Reference no: EM132423287

Problem: You collect 500 liters of water (containing its usual aquatic organisms) from near the surface of a lake, place it in a large clear plastic bag floating in the lake, and add to it a gram of the sugar glucose labeled with stable isotopes ¹³C and ¹⁸O (dual label in a single experiment). Expect the sugar to be taken up directly within a day or two by heterotrophic bacteria and then its component elements moved through the ecosystem by trophic processes, respiration, photosynthesis, and recycling. For the purposes of this question, use only the basic chemical transformations of respiration, photosynthesis, and trophic transfer, not secondary or exchange reactions. Also ignore background levels of these stable isotopes that occur in nature.

After one week, you take samples from the bag and examine them for the ¹³C and ¹⁸O originating from the added glucose. For the following subsamples, say which ones would have ¹³C and which ¹⁸O, and explain in a sentence or two how it got there:

A. Bacterial biomass (e.g. carbohydrate)

B. Biomass of protists that eat bacteria 

C. Phytoplankton (microscopic primary producers) biomass

D. Dissolved CO₂

E. Dissolved O₂ 

F. Water (H₂O)