Photosynthesis Complete Explanation (Class 10 ICSE)
Photosynthesis is the process by which green plants make their own food using sunlight, carbon dioxide, and water in the presence of chlorophyll.
Balanced Chemical Equation
6CO_2 + 6H_2O xrightarrow[text{chlorophyll}]{text{sunlight}} C_6H_{12}O_6 + 6O_2
This means:
- Carbon dioxide + Water Glucose + Oxygen
Steps of Photosynthesis
1. Light Reaction (Occurs in chloroplasts)
- Sunlight is absorbed by chlorophyll
- Water splits into:
- Oxygen (released into air)
- Hydrogen ions and electrons
- Energy is stored as ATP
2. Dark Reaction (Calvin Cycle)
- Takes place in the stroma of chloroplast
- Carbon dioxide combines with hydrogen to form glucose
- Does not need sunlight directly
Factors Affecting the Rate of Photosynthesis
1. Light Intensity
- More light faster photosynthesis (up to a limit)
- Very high light can damage chlorophyll
2. Carbon Dioxide Concentration
- Increased CO increases rate (till saturation point)
3. Temperature
- Optimum: 25C 35C
- Low temp slows enzymes
- High temp enzymes denature
4. Water
- Shortage reduces photosynthesis
- Causes stomata to close less CO intake
5. Chlorophyll Content
- More chlorophyll higher rate
- Less chlorophyll reduced photosynthesis
Important Definitions
- Chlorophyll: Green pigment that absorbs sunlight
- Stomata: Tiny pores for gas exchange
- Glucose: Food produced by plants
- Photolysis: Splitting of water using light
Quick Revision
- Photosynthesis = Food-making process in plants
- Requires: Sunlight, CO, Water, Chlorophyll
- Produces: Glucose + Oxygen
- Happens in chloroplasts
- Two stages: Light reaction & Dark reaction
Practice Questions
- Define photosynthesis.
- Write the balanced equation of photosynthesis.
- Name two stages of photosynthesis.
- What is the role of chlorophyll?
- How does temperature affect photosynthesis?
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