1. C 1.3 SL Photosynthesis

Photosynthesis Overview

• Photosynthesis is the process by which plants, algae, and some bacteria convert light energy from the sun into chemical energy in the form of glucose.

• It involves two critical stages: the light-dependent reactions and the light-independent reactions (Calvin Cycle).

• Key reactants include carbon dioxide (CO2) and water (H2O). The primary product is glucose (C6H12O6), and oxygen (O2) is released as a by-product.

Key Concepts in Photosynthesis

Energy Transformation

• Definition: Transformation of light energy into chemical energy.

• Organisms: Plants are photoautotrophs using sunlight to synthesize organic compounds. Heterotrophs must derive their energy from consuming other organisms.

• Significance: This energy transformation is essential for the chemical energy needed for life processes.

Electromagnetic Spectrum and Light Absorption

• Photosynthesis occurs primarily in the visible range of the electromagnetic spectrum (400-700 nm).

• Dispersion of Light: White light can be separated into its component colors when passing through a prism.

• Chlorophyll pigments absorb specific wavelengths of light, mainly red and blue, while reflecting green light.

Photosynthetic Pigments

Main Pigments

• Chlorophyll A: Primary pigment in photosynthesis that absorbs light effectively.

• Chlorophyll B: Assists by absorbing light at different wavelengths.

Accessory Pigments

• Other pigments that absorb different wavelengths and pass the energy to chlorophyll:

  • Carotenoids: Orange pigments.

  • Xanthophylls: Yellow pigments.

  • Anthocyanins: Red pigments often associated with autumn leaf colors.

Effects of Seasonal Changes

• In autumn, chlorophyll breaks down, revealing accessory pigments, leading to the color changes in leaves.

• Carotenoids and flavonoids continue to be present and contribute to leaf coloration during this time.

Photosynthesis Process

Light-Dependent Reactions

• Occur in thylakoid membranes of chloroplasts.

• Light energy excites electrons in chlorophyll, which leads to the splitting of water (photolysis).

• Products: ATP, NADPH, and O2 are generated.

Light-Independent Reactions (Calvin Cycle)

• Occur in the stroma of chloroplasts.

• Use ATP and NADPH produced from light reactions to convert CO2 into glucose.

Factors Affecting Photosynthesis

Limiting Factors

• Temperature: As temperature increases, photosynthesis rate can rise to a point, then decline.

• Light Intensity: Increased light intensity enhances photosynthesis up to a saturation point.

• CO2 Concentration: More CO2 can enhance the rate until other factors become limiting.

Experimental Investigation

• Experiments often use aquatic plants like Elodea to measure O2 production as an indicator of photosynthetic activity.

• Ensuring controlled conditions (e.g., temperature, CO2 levels) is critical.

Practical Applications and Implications

• Greenhouses may enhance CO2 levels to boost photosynthesis rates for crop production.

• Iron seeding in aquaculture shows potential for stimulating phytoplankton blooms, affecting marine productivity and CO2 levels.

Data Interpretation in Photosynthesis Experiments

Graphs and Trends

• Understanding graphs depicting light intensity vs. rate of photosynthesis is vital for interpreting how different factors affect the process.

• Experimentation often involves collecting multiple data points to determine limiting factors.

Summary

• Photosynthesis is critical for life on Earth. By converting sunlight into chemical energy, it sustains ecosystems both on land and in aquatic environments.