required practicals

• Preparing a slide

  1. add a drop of water to the microscope slide
  2. place a thin layer of tissue on the slide
  3. stain the tissue with a couple drops of iodine solution
  4. place the coverslip on top
• Observing a slide

  1. place the slide on the stage and use the lowest power objective lens
  2. turn the course focus wheel to bring the image to a focus
  3. increase the power of the objective lens to increase magnification
  4. turn the fine focus wheel to bring the image into clearer focus
• 1000 um - 1 mm
• Osmosis required practical

  1. cut tubes of potato using a cork borer
  2. trim the potato cylinder so it is at a controlled length
  3. record the mass of the potato cylinder
  4. put the cylinder in a boiling tube of solution and leave for a fixed period of time
  5. remove the cylinder and blot dry
  6. record the mass of the potato cylinder
  7. measure and record the new length
  8. repeat two more times to identify outliers and calculate average
  9. repeat for different concentrations
  10. calculate percentage by mass
• What piece of apparatus is used to measure mass

  Balance
• Why should you dry the potato piece before weighing it again?

  so that excess water does not contribute to the mass
• What are some of the potential sources of error when investigating osmosis?

  • concentrations of solutions
  • drying of pieces before weighing
  • accuracy of balance
  • evaporation from tubes
• what are the control variables when determining the concentration of a potato piece?

  • time in solution
  • surface area of potato piece
  • volume of solution
  • amount of blotting dry
• Testing for proteins

  • add biuret reagent to the food sample
  • if there is no protein the sample remains blue
  • if there is protein the sample turns purple
• If the food is solid it needs to be ground up using a pestle and mortar and added to water to make a solution
• Testing for starch

  • add iodine to the food sample
  • if there is no starch the sample remains orange
  • if there is starch the sample turns black
• Testing for glucose

  1. add benedicts reagent to the food sample
  2. heat the food sample
  3. if there is no glucose the sample remains blue
  4. if there is glucose the sample turns red/orange/yellow
• Investigating enzymes

  1. add a few drops of iodine solution to Evan dimple in a spotting tile
  2. add a fixed volume of starch, amylase and pH buffer solutions to a water bath at a set temperature, leave for 5 minutes
  3. mix the starch solution and amylase solution together
  4. every 30 seconds add a few drops to the spotting tile, repeat until the iodine does not turn blue/black
  5. repeat for different pHs or different temperatures
• What piece of equipment would you use to keep your solutions at a certain temperature?

  Waterbath
• around what temperature would you expect amylase to work the best and why?

  37 degrees which is the temperature of the human body
• Around what pH does amylase work the best?

  7
• why should you leave the solutions in the water bath for at least 5 minutes before testing?

  to allow the solutions time to get to the same temperature
• why would you expect it to take a longer for starch to disappear at low temperatures?

  molecules have low kinetic energy and so fewer collisions between starch and amylase
• how could you use this experiment to determine the temperature or pH amylase works best?

  look for the quicker time that iodine stopped turning blue/black
• Amylase added to starch at different temperatures

  1. At 5°C the starch was not broken down

  2. At 35°C it took 2 mins for the starch to be broken down

  3. At 80°C the starch has not been broken down
• At low temperature (5°C)

  Molecules have low kinetic energy, fewer collisions
• As temperature increases

  Enzyme activity increases
• At 35°C

  Enzyme activity peaks
• As temperature continues to increase

  Enzyme activity falls
• Denaturation

  At warmer temperatures, the enzyme is denatured
• At 80°C the starch has not been broken down because the enzyme has been completely denatured
• When investigating the rate of photosynthesis what are the control variables

  • light intensity
  • temperature
  • carbon dioxide concentration
  • type of plant
  • pH
  • colour of plant
  • surface area of leaf
• Why do you leave the pondweed 5 minutes after the lamp has been turned on before counting any bubbles?

  gives the pondweed time to acclimate
• Why should you use a LED bulb when investigating the rate of photosynthesis?

  It does not heat up and raise the temperature of the water