Biological molecules Flashcards iGCSE Biology
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[h] Biological molecules Flashcards iGCSE Biology
[q] DNA is composed of?
[a] Two strands coiled around each other to form a double helix. Each strand is made up of a sugar backbone with bases attached. These bases bind to bases on the other strand to form cross-links when they are wound together. There are four types of base: G, C, A and T. G always binds to C and A always binds to T.
[q] Lipids (like Fats and Oils) are made up of?
[a] Fatty acids and glycerol
[q] Test for Protein
[a]
- Add drops of Biuret solution to the food sample
- Colour change: blue → violet
[q] Test for Starch
[a]
- Add drops of iodine solution to the food sample
- Colour change: orange–brown → blue-black
[q] Test for Vitamin C
[a]
- Gently add a drop of DCPIP solution to food sample (as a solution) using a syringe and shake.
- Repeat until food solutions turns colourless.
- Colour change: Blue → Colourless
- Few drops/Less volume→ strong vitamin C solution
- Many drops/More volume → weak vitamin C solution
[q] Test for reducing sugar
[a]
- Add 2cm3 Benedict’s solution into sample solution in test tube
- Boil in water bath for 5 minutes
- Colour change:
- Blue → Green → Yellow → Orange → Brick-Red
- None → Trace → Low → Moderate → High
[q] Test for Lipids
[a]
- Food sample is mixed with 2cm3 of ethanol and shaken
- The ethanol is added to an equal volume of cold water
- A positive test will show a Milky-white cloudy emulsion forming
[q] What chemical elements do these molecules contain?
[a]
[q] When conducting a food test
[a] all solids must be crushed and mix with pure water (solution)
[q] Iodine solution to test for starch
[a] Starch
[q] Benedict’s solution to test for
[a] reducing sugars
[q] Biuret test for
[a] proteins
[q] Ethanol emulsion test for
[a] fats and oils
[q] DCPIP test for
[a] Vitamin C
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