Lecture_3 - Lecture #3 BioS 230 Fall 2009 Importance of...

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Lecture #3 BioS 230 Fall 2009 Importance of Plants Chapter 6 (Chapter 5 dealt with in Evolution section of course,) Life is dependent on autotrophs – organisms that can use a source of energy and simple materials to build the macromolecules that are necessary to sustain living process. What are the elements that are part of all carbohydrates, lipids, proteins and nucleic acids? At the present time on earth the atmosphere was a lot of O 2 (200,000 ppm) and very little CO 2 370 ppm. Oxygen is a by-product of photosynthesis and a reactant of respiration ←photosynthesis Sugar + oxygen respiration→ water + carbon dioxide Plants are the organisms that are able to capture the energy of sunlight to produce the reduced organic compounds that are necessary for life and which are utilized by animals. Photosynthesis has two distinct components: 1) the Light Reaction centers and 2) the Dark Reaction Center. The Light Reaction Centers How does photosynthesis capture light energy and convert it to bond energy? (Fig. 6.1) Blue and red wave lengths of light are utilized most efficiently by the light reaction center including pigments such as chlorophyll to produce ATP and NADPH (from NADP). The light reaction centers (PS I and PS II) absorb energy and generate a high oxidation reduction potential. This boosts energy level (quantum states) then goes through the Electrong Transport Chain ( ETC ) before returning to ground level. It is the movement of electron in the ETC that results in production of ATP (from ADP & P) and NADPH (from NADP & H2O). These ‘light reactions’ take place within chloroplasts (organelles with their own DNA). The biochemical assimilation of CO2 will not move forward unless there is ATP and NADPH generated from the LRC. This is why light is considered as substrate for PS and, any limitations in light availability will affect PS. The Dark Reaction center or Calvin/Benson Cycle Carbon enters the system when CO2 combines with a 5 carbon sugar, Ribulose-1,5- bisphosphate (RuBP) to form two 3 carbon compounds. In overwhelming majority of plants, the first stable products of PS are these C3 compounds hence this path way of PS is referred to as C3 path way of PS. In this pathway, the reaction is catalyzed by the enzyme named RBUPcarboxylase (rubisco). In a small subgroup of plants, the first stable compound produced by PS is a 4-C compound hence this is called C4 pathway of PS. In C4 plants the initial enzyme responsible for CO2 fixation is PEPcarboxylase but the final stages of CO2 fixation will still go through Rubisco.
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These differences between C3 and C4 pathway of photosynthesis, give rise to different ecological adaptation. Generally, C4 species exhibit higher water use efficiency (WUE) than C3 plants thus they are more drought resistant. They also have a higher tolerance for heat stress. So, it is not surprising that they often occupy hot dry climates. C4 plants also have a better
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This note was uploaded on 01/23/2010 for the course BIOS 230 taught by Professor Gibbons during the Fall '08 term at Ill. Chicago.

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Lecture_3 - Lecture #3 BioS 230 Fall 2009 Importance of...

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