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A photosynthesis experiment uses Chlorella to track the route taken by 14C in photosynthesis. The 14C is provided from CO2 and no new sources of CO2 are available. After the experiment the scientist extracts all of the starch produced and analyses the Carbon present. She finds that only half of the carbon is 14C. She repeats the experiment with more time and twice as much CO2 and finds that three quarters of the Carbon in the starch is radioactive.
Answer the following questions about the experiment:
Why is there radioactive Carbon in the starch? 2 marks
Why is only some of the Carbon in starch radioactive after the experiment? 2 marks
Using ideas from the Calvin cycle explain why doubling the amount of radioactive Carbon does not lead to all of the Carbon in starch being radioactive. 5 marks
How did Calvin himself use radioactive carbon? 5 marks
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To answer the questions about the experiment, let's break them down one by one:
1. Why is there radioactive Carbon in the starch?
There is radioactive Carbon in the starch because the experiment used Chlorella, a photosynthetic organism, to track the route taken by 14C in photosynthesis. The 14C is provided from CO2, which means that the carbon dioxide used in the experiment contains a radioactive isotope of carbon (14C). As the Chlorella performs photosynthesis, it incorporates the radioactive 14C into its organic molecules, including starch.
2. Why is only some of the Carbon in starch radioactive after the experiment?
After the experiment, only half of the carbon in the starch is radioactive. This could be due to the fact that the Chlorella might have only utilized a portion of the available CO2 during the photosynthesis process. Not all of the carbon dioxide taken up by the organism would contain the radioactive isotope (14C), resulting in a mixture of radioactive and non-radioactive carbon in the starch.
3. Using ideas from the Calvin cycle, explain why doubling the amount of radioactive Carbon does not lead to all of the Carbon in starch being radioactive.
The Calvin cycle is a series of reactions that take place in the chloroplasts of plants during photosynthesis. During this process, CO2 is converted into organic molecules, such as glucose, through a series of enzyme-catalyzed reactions.
Doubling the amount of radioactive Carbon (14C) does not lead to all of the Carbon in starch being radioactive because the Calvin cycle has a mechanism known as "carbon fixation" that involves the incorporation of CO2 into organic molecules. However, this process is not solely dependent on the availability of CO2 or the amount of radioactive Carbon.
The Calvin cycle has several enzymatic steps, and although additional 14C will increase the overall concentration of radioactive Carbon available, it does not directly impact the conversion of CO2 into organic molecules. The rate of carbon fixation is determined by the activity of the enzymes involved in the Calvin cycle and other factors such as temperature, light availability, and the availability of other necessary molecules, rather than simply the concentration of 14C.
4. How did Calvin himself use radioactive carbon?
Melvin Calvin, a scientist known for his work on the photosynthetic pathway called the Calvin cycle, used radioactive carbon (specifically 14C) to trace the flow of carbon during photosynthesis. He conducted experiments where he supplied plants with radioactive carbon dioxide (14CO2) and tracked its incorporation into organic molecules, including sugars and other compounds.
Using the radioactive carbon, Calvin was able to identify the intermediate molecules involved in the Calvin cycle and determine the sequence of reactions in this pathway. His experiments with radioactive carbon played a crucial role in elucidating the details of the carbon fixation process and understanding the flow of carbon during photosynthesis.