Identifying visible cell structures in plant cell electron micrograph

Steps:

• Locate the large, double-membrane organelle with nucleolus and chromatin: identifies nucleus (1).
• Spot small, dense granules (10-30 nm) free in cytoplasm or on rough ER: confirms ribosomes (4).
• Identify narrow channels (20-50 nm) through cell walls connecting adjacent cells: reveals plasmodesmata (6).
• Absence of green plastids with thylakoids rules out chloroplasts; no tubular 25-nm filaments excludes microtubules; lack of double-membrane cristae eliminates mitochondria.

Why B is correct:

• Plasmodesmata are plant-specific cytoplasmic connections visible in EM as desmotubules linking cells, alongside universal nucleus and ribosomes.

Why the others are wrong:

• A: Chloroplasts (2) absent; no stacked thylakoid membranes shown.
• C: Chloroplasts (2) and microtubules (3) missing; no 25-nm hollow tubes or green organelles.
• D: Chloroplasts (2) not present; micrograph lacks photosynthetic structures.

Final answer: B