Question

In an experiment that carbon dioxide
available to a C3 plant was labeled with
a radioactive isotope and the amount of
radioactivity in the chloroplast was
measured. As photosynthesis proceeded,
in which of the following molecules did
the radioactivity first appear?
(A) PGAL
(B) Glucose
(C) PGA
(D) RuBP
​

Answer 1

Explanation:

Glucose

option c is the correct answer

Answer 2

Answer:

Calvin used the radioactive isotope of carbon (

1

4

C) of Chlorella. He observed that after second exposure of Chlorella in presence of

14 CO

2, the radioactive isotope of carbon was found mainly in 3-phosphoglyceric acid (PGA). This clearly indicated that the three carbon compound 3- phosphoglyceric acid was the first stable product photosynthesis and the carbon from the CO

2 is fixed in the preparation of the photosynthates.

Hence, the correct answer is 'PGA