due to gravity

  4. Repeat multiple times and calculate the mean reaction time

  5. Can also test how reaction time changes with an independent variable like distractions or stimulants
• Quadrats


  1. Use a random number generator to choose grid positions to place the quadrat

  2. Count the number of the chosen organism inside each quadrat

  3. Calculate the mean number per square metre

  4. Multiply the mean by the total area to estimate the total population

  5. Can also use a transect line to see how population density varies with distance
• Microbiology


  1. Spot different bacterial cultures on agar and observe growth over time

  2. Or spread a culture over the agar to make a lawn and add antibiotic discs

  3. Use aseptic technique - sterilize equipment, work near a Bunsen flame, etc.

  4. Incubate for days then measure colony diameters or areas with no growth around antibiotics
• Germination


  1. Place seeds on damp cotton wool in a Petri dish in the dark

  2. Observe the roots growing downwards due to geotropism

  3. Allow a small amount of light and observe the shoot growing towards it due to phototropism
• Decay


  1. Measure out a volume of milk/cream and add sodium carbonate and phenolphthalein indicator

  2. Add the enzyme lipase and use a water bath to maintain a set temperature

  3. Time how long it takes for the solution to decolorize as the milk decays

  4. Plot the time taken to decolorize against temperature to find the optimum