Sucrose maintains isotonic conditions for mitochondrial integrity

Steps:

• Mitochondria are isolated from cells and must retain natural structure for accurate microscopy.
• Exposure to hypotonic or hypertonic solutions causes osmotic water flow, altering organelle size.
• 0.25M sucrose provides an isotonic environment matching intracellular osmolarity.
• This prevents swelling or shrinking, preserving dimensions for clear imaging.

Why C is correct:

• Isotonic solutions like 0.25M sucrose balance osmotic pressure with the cell interior, preventing net water movement and dimensional changes (definition of isotonicity).

Why the others are wrong:

• A: Water acts as the solvent; sucrose is the osmoprotective solute.
• B: Sucrose isolation doesn't measure reaction rates; that's for enzymatic assays.
• D: Mitochondria use substrates like glucose or Krebs cycle intermediates for energy, not sucrose.

Final answer: C