Answer:
The correct answer is nucleus
Explanation:
DNA is made up of nucleotides, a deoxyribose sugar, and a phosphate group. There are four types of nucleotides which make the DNA that are adenine, guanine, cytosine, and thymine. DNA is formed inside the nucleus and after transcription, it forms RNA that moves out of the nucleus through the nuclear pore.
So if a plant cell containing radioactive nucleotides is grown in a test tube than after examination of cell the radioactivity will be concentrated in the nucleus because DNA is formed in the nucleus and nucleotide are its constituent.