Bio paper 1 (RP)

• Microscopy (practice)


  1. Add a drop of water to the middle of a clean slide

  2. Cut an onion and separate it out into layers

  3. Use tweezers to peel off some epidermal tissue from the bottom of the one of the layers

  4. Using the tweezers, place the epidermal tissue into the water on the slide

  5. Add a drop of iodine solution (iodine solution is a stain)

  6. Place a cover slip on top
• Magnification


  Image size (mm) / real size (mm)
• Light microscopes


  • Have a limited magnification and limited resolution
• Electron microscopes


  • Have a much higher magnification and resolution than light microscopes
• Culturing Microorganisms (practical)


  1. Place a paper disc soaked in different types of antibiotics on an agar plate that has an even covering of bacteria (leave some space between the discs)

  2. The antibiotics should diffuse (soak) into the agar jelly

  3. Antibiotic-resistant bacteria that aren't affected will continue to grow around the paper disc, but non-resistant strains will die; a clear area will be left where the bacteria have died- this is called inhibition zone

  4. Use a control (a paper disc soaked in sterile water) to see the difference between the growth of the bacteria around the control disc and one of the antibiotic disc

  5. Leave the plate for 48 hours at 25°C
• The more effective the antibiotic is against the bacteria

  The larger the inhibition zone
• Effect of pH on amylase (required practical)

  1. Place one drop of iodine solution into each well of a spotting tile

  2. Take 3 test tubes (in the first test tube add 2cm³ amylase solution, in the second one 2 cm³ starch solution, and in the 3rd one add 2cm³ of a pH 5 buffer solution)

  3. Place all 3 test tubes in a water bath at 30°C and leave them for 10 minutes

  4. Combine the 3 solutions into 1 test tube and mix with a stirring rod

  5. Return the test tube to the waterbath and start a stopwatch

  6. After 30s, use the stirring rod to transfer one drop of solution to a well in the spotting file which contains iodine

  7. The iodine should turn blue-black showing that starch is present

  8. Now take a sample every 30s and continue until the iodine remains orange

  9. When iodine remains orange, starch is no longer present (reaction has completed)

  10. Repeat the whole experiment several times using different pH buffers (e.g. 6,7+8)
• Food tests (Practical)


  1. Use Benedict's Test to test for sugars

  2. Prepare a good sample and transfer 5cm³ to a test tube

  3. Add some Benedict's solution to the test tube (about 10 drops) using a pipette

  4. Place the test tube in the waterbath for 5 minutes

  5. If the sample contains a reducing sugar, the solution in the test tube will change from the normal blue colour to green, yellow, or brick-red

  6. Use Iodine Solution to test for starch

  7. Make a food sample and transfer 5cm³ of your sample to a test tube

  8. Then add a few drops of iodine solution and gently shake the tube to mix it

  9. If the sample contains starch, the solution will change from browny-orange to black or blue-black