chapt06_lecture_anim (1)Photsynthesis Light reaction

Chapter 6: Energy for Life - Photosynthesis Part 1: Light Reaction

Introduction

  • Focus on the process of photosynthesis

  • Understanding light reactions and the Calvin Cycle

Student Outcomes

  • Ability to describe photosynthesis

  • Explain the light reaction’s role in photosynthesis

  • Explain the Calvin Cycle and its importance

  • Differentiate between C-3, C-4, and CAM photosynthesis

Key Concepts

Role of Producers

  • Producers convert solar energy into chemical energy.

  • Essential part of ecosystems, supporting consumers.

Chloroplast Structure

  • Chloroplast: site of photosynthesis

    • Double membrane surrounding stroma

    • Thylakoids stacked in grana

    • Pigments absorb solar energy

Photosynthesis Overview

  • Definition: A process that converts solar energy into chemical energy in carbohydrates.

  • Location: Occurs in plants, algae, and cyanobacteria.

  • Importance: Supplies energy for all living organisms.

Photosynthesis Process

  • Captures solar energy, reducing CO2 into carbohydrates.

  • Inputs: Carbon dioxide (CO2) and water (H2O)

  • Outputs: Organic compounds (like glucose) and oxygen (O2)

Mechanisms of Photosynthesis

Light Reactions

  • Location: Occur in the thylakoid membranes.

  • Key Functions:

    • Solar energy absorption by chlorophyll.

    • Water oxidation, releasing electrons, hydrogen ions, and oxygen.

    • ATP produced through the electron transport chain.

    • NADP+ reduced to NADPH.

Calvin Cycle (Dark Reaction)

  • Occurs in the stroma.

  • Uses ATP and NADPH to convert CO2 into carbohydrates.

Energy in Photosynthesis

  • Solar Energy: Defined by its wavelength and energy content.

    • Visible light: Most used by plants.

    • Shorter wavelengths = higher energy; longer wavelengths = lower energy.

  • Only 42% of solar radiation is used in photosynthesis.

Photosynthetic Pigments

  • Chlorophyll a and b: Absorb violet, blue, and red light; reflect green (hence leaves appear green).

  • Carotenoids: Accessory pigments that absorb violet, blue, and green; reflect yellow-orange.

  • Changes in seasons (fall) reveal carotenoids as chlorophyll degrades.

Electron Pathway in Light Reactions

  • Two Photosystems (PSII and PSI) generate ATP and NADPH:

    • PSII: Absorbs solar energy, oxidizes water.

    • PSI: Captures electrons, reduces NADP+.

  • End Products: ATP, NADPH, and oxygen as a by-product.

Organization of Thylakoid Membrane

  • Critical for efficient electron transfer.

  • ATP synthase: Converts H+ gradient into ATP.

Summary of the Light Reaction

  • Uses light to create energy carriers (ATP and NADPH).

  • Key roles of photosystems and electron transport in energy transformation.

  • Establishes H+ gradient to synthesize ATP, capturing and utilizing solar energy effectively.