If plants are grown for several days in an atmosphere containing 14CO2 in place of 12CO2, one would expect to find:
very little radioactivity in the growing leaves
large amounts of radioactive water released from the stomates
a large increase in 14C in the starch stored in the roots - Correct!!!
a large decrease in the rate of carbon fixation in the guard cells
an increase in the activity of RuBP carboxylase in the photosynthetic cells
Can someone explain why this answer (#3) is correct?
I think this is a poorly worded question andthe answers are poor too. Why?
If plants are grown for several days in "how much 14CO2" in place of "how much 12CO2" doesn't tell us the conditions initially.
The answers are not much better. "A large/small increase/decrease" doesn't tell us much. How much is large and how much is small. However, in view of all of this, I think your answer probably is the one your prof wants.
The answer (#3) is correct because during photosynthesis, plants reduce carbon dioxide (CO2) to form organic molecules, such as glucose or starch. The carbon atoms in CO2 are utilized by plants to build these organic molecules. In the given scenario, if plants are grown in an atmosphere containing 14CO2 instead of the normal 12CO2, the plants will incorporate the radioactive carbon isotope (^14C) into the organic molecules they produce.
Since plants store excess sugars and other organic molecules in their roots as starch, a large increase in ^14C in the starch stored in the roots can be expected. This is because ^14C is readily incorporated into the organic molecules, including starch, during photosynthesis when plants are exposed to ^14CO2.
Therefore, the correct answer is that one would expect to find a large increase in ^14C in the starch stored in the roots.
Yes, I can explain why option 3 is the correct answer in this scenario.
To understand why a large increase in 14C (radiocarbon) would be expected in the starch stored in the roots, we need to understand the process of photosynthesis and how plants acquire and use carbon dioxide (CO2) during this process.
During photosynthesis, plants take in CO2 from the atmosphere through tiny openings called stomata on their leaves. Inside the plant cells, CO2 is converted into glucose (a simple sugar) through a series of chemical reactions. Some glucose is used immediately for energy by the plant, but excess glucose is converted into starch and stored in the roots for later use.
Now, let's consider the scenario where plants are grown in an atmosphere containing 14CO2 instead of the usual 12CO2. This means that the CO2 available for photosynthesis has an additional two neutrons, making it radioactive.
As plants continue to carry out photosynthesis using 14CO2, the radioactive carbon will be incorporated into the glucose molecules formed during the process. Since excess glucose is converted into starch and stored in the roots, the starch in the roots will contain the radioactive carbon.
Therefore, by exposing plants to an atmosphere with 14CO2 for several days, we would expect a large increase in 14C in the starch stored in the roots. This is because the radioactive carbon from the 14CO2 would be incorporated into the glucose molecules, which are then converted into starch and stored in the roots. It is important to note that the starch stored in the roots would have the highest concentration of 14C compared to other plant parts, such as leaves or stems.
Hence, option 3 is the correct answer as it explains the expected outcome of exposing plants to an atmosphere containing 14CO2.