Mader: Biology 8 th Ed. Photosynthesis Chapter 7

Mader: Biology 8th Ed.

Photosynthesis

Chapter 7


Outline

• Flowering Plants• Photosynthetic Pigments• Photosynthesis

– Light ReactionsNoncyclicCyclic

– Calvin Cycle Reactions– C4

– CAM


Photosynthetic Organisms

• Photosynthesis transforms solar energy into the chemical energy of a carbohydrate.– All organisms use organic molecules

produced by photosynthesizers as a source of chemical energy.


Flowering Plants

• The green portions of plants, particularly leaves, carry on photosynthesis.– Leaf of flowering plant contains mesophyll

tissue.Contains cells specialized to carry on

photosynthesis.


Flowering Plants

• CO2 enters leaf through stomata.

• CO2 and water diffuse into chloroplasts.

– Double membrane surrounds fluid (stroma).Inner membrane system within stroma

form flattened sacs (thylakoids). Often stacked to form grana.

– Chlorophyll and other pigments within thylakoid membranes are capable of absorbing solar energy.


Photosynthetic Pigments

• Most pigments absorb only some wavelengths of light and reflect or transmit the other wavelengths.– Absorption Spectra

Organic molecules and processes within organisms are chemically adapted to visible light.


Photosynthetic Pigments and Photosynthesis


Photosynthetic Reaction

• Light Reaction - Chlorophyll absorbs solar energy and energizes electrons.– Electrons move down electron transport

chain.Solar energy ATP, NADPH

• Calvin Cycle Reaction - CO2 is taken up and reduced to a carbohydrate. – Reduction requires ATP and NADPH.

ATP, NADPH Carbohydrate


Photosynthesis Overview


Light Reactions

• Light reactions consist of two electron pathways:– Noncyclic electron pathway– Cyclic electron pathway

• Both pathways produce ATP, but only the noncyclic pathway also produces NADPH.


Noncyclic Electron Pathway

• Electron flow can be traced from water to a molecule of NADPH.

• Uses two photosystems, PS I and PS II.– Photosystem consists of pigment complex

and electron acceptor molecules in the thylakoid membrane.

Pigment complex helps gather solar energy.



Cyclic Electron Pathway

• Cyclic pathway begins when PS I pigment complex absorbs solar energy and is passed from one pigment to another until it is concentrated in a reaction center.– Pathway only results in ATP production.



Thylakoid Organization


Calvin Cycle Reactions

• Calvin cycle is a series of reactions that produce carbohydrates before returning to the starting point again.– Utilizes atmospheric carbon dioxide to

produce carbohydrates. Includes: Carbon dioxide fixationCarbon dioxide reductionRuBP Regeneration




• Carbon Dioxide Fixation– CO2 is attached to RuBP. The result is a 6-

carbon molecule which splits into two 3-carbon molecules.

Rubisco speeds up this reaction.



• Reduction of Carbon Dioxide



• Regeneration of RuBP


Importance of Calvin Cycle

• PGAL (glyceraldehyde-3-phosphate) is the product of the Calvin cycle that can be converted to a variety of organic molecules.– A plant can utilize the hydrocarbon

skeleton of PGAL to form fatty acids and glycerol, which are combined in plant oils.



C4 Photosynthesis

• In C4 leaf, bundle sheath cells and mesophyll cells contain chloroplasts.

• Mesophyll cells are arranged concentrically around the bundle sheath cells.

• In hot, dry climates, net photosynthetic rate of C4 plants is about 2-3 times that of C3 plants.– Avoid photorespiration


C3 vs C4


Carbon Dioxide Fixation in C3 and C4 Plants


CAM Photosynthesis

• Crassulacean-Acid Metabolism– C4 plants partition carbon fixation in

space, while CAM partitions by time.During the night, CAM plants fix CO2,

forming C4 molecules, which are stored in large vacuoles.

C4 molecules release CO2 to Calvin cycle when NADPH and ATP are available.

Water Conservation



Review

• Flowering Plants• Photosynthetic Pigments• Photosynthesis

– Light ReactionsNoncyclicCyclic

– Calvin Cycle Reactions– C4

– CAM


Documents

Mader: Biology 8 th Ed. Photosynthesis Chapter 7