Photosynthesis

6.1 Photosynthesis

6.1.1 Photosynthesis

  • Definition: Photosynthesis is an endothermic reaction where energy from sunlight is absorbed by chloroplasts in green plants, enabling them to convert carbon dioxide and water into glucose.

  • Key Components:

    • Raw materials: Carbon dioxide (CO₂) and water (H₂O).

    • Products: Glucose (C₆H₁₂O₆) and oxygen (O₂) released as a waste product.

  • Summary:

    • Plants as Autotrophs: Plants can synthesize complex molecules from simpler ones (e.g., glucose from CO₂ and H₂O).

    • Role in Ecosystem: They are producers, forming the basis of food chains (e.g., plants, algae).

  • Word Equation:

    • Photosynthesis can be summarized as:CO₂ + H₂O + light energy → C₆H₁₂O₆ + O₂

  • Balanced Chemical Equation:

    • 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

6.1.2 The Products of Photosynthesis

  • Plants utilize glucose for:

    • Energy source in respiration.

    • Storage as starch.

    • Lipids production for energy stores in seeds.

    • Cellulose formation for cell walls.

    • Amino acids synthesis (for proteins) in combination with nitrogen and mineral ions from the soil.

6.1.3 Limiting Factors

  • Definition: A limiting factor is something present in short supply that restricts the rate of photosynthesis.

  • Main Limiting Factors:

    1. Temperature: Affects kinetic energy, collision frequency, and enzyme activity.

      • High temperatures can denature enzymes, reducing photosynthesis rate.

    2. Light Intensity: More light increases the rate until another factor limits it.

    3. Carbon Dioxide Concentration: More CO₂ can enhance photosynthesis until limited by another factor.

  • Water is necessary but not typically a limiting factor due to its abundance compared to transpiration.

  • Chlorophyll: The number of chloroplasts and chlorophyll can influence photosynthesis efficiency. Factors affecting chloroplast quantity include diseases and nutrient availability.

6.1.4 Light & The Rate of Photosynthesis

  • Direct Relationship: The rate of photosynthesis increases with light intensity until limited by another factor.

  • Distance Relationship: Light intensity decreases inversely with distance from the source (inverse square law).

    • Light intensity ∝ 1/distance²

  • Graphical Representation: At low intensities, increase in light enhances photosynthesis until saturation occurs due to another limiting factor.

6.1.5 Practical Investigations

  • Investigating Light and Photosynthesis:

    • Aquatic Plants: Such as Elodea and Cabomba are ideal for experiments.

  • Methods for Investigating Limiting Factors:

    1. Light Intensity: Change distance from the light source.

    2. Carbon Dioxide Concentration: Use sodium hydrogencarbonate to increase CO₂ levels in water.

    3. Temperature: Use water baths to maintain specific temperatures.

  • Set-Up and Steps for Investigation:

    • Aerate water, ensure illumination, use controlled conditions, and measure oxygen production in specified time intervals (e.g., using a gas syringe).

    • Record and analyze data, plotting oxygen production against independent variables.

6.1.6 CORMS Evaluation in Experiments

  • Considerations:

    • C: Change one variable (distance of light source).

    • O: Use the same species and size of plants.

    • R: Repeat trials for reliability.

    • M: Measure volume of oxygen produced.

    • S: Control temperature and CO₂ concentration to ensure valid results.