Photosynthesis

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• Introduction
  • Overview
    • Equation
    • Main Steps in Photosynthesis
      • Light Dependent Reactions:
      • Calvin Cycle
      • Relationship between Light Independent/Dependent Reactions
• Details
• The Spectrum
• Electrons and energy
• Photovoltaics and photosynthesis
• The Chloroplast.
• Photosynthesis: the thylakoid and stroma
• Light reaction.
• The "Dark" reactions
• Energy difference PGA to G3P
• Photosynthesis in Other Critters
  • Prokaryotes
  • Eukaryotes
• Coping with Oxygen

Introduction

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Photosynthesis is the process by which plants and other organisms such as these algae from the Kingdom Protista shown here take light energy and convert it into chemical energy in the form of carbohydrates. This one process is the source just about all the energy used by animals and other non photosynthetic organisms.

All our food, wood, clothing ultimately are produced directly or indirectly by photosynthesis. In a sense, all flesh IS grass, for the energy used to make our flesh comes from grass, symbolically meaning photosynthetic organisms.

Photosynthesis illustrates the laws of thermodynamics and you should review thermodynamics before proceeding.

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Overview:

Equation for photosynthesis

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Photosynthesis is often summarized as shown here.

Carbon dioxide and water are the raw materials that the plant needs from the environment. The products are carbohydrate(CH2O) , water and oxygen. Light is not considered a raw material since light is energy and is not matter.

Water molecules are the source of the oxygen produced by photosynthesis by a process called photolysis.

Main Steps in Photosynthesis:

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Light dependent reactions: In the light dependent reactions, the photosynthetic organism converts the light energy into energy carried by electrons. The analogy is with solar cells converting sunlight into electricity which can do work. In photosynthesis the electrons are picked up by electron transport systems which use the energy in the electrons to make an energy carrying compound called ATP and a second compound, NADPH. The ATP and the NADPH are used for the next main step, the Calvin cycle,or "Light independent reactions".

• Basic components
• Map

Calvin Cycle

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The Calvin cycle is the main process in the Light Independent reactions of photosynthesis ('Dark Reactions'). In the Calvin cycle, carbon dioxide is first incorporated into a five carbon molecule called ribulose biphosphate or RuBP. Then in a series of chemical reactions, hydrogens and electrons from the NADPH are progressively added to form a simple, energy rich, phosphorylated carbohydrate called GP3 or PGAL.  In turn the PGAL is used to make glucose and other carbohydrates for use by the plant.

• The "Dark" reactions
• Energy difference PGA to G3P

Relationship between the Light Dependent and Light Independent reactions

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In plants photosynthesis takes place in specialized organelles called the chloroplast. The light dependent reactions take place in part of the chloroplast called a thylakoid and the light independent reactions take part in the fluid medium surrounding the thylakoids. This fluid is called the stroma. The accompanying diagram provides a quick summary of the relationship between the light dependent and light independent parts of photosynthesis.

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pgd 07/02/02