Question

A plant cell was grown in a test tube containing radioactive nucleotides, the parts from which DNA is built. Later examination of the cell showed the radioactivity to be concentrated in the
A. Rough ER
B. Dictyosome
C. Smooth ER
D. Nucleus

Answer 1

Nucleic Acids are the basic constitute of the nucleus and the nucleus made up of DNA, and the basic structural and functional unit of the DNA is nucleotide, where it is made up of nitrogen base, and phosphate and sugar molecule, if the phosphate is absent, then it is said called as nucleoside.

Complete answer:
In the above question they said that the plant cell was grown in a test tube, as we know that plant cell has various structures.
The plant cell is eukaryotic, and the plant cell has a cell wall made up of cellulose, hemicellulose and pectin.
Various cell organelles are present, and the special organelle present in the eukaryotic plant cells is plastids, because of this plastids plants able to undergo photosynthesis, and other important organelles are mitochondria, which is power house of the cell and the endoplasmic reticulum which are of two types, that is rough and smooth.
So the plant cells growing with radioactive nucleotides, as we know that nucleotides are a part of DNA, as plant is culturing, which is means it dividing and differentiated into different parts, as the plant cell is dividing, DNA also divides, this DNA is present in nucleus, so the Radioactive nucleotides are present in the nucleus of the plant cells.

So the correct option is D.

Note: To understand in simple manner, radioactive nucleotides are part of DNA, and this DNA is generally present in the Nucleus so as the plant is culturing and growing, the cells are divided so this radioactive nucleotides are more concentrated in the nucleus.