Osmosis in Hypertonic Saltwater

Steps:

• Frogs absorb water through permeable skin and maintain low internal ion concentration compared to freshwater.
• Sea water is hypertonic, with higher ion concentration outside the frog.
• Osmosis moves water from high to low concentration across the skin.
• Water exits the frog, causing dehydration.

Why D is correct:

• Osmosis is the net movement of water from a region of higher water potential (inside frog) to lower (sea water), defined by the concentration gradient.

Why the others are wrong:

• A: Incorrect; osmosis drives water out due to hypertonic external solution.
• B: Incorrect; ions diffuse into the frog down their concentration gradient, not out.
• C: Possible but not the primary threat; question focuses on water loss endangering frogs.

Final answer: D