Cambridge IGCSE Chemistry · Syllabus 0620 · Chemistry of the Environment
Photosynthesis
What is Photosynthesis?
The reaction in which green plants make glucose and oxygen from carbon dioxide and water, in the presence of chlorophyll and using energy from light. Every candidate must give the word equation, carbon dioxide plus water gives glucose plus oxygen. Extended candidates must also give the symbol equation, six carbon dioxide plus six water giving one glucose plus six oxygen. Light energy and chlorophyll are conditions written above the arrow, not reactants; the reaction removes carbon dioxide from the atmosphere.
This definition is part of the Chemistry of the Environment chapter in Cambridge IGCSE Chemistry.
Common mistakes with Photosynthesis
- “Photosynthesis uses oxygen and gives out carbon dioxide.” Defect The equation has been written backwards. Chemistry Photosynthesis takes in carbon dioxide and water and releases oxygen. The reverse is respiration. Repair · Core carbon dioxide + water → glucose + oxygen. The direction is the whole of the error, and the word equation fixes it. Repair · Extended \(\mathrm{6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2}\). Transfer Which side of the arrow does glucose sit on? The right — it is a product.
- “Planting trees will solve climate change.” Defect A real strategy stated as a complete solution. Chemistry Photosynthesis removes carbon dioxide, but slowly, only while the trees grow, and only for as long as the carbon stays locked up. It does nothing about methane, sulfur dioxide or oxides of nitrogen. Repair Add the benefit and a limitation — both are credited. Transfer Name a strategy that addresses methane instead. Reduction in livestock farming.