paper 1

• microscopy

  method:

  1. add a drop of water to a clean slide
  2. cut an onion and separate into layers. use tweezers to peel of the epidermal tissue from the bottom of one of the layers
  3. place the epidermal tissue into the water on the slide
  4. add a drop of iodine solution
  5. place a cover slip on top, being careful to avoid air bubbles.
  6. clip slide onto the stage
  7. use the lowest magnification
  8. move stage up to just below the objective lens
  9. move stage downwards until fully focussed
• Growing bacteria

  1. Pour hot agar jelly into a petri dish

  2. Use inoculating loops/a sterile pipette and spreader to transfer microorganisms
• Culturing microorganisms in school labs

  • Culture the microorganisms at 25 degrees
  • Harmful bacteria can grow above this temperature
• culturing microorganisms: effect of antibiotics

  1. Place paper discs soaked in different types/concentrations of antibiotics on an agar plate

  2. Antibiotic resistant bacteria will continue to grow around the discs but non-resistant strains will die

  3. A clear area will be left called the zone of inhibition

  4. Use a control sample

  5. Leave plate for 48 hours at 25 degrees
• Zone of inhibition

  The more effective the antibiotic, the larger the zone of inhibition
• culturing microorganisms: avoiding contamination

  1. Sterilise petri dish by heating to a high temperature

  2. Sterilise inoculating loop by passing through hot flame

  3. Tape the lid of the petri dish to stop microorganisms from the air entering

  4. Store petri dish upside down to prevent condensation
• osmosis

  method:

  1. cut up a potato into identical cylinders
  2. get some beakers with different sugar solutions. (one should be pure water)
  3. measure the mass of the cylinders and leave each one in each beaker for around 24 hours
  4. take out the potato and re-measure their masses
  5. if the cylinders have drawn in water by osmosis, they will have increased in mass, if they have lost water, the will have decreased in mass.

  variables

  control- temperature, volume of solution, time, type of sugar

  independent- concentration of sugar solution

  dependent- mass of potato
• Effect of pH on enzyme activity

  1. Add a drop of iodine solution into every well of a spotting tile

  2. Heat a beaker of water to 35 degrees using a Bunsen burner

  3. Add 1cm^3 of amylase solution and 1cm^3 of a buffer solution (pH 5) to a boiling tube

  4. Place the boiling tube into the beaker and wait 5 mins

  5. Add 5cm^3 of starch solution to the boiling tube

  6. Mix the contents and start a timer

  7. Take a sample from the boiling tube every 30 seconds and drop into a well with a pipette

  8. When the iodine solution remains orange, the starch is no longer present
• effect of pH: variables

  • Control- concentration/volume of amylase solution
  • Independent- pH of buffer solution
  • Dependent- time taken for starch to be broken down
• food tests

  sugar:

  1. prepare a food sample and transfer 5cm^3 to a test tube
  2. prepare a water bath set to 75 degrees
  3. add some benedict's solution using a pipette
  4. leave for 5 minutes
  5. if positive, solution will change from blue to brick-red
• food tests

  starch:

  1. prepare a food sample and transfer 5cm^3 to a test tube
  2. add a few drops of iodine solution and gently shake the tube to mix
  3. if positive, solution will turn from brown-orange to blue-black
• food tests

  proteins:

  1. prepare a food sample and transfer 2cm^3 to a test tube
  2. add 2cm^3 of biuret solution to test tube and gently shake to mix
  3. if positive, solution turns from blue to purple
• food tests

  lipids:

  1. prepare a food sample and transfer 5cm^3 to a test tube
  2. add 3 drops of sudan III solution with a pipette and gently shake
  3. if positive, the top layer will turn a bright red

  OR

  1. prepare a food sample and transfer 5cm^3 to a test tube
  2. add ethanol
  3. shake vigourously and add distilled water
  4. if positive, turns from colourless to cloudy
• rate of photosynthesis

  method:

  1. a source of white light is placed a specific distance from the pondweed
  2. left to photosynthesise for a certain amount of time
  3. oxygen will be released and collected in the capillary tube
  4. a syringe is used to draw up the gas bubble and the length is measured
  5. the length is proportional to the volume of O2 produced
  6. repeat with the light source at different distances