[Campbell Biology P.1031] Based on Figure 44.5 and general biological principles, why does th... | Practice Question

Based on Figure 44.5 and general biological principles, why does the movement of salt from the blood into the secretory tubules of a marine bird's nasal gland likely require energy expenditure in the form of ATP?

  • A: Salt movement always occurs against its concentration gradient in biological systems.
  • B: The transport epithelium actively pumps salt ions from an area of lower concentration in the blood to a higher concentration in the tubules.
  • C: The process is primarily driven by osmosis, which requires ATP to maintain water balance.
  • D: ATP is needed to synthesize the salt ions before they are secreted.

Explanation

Marine birds consume saltwater, leading to an excess of salt in their blood. To excrete this excess, salt must be moved from the blood likely lower concentration into the secretory tubules likely higher concentration against its electrochemical gradient. This type of movement, against a concentration gradient, requires active transport, which is powered by ATP, as hinted by the concept check question about freshwater fish.