3.3.1Inquiry Process
The Process of Photosynthesis — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 2 of 10
Curriculum Equation Key معادلة البناء الضوئي الموزونة - Balanced Photosynthesis EquationFast Exam Solution
6CO₂ + 6H₂O ➔ C₆H₁₂O₆ + 6O₂
Word Equation & Conditions: Carbon Dioxide + Water (+ Light & Chlorophyll) -> Glucose + Oxygen | ثاني أكسيد الكربون + ماء (في وجود الضوء والكلوروفيل) ← جلوكوز + أكسجين
Location & Specifications: البلاستيدات الخضراء (Chloroplast): التفاعلات الضوئية في الثايلاكويد، ودورة كالفن في الستروما.
Part 1 of 5Overview
Equation
- Equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ in the presence of light and chlorophyll.
Energy conversion
- Energy conversion Light energy is converted into chemical energy stored in the bonds of organic compounds such as glucose.
Autotrophs
- Autotrophs Plants, algae and cyanobacteria carry out photosynthesis and form the base of most food chains.
Chloroplast
- Chloroplast The chloroplast contains thylakoid membranes stacked into grana, surrounded by the fluid stroma.
Pigments
- Pigments Chlorophyll in the thylakoid membranes absorbs light energy to drive the reactions.
Part 2 of 5Light-dependent Reactions
1
Chlorophyll in the thylakoid membranes absorbs light, which excites electrons.
2
Light energy splits water in a process called photolysis, releasing oxygen as a by-product.
3
Energy from the excited electrons is used to make ATP.
4
Electrons and hydrogen are accepted by NADP to produce reduced NADP.
5
ATP and reduced NADP then pass to the stroma for the next stage.
Part 3 of 5Light-independent Reactions
1
Carbon dioxide diffuses into the stroma and is fixed by the enzyme rubisco onto ribulose bisphosphate.
2
The products are reduced using ATP and reduced NADP to form triose phosphate.
3
Some triose phosphate is used to regenerate ribulose bisphosphate so that the cycle can continue.
4
The rest is converted to glucose, starch, cellulose, amino acids and other organic compounds.
5
These steps do not need light directly, but depend on the products of the light-dependent stage.
Part 4 of 5Products of Photosynthesis
Products of Photosynthesis
Glucose
- Glucose Triose phosphate can be joined to form glucose, which is used in respiration or to make other compounds.
Storage
- Storage Glucose is converted to starch for storage in chloroplasts and in storage organs.
Structural
- Structural Glucose is also used to make cellulose for cell walls, and with nitrates to make amino acids.
Part 5 of 5Exam Checklist & Tips
3.3.1 – Key Points for the Exam
- Photolysis The splitting of water molecules using light energy.
- Carbon fixation Attachment of carbon dioxide to an organic molecule, catalysed by rubisco.
- Thylakoid A membrane-bound flattened sac in the chloroplast where light is absorbed.
- Stroma The fluid of the chloroplast, where the light-independent reactions occur.
Common Mistakes
- Writing that the oxygen released comes from carbon dioxide; it comes from the splitting of water.
- Saying that the light-independent reactions occur in the dark only.
- Confusing the stroma (light-independent) with the thylakoid membrane (light-dependent).
- Stating that plants only photosynthesise and do not respire.
Last updated:
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.