CAIE IGCSE Biology revision note on photosynthesis factors: necessity of chlorophyll, light, and CO₂ shown via destarching, ethanol decolorization, and iodine starch tests with expected color changes. Practical setups to vary light intensity, CO₂ (NaHCO₃/NaOH), and temperature using pondweed, plus controls to avoid heat artifacts—ideal for Alternative to Practical prep.