The Photosynthesis Equation and Chemical Symbols Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Learn the word equation for photosynthesis, understand the chemical symbols CO2, H2O, O2 and C6H12O6, and explore how photosynthesis is an endothermic r...

• Write the word equation and balanced symbol equation for photosynthesis
• Recognise and use the chemical symbols CO₂, H₂O, O₂ and C₆H₁₂O₆
• Describe photosynthesis as an endothermic reaction requiring light energy
• Explain how energy is transferred from the environment to chloroplasts during photosynthesis

Key ideas to keep in view

Use this lesson to stay inside B1.4 Photosynthesis while connecting the detail back to the wider B1: Cell level systems topic.

• B1: Cell level systems
• B1.4 Photosynthesis
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from The Photosynthesis Equation and Chemical Symbols before testing yourself from memory.

• Every leaf on every plant is running the same chemical reaction right now. It's taking two simple ingredients from the environment and building something complex - glucose. This process keeps every food chain on Earth running, but how does it actually work at the molecular level?
• The secret lies in understanding the chemical equation. Once you can read the symbols, you'll see exactly what goes in, what comes out, and why plants need sunlight to make it happen.
• 2. The Photosynthesis Equation - Two Ways to Write It
• Scientists write chemical reactions in two ways: word equations (clear to understand) and symbol equations (precise and compact). Let's start with the version that makes sense in plain English.
• carbon dioxide + water → glucose + oxygen (in the presence of light)
• Required equation: carbon dioxide + water → glucose + oxygen, with light energy needed for the reaction. In symbols, this is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ with light above the arrow.
• This tells us the story: plants take carbon dioxide from the air and water from their roots. With light energy, they build glucose (sugar) and release oxygen as a waste product. But examiners want precision, which means chemical symbols.
• The balanced chemical equation showing exact quantities of reactants and products
• Notice the numbers in front - these balance the equation. You need 6 molecules of carbon dioxide and 6 molecules of water to make 1 molecule of glucose and 6 molecules of oxygen. The arrow shows light energy is needed to make this reaction happen.
• Chemical symbols look intimidating, but they follow simple rules. Each symbol tells you exactly which atoms are present and how many of each. Let's decode the four key symbols you must recognise for photosynthesis.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.