Which of the following describes the Cohesion-Tension Theory in plants?

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BlackTom AI · Accepted Answer

The question asks for a description of the Cohesion-Tension Theory in plants, so we need to evaluate how water movement is driven within the plant.
Option a: It states that tension is placed on water by condensation at a plant's surface and that this pulls a constant stream from the soil. Condensation is the process of water vapor turning into liquid, which is not the mechanism driving water ascent in plants. The theory centers on evaