Biology Short Enzymes are proteins in nature and speed up the rate of reaction. Microorganisms are used to make products like cheese, beer and yoghurt. Photosynthesis and respiration are enzyme-controlled reactions. Use of carbohydrates in plants (I) Starch as a source of energy (II) Cellulose to build cell wall (III) Glucose used in respiration for providing energy (IV) Sucrose from transportation through the plant