EDEXCEL IGCSE BIOLOGY PRACTICLES Proctored Exam With Verified Complete Questions And Answers.

Investigate food samples for the presence of glucose - correct answer - add benedict's solution and sample of food to a test tube - heat in 60-70 degree water for 5 minutes - observe colour GLUCOSE = orange / brick red NO GLUCOSE = blue Investigate food samples for the presence of starch - correct answer - add a few drops of iodine solution to the sample STARCH = blue/black NO STARCH = brown Investigate food samples for the presence of protein - correct answer - add a few drops of biuret solution to the sample PROTEIN = violet/purple NO PROTEIN = blue Investigate food samples for the presence of fat (lipids) - correct answer - Food sample is mixed with 2cm3 of ethanol and shaken - ethanol is added to an equal volume of cold water LIPIDS = cloudy emulsion forming investigate how enzyme activity can be affected by changes in temperature - correct answer - Starch solution is heated to a set temperature - Iodine is added to wells of a spotting tile - Amylase is added to the starch solution and mixed well - Every minute, droplets of solution are added to a new well of iodine solution - This is continued until the iodine stops turning blue-black (this means there is no more starch left in the solution as the amylase has broken it all down) - Time taken for the reaction to be completed is recorded - Experiment is repeated at different temperatures - The quicker the reaction is completed, the faster the enzyme is working investigate how enzyme activity can be affected by changes in pH - correct answer Place single drops of Iodine solution in rows on the tile Label a test tube with the pH to be tested Use the syringe to place 2cm3 of amylase in the test tube Add 1cm3 of buffer solution to the test tube using a syringe Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette After 10 seconds, use pipette to place one drop of mixture on the first drop of iodine, which should turn blue-black Wait another 10 seconds and place another drop of mixture on the second drop of iodine Repeat every 10 seconds until iodine solution remains orange-brown Repeat experiment at different pH values - the less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH investigate diffusion and osmosis using living and non-living systems - correct answer Diffusion in a Non-Living System - A crystal (Potassium permanganate) is added to water (solvent) - The potassium permanganate particles will diffuse with solvent particles - The potassium permanganate particles will be less concentrated in one place in the end, so the colour will not be as deep Diffusion in a Living System During inhalation, oxygen rich air enters alveoli There is a higher concentration of oxygen in the alveoli than in the blood running past the alveoli Oxygen will diffuse out of alveoli down the concentration gradient into blood At the same time, there is a higher concentration of carbon dioxide in the blood (from respiration) than in the alveoli Carbon dioxide will diffuse out of blood down the concentration gradient into the alveoli