3.3.1Inquiry Process
The Process of Photosynthesis — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 116 of 160
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 4Energy Conversion
Photosynthesis builds energy-rich organic compounds from carbon dioxide and water using light.
Autotrophs
- Autotrophs Plants, algae and cyanobacteria make their own organic compounds from simple inorganic substances using light as the energy source.
Light to chemical energy
- Light to chemical energy Energy from light is converted into chemical energy and stored in the bonds of organic molecules such as glucose,
- which form biomass.
Source of ecosystem energy
- Source of ecosystem energy The chemical energy stored in biomass supports nearly all the food chains in ecosystems,
- because consumers obtain energy by eating producers.
Energy conservation
- Energy conservation Energy is never created or destroyed in photosynthesis;
- it is only changed from one form into another.
Part 2 of 4Reactants and Products
Reactants
- Reactants Carbon dioxide and water are the raw materials;
- carbon dioxide enters leaves through stomata and water is brought from roots in xylem.
Products
- Products Glucose is the main product and oxygen is released as a by-product.
Word equation
- Word equation carbon dioxide + water → glucose + oxygen, with light energy absorbed by chlorophyll as the energy source.
Origin of oxygen
- Origin of oxygen The oxygen comes from the splitting of water molecules, which also provides the hydrogen used to build glucose.
Chloroplast sites
- Chloroplast sites Light-dependent reactions take place on the thylakoid membranes, while light-independent reactions take place in the stroma.
| Feature | Photosynthesis | Aerobic respiration |
|---|---|---|
| Reactants | Carbon dioxide, water | Glucose, oxygen |
| Products | Glucose, oxygen | Carbon dioxide, water |
| Energy | Stores light energy as chemical energy | Releases chemical energy as ATP |
| Site | Chloroplast | Cytoplasm and mitochondrion |
Part 3 of 4Linking Photosynthesis and Respiration
1
Producers use light to make glucose and release oxygen into the air or water.
2
The glucose is used in respiration by producers and by consumers to make ATP.
3
Oxygen released by photosynthesis is the final electron acceptor for aerobic respiration.
4
Respiration releases carbon dioxide and water, which are the raw materials for photosynthesis.
5
This links the two processes in a cycle for matter, but energy flows one way, entering as light and leaving as heat.
Part 4 of 4Exam Checklist & Tips
3.3.1 – Key Points for the Exam
- Photosynthesis The process in which light energy is used to make glucose from carbon dioxide and water.
- Autotroph An organism that makes its own organic compounds from inorganic substances.
- Chlorophyll The green pigment that absorbs light for photosynthesis.
- Biomass The organic matter that stores chemical energy in living organisms.
Common Mistakes
- Saying the oxygen released comes from carbon dioxide; it comes from the splitting of water.
- Thinking plants respire only in the dark;
- they respire all the time, and in the light photosynthesis is faster than respiration.
- Describing photosynthesis as making energy, when it only converts it into another form.
- Mixing up the reactants and products of photosynthesis and aerobic respiration.
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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.