lecture recording on 03 February 2025 at 12.30.16 PM

Photosynthesis Overview

• Photosynthesis occurs in chlorophyll.

• Trees with lost photosynthesis ability rely on nutrient exchange with normal redwood trees through roots.

Stages of Photosynthesis

Photosynthesis occurs in two main stages:

Light Reactions

• Convert solar energy into chemical energy stored in chemical bonds.

• Sunlight activates chlorophyll in chloroplasts' photosystems.

• Generates ATP from ADP and NADPH from NADP+.

  • ATP: Energy currency used in cellular processes.

  • NADPH: Another form of cellular energy used in the Calvin cycle.

Dark Reactions (Calvin Cycle)

• Uses ATP and NADPH from light reactions to fix carbon dioxide into sugar.

• Enzyme Rubisco catalyzes carbon fixation, incorporating CO2 into organic molecules.

  • Glucose is one of the primary products of this process.

Photosystems in Light Reactions

Photosystem II

• Initiates photosynthesis by absorbing light, facilitating electron flow through pigment molecules, and generating energy.

• Converts light energy into chemical energy by splitting water into O2 and sending electrons along.

• ATP production occurs as part of the electron transport chain.

Photosystem I

• Also activated by light, facilitating further electron movement and NADPH production.

• Operates after Photosystem II but is termed 'Photosystem I' based on its discovery order.

Inputs and Outputs of Light Reactions

Inputs

• Energy: Light energy.

• Mass: Water, NADP+, ADP + inorganic phosphate.

Outputs

• Mass: O2 (oxygen gas), ATP, NADPH.

• The outputs indicate that glucose is not produced during light reactions.

Calvin Cycle Mechanics

• Takes place after light reactions and depends on them for ATP and NADPH.

• Major Inputs: ATP, NADPH, CO2.

• Major Output: G3P (glyceraldehyde 3-phosphate), which serves as a precursor for glucose.

Regeneration of Rubisco

• After G3P production, Rubisco must be regenerated to maintain its function.

• This regeneration requires ATP.

Summary of Mass and Energy Flow

• Light reactions produce O2 and energy (ATP, NADPH) from water.

• Calvin cycle uses ATP and NADPH to convert CO2 into sugar, returning ADP, NADP+.

• They are interconnected through the production and use of cellular energy carriers.

Oxygen Sources in Photosynthesis

• The oxygen gas produced in photosynthesis originates solely from water, not CO2.

• Glucose is formed during the Calvin cycle from carbon dioxide.

Radish Experiment Analysis

• Experimental setup investigates mass changes in plants regarding photosynthesis.

• Condition B contains both necessary water and light, allowing for photosynthesis.

Photosynthesis and Cellular Respiration Connection

• Cellular respiration transforms energy from food (glucose) into ATP:

  • Glucose + O2 -> CO2 + H2O (with energy release).

• Products: 6 CO2 molecules and 6 H2O molecules are formed, correctly balancing mass.

Purpose of Cellular Respiration

• Transform chemical bond energy in food into a usable energy form (ATP).

• Powers endergonic reactions necessary for cellular processes.

ATP Production Process

• ATP synthesis from glucose involves a reaction (chemiosmosis) that transfers energy to convert ADP + inorganic phosphate into ATP, releasing energy for the cell's use.