Circular DNA in Plant Cells Steps:

• Identify small circular DNA as mitochondrial or chloroplast genomes in eukaryotic cells.
• Note that P has uniform DNA sequence, indicating one organelle type (mitochondria only).
• Note that Q has two different DNA sequences, indicating two organelle types (mitochondria and chloroplasts).
• Match to plant cells: roots lack chloroplasts, leaves have both.

Why D is correct:

• Leaf mesophyll cells contain chloroplasts (unique cpDNA) and mitochondria (mtDNA), yielding two distinct circular DNAs; root cortical cells have only mtDNA with identical sequences.

Why the others are wrong:

• A: Mature red blood cells lack organelles and DNA; heart cells have only uniform mtDNA, no bacterial involvement.
• B: Mature blood cells lack DNA; phloem sieve tubes lack nuclei but not dual circular DNAs from bacteria.
• C: Identical to D, but assumes no distinction in cell types for dual DNA.

Final answer: D