Biology · Biological molecules. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Water makes up 70 to 90% of protoplasm. Its molecules are polar and form hydrogen bonds with each other. This makes water an excellent solvent for ionic and polar substances, gives it a high specific heat capacity (its temperature changes slowly) and a high heat of vaporisation (evaporation cools the body).
Carbohydrates are grouped by size: monosaccharides are single sugars, oligosaccharides have 2 to 10 sugar units, and polysaccharides are long chains used for storage or support.
Lipids do not dissolve in water but dissolve in organic solvents. Fats and oils are acylglycerols: glycerol joined to fatty acids by ester bonds. Lipids store about twice as much energy per gram as carbohydrates.
Students think starch, glycogen and cellulose are made of different sugars. All three are made of glucose only; they differ in the type of link and the branching. Keep the iodine colours apart: starch blue, glycogen red, cellulose none.
Answer: C12H22O11
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