CIE iGCSE Co-ordinated Sciences-B6.1 Photosynthesis- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B6.1 Photosynthesis – Study Notes
CIE iGCSE Co-ordinated Sciences-B6.1 Photosynthesis – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe photosynthesis as the process by which plants synthesise carbohydrates from raw materials using energy from light
- State the word equation for photosynthesis as: carbon dioxide + water → glucose + oxygen in the presence of light and chlorophyll
- State that chlorophyll is a green pigment that is found in chloroplasts
- Investigate and understand the need for chlorophyll, light and carbon dioxide for photosynthesis
Supplement
- State the balanced symbol equation for photosynthesis as: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- State that chlorophyll transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
- Outline the subsequent use and storage of the carbohydrates made in photosynthesis:
(a) starch as an energy store
(b) cellulose to build cell walls
(c) glucose used in respiration to provide energy
(d) sucrose for transport in the phloem
(e) nectar to attract insects for pollination - Explain the importance of:
(a) nitrate ions for making amino acids
(b) magnesium ions for making chlorophyll - Understand and describe the effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis
- Understand and describe the effect of light and dark conditions on gas exchange in an aquatic plant using hydrogencarbonate indicator solution
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Photosynthesis
📌 Definition
Photosynthesis is the process by which plants manufacture carbohydrates (like glucose) from raw materials (carbon dioxide + water) using energy from light.
🔑 Key Points
1. Raw materials needed
- Carbon dioxide (CO₂): from the air
- Water (H₂O): from the soil
- Mineral salts: needed for proteins & other compounds (not for carbs directly)
2. Energy & enzymes
- Sunlight provides energy.
- Chlorophyll (in chloroplasts) absorbs light and converts it into chemical energy.
- Enzymes in plant cells help drive the reactions.
3. Products formed
- Glucose (C₆H₁₂O₆): used for respiration, converted into sucrose, starch, or other molecules.
- Oxygen (O₂): released as a by-product.
⚗️ Word Equation
Carbon dioxide + Water →(light, chlorophyll)→ Glucose + Oxygen
📚 Historical Note (Van Helmont’s experiment)
- He grew a willow tree in soil with only water supply.
- Found the tree gained weight while soil mass stayed almost same.
- Concluded growth was due to water.
- Later discovered → CO₂ from air + minerals from soil also contribute.
📋 Summary Table
| Requirement | Source | Role |
|---|---|---|
| Carbon dioxide | Air | Carbon + oxygen for glucose |
| Water | Soil | Hydrogen for glucose |
| Light energy | Sun | Provides energy |
| Chlorophyll | Leaves | Captures light & drives reaction |
📝 Quick Recap
Photosynthesis = making carbs using light.
Needs CO₂ + H₂O + light + chlorophyll.
Produces glucose (stored/transported/used) + O₂ (waste gas).
Chlorophyll = converter of light energy → chemical energy.
Photosynthesis – Word Equation
📌 Definition of the equation
The chemical process of photosynthesis can be summarised as a word equation showing the raw materials and products, along with the conditions needed:
Word Equation:
\( \text{Carbon dioxide (CO₂) + Water (H₂O) → Glucose (C₆H₁₂O₆) + Oxygen (O₂)} \)
(in the presence of light and chlorophyll)
🔑 Key Points
1. Reactants (Inputs):
- Carbon dioxide (CO₂): taken in from the air through stomata.
- Water (H₂O): absorbed by roots from the soil.
2. Products (Outputs):
- Glucose (C₆H₁₂O₆): used for energy, storage (as starch), or building other molecules.
- Oxygen (O₂): released as a by-product into the air.
3. Conditions:
- Light: provides energy to drive the reaction.
- Chlorophyll: captures light energy and converts it into chemical energy.
📌 Practical Evidence
- Starch tests show photosynthesis has occurred: iodine turns blue in presence of starch.
- Experiments confirm that without light, CO₂, or chlorophyll, photosynthesis does not occur.
📝 Quick Recap
Word equation: \( \text{CO₂ + H₂O → C₆H₁₂O₆ + O₂} \) (light + chlorophyll)
Glucose = energy + storage; O₂ = released.
Light & chlorophyll = essential for the process.
