Topic 1- Biological Molecules & Energy In Food Flashcards
What is a biological molecule?
Molecules found in living organisms such as carbohydrates, lipids and proteins.
What solution do you use to test for sugar?
Benedict’s solution/reagent
What solution do you use to test for starch?
Iodine solution
What solution do you use to test for lipids?
Ethanol. It is known as the Emulsion Test
What solution do you use to test for proteins?
Potassium hydroxide and copper sulfate. It is known as the Biuret Test.
What is the method used for testing starch?
1) add iodine solution (which is browny-orange) to the test sample
2) if starch is present it will change to a blue-black colour
3) if starch isn’t present it will stay browny-orange
What is the method used for testing for lipids (emulsion test)?
1) Shake the test substance with ethanol for 1 minute or until it dissolves, then pour the solution into water
2) if lipids are present they will precipitate out of the liquid and show a milky emulsion on the top of the water
3) the more lipids, the more noticeable the milky colour will be
What is the method used for testing for proteins (Biuret test)?
1) add a few drops of potassium hydroxide solution to make the solution alkaline
2) then some copper(ll) sulfate solution which is blue
3) if there’s no protein, the solution will stay blue
If protein is present the solution will turn purple
What does emulsion mean?
An emulsion is when one liquid doesn’t dissolvein another and so just forms little droplets on the top or bottom.
What is the method used for testing for sugar?
1) add Benedict’s reagent which is blue to a sample and heat it in a water bath at 75°C. If the test is positive it will form a coloured precipitate (solid particles suspended in the solution)
2) the higher the concentration of sugar the further the colour changes goes.
What is the order of the colour change when testing for sugar using Benedict’s solution?
Blue→green→yellow→orange→brick red
What is the posh name for burning food to see how much energy it contains?
Calorimetry
How do you calculate the amount of energy in food?
Mass of water (g) X temp change of water (°C) X 4.2 = energy in food (J)
How do you work out how many joules are in each gram of food?
Energy in food(J)/Mass of food(g) = energy per gram of food (J/g)
