iGCSE CIE Biology Paper 6 Revision

iGCSE CIE Biology Paper 6 Revision What is an independant variable? - ANSWERS-The variable that is changed by the investigator What is a dependant variable? - ANSWERS-A variable that changes and is measured What is a control variable? - ANSWERS-A variable that should be kept constant so as to not affect the result of the dependant variable How can you make an experiment better? - ANSWERS-Do it 3 times and then take an average. Exclude anomalies from your average. How many decimal places should you answer with? - ANSWERS-If the rest of the table is to 1 decimal place then you should answer with 1 decimal place even if your answer is a whole number. What is the test for protein? - ANSWERS-Add a few drops of Biuret Reagent, gently shake, it should turn from blue to mauve/purple What is the test for Starch? - ANSWERS-Add a few drops of Iodine Solution, gently shake, it should turn from brown/orange to blue/black What is the test for Reducing Sugars? - ANSWERS-Add 2cm³ Benedict's Reagent, heat/boil, it should turn from blue to green to yellow to orange to red What is the test for Fat (Lipids)? - ANSWERS-The emulsion test: Add 2cm³ of ethanol to the unknown solution, gently shake, pour into equal volume of distilled water. If present a milky-white emulsion is formed. What is the test for Oxygen? - ANSWERS-A glowing splint is held above a glass tube, in which oxygen gas is trapped. When the stopcock is opened, oxygen gas rushes out, and ignites the glowing splint What is the test for Carbon Dioxide? - ANSWERS-Bubble the test gas through limewater (calcium hydroxide solution). Carbon dioxide turns limewater cloudy white. What is the test for Vitamin C? - ANSWERS-Add drops of DCPIP to the solution slowly. It will turn from blue to red if it is acidic. Continue and if it contains Vitamin C the solution will turn colourless. How should you design an experiment? - ANSWERS-*Find the variable which is to be changed (from the question) and mention how you are going to change it (ex: to change temperature, use thermometer-controlled water bath at temperatures 10 to 50 degree Celsius