Question

the scientists tested the tissue samples at the end of the investigation. their results are presented in the table. fatty acids and glycerol are carbon - based molecules that make up adipose tissue.

product	% labeled c1 in product	% labeled c6 in product	% labeled h1 in product	% labeled h3 in product
glycerol	8.15	12	9.7	5.35

how can the scientists best explain the presence of labeled carbon and hydrogen in fatty acids and glycerol?

a. the fatty acids and glycerol naturally contain labeled carbon and hydrogen and transferred the labeled atoms to the glucose molecules.

b. the labeled glucose was broken down into smaller molecules containing labeled carbon and hydrogen, which were then used to build fatty acids and glycerol.

c. the glucose molecules released energy that was then used to directly transfer labeled carbon and hydrogen from glucose to fatty acids and glycerol.

d. the labeled carbon and hydrogen atoms from glucose were directly exchanged with unlabeled carbon and hydrogen atoms in fatty acids and glycerol.

Explanation:

• Option A: Fatty acids/glycerol don't naturally have labeled atoms to transfer to glucose; this is illogical.
• Option B: Glucose (a carbohydrate) can be broken down into smaller molecules (like acetyl - CoA) which are used to synthesize fatty acids and glycerol (components of lipids). If glucose was labeled, these smaller molecules would carry the label, explaining the labeled C and H in fatty acids/glycerol.
• Option C: Energy release from glucose (like in respiration) doesn't directly transfer atoms to build lipids; atom transfer for building occurs via metabolic pathways (like synthesis), not energy transfer.
• Option D: There's no direct exchange of atoms between glucose and fatty acids/glycerol; lipid synthesis uses building blocks from glucose breakdown, not direct atom exchange.

Answer:

B. The labeled glucose was broken down into smaller molecules containing labeled carbon and hydrogen, which were then used to build fatty acids and glycerol.