required practicals

• photosynthesis

  • place piece of pndweed in boiling tube with sodium hydrogen carbonate solution
  • place boiling tube 10cm aay from lamp
  • switch lamp on and wait 5 mins
  • start stopwatch and count and record the number of bubbles produced in 1 min
  • repeat the 1 min, at different distances from the lamp (10cm away), and count to calculate a mean number of bubbles produced
• photosynthesis

  • it is imprtant to keep temperature and CO2 concentration the same throughout
  • use and LED light as they release less heat
  • putting a glass tank with water in between light and pondweed to prevent it from being heated
  • to get an accurate result, oxygen bubbles can be collected using an inverted funnel
  • volume of gas can be measured using a syringe
• microscopes


  preparing the slide:

  • add drop of water to clean the slide and place onion skin on top
  • add a drop of iodine to stain the cell to make it more visible
  • place a cover slip on top of onion cell

  viewing slide:

  • carefull place slid onto stage nd clip in place
  • select the objective lens with the lowest power
  • while looking down the eyepiece, use coarse adjustment knob to move stage up and down until its more focused
  • use fine adjustment knob until the image is clear
  • switch to higher powered objecive lens and refocus if greater magnification is required
• food tests 


  to prepare food:

  • crush food samples in pestle and mortar
  • add water to samples and filter any undissolved solids
  • place food sample in 4 test tubes
• food tests 


  benedict's test for sugar - blue to red

  • put tube in water bath for 5 mins at 80 degrees and add few drops of benedicts solution

  iodine test for starch - orange - blue/black

  • add few drops of iodine solution to test tube and wait for results

  buiret test for protein - blue to purple

  • add few drops of buiret A and buiret B to test tube and shake gently

  ethanol test for lipids - colourless to cloudy

  • add few drops of distilled water and ethanol to test tube and shake gently
• osmosis

  • set up tubes containing different sucrose solutions (from pure water to concentrated solution (1mol/dm*3))
  • cut potato eaqually. then measure and record their masses before placing them in the different test tubes
  • after a set time, take potatoes out and dry them. measure and record their masses once again

  independent variable: concentration of sucrose solution

  controlvariable: time or temperature
• osmosis 


  analysing results:

  • look at masses to see if they increased or decreased
  • if increased, water has been moved by osmosis

  rate of change = change in mass/time

  • then calculate percentage change in mass to see if they had a positive or negative effect of osmosis
  • if percentage is positive, mass has increased

  percentage change in mass = final mass - original mass/original mass *100
• enzymes (effect of pH on rate of reaction)

  • using pipette, place a drop of iodine solution in each hole of spotting tile
  • prepare the first test tube with 2cm*3 amylase (enzyme) and 1cm*3 buffer solution with a known pH. Place in water bath at 35 d
  • prepare second test tube with 2cm*3 starch solution. pour second test tube in forst test tube. start timer
  • every 10 seconds, put one drop of solution onto a hole of spotting tile - colour will turn blue/black. continue until colour remains blue/black (all starch has been turned to maltose)
  • repeat experiment using a buffer of different pH values
• enzymes 


  it is important to keep temperature the same