Monday, December 15, 2008

Chapter 10 Notes

There are two other ways in which plants can fix carbon—C4 photosynthesis and CAM photosynthesis

Lots of plants living in hot, dry climates use C4 fixation instead of C3 fixation (the standard Calvin cycle). In C4 fixation, the first carbon compound formed in the Calvin cycle contains four carbons instead of three.

C4 plants have two different kinds of photosynthetic cells: bundle-sheath cells and mesophyll cells. The bundle-sheath cells are grouped around the leaf’s veins, and the mesophyll cells are dispersed elsewhere around the leaf.

The steps of C4 photosynthesis are as follows:

1. CO2 is added to phosphoenolpyruvate (PEP) to form the four carbon compound oxaloacetate of oxaloacetate acid. This enzyme is catalyzed by PEP carboxylase, and this process is very quick and efficient.

2. Mesophyll cells export the oxaloacetate to the bundle sheath cells, which break the oxaloacetate back down into CO2.

3. The CO2 is converted into carbohydrate through the regular Calvin cycle.

Basically C4 photosynthesis is just a way to speed up regular photosynthesis, since PEP carboxylase works much faster than rubisco, the enzyme o fC3 photosynthesis.

The alternative to C3 photosynthesis is CAM photosynthesis

CAM photosynthesis is also an adaption to hot dry climates. The plants that participate in this kind of photosynthesis open their stomata at night and close them during the day, so that they experience minimal water loss during the day when the sun is out. (Non-CAM plants do the opposite of this). Because their stomata are closed during the day, CO2 can’t get into the leaves during the day—so they take it up at night.

CAM plants take CO2 into their leaves at night, convert it into carious rganic compounds, and put it into temporary storage in their vacuoles. When morning comes and their stomata close, these plants release the stored CO2 so that they can use light energy to perform the normal reactions of photosynthesis.

In both C4 and CAM photosynthesis, CO2 is first transformed into an organic intermediate before it enters the Calvin cycle. All of the processes—C3, C4 and CAM photosynthesis—use the Calvin cycle; they just have different methods for getting there.

What are the two ways in which plants can fix carbon?
a) C4 photosynthesis
b) the Calvin Cycle
c) CAM phosphorylation
d) ATP synthase

Which process is most directly driven by light energy?
a) creation of a pH gradient by pumping protons across teh thylakoid membrane
b)carbon fixation in the stroma
c)reduction of NADP+ molecules
d) removal of electrons from the chloroplasts from chlorophyll molecules
e)ATP synthase

Cooperation of the two photosystems of the chloroplast is required for?
a) ATP synthesis
b)reduction of NADP+
c)cyclic photophosphorylation
d) oxidation of the reaction center of photosystem I
e)generation of a proton-motive force

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