In-Depth Notes on Photosynthesis

Learning Goals

• Importance of Photosynthesis: Understanding its role in energy transformations and impact on life.
• Relation to Cellular Respiration: Exploring how photosynthesis and respiration are interconnected metabolic processes.
• Photosynthesis Location: Identifying where photosynthesis occurs in cells, particularly in chloroplasts.

The Sun: Energy Source for Life

• Photosynthesis Efficiency: Only utilizes 1-2% of the Sun’s energy.

What is Photosynthesis?

• Terminology:
  • Photo: Refers to light-capturing reactions.
  • Synthesis: Refers to the production of carbohydrates (glucose).

Basics of Photosynthesis

• Photosynthetic Organisms: Includes nearly all plants, some bacteria, and protists.
  • Autotrophs: Organisms that produce their own organic matter through photosynthesis.
  • Energy Transformation: Sunlight energy is converted into chemical energy stored in glucose molecules.

Why is Photosynthesis Important?

• Dependency of Other Organisms:
  • Organisms depend on products of photosynthesis for energy.
  • Glucose is utilized as food or stored by plants.

Photosynthesis Process

• General Equation: The process converts CO2 and water into glucose and oxygen:
  6 CO2 + 6 H2O + ext{light energy}
  ightarrow C6H{12}O6 + 6 O2
• Inputs and Outputs:
  • Carbon dioxide enters through stomata in leaves.
  • Water enters through roots and is transported to leaves.
  • Oxygen is released primarily through stomata.

The Calvin Cycle

• Sugar Production: Utilizes CO2 to produce sugar.
  • Energy Supply: ATP generated in the light reactions powers the Calvin cycle.
  • Electron Supply: NADPH provides electrons needed to reduce CO2 to glucose.

Light Reactions vs. Calvin Cycle

• Light Reactions:
  • Convert solar energy into chemical energy (ATP and NADPH).
  • Occur in the thylakoid membranes of chloroplasts.
  • Capture light energy via chlorophyll and other pigments.

Electromagnetic Spectrum and Visible Light

• Wavelength Characteristics:
  • Longer wavelengths (red) hold less energy than shorter wavelengths (violet).

Why are Plants Green?

• Absorption and Reflection: Plants absorb all colors except green, which is reflected, making them appear green.
• Chloroplast Structure: Contain pigments (chlorophylls and carotenoids) embedded in thylakoid membranes that facilitate light absorption.

Chloroplast Structure and Function

• Components of Chloroplasts:
  • Outer and Inner Membranes: Enclose the chloroplast.
  • Stroma: Fluid matrix containing enzymes for the Calvin cycle.
  • Thylakoids and Grana: Structures that house chlorophyll for light reactions.
• Photosynthesis Location: Occurs primarily in the mesophyll cells of leaves.

Pigments in Chloroplasts

• Types of Pigments:
  • Chlorophyll a: Participates directly in light reactions.
  • Chlorophyll b: Assists in light absorption.
  • Carotenoids: Absorb blue and green light, reflecting yellow, orange, and red.

Light Absorption and Action Spectrum

• Graphs Summary:
  • Absorption Spectrum: Shows wavelengths absorbed by pigments.
  • Action Spectrum: Indicates oxygen release related to light wavelengths used in photosynthesis.

Seasonal Color Change in Leaves

• Chlorophyll Breakdown: In autumn, chlorophyll degradation allows carotenoid and flavonoid pigments to show, resulting in yellow and red leaves.

Photosystems

• Functionality of Photosystems:
  • PS1 and PS2: Photosystems in thylakoid membranes that capture photons and facilitate energy transfer.
  • Antenna Complex: Composed of chlorophyll and carotenoids that capture light and relay energy.
  • Reaction Center: Contains chlorophyll a that converts light energy into chemical energy and transfers electrons to electron acceptors.

Energy Transport in Photosystems

• Electron Excitation: Absorbed light energy excites electrons in chlorophyll a, leading to energy transfer in the photosystems.
  • Electron Transport Chain: Electrons are passed through various molecules, initiating redox reactions.

Summary of Energy Transfer in Photosystems

• Step-by-Step Energy Capture:
  1. Sunlight photons excite electrons in the antenna complex.
  2. Energy is relayed to the reaction center, exciting one of its electrons.
  3. Excited electrons are transferred to primary electron acceptors, continuing the energy transformation process.