Photosynthesis Review

1) After Thanksgiving break you return to the HTHMA garden to find that your crops have not been watered in over two weeks. Most of your plants are dead and those that are alive are barely hanging on.  In relation to the process of photosynthesis, describe what has happened to your plants.

 

 In photosynthesis, CO2, H2O, and sunlight come together to create O2 and sugars. If any of the main reactants were limited or nonexistent, the process of photosynthesis would either stop entirely or be greatly impaired. Therefore, if water supply of our crops were to be cut off for two weeks, photosynthesis would eventually come to a halt during that time. The light dependent reactions would be those most affected because they use H2O and light to produce O2, but, without one working, the Calvin Cycle would not work either. Because plants are autotrophs, and rely on photosynthesis to make their own food, without water they have no photosynthesis, and without photosynthesis they basically have no food or nutrients. So, during your two week hiatus, your plants would pretty much starve and wither away.

2) Upon microscopic inspection of the underside of your plant’s leaves, you notice that in an attempt to conserve water the stomata (aka stomates) are closed. Explain in detail how this impacts the light independent reactions of photosynthesis.

The stomata are the openings on the underside of the leaf through which CO2, O2, and H2O can pass through, so when the stomata are closed, none of the above can move in or out of the plant.  Because CO2 is used in the light independent reactions during photosynthesis to produce sugars, if the stomata were closed and CO2 was unable to move around, the photosynthesis (or at least the Calvin Cycle) would be impaired or altogether halted.