Question

If photosynthesizing green algae are provided with CO2 containing an isotope of oxygen called "heavy oxygen" (18O), later analysis will show that all of the following molecules produced by the algae contain 18O except

A. O2.
B. glucose.
C. Glyceraldehyde 3-phosphate (G3P).
D. ribulose bisphosphate (RuBP).

Answer 1

A. O2.

Step-by-step explanation:

Carbon dioxide is known to have radioactive oxygen. We have to find where this radioactive oxygen is incorporated. This carbon dioxide couples to the RuBisCO enzyme and transforms ribulose bisphosphate into two 3-phosphoglyceric acid molecules. This is then transformed into glucose and ribulose bisphosphate is regenerated by 3-phosphoglyceric acid. Radioactive oxygen binds to 3-phosphoglyceric acid, glucose, and ribulose bisphosphate.

Answer 2

A) O2

Step-by-step explanation:

The CO2 is used for the synthesis of high energy molecules in photosynthesis. The carbon molecules are joined in the dark reaction of photosynthesis on the expenditure of energy produced in light reaction (ATP and NADPH).

• In the calvin cycle 3 molecules of CO2 are combined with three molecules of ribulose bisphosphate to produce six molecules of PGA (Phosphoglyceric acid). This molecule is converted to glucose after several steps and ribulose bisphosphate again formed from G3P.
• So each of the molecule which incorporated the CO2 in it would have O18 in it and that includes glucose, G3p and RuBP.
• As O2 is produced by splitting of water in the light reaction of photosynthesis , so it did not incorporate O18.