Everything from the 2 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
Carbohydrates and fats contain carbon, hydrogen and oxygen only. Proteins contain carbon, hydrogen, oxygen and nitrogen (some also contain sulfur). Large biological molecules are made by joining many small molecules together: starch, glycogen and cellulose are made from glucose; proteins from amino acids; fats and oils from fatty acids and glycerol.
Nitrogen is the element that separates proteins from the other two groups. "Carbon, hydrogen and oxygen" is a correct answer for carbohydrates and for fats, but it loses the mark for proteins unless you add nitrogen.
"Fats are made from fatty acids" is only half an answer. Always name both parts: fatty acids and glycerol. Likewise, cellulose is made from glucose, not from starch.
Iodine solution turns from orange-brown to blue-black with starch. Benedict's solution, heated in a water bath, turns from blue to green, yellow, orange or brick red with reducing sugars. Biuret turns from blue to purple with protein. Shaking a food with ethanol and pouring it into water gives a cloudy white emulsion if fat is present. Vitamin C turns blue DCPIP colourless. Extended: DNA is two strands coiled into a double helix; each strand carries bases, bonds between pairs of bases hold the strands together, and the bases always pair A with T and C with G.
State both colours: the colour of the reagent at the start and the colour it turns. "Iodine turns blue" instead of blue-black, or a Benedict's result given without heating, are classic lost marks.
Do not read the number of drops as the amount of vitamin C. More drops means less vitamin C in each drop of juice.
Pair the bases A with T and C with G, never A with G or C with T. And it is the bonds between pairs of bases that hold the two strands together.