GCSE Biology 05 — Photosynthesis
PublicTopics include Photosynthesis Fundamentals, Fate of Glucose in Plants, Leaf Structure and Adaptations, Stomata and Guard Cell Function, Limiting Factors of Photosynthesis, Gas Exchange and Compensation Points, Practical: Testing Leaves for Starch, and Practical: Investigating the Rate of Photosynthesis.
Biology
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Photosynthesis Fundamentals
The endothermic chemical process by which plants synthesize glucose from carbon dioxide and water using light energy.
Key points
- Definition: An endothermic reaction converting light energy into chemical potential energy stored in glucose.
- Location: Occurs in chloroplasts containing the pigment chlorophyll.
- Word Equation: Carbon dioxide + Water -> Glucose + Oxygen
- Symbol Equation:
- Light Absorption: Chlorophyll absorbs red and blue light but reflects green light (limiting photosynthesis in green light).
Worked example
Question
Explain why photosynthesis is described as an endothermic reaction.
Solution
An endothermic reaction absorbs energy from the surroundings. Photosynthesis requires a continuous input of light energy, which is absorbed by chlorophyll in the chloroplasts to drive the conversion of reactants (carbon dioxide and water) into products (glucose and oxygen). Without this energy input, the reaction stops.
Common pitfalls
- Confusing the energy source: Plants do not use 'heat' for photosynthesis; they strictly use light energy.
- Forgetting the arrow labels: When writing the equation, you must write 'light' and 'chlorophyll' on/under the arrow to show they are conditions, not reactants.
Prerequisites
- Basic chemical equations
- Energy stores (light vs chemical)
- Cell structure (chloroplasts)
Further resources
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Photosynthesis - BBC Bitesize
Overview of the process and equations.