All of the following things occur during meiosis I. Select the statement below that does NOT occur during meiosis I.

A. osmosis. Water moves passively across the renal tubular epithelium following osmotic gradients established by the active transport of solutes like sodium. This process, often referred to as obligatory water reabsorption in the proximal tubule, allows water to diffuse through aquaporins. It does not require direct ATP consumption for the water molecules themselves.

B. filtration. Filtration is the process that occurs exclusively in the renal corpuscle where blood is processed into filtrate. Once the fluid enters the renal tubules, the movement of substances back into the blood is classified as reabsorption. Filtration is driven by hydrostatic pressure, whereas tubular water movement is driven by osmotic concentration differences.

C. active transport. There are no known biological pumps that directly use ATP to move water molecules against a concentration gradient. Biological systems move water by actively transporting solutes and allowing water to follow passively. All water movement in the kidney is a response to osmotic or hydrostatic forces rather than direct active pumping.

D. cotransport with sodium ions. While many solutes like glucose and amino acids use secondary active transport (cotransport) with sodium, water moves through separate channel proteins called aquaporins. Sodium reabsorption creates the osmotic drive, but the water molecules do not bind to the carrier proteins alongside sodium. Water movement is the result of the sodium transport, not a shared transport mechanism.

A. decreases surface area of the scrotum, increases its thickness, and prevents heat loss: The dartos is a layer of smooth muscle within the superficial fascia of the scrotum. When it contracts in response to cold temperatures, it causes the scrotal skin to wrinkle and tighten. This reduction in surface area and the resulting thickening of the wall minimizes radiant heat loss to the environment.

B. allows scrotum and testes to hang lower from the body: This occurs when the dartos and cremaster muscles relax, typically in response to warm temperatures. Moving the testes away from the pelvic cavity promotes cooling by increasing the distance from core body heat. Relaxation is a heat-dissipating mechanism rather than a result of muscle contraction.

C. elevates the scrotum: While the dartos contributes to the tightening of the sac, the primary muscle responsible for the vertical elevation of the testes toward the inguinal canal is the skeletal cremaster muscle. The dartos primarily affects the texture and surface area of the skin itself. Elevation is a coordinated effort but is specifically the cremasteric reflex.

D. increases surface area of the scrotum, decreases its thickness, and allows heat loss: This description characterizes the physiological state of the scrotum during heat exposure. When the dartos muscle is flaccid, the skin becomes thin and smooth, maximizing the area available for cooling. This is the opposite effect of the contraction described in the question stem.