1. How has the process of photosynthesis evolved in a C3 plant?
A) The process uses a RuBP enzyme to fix CO2 to create a 3-carbon compound.
B) Extra CO2 is stored in a C4 compound and can be released when needed.
C) Stomata can remain closed during hot and dry conditions, but available CO2 in tissues allows photosynthesis to proceed when light is available.
D) During the day, malic acid is broken down to release CO2 to the Calvin-Benson cycle
Called C3 because the CO2 is first incorporated into a 3-carbon compound. Stomata are open during the day. RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of CO2. Photosynthesis takes place throughout the leaf.
Adaptive Value: more efficient than C4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy). Most plants are C3.
2. How has the process of photosynthesis evolved in a C4 plant?
A) Use a different enzyme to fix CO2 to create a 4- carbon compound (oxaloacetate).
B) Extra CO2 is stored in a C4 compound and can be released when needed.
C) Stomata can remain closed during hot and dry conditions, but available CO2 in tissues allows photosynthesis to proceed when light is available.
D) The compound can be broken down to pyruvate and CO2 when needed.
E) All of the above
Called C4 because the CO2 is first incorporated into a 4-carbon compound. Stomata are open during the day. Uses PEP Carboxylase for the enzyme involved in the uptake of CO2. This enzyme allows CO2 to be taken into the plant very quickly, and then it "delivers" the CO2 directly to RUBISCO for photsynthesis. Photosynthesis takes place in inner cells.
Adaptive Value:
Photosynthesizes faster than C3 plants under high light intensity and high temperatures because the CO2 is delivered directly to RUBISCO, not allowing it to grab oxygen and undergo photorespiration.
Has better water use efficiency because PEP Carboxylase brings in CO2 faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis. C4 plants include several thousand species in at least 19 plant families. Example: fourwing saltbush pictured here, corn, and many of our summer annual plants.
3. How has the process of photosynthesis evolved in a CAM plant?
A) CO2 is stored during the night and is converted to a 4-carbon compound (malic acid) which accumulates in the central vacuole of cells.
B) During the day, malic acid is broken down to release CO2 to the Calvin-Benson cycle.
C) Stomata can remain closed during hot and dry conditions, but available CO2 in tissues allows photosynthesis to proceed when light is available.
D) The stomata can remain closed during hot and dry conditions and be open at night to allow photosynthesis to proceed when light is available
E) All of the above
Stomata open at night (when evaporation rates are usually lower) and are usually closed during the day. The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released to RUBISCO for photosynthesis.
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