Pathways of Photosynthesis Flashcards
What is the adaptive purpose of photosynthesis?
Photosynthesizers must adapt to Earth’s variable climate.
State the chemical equation of photosynthesis.
6CO2 + 12H2O + Light —> C6H12O6 + 6O2 + 6H2O
REACTANTS PRODUCTS
What is the status of CO2 concentrations in the atmosphere in relation to other gases?
CO2 concentration is low in the atmosphere.
How much of the water that is absorbed by the plant used for photosynthesis?
Less than 1%
A plant’s light availability is dependent on what conditions?
- atmospheric conditions.
- altitude
- season
- latitude
What part of a plant is considered the major “organ” of photosynthesis?
leaves
Describe the process of gas exchange in a plant during photosynthesis.
The stomata allows for gas exchange between the mesophyll and the atmosphere.
Where are the chloroplasts found in the plant?
Mesophyll
Where is the site of light reactions found in a plant?
thylakoids located in the chloroplast
What is the process of the light reactions and what do they ultimately result in?
“Light striking chlorophyll within the chloroplasts.”
- Converts light energy into chemical energy for the plant.
What are the two processes that occur when the light is absorbed by the chlorophyll.
*HINT: transfer & formation
- A transfer of hydrogen (from H2O) and electrons cause NADP+ to convert to NADPH.
The NADPH is used to energize Calvin Cycle - Formation of ATP from ADP: Phosphorylation
What are the inputs and outputs of the light reactions.
Water enters –> LIGHT RXN –> produces oxygen
What are the inputs and outputs of the Calvin Cycle?
AKA: Light independent or dark rxn
carbon dioxide enters –> DARK RXN –>produces sugar
(CH2O)
*Calvin Cycle uses NADPH & ATP from the light rxns.
What is the initial step of the Calvin Cycle?
STEP A. Carbon Fixation: CO2 enters Calvin cycle attached to RuBP (5carbon ribulose biphosphate)
6 carbon sugar is unstable so it splits into two 3PGA (3-carbon phosphoglycerate)
Carbon fixation is catalyzed by enzyme: Rubisco
What is the second step of the Calvin Cycle?
STEP B: Each 3PGA (2 total) receives phosphate from ATP.
NADPH donates electrons, reducing 3GPA to a sugar.
1 molecule of the sugar leaves the cycle to be used in other part of plant. Remaining sugar is used to rebuild RuBP.
What is step three of the Calvin Cycle?
Regeneration of RuBP via leftover sugars from second step.
What is Rubisco? What are the two substances Rubisco has an affinity for?
Rubisco is the enzyme responsible for carrying CO2 and O2. (Carbon dioxide & oyygen)
What three (3) mechanisms convert CO2 (carbon dioxide) to carbohydrates during light-independent reactions?
a. 3-Carbon pathway “C3” (AKA Calvin Cycle)
b. 4-Carbon pathway “C4”
c. Crassulacean Acid Metabolism “CAM”
Define:
Photorespiration
Using oxygen to produce a 3-carbon compound and 2-carbon compound.
What properties are unique to photorespiration?
Compare to photosynthesis
Uses O2 (oxygen), produces 2-carbon and 3-carbon compounds, output = CO2 (carbon dioxide).
Fewer carbohydrates produced.
Short-term response to hot temperatures when stomata are closed.
What properties are unique to photosynthesis?
Compare to photorespiration
Uses CO2 (carbon dioxide)
produces 3-carbon compounds
output = O2
What properties do photosynthesis and photorespiration share? (similarities)
Both use rubisco.
Both do light reactions.
Both do calvin cycle
Both produce carbohydrates.
What are plants called when they have a C3 pathway? Explain why.
They’re called “cool season” plants because the rate of photorespiration increases with rising temperatures.
As temp. rises, the stomata close, the rubisco uses up the oxygen and therefore can’t photosynthesize as there is no glucose.
Examples of C3 plants: onions, potatoes, spinach, wheat.
What are two adaptations that arose in order to decrease photorespiration?
C4 and CAM pathways
