required practicals paper 1 bio

• microscopy


  Aim :measure length of cells under a microscope

  -peel a one cell layer of skin from an onion using a scalpel and tweezers

  -place this on a microscope slide, add a drop of iodine to stain the cells, place a cover slip on top and place on the microscope stage

  -turn on the light and use the lowest magnification objective lens

  -use the coarse and fine focus knobs to focus and increase the magnification and refocus if needed

  -use a graticule to measure the length of cells in micrometres
• osmosis


  Aim: to determine the sugar concentration in potato cells

  -cut equal size cylinders from potato and remove any skin(non-permeable).Remove excess water from surface and weigh using top pan balance

  -place each test tube with different concentrations of sugar solution, and leave for one day

  -remove cylinders and dab off excess water ,reweigh and calculate:%change in mass
• food tests

  •sudan lll test 

  -test for lipids 

  -mixture will seperate out into two layers the top layer will turn bright red 

  •biuret test 

  -test for protein

  —colour change from blue to purple

  •iodine solution 

  -test for starch

  —colour changes from browny orange to blue or black

  •benedicts test 

  -test for sugars

  -colour changes from blue to green,yellow or brick redness
• enzymes 


  Aim :determine optimum temperature/pH of an enzyme

  -Measure out the starch ad amylase and place separately in a water bath, along with buffer solution if changing the pH . Prepare a spotting tile with iodine drops. Mix the reactants together and start timer

  -every ten seconds, remove a drop of the mixture and put it in a dimple of iodine. If it changes colour there is still starch present. Once all the starch is broken down , it will no longer change colour

  -repeat this process for different temperatures 
• Method


  1. Set up a boiling tube containing sodium hydrogencarbonate solution

  2. Allow the tube to stand for a few minutes and shake to disperse any air bubbles that might form

  3. Cut a piece of the pondweed, 8cm long

  4. Use forcepts to place the pondweed in the boiling tube, without damaging it or causing the liquid to overflow

  5. Position the boiling tube so that the pondweed is 10 cm away from the light source

  6. Allow the boiling tube to stand for five mins

  7. Count the number of bubbles emerging from the cut end of the stems in one min, repeat five times and record results

  8. Calculate the average number of bubbles produced per min