Question

low levels in plants. as a result, the enrichment of tissues with $^{14}$c indicates that the radio - labeled carbon from the air has been incorporated into those tissues.
the researchers measured the proportion of molecules containing $^{14}$c in a leaf of the plant over time in the chamber. the table below shows a sample of these findings.

time (minutes)	$^{14}$c in starch	$^{14}$c in proteins
60	34.4%	4.6%
180	37.2%	4.2%

data adapted from kolling et al 2019. plant methods. licensed under cc by 2.0.

based on this information, are the researchers likely to find $^{14}$c in nucleic acids in the leaf?

a. yes, the data suggest that the plant can uptake $^{14}$co$_2$ and use it to produce proteins, which are needed to synthesize nucleic acids.

b. yes, the data suggest the plant can uptake $^{14}$co$_2$ and use it to synthesize glucose, which can be modified to produce nucleotides.

c. no, the images show that the carbon atoms in nucleotides do not come from the glucose that a plant produces.

d. no, the data show that the plant is only able to synthesize starch and proteins using $^{14}$c from co$_2$.

Explanation:

1. Analyze the data: The table shows that \(^{14}\text{C}\) is incorporated into starch (a carbohydrate, related to glucose synthesis) and proteins over time, indicating the plant takes up \(^{14}\text{CO}_2\) and uses it in metabolic pathways.
2. Recall biological pathways: Glucose (from photosynthesis using \( \text{CO}_2\)) can be modified to form nucleotides (the building blocks of nucleic acids). Starch is a storage form of glucose, so the presence of \(^{14}\text{C}\) in starch implies glucose synthesis with \(^{14}\text{C}\), which can then be used for nucleotide (and thus nucleic acid) synthesis.
3. Evaluate options:

• Option A: Proteins are not directly used to synthesize nucleic acids (nucleic acids use nucleotides, which come from sugar - phosphate - base, not protein breakdown for synthesis). Eliminate A.
• Option B: The plant takes up \(^{14}\text{CO}_2\), uses it in photosynthesis to make glucose (starch is a glucose polymer, so \(^{14}\text{C}\) in starch shows glucose synthesis). Glucose can be modified to make nucleotides (for nucleic acids). This is correct.
• Option C: The data shows \(^{14}\text{C}\) in starch (glucose - based), and nucleotides can be made from glucose - derived molecules. So this is incorrect.
• Option D: The data shows \(^{14}\text{C}\) in starch and proteins, but metabolic pathways allow for other molecules (like nucleic acids) to be synthesized from the same carbon source. Eliminate D.

Answer:

B. Yes, the data suggest the plant can uptake \(^{14}\text{CO}_2\) and use it to synthesize glucose, which can be modified to produce nucleotides.