Biology ch7

Chapter 7: Photosynthesis

What is Photosynthesis?

• Definition: Photosynthesis is the process by which photosynthetic organisms convert solar energy into chemical energy stored in carbohydrates.

• Importance: It is crucial for life as it forms the foundation of the food chain by producing organic compounds that feed both photosynthetic organisms (autotrophs) and non-photosynthetic organisms (heterotrophs).

Key Components of Photosynthesis

• Raw Materials:

  • Carbon Dioxide (CO2)

  • Water (H2O)

• Main Product:

  • Carbohydrates (C6H12O6)

  • Oxygen (O2) is released as a byproduct.

• Energy Source: Solar energy captured by chlorophyll and other pigments inside chloroplasts.

Photosynthetic Organisms

• Types:

  • Algae

  • Plants

  • Cyanobacteria

• Characteristics:

  • Autotrophs that produce their own food through the photosynthesis process.

The Process of Photosynthesis

• Stages:

  1. Light Reactions:

     • Occur in the thylakoid membrane.

     • Solar energy is converted into chemical energy (ATP and NADPH).

     • Water is split, releasing oxygen.

  2. Calvin Cycle:

     • Takes place in the stroma.

     • Uses ATP and NADPH to convert CO2 into glucose (carbohydrates).

Importance of Water and Carbon Dioxide

• Water:

  • Absorbed by roots and moves to leaves via vascular tissue.

  • Essential for the light reactions.

• Carbon Dioxide:

  • Enters through stomata and diffuses into chloroplasts for the Calvin cycle.

Photosynthetic Pigments

• Chlorophyll:

  • Main pigment responsible for absorbing sunlight.

  • Absorbs red and blue light, reflects green light.

• Accessory Pigments:

  • Carotenoids absorb light in the violet-blue-green range and reflect yellow and orange light.

Light Reactions vs. Calvin Cycle

• Light Reactions:

  • Noncyclic and cyclic pathways exist.

  • Capture solar energy and convert it into ATP and NADPH.

• Calvin Cycle Reactions:

  • Fixes carbon dioxide into glucose using energy from ATP and NADPH.

Electron Transport Chains

• Photosystem II and Photosystem I:

  • Photosystems capture solar energy and initiate electron transport.

• ATP Production:

  • Chemiosmosis allows ATP synthase to produce ATP from ADP + P using the H+ gradient created during light reactions.

Summary of Photosynthesis Equation

• General equation:

  • CO2 + H2O + Light Energy -> C6H12O6 + O2

Water and Mineral Uptake in Plants

• Mechanism:

  • Water enters roots through osmosis; minerals are actively absorbed.

  • Water and nutrients are transported through xylem to various parts of the plant.

Transport Mechanisms in Plants

• Cohesion-Tension Model for Xylem:

  • Explains water movement upwards due to transpiration.

• Pressure-Flow Model for Phloem:

  • Explains sugar transport from source (leaves) to sink (roots).