Answer: 2 graph
Explanation: The rotational-countercurrent system is represented by parallel knees of the Henle loop and the collecting tube, along which the liquid moves in different directions (countercurrent).
The countercurrent mechanism consists in the fact that the movement of the tubular fluid in the descending and ascending sections of the Henle loop, as well as in the direct arterial and venous vessels of juxtamedullary nephrons occurs in the OPPOSITE direction.
Potassium ions pass through the capillary wall and move along with the blood flow, and this is a different direction (that is, not along the Henle loop). The rotary mechanism is carried out in the knee of the Henle loop itself, where the movement of the tubular fluid receives the opposite direction.