Low plasma proteins reduce osmotic pull, causing edema

Steps:

• Protein deficiency lowers plasma albumin, reducing colloid osmotic pressure in blood.
• This makes blood water potential less negative (higher) than in tissues.
• Fluid leaks out of capillaries into tissues but fails to return effectively.
• Excess fluid accumulates in abdomen, causing edema.

Why B is correct:

• Shortage of plasma proteins decreases solute concentration, raising blood water potential (ψ = ψ_s + ψ_p; less negative ψ_s means higher ψ), so less fluid re-enters via osmosis.

Why the others are wrong:

• A: Shortage actually increases (not decreases) blood water potential.
• C: Protein shortage affects plasma (not tissue fluid) water potential; more water leaves due to blood changes.
• D: Incomplete and irrelevant; diet shortage impacts plasma proteins, not directly causing weakness here.

Final answer: B