1. Name the three main types of carbohydrates.
Answer
Monosaccharides, disaccharides, polysaccharides.
2. Define what a polymer is.
Answer
A polymer is a large molecule made from many repeating smaller units called monomers, which are joined together by condensation reactions.
3. What type of bond is formed between two monosaccharides ?
Answer
Glycosidic bond.
4. What is the difference between an alpha glucose and a beta glucose molecule ?
Answer
They are arranged in different ways. In alpha glucose, both –H groups are above the carbon atoms, and both –OH groups below the carbon atoms. In beta glucose they are bonded the opposite way around, one –OH below and one above.
5. If you test a solution containing both glucose and sucrose, you cannot show the presence of sucrose by carrying out the non-reducing sugar test. Explain why.
Answer
The mixture will give a positive reducing sugar test because glucose is present. After boiling with dilute hydrochloric acid, the glucose will still be there and would give a positive non-reducing sugar test even if sucrose was not there. Hydrolysis of the sucrose simply adds more monosaccharides to the solution, which will not be shown by this test.
6. Place a tick in the box if the statement applies to the specific carbohydrate.
Answer
7. The test for starch using iodine causes a blue/black colour to form. This happens because the iodine forms an ion that sticks inside the amylose (starch) helix as shown in the figure below. If the starch/iodide complex is boiled, the blue/black colour disappears. Suggest why.
Answer
Boiling increases kinetic energy. The bonds that cause the amylose helix to form break, and the helix opens. Iodine/iodide is no longer able to assemble within the helix to produce the blue-black colour.
8. The figure below shows a molecule of mannose. Use a diagram to show how two molecules of mannose join together.
Answer
Drawing shows OH from one molecule and H from another removed to form water. Glycosidic bond correctly shown with O joining the two carbon atoms.
9. Give one way in which the structure of mannan is similar to the structure of cellulose and one way in which its structure is different.
Answer
Similarity: Cellulose forms long straight chains.
Difference: Mannan can form side chains/branches/cellulose made of beta glucose not mannose.