A researcher wants to determine if a unicellular organism he discovered is an autotroph or a heterotroph. He radioactively labels the carbon in CO2 and C6H12O6 and exposes one culture of his organism to the labeled CO2 and another culture to the labeled C6H12O6. What would happen if his organism is an autotroph?

The labeled Cabon will be present in carbohydrate of organism in  the culture labelled with CO2.

Explanation:

Organism with ability to produce their own foods as complex organic subtance, from simple inorganinc form are called Autotroph.They do not depend on other organins for survivals.Rather they make use of sunlight as source of energy as in photosynthensis, or byproducts of some inorganic chemical reactions as in Chemosynthesis.

In this scenario, the researcher  was investigating photosynthesis.

the first step in photosynthesis is the splitting of water molecules to; H+ , e-and O2, during light dependent stage.This is photolysis of water.

the second stage which is light independent stage, involved the reduction of the C02 by H+ in Calvin Cycle to form   carbohydrate as C6H12O6.

Therefore, if the organism happens to be an autotrophs it should reduces the labelled CO2 to glucose as C6H1206, Therefore  labelled Carbon of C02 must be present in the carbohydrate of the organism.Autotrops makes use of inorganic molecules to synthesize their foods. CO2 is inorganic. This further prove that the labeled C  of CO2 must be present in the CHO of the organism.

i think the answer would d