Through studies of insect Malpighian tubules, researchers found that K+ accumulated on the inner face of the tubule, against its concentration gradient. What can you infer about the mechanism of transport?
A) Potassium transport is a passive process.
B) Movement of potassium into the lumen of the Malpighian tubules is an energy-requiring process.
C) Potassium moves out of the tubules at a faster rate than it moves into the lumen of the tubules.
D) Sodium ions will follow potassium ions.
Answer: B