iii. light dependent reactions a. photo-oxidation of chlorophyll b. chemiosmotic model of atp...
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
Night Day
7
14
1
Turn to your neighbor and…
Night
6 PM
4
9No ATP No ATP
The Big PictureWhat have we produced so far?
ATP NADPH CO2
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) CO2 molecules enterRubisco attaches the CO2 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 RespirationIn CR electron carriers bring electrons to the ETC, and O2 finally accepts them and is reduced to H2O.
In photosynthesis H2O brings electrons to the ETC and becomes O2, an electron carrier finally accepts the electrons.
Differences between cellular respiration and photosynthesis.During the Calvin cycle, CO2 is being reduced into sugar
CO2
During the Krebs cycle, sugars are oxidized and become CO2
Photosynthetic Adaptations
What problems may a plant experience when it is exposed to arid (dry) conditions?
Dehydration
Elevated O2 levels in the leaves
Response
Close stomata to prevent dehydration
Photorespiration Rubisco – an enzyme that catalyzes the addition of CO2 to RuBP.
O2 competes with CO2 for the active site on Rubisco.
PhotorespirationCalvin cycle sometimes called the C3 pathway
Rubisco
RuBp CO2
RuBp
Rubisco
P G A P G A
P G A
Later becomes glucose!
CO2CO
2
O2
Photorespiration – these CO2’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!!!
CO2 + RuBP2 molecules of 3-phosphoglycerate
CO2
Com
peti
ng
react
ion
s
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 CO2 and O2
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 (C4 plants)… O2
C4 pathway
C3 pathway
Separate CO2 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 CO2 in organic acids.
Organic acid
CO2
CO2
Calvin Cycle
sugar• CO2 is released from organic acids in the day and used in the Calvin cycle.
The Silversword