Alternative Mechanisms of Carbon Fixation
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11 Terms
1
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rubisco, moderate, mesophyll, rubisco, photorespiration
**C3 Plants**
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C3 plants include rice, wheat, and soybeans, trees, most flowers and lawn grasses. In most plants (C3 plants), ______ catalyzes the initial fixation of CO2 forming a three-carbon compound, 3-phosphoglycerate.
C3 plants have a ________ temperature range for proper photosynthetic efficiency.
Photosynthesis takes places at temperatures between **10 C – 30 C**
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When terrestrial plants close their stomata a hot, dry day, CO2 (g) levels inside the __________ drop as CO2 is consumed in the Calvin cycle. At the same time, O2(g) levels in the mesophyll rise as the light reaction converts light to chemical energy.
Remember that while _______ normally accepts CO2, when the concentration of O2 increases Rubisco can add O2 to RuBP. When this happens, RuBP splits into a three-carbon piece and a two-carbon piece in a process called **photorespiration**.
In fact, __________ decreases production of carbohydrates by up to 25% of the carbon fixed by the Calvin cycle on a hot, dry day.
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C3 plants include rice, wheat, and soybeans, trees, most flowers and lawn grasses. In most plants (C3 plants), ______ catalyzes the initial fixation of CO2 forming a three-carbon compound, 3-phosphoglycerate.
C3 plants have a ________ temperature range for proper photosynthetic efficiency.
Photosynthesis takes places at temperatures between **10 C – 30 C**
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When terrestrial plants close their stomata a hot, dry day, CO2 (g) levels inside the __________ drop as CO2 is consumed in the Calvin cycle. At the same time, O2(g) levels in the mesophyll rise as the light reaction converts light to chemical energy.
Remember that while _______ normally accepts CO2, when the concentration of O2 increases Rubisco can add O2 to RuBP. When this happens, RuBP splits into a three-carbon piece and a two-carbon piece in a process called **photorespiration**.
In fact, __________ decreases production of carbohydrates by up to 25% of the carbon fixed by the Calvin cycle on a hot, dry day.
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dehydration, stomata
Temperatures and amount of precipitation or ground water varies in different climates.
One of the major problems facing terrestrial plants is __________. At times, solutions to this problem require tradeoffs with other metabolic processes, especially photosynthesis.
The _______ are not only the major route for gas exchange (CO2 in and O2 out), but also for the evaporation of water. On hot, dry days, plants close their stomata to conserve water. This causes problems for photosynthesis.
One of the major problems facing terrestrial plants is __________. At times, solutions to this problem require tradeoffs with other metabolic processes, especially photosynthesis.
The _______ are not only the major route for gas exchange (CO2 in and O2 out), but also for the evaporation of water. On hot, dry days, plants close their stomata to conserve water. This causes problems for photosynthesis.
3
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photorespiration, spatial separation, mesophyll
C4 Plants
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Certain plant species have evolved alternate modes of carbon fixation to minimize __________. Examples of C4 plants are sugarcane, corn and weeds. C4 plants thrive in hot regions with intense sunlight.
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C4 plants first fix CO2 in a four-carbon compound using **_____ __________**.
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A unique leaf anatomy is correlated with the mechanism of C4 photosynthesis. In C4 plants, there are two distinct types of photosynthetic cells: bundle-sheath cells and _________ cells.
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Certain plant species have evolved alternate modes of carbon fixation to minimize __________. Examples of C4 plants are sugarcane, corn and weeds. C4 plants thrive in hot regions with intense sunlight.
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C4 plants first fix CO2 in a four-carbon compound using **_____ __________**.
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A unique leaf anatomy is correlated with the mechanism of C4 photosynthesis. In C4 plants, there are two distinct types of photosynthetic cells: bundle-sheath cells and _________ cells.
4
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bundle-sheath, mesophyll, chloroplasts, mesophyll, oxaloacetate
C4 Plants
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__________ cells are arranged into tightly packed sheaths around the veins of the leaf. _________ cells are more loosely arranged cells located between the bundle sheath and the leaf surface.
The Calvin cycle is confined to the ________ of the bundle-sheath cells. However, the cycle is preceded by the incorporation of CO2 into organic molecules in the ________.
The key enzyme, phosphoenolpyruvate carboxylase, adds CO2 to phosphoenolpyruvate (PEP) to form __________. PEP carboxylase has a very high affinity for CO2 and can fix CO2 efficiently when rubisco cannot (i.e., on hot, dry days when the stomata are closed).
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__________ cells are arranged into tightly packed sheaths around the veins of the leaf. _________ cells are more loosely arranged cells located between the bundle sheath and the leaf surface.
The Calvin cycle is confined to the ________ of the bundle-sheath cells. However, the cycle is preceded by the incorporation of CO2 into organic molecules in the ________.
The key enzyme, phosphoenolpyruvate carboxylase, adds CO2 to phosphoenolpyruvate (PEP) to form __________. PEP carboxylase has a very high affinity for CO2 and can fix CO2 efficiently when rubisco cannot (i.e., on hot, dry days when the stomata are closed).
5
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carbon, mesophyll, rubisco, high, minimizes
C4 Plants
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**The mesophyll cells pump these four-carbon compounds into bundle-sheath cells.**
### The bundle-sheath cells strip a ___ from the four-carbon compound as CO2, and return the three-carbon remainder to the _______ cells. The bundle-sheath cells then use ______ to start the Calvin cycle with an abundant supply of CO2.
**This means the mesophyll cells pump CO2 into the bundle-sheath cells, keeping CO2 levels ____ enough for rubisco to accept CO2 and not O2.**
**C4 photosynthesis _________ photorespiration and enhances sugar production.**
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**The mesophyll cells pump these four-carbon compounds into bundle-sheath cells.**
### The bundle-sheath cells strip a ___ from the four-carbon compound as CO2, and return the three-carbon remainder to the _______ cells. The bundle-sheath cells then use ______ to start the Calvin cycle with an abundant supply of CO2.
**This means the mesophyll cells pump CO2 into the bundle-sheath cells, keeping CO2 levels ____ enough for rubisco to accept CO2 and not O2.**
**C4 photosynthesis _________ photorespiration and enhances sugar production.**
6
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minimize, temporal separation
CAM Plants
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Another strategy to ________ photorespiration is found in succulent plants, cacti, pineapples, aloe and several other plant families. These plants are known as CAM plants for **crassulacean acid metabolism**.
Because Cam Plants live in hot, dry conditions, they collect light energy all day long with their stomata closed then open their stomata during the night for their carbon fixation reactions.
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This is called **______ _________**.
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Another strategy to ________ photorespiration is found in succulent plants, cacti, pineapples, aloe and several other plant families. These plants are known as CAM plants for **crassulacean acid metabolism**.
Because Cam Plants live in hot, dry conditions, they collect light energy all day long with their stomata closed then open their stomata during the night for their carbon fixation reactions.
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This is called **______ _________**.
7
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rate
**There are 5 factors in the environment that can affect the ____ of photosynthesis.**
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__**Light Intensity and the Rate of Photosynthesis**__
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__**Temperature and the Rate of Photosynthesis**__
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__**O2 Concentration and the Rate of Photosynthesis**__
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__**Photosynthetic Efficiency**__
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__**Sun Vs. Shade Plants**__
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__**Light Intensity and the Rate of Photosynthesis**__
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__**Temperature and the Rate of Photosynthesis**__
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__**O2 Concentration and the Rate of Photosynthesis**__
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__**Photosynthetic Efficiency**__
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__**Sun Vs. Shade Plants**__
8
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Irradiance, Compensation, Saturation
__**Light Intensity and the Rate of Photosynthesis**__
_________ = light intensity/unit area of leaf
Irradiance is zero in the dark and CO2 uptake into the leaf is (-). No photosynthesis occurs.
As irradiance increases, photosynthesis begins and increases until it equals CO2 released by photorespiration. This is called the **Light ___________ Point**. The point where CO2 uptake = the rate of CO2 evolution (output).
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Beyond the Light Compensation Point, photosynthesis increases in direct proportion to irradiance until the **Light _________ Point** is reached. The Light Saturation Point is the point where carbon fixation reactions are at the maximum.
_________ = light intensity/unit area of leaf
Irradiance is zero in the dark and CO2 uptake into the leaf is (-). No photosynthesis occurs.
As irradiance increases, photosynthesis begins and increases until it equals CO2 released by photorespiration. This is called the **Light ___________ Point**. The point where CO2 uptake = the rate of CO2 evolution (output).
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Beyond the Light Compensation Point, photosynthesis increases in direct proportion to irradiance until the **Light _________ Point** is reached. The Light Saturation Point is the point where carbon fixation reactions are at the maximum.
9
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redox, temperature
__**Temperature and the Rate of Photosynthesis**__
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Light reactions of photosynthesis are a series of _____ reactions occurring in the thylakoid membrane.
The rate of these reactions is affected by ___________. In general, an increase in temperature above 10C will increase the rate of photosynthesis.
C3 plants function best from 15C – 25C.
C4 plants function best at temps from 25C – 40C.
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Light reactions of photosynthesis are a series of _____ reactions occurring in the thylakoid membrane.
The rate of these reactions is affected by ___________. In general, an increase in temperature above 10C will increase the rate of photosynthesis.
C3 plants function best from 15C – 25C.
C4 plants function best at temps from 25C – 40C.
10
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competes
__**O2 Concentration and the Rate of Photosynthesis**__
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High oxygen concentrations inhibit photosynthesis because O2 _______ directly for Rubisco’s active site.
Therefore, as the **↑level of O2 increases = ↓decreasing photosynthesis**.
They are inversely proportional to each other.
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High oxygen concentrations inhibit photosynthesis because O2 _______ directly for Rubisco’s active site.
Therefore, as the **↑level of O2 increases = ↓decreasing photosynthesis**.
They are inversely proportional to each other.
11
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photons, moderate, higher
__**Photosynthetic Efficiency**__
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Photosynthetic Efficiency = __Net amount of CO2 uptake__
Unit area of light energy(______) absorbed
C3 plants are more efficient at ________ temperatures.
C4 plants are more efficient at ______ temperatures.
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Photosynthetic Efficiency = __Net amount of CO2 uptake__
Unit area of light energy(______) absorbed
C3 plants are more efficient at ________ temperatures.
C4 plants are more efficient at ______ temperatures.
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Note 
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