AP Bio 8.3
Photorespiration
A metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide.
C3 plants
A plant that uses the Calvin cycle for the initial steps that incorporate CO2 RuBp into three carbon compound 3 phosphoglycerate, forming a three-carbon compound as the first stable intermediate.
glyceraldehyde 3-phosphate (G3P)
A three-carbon carbohydrate that is the direct product of the Calvin cycle; For net synthesis of one molecule of G3P, the cycle must take place three times, fixing three molecules of CO2-one per turn of the cycle.
crassulacean acid metabolism (CAM)
A type of metabolism in which carbon dioxide is taken in at night and incorporated into a variety of organic acids. During the day, CO2 is released from the organic acids made the night before to become incorporated into sugar in the chloroplasts
Reduction
Each molecule of 3 -phosphoglycerate receives an additional phosphate group from ATP, becoming 1,3-bisphosphoglycerate. Next, a pair of electrons donated from NADPH reduces 1,3-bisphosphoglycerate, which also loses a phosphate group, becoming G3P.
What happens in carbon fixation?
The Calvin cycle binds CO2 to RuBP ( 5 Carbon ribulose bisphophate) through rubisco(an enzyme that catalyzes this process). The product of the reaction is a six-carbon intermediate so unstable that it immediately splits in half, forming two molecules of 3-phosphoglycerate (for each CO2 fixed).
How is stomata and water related?
They are the main avenues of the evaporative loss of water from leaves and may be partially or fully closed on hot, dry days. This prevents water loss, but it also reduces CO2 levels; doesn't have photosynthetic adaptations to reduce photorespiration
What happens in the Calvin Cycle?
Carbon enters the Calvin cycle in CO2 and leaves in sugar
Explain why a poison that inhibits an enzyme of the Calvin cycle will also inhibit the light reactions
The light reactions require ADP and NADP+ , which would not be formed in sufficient quantities from ATP and NADPH if the Calvin cycle stopped.
What happens when weather is hot in the C4 plants?
a C4 plant partially closes its stomata, thus conserving water
How are the large numbers of ATP and NADPH molecules used during the Calvin cycle consistent with the high value of glucose as an energy source?
Glucose is a valuable energy source because it is highly reduced storing lots of potential energy in its electrons. To reduce CO2 to glucose, a large amount of energy and a lot of reducing power are required in the form of large numbers of ATP and NADPH
Regeneration
In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle into three molecules of RuBP. To accomplish this, the cycle spends three more ATPs. The RuBP is now prepared to receive CO2 again, and the cycle continues.
C4 plants
Light-dependent reactions occurring in the mesophyll cells (spongy tissue in the middle of the leaf) and the Calvin cycle occurring in bundle health cells. atmospheric Co2 is incorporated to form 4 carbon molecule
Describe how photorespiration lowers photosynthetic output.
by adding oxygen, instead of carbon dioxide, to the Calvin cycle. As a result, no sugar is generated (no carbon is fixed), and 02 is used rather than generated.
