5.1.2Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
The Role of ATP in Photosynthesis — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 5 parts Lesson 9 of 36 Unit quiz
Curriculum Equation Key Balanced Photosynthesis EquationFast Exam Solution
6CO₂ + 6H₂O ➔ C₆H₁₂O₆ + 6O₂
Word Equation & Conditions: Carbon Dioxide + Water (+ Light & Chlorophyll) -> Glucose + Oxygen
Part 1 of 5ATP as an Energy Carrier
ATP is a phosphorylated nucleotide used to move energy within cells.
Structure
- ATP contains adenine, the sugar ribose and three phosphate groups joined in a chain.
Hydrolysis
- ATP hydrolysis to ADP and inorganic phosphate releases energy in a small, manageable amount.
Soluble and small
- ATP is soluble and small, so it diffuses easily to places in the cell where energy is needed.
Rapid turnover
- ATP is not stored in large amounts but is made and used quickly.
Universal
- The same molecule is used in all living organisms, so it is called the universal energy currency.
Part 2 of 5Making ATP in the Chloroplast
Photophosphorylation means adding phosphate to ADP using light energy.
1
Light excites electrons in chlorophyll molecules, which then pass along an electron transport chain.
2
As the electrons flow, energy released is used to pump protons into the thylakoid space.
3
A proton gradient forms across the thylakoid membrane, with a high concentration inside the thylakoid.
4
Protons flow back through ATP synthase down their gradient, which joins ADP and inorganic phosphate to form ATP.
Part 3 of 5Using ATP in the Calvin Cycle
Using ATP in the Calvin Cycle
Reduction
- ATP supplies energy when glycerate 3-phosphate is reduced to triose phosphate.
Regeneration
- ATP is needed to convert triose phosphate back into ribulose bisphosphate.
Other uses
- In a plant, ATP also supports active transport, protein synthesis and cell division.
Reaction
- ADP + Pᵢ ⇌ ATP + H₂O, with ATP synthase catalysing the forward reaction.
Part 4 of 5Linking Light and Chemistry
Chemiosmosis
- Making ATP using a proton gradient across a membrane is called chemiosmosis.
Location
- The ATP synthase enzymes are embedded in the thylakoid membranes of the grana.
Dependent link
- Without light, no proton gradient forms and the Calvin cycle soon runs out of ATP.
Respiration comparison
- Mitochondria make ATP by oxidative phosphorylation using the same chemiosmotic idea.
Part 5 of 5Exam Checklist & Tips
5.1.2 – Key Points for the Exam
- ATP Adenosine triphosphate, the molecule that carries energy for cell reactions.
- Photophosphorylation Formation of ATP from ADP and Pᵢ using light energy.
- Chemiosmosis Movement of protons across a membrane through ATP synthase to make ATP.
- ATP synthase An enzyme embedded in the membrane that makes ATP from ADP and phosphate.
Common Mistakes
- Saying ATP is an energy store; it is an immediate energy carrier that is rapidly recycled.
- Writing that energy is released when the phosphate bond forms; energy is needed to form it.
- Stating that ATP is made in the Calvin cycle; it is made in the light-dependent stage.
- Forgetting that protons move down a gradient through ATP synthase.
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Biology 0610 & 9700 Exam Model
Limiting Factors Master
Photosynthesis: Limiting Factors & Graph Plateau
6CO2 + 6H2O → C6H12O6 + 6O2 (Light & Chlorophyll required)
- Limiting Factor Definition: Something present in the environment in such short supply that it restricts life processes.
- Graph Plateau: When rate levels off as light intensity increases, light is no longer the limiting factor; CO2 concentration or temperature has become limiting.
- High Temperature Drop: Beyond optimum temp (~40°C), enzymes (e.g. RuBisCO) denature, permanently decreasing rate.