Plant Metabolism

Outline Photosynthesis  Major Steps of Photosynthesis  Light-Dependent Reactions  Light-Independent Reactions  C 4 Photosynthesis  CAM Photosynthesis Respiration  Glycolysis  Electron Transport Chain

Enzymes and Energy Transfer Enzymes regulate most metabolic activities.  Anabolism - Storing Energy. - Photosynthesis reactions  Catabolism - Consuming Stored Energy. - Respiration reactions Oxidation-Reduction Reactions  Oxidation - Loss of electron(s).  Reduction - Gain of electron(s) - Usually coupled

Photosynthesis Energy for most cellular activity involves adenosine triphosphate (ATP).  Plants make ATP using light as an energy source. - Take place in cholorpolasts and other green parts of the organisms. 6CO 2 +12H 2 O + light  C 6 H 12 O 6 +6O 2 +6H 2 O

Carbon Dioxide Carbon dioxide reaches cholorplasts in the mesophyll cells by diffusing through the stomata into the leaf interior.  Use of fossil fuels, deforestation, and other human activities have added excess carbon dioxide to the atmosphere. - May enhance photosynthesis.  Plants may counter-balance by developing fewer stomata.

Water Less than 1% of all the water absorbed by plants is used in photosynthesis.  Most of the remainder is transpired or incorporated into plant materials. If water is in short supply, stomata usually close and thus reduce the supply of carbon dioxide available for photosynthesis.

Light About 40% of the radiant energy received on earth is in the form of visible light.  Leaves commonly absorb about 80% of the visible light reaching them. - Light intensity varies with time of day, season, altitude, latitude, and atmospheric composition.  Considerable variation in the light intensities necessary for optimal photosynthetic rates.

Light Wavelengths

Effects of Light and Temperature on Photosynthesis

Chlorophyll Several different types of chlorophyll.  Most plants contain both chlorophyll a (blue-green) and chlorophyll b (yellow- green). - Other pigments include carotenoids (yellow and orange) phycobilins (blue or red), and several other types of chlorophyll. - About pigment molecules group as a photosynthetic unit.

Major Steps of Photosynthesis Light Dependent Reactions  Water molecules split apart.  Electrons passed along electron transport.  ATP produced.  NADPH produced.

Major Steps of Photosynthesis Light Independent Reactions  Calvin Cycle - Carbon dioxide combined with RuBP and then combined molecules are converted to sugars (Glucose).  Energy furnished by ATP and NADPH from Light-Dependent Reactions.

Light Dependent Reactions - In Depth Each pigment has its own distinctive pattern of light absorption.

Light Dependent Reactions - In Depth Two types of photosynthetic units present in most chloroplasts make up photosystems.  Photosystems I and II - Both can produce ATP. - Only organisms with both photosystem I and photosystem II can produce NADPH and oxygen as a consequence of electron flow.

Photosystems

Light Independent Reactions - In Depth Calvin Cycle  Six molecules of CO 2 combine with six molecules of RuBP with the aid of rubisco.  Resulting complexes split into twelve 3PGA molecules.  NADPH and ATP supply energy and electrons that reduce 3PGA to 12 GA3P.  Ten of the twelve GA3P molecules are restructured into six RuBP molecules.

The Calvin Cycle

Photorespiration Stomata usually close on hot, dry days.  Closed stomata prevent carbon dioxide from entering the leaf. - When carbon dioxide levels drop below about 50 parts per million, photorespiration is initiated.  Rubisco fixes oxygen instead of carbon dioxide.

Light Independent Reactions - In Depth 4-Carbon Pathway  Plants have Kranz Anatomy. - Large chloroplast with few to no grana in the bundle sheath cells surrounding the veins. - Smaller chloroplasts with well-developed grana in the mesophyll cells.

Corn (Zea Mays) Cross-Section

4-Carbon Pathway Plants with Kranz Anatomy produce oxaloacetic acid (4-carbon compound).  Phosphoenolpyruvate (PEP) and carbon dioxide combined in mesophyll cells with the aid of PEP carboxylase. - Provides a major reduction in photorespiration.

CAM Photosynthesis Similar to C4 photosynthesis in that 4-carbon compounds are produced during the light- independent reactions.  However, in CAM, the organic acids accumulate at night and break down during the day, releasing carbon dioxide. - Allows plants to function well under limited water supplies, as well as high light intensity.

CAM Photosynthesis

Respiration Respiration is essentially the release of energy from glucose molecules that are broken down to individual carbon dioxide molecules. C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy

Respiration Fermentation C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 + ATP C 6 H 12 O 6  2C 3 H 6 O 3 + ATP

Factors Affecting the Rate of Respiration Temperature Water Oxygen

Major Steps of Respiration Glycolysis  Glucose molecule becomes a fructose molecule carrying two phosphates.  Fructose molecule is split into two GA3P molecules.  Some hydrogen, energy, and water are removed, leaving pyruvic acid.

Major Steps of Respiration Aerobic Respiration  Citric Acid (Krebs) Cycle O.A. + acetyl CoA + ADP+P+3NAD + FAD  O.A. + CoA+ATP+3NADH+H + + FADH 2 +2CO 2 Electron Transport  Oxidative Phosphorylation  Chemiosmosis

Assimilation and Digestion Assimilation is the process of using organic matter produced through photosynthesis to build protoplasm and cell walls. Digestion is the conversion of starch and other insoluble carbohydrates to soluble forms.  Nearly always hydrolysis.

Review Photosynthesis  Major Steps of Photosynthesis  Light-Dependent Reactions  Light-Independent Reactions  C 4 Photosynthesis  CAM Photosynthesis Respiration  Glycolysis  Electron Transport Chain

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