III. Light Dependent Reactions A. Photo-oxidation of Chlorophyll B. Chemiosmotic model of ATP production. IV. Light Independent Reactions A. Calvin Cycle.

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Presentation transcript:

III. Light Dependent Reactions A. Photo-oxidation of Chlorophyll B. Chemiosmotic model of ATP production. IV. Light Independent Reactions A. Calvin Cycle II. How plants harness sunlight I. Anatomy of Photosynthesis

Non-cyclic Photophosphorylation pH = 4 pH = 8 + charge - charge

Cyclic photophosphorylation Make extra ATP

Graph changes in pH of the thylakoid interior over one 24 hr period. Indicate when ATP production during the light reactions is zero. 6AM pH NightDay Turn to your neighbor and… Night 6 PM 4 9 No ATP

The Big Picture What have we produced so far? ATP NADPHCO 2 provides the energy provides high energy electron and H + ions provides the carbon and oxygen Used to make energy rich sugar molecules during the light independent reactions!

The Calvin Cycle

(3) CO 2 molecules enter Rubisco attaches the CO 2 to RuBP CARBON FIXATION

6 ATP and 6 NADPH used REDUCTION 1 G3P molecule produced

Regenerate RuBP Use 3 more ATP

And boy can plants fix carbon!

What do plants do with the sugars they make? most! Fuel cellular respiration

Similarities between photosynthesis and cellular respiration… Chemiosmosis Energy Coupling Examples

Differences between cellular respiration and photosynthesis. Photosynthesis Cellular Respiration In CR electron carriers bring electrons to the ETC, and O 2 finally accepts them and is reduced to H 2 O. In photosynthesis H 2 O brings electrons to the ETC and becomes O 2, an electron carrier finally accepts the electrons.

Differences between cellular respiration and photosynthesis. During the Calvin cycle, CO 2 is being reduced into sugar CO 2 During the Krebs cycle, sugars are oxidized and become CO 2

Photosynthetic Adaptations What problems may a plant experience when it is exposed to arid (dry) conditions? Dehydration Elevated O 2 levels in the leaves Response Close stomata to prevent dehydration

Photorespiration Rubisco – an enzyme that catalyzes the addition of CO 2 to RuBP. O 2 competes with CO 2 for the active site on Rubisco. Photorespiration Calvin cycle sometimes called the C 3 pathway

Rubisco RuBp CO 2 RuBp Rubisco P G A Later becomes glucose! CO 2 O2O2 Photorespiration – these CO 2 ’s did not get incorporated into glucose this time!

Photorespiration can lead to lower photosynthetic output by siphoning carbon from the Calvin cycle! They produce less sugar!!!

CO 2 + RuBP 2 molecules of 3- phosphoglycerate CO 2 Competing reactions rubisco Turn to your neighbor and discuss the following questions… 1) What factor determines which reaction below occurs more often? a)The concentration of rubisco b)The relative concentration of CO 2 and O 2 c)The concentration of RuBp 2) This is most similar to which of the mechanisms of enzyme regulation we discussed earlier in the semester?

Adaptations to arid climates A) C4 plants - spatial separation of steps B) CAM plants - temporal separation of steps

Leaf anatomy of plants adapted for hot/arid conditions (C 4 plants)… O2O2 C 4 pathway C 3 pathway Separate CO 2 fixation and sugar making into two different cells

CAM Plants - steps performed at different times Close their stomata during the day to minimize water loss, and open stomata at night. Desert plants…cacti, succulent plants, pineapples… At night they store CO 2 in organic acids. Organic acid CO 2 Calvin Cycle sugar CO 2 is released from organic acids in the day and used in the Calvin cycle.

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