required practicals

• What are the steps in the microscopy practical

  1. use tweezers to seperate some epidermal tissue of an onion and place on the slide
  2. add a drop of iodine solution to stain organelles
  3. place a cover slip on top
  4. clip slide onto the stage
  5. select the lowest power objective lens
  6. use coarse adjustment knob to move stage just below objective lens
  7. look down eyepeice and adjust until in focus
  8. swap to a higher powered objective lens and refocus
• What is the osmosis practical?

  1. set up 6 boiling tubes with different each containing same volume but different concentrations of sugar water
  2. Prepare 6 potatoes in cylinders and make sure their completely dry before recording start mass
  3. record start mass and place into different concs of sugar water
  4. leave them in for 20 mins
  5. remove each potato and wipe dry with paper towel to remove excess water so it dont affect end mass
  6. record end mass
  7. do the experiment again to remove anomalies and calculate a mean
• How do you calculate % change in mass of potato

  (Change in mass ÷ Starting mass) x 100
• Why do you dry the potato before recording end mass?

  To remove excess water
• Why do you calculate %change in mass of a potato chip rather than just change in mass?


  So that you can compare different chips, as the starting mass of each potato may not be the same
• Why is there a mass gain in osmosis?

  because water moves in as there is a higher conc of water in solution than in potato
• where is there a mass loss in osmosis?

  water moves out as there is a higher conc of water in potato than in solution
• What is the agar jelly practical?

  1. agar jelly heated to 121 degrees to sterilise it the places in fridge to reduce bacteria before use
  2. attach lid to petri dish using tape to prevent any microorganisms entering
  3. place agar plate upside down to avoid moisture dripping onto bacteria
• How do you find the zone of inhibition?

  pie x radius squared