Chlorophyll
📌 Location & Nature
- Found in chloroplasts of plant cells.
- It is a green pigment essential for photosynthesis.
📌 Function in Photosynthesis
- Absorbs sunlight and converts it into chemical energy.
- Enables the plant to synthesise carbohydrates from carbon dioxide and water.
📌 Experimental Evidence
- Variegated leaf experiment:
- Destarched leaf exposed to sunlight.
- Only green areas (with chlorophyll) produced starch → turned blue with iodine.
- White areas (lacking chlorophyll) → no starch → stayed brown/yellow.
- Conclusion: Chlorophyll is necessary for photosynthesis.
📌 Importance
- Without chlorophyll, plants cannot convert light energy into chemical energy.
- Directly affects growth and food production in plants.
📝 Quick Recap
| Feature | Details |
|---|---|
| Pigment | Green |
| Location | Chloroplasts |
| Function | Capture light energy for photosynthesis |
| Evidence | Starch forms only in green parts of leaves |
Factors Needed for Photosynthesis
🌱 1. Chlorophyll
- Green pigment found in chloroplasts.
- Captures light energy for photosynthesis.
- Evidence: Variegated leaf experiment → only green parts produce starch (turn blue with iodine), white parts (no chlorophyll) → no starch.
- Conclusion: Chlorophyll is essential for photosynthesis.
💡 2. Light
- Provides energy required to synthesise carbohydrates.
- Evidence: Aluminium foil experiment → part of a destarched leaf covered with foil → no starch formed; exposed part → starch formed.
- Conclusion: Light is necessary for starch production.
🌬️ 3. Carbon Dioxide (CO₂)
- Source of carbon for building glucose.
- Evidence: Soda-lime and NaHCO₃ experiment → plant with CO₂ removed (soda-lime) → no starch; plant with CO₂ supplied (sodium hydrogencarbonate) → starch formed.
- Conclusion: CO₂ is required for photosynthesis.
📊 Summary Table
| Factor | Role in Photosynthesis | Evidence from Experiment |
|---|---|---|
| Chlorophyll | Captures light energy | Variegated leaf → starch only in green parts |
| Light | Provides energy for reactions | Leaf covered with foil → no starch in dark parts |
| CO₂ | Source of carbon for glucose | Soda-lime removes CO₂ → no starch; CO₂ present → starch formed |
🔑 Key Idea
Destarching ensures no pre-existing starch affects results.
Starch formation is used as evidence for photosynthesis.
All three factors (chlorophyll, light, CO₂) are essential, otherwise photosynthesis does not occur.
Photosynthesis – Balanced Symbol Equation
Equation:
\[ 6 \text{CO}_2 + 6 \text{H}_2\text{O} \xrightarrow{\text{light, chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2 \]
Explanation:
- 6CO₂ → 6 molecules of carbon dioxide (from air)
- 6H₂O → 6 molecules of water (from soil)
- C₆H₁₂O₆ → glucose (food made by the plant)
- 6O₂ → oxygen released as a by-product
- Requires light energy and chlorophyll to drive the reaction.
📌 Tip to remember:
6 Carbon dioxide + 6 Water → 1 Glucose + 6 Oxygen
Count the numbers carefully; the “6’s” match on both sides for balance.
Chlorophyll and Its Role in Photosynthesis
📌 Introduction
Photosynthesis is the process by which plants make carbohydrates from raw materials (CO₂ and H₂O) using light energy.
Chlorophyll is a green pigment in the chloroplasts of plant cells. It is essential for photosynthesis.
🧬 Function of Chlorophyll
- Light Absorption: Chlorophyll absorbs sunlight, mainly red and blue light. Green light is mostly reflected, which is why plants appear green.
- Energy Transfer: Light energy absorbed by chlorophyll is converted into chemical energy, which is used to synthesise carbohydrates like glucose from CO₂ and H₂O.
- Enabling Chemical Reactions: Energy from chlorophyll powers enzymatic reactions in the chloroplast, combining CO₂ and H₂O to form sugars.
⚡ Energy Flow
Sunlight → Chlorophyll → Chemical energy → Carbohydrate synthesis
Chlorophyll acts like a biological solar panel, capturing and converting energy efficiently.
🧪 Evidence for the Role of Chlorophyll
- Experiment: Variegated Leaf Test
- Use a leaf with green (chlorophyll) and white (no chlorophyll) areas.
- After exposure to light and testing with iodine solution:
- Green areas → turn blue/black (starch formed)
- White areas → remain brown/yellow (no starch)
- Interpretation: Only areas with chlorophyll can photosynthesise. Confirms that chlorophyll is necessary for converting light energy into chemical energy.
📝 Summary Table
| Feature | Chlorophyll Role | Example/Tip |
|---|---|---|
| Location | Chloroplasts in plant cells | Mesophyll cells of leaves |
| Function | Absorbs light, transfers energy | Like a “solar panel” |
| Outcome | Energy stored in chemical bonds of carbohydrates | Glucose formation |
| Evidence | Variegated leaf starch test | Green → starch; White → no starch |
💡 Quick Recap
Chlorophyll = green pigment in chloroplasts
Captures sunlight → converts to chemical energy
Powers the synthesis of glucose from CO₂ + H₂O
Starch forms only in areas containing chlorophyll
Acts as the energy converter for photosynthesis
Fate of Carbohydrates Made in Photosynthesis
📌 Introduction
Carbohydrates (mainly glucose) made during photosynthesis are not all stored as glucose. Plants use or convert them into different forms depending on need: energy, growth, structure, transport, or reproduction.
🧬 Uses and Storage
- Starch – Energy Store
Glucose molecules are joined to form starch, an insoluble polysaccharide. Stored in chloroplasts and root/tuber cells (e.g., potato tubers, carrot roots). Provides long-term energy for the plant when photosynthesis is not occurring (night or winter). - Cellulose – Building Cell Walls
Glucose is polymerised into cellulose, a strong structural polysaccharide. Used to build rigid cell walls, giving shape and support to plant cells. Essential for plant growth and stability. - Glucose – Respiration to Release Energy
Glucose is broken down in cellular respiration to release ATP, the energy currency. Energy supports growth, reproduction, active transport, and metabolic reactions. Example: root hair cells respiring to absorb minerals from soil. - Sucrose – Transport in Phloem
Glucose is converted to sucrose, a soluble sugar, for transport through phloem. Delivered from leaves (source) to roots, stems, fruits, and growing parts (sink). Enables distribution of energy throughout the plant. - Nectar – Attracting Insects for Pollination
Some glucose is converted into nectar, a sugary fluid. Nectar attracts insects and animals, aiding in pollination. Indirectly helps in reproduction and species survival.
📝 Summary Table
| Carbohydrate Form | Main Function | Location / Example |
|---|---|---|
| Starch | Energy storage | Chloroplasts, roots, tubers |
| Cellulose | Structural support for cell walls | Cell walls |
| Glucose | Energy via respiration | Cytoplasm / mitochondria |
| Sucrose | Transport sugar | Phloem sap |
| Nectar | Attract pollinators | Flowers |
💡 Quick Recap
Starch → stored energy
Cellulose → builds cell walls
Glucose → respiration → ATP energy
Sucrose → transported via phloem
Nectar → attracts insects → aids pollination
Importance of Mineral Ions in Plants
📌 Introduction
Plants need mineral ions from the soil to make important molecules. Two key ions: nitrate (NO₃⁻) and magnesium (Mg²⁺).
🧬 Nitrate Ions (NO₃⁻) – For Amino Acids and Proteins
- Function: Provide nitrogen, essential for making amino acids, the building blocks of proteins.
- Proteins are needed for:
- Enzymes (catalysts for reactions)
- Structural proteins (cell walls, membranes)
- Growth and repair of plant tissues
- Deficiency Symptoms:
- Poor growth
- Yellowing of older leaves (chlorosis)
- Reduced protein content
🍀 Magnesium Ions (Mg²⁺) – For Chlorophyll
- Function: Central atom in chlorophyll molecule. Chlorophyll is needed for photosynthesis to absorb light energy.
- Deficiency Symptoms:
- Leaves turn yellow between veins (interveinal chlorosis)
- Reduced photosynthesis → stunted growth
📝 Summary Table
| Ion | Purpose | Deficiency Symptoms |
|---|---|---|
| Nitrate (NO₃⁻) | Amino acids → proteins | Poor growth, yellow older leaves |
| Magnesium (Mg²⁺) | Chlorophyll → photosynthesis | Yellow leaves (interveinal), stunted growth |
💡 Quick Recap
Nitrate → Nitrogen → Amino acids → Proteins → Growth & enzymes
Magnesium → Chlorophyll → Photosynthesis → Energy for plant
Factors Affecting the Rate of Photosynthesis
📌 Introduction
Photosynthesis is affected by external environmental factors. Key factors: light intensity, carbon dioxide concentration, temperature. The rate is usually measured by oxygen production or starch formation.
1. Light Intensity 🌤️
- Effect: Light provides energy for photosynthesis.
- Observation: Rate increases with light intensity up to a maximum (saturation) point. Beyond this, rate no longer increases; another factor becomes limiting.
- Explanation: More light → more energy for chlorophyll → faster conversion of CO₂ and H₂O into glucose. If light is too low → photosynthesis slows down → less glucose and oxygen.
2. Carbon Dioxide Concentration 🌬️
- Effect: CO₂ is a raw material for making glucose.
- Observation: Rate increases with CO₂ concentration up to a point. Too little CO₂ → rate limited, even if light and temperature are optimal.
- Explanation: CO₂ combines with H₂O in the Calvin cycle to produce glucose. Low CO₂ → fewer molecules available → slower glucose formation.
3. Temperature 🌡️
- Effect: Temperature affects enzyme activity in photosynthesis.
- Observation: Rate increases with temperature up to optimum (~25–35°C for plants). Above optimum → rate decreases rapidly.
- Explanation: Higher temperature → more kinetic energy → more frequent effective collisions between enzymes and substrates. Too high → enzymes denature → active site loses shape → photosynthesis stops. Too low → enzyme activity slows → reaction rate decreases.
📝 Summary Table
| Factor | Effect on Photosynthesis Rate | Reason/Explanation |
|---|---|---|
| Light Intensity | Increases until saturation | More energy for chlorophyll → faster reaction |
| Carbon Dioxide | Increases until saturation | CO₂ needed for glucose synthesis |
| Temperature | Increases to optimum, then decreases | Kinetic energy ↑ collisions ↑, but high temp → enzymes denature |
💡 Quick Recap
Light: Energy source → faster reaction up to saturation.
CO₂: Raw material → low CO₂ limits glucose production.
Temp: Affects enzymes → optimum temperature gives maximum rate; high temp denatures enzymes.
Investigating Gas Exchange in Aquatic Plants
📌 Key Idea
Aquatic plants take in CO₂ and release O₂ during photosynthesis. In the dark, photosynthesis stops, but respiration continues.
Hydrogencarbonate indicator detects CO₂ concentration changes in water:
- Red: Normal CO₂ concentration (~neutral pH)
- Yellow: High CO₂ → acidic → pH ↓
- Purple: Low CO₂ → alkaline → pH ↑
🧪 Experimental Setup
- Place fresh aquatic plant (e.g., Elodea) in a test tube with hydrogencarbonate solution.
- Set up two conditions:
- Light: Place under a light source.
- Dark: Cover completely with foil.
- Observe colour changes in the indicator over time.
💡 Observations
| Condition | Indicator Colour | Explanation |
|---|---|---|
| Light | Purple / Pink | CO₂ is used in photosynthesis → solution becomes more alkaline. O₂ released. |
| Dark | Yellow | Photosynthesis stops → CO₂ from respiration accumulates → solution becomes acidic. |
🔬 Explanation
- Light: Photosynthesis > respiration. CO₂ is absorbed → hydrogencarbonate indicator turns purple. O₂ produced → gas bubbles may appear on leaves.
- Dark: Only respiration occurs. CO₂ released → indicator turns yellow. No O₂ production.
📝 Tips
- Use destarched plants to avoid stored sugars affecting results.
- Keep temperature constant to prevent rate changes due to enzymes.
- Multiple replicates improve reliability.
💡 Quick Recap
Light: CO₂ ↓ → solution turns purple (alkaline), O₂ ↑
Dark: CO₂ ↑ → solution turns yellow (acidic), O₂ ↓
Hydrogencarbonate indicator shows CO₂ changes, not O₂ directly.