Required practicals

• Osmosis required practical - Effect of sugar solution on plant tissues

  1)Cut up potato into identical cylinders using a cork borer

  2)Get beakers with different sugar solutions - one with a very concentrated solution, and pure water to present to concentration gradient

  3)Measure the mass of potato cylinders then one cylinder in each beaker and leave for 24 hours

  4)Take them out, pat dry with paper towel and measure masses again

  5) If mass increases, osmosis has taken place, if mass decreases osmosis hasn't taken place
• Variables in osmosis pratical?

  Dependent - Potato mass

  Independent - Conc of sugar solution

  Control Variable - Time, volume of solution
• Error of osmosis practical?

  If potato cylinders weren't fully dry once out - excess water would give a higher mass

  If water evaporated from beakers changing concentrations of sugar solutions
• Investigating pH level on enzyme activity

  1)Drop of iodine in each well of spotting tile

  2)Place tripod and gauze over bunsen, put baker of water onto of bunsen and heat until 35℃ - use thermometer

  3)Add 1cm^3 of amylase and 1cm^3 of buffer solution of pH5 to boiling tube and put into beaker of water

  4)Add 5cm^3 of starch solution to boiling tube then mix and start clock

  5)
• Oxygen production on the rate of photosynthesis

  1)Source of white light placed at specific distance from pondweed

  2)Pondweed is left to photosynthesise, oxygen will be released into capillary tube

  3)At the end, syringe is used to draw gas bubble and the length is measured which is directly proportional to the volume of O2 produced
• Variables in the pondweed experiment

  Independent - N/A

  Dependant - the length of oxygen bubble

  Control - temperature and time pondweed is left
• Light intensity = 1 / (distance)^2
• Benedicts solution tests for the presence of sugars and if present, the solution will change from blue to green or yellow or brick-red
• Iodine tests for the presense of starch and changes to a blue-black colour when it reacts with starch
• Biuret solution tests for the presence of protein and changes from blue to purple when present
• Water baths are used to heat and accelerate the reactions
• You use a water bath when you add Benedict's solution to observe a colour change
• Ph Experiment

  1. Add amylase and a starch solution to separate test tubes
  2. Prepare a series of buffer solutions with different pH values in different test tubes using a pipette ensuring the solutions are fully mixed
  3. Mix the amylase and starch and add a buffer solution
  4. Prepare a spotting tile with iodine in each tile and every 30 seconds take a drop of the mixture onto each tile
  5. Record the time it takes for the iodine to stop turning blue-black
• Perform the pH test at a constant temperature such as at 37℃ for optimum enzyme activity
• Photosynthesis practical

  1. Place pondweed in a beaker of water with sodium bicarbonate
  2. Set up a light source a measured distance away from the beaker
  3. Count the number of oxygen bubbles released in a set time
  4. Repeat at different distances from the pondweed
  5. Record the number of bubbles produced at each distance to determine the effect if light intensity
• You can use a thermometer to check the water temperature as this can affect the rate of photosynthesis
• Accuracy for the pondweed experiment

  Allow the pondweed to equilibrate in the light for a few minutes before taking measurements, use a measuring cylinder to collect the oxygen gas produced and repeat the process and discard anomalies
• Mention discrete data vs continuous data
• Preparing food samples

  • Grind up food → put into a beaker → add distilled water and mix with a glass rod until some dissolves → filter out the solution using filter paper and a funnel to get rid of larger food pieces
• Benedicts Test

  • Add drops of the reagent to food sample
  • Heat in a water bath of 75°C for 5 minutes
  • Observe a colour change of green or orange or brick red
• When using a water bath, use a test tube holder and point the tube away to be safe
• Sudan III test

  • Get the food sample - not filtered
  • Add 3 drops of the Sudan III stain
  • Gently shake
  • If lipids if present, it will separate from the water as it isn’t soluble and there will be a red layer of stained lipids
• pH on enzyme activity

  • Add drops of iodine to spotting tile
  • 3 test tubes - starch and amylase and a buffer solution
  • Test tubes in a water bath for 30 mins at 30 degrees to allow them to all reach the right temp
  • Combine the 3 solutions and mix
  • Add back into the water bath
  • Transfer drops of solution into each well every 30 seconds