Why is there radioactive Carbon in the starch?


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

i got a deadline please help me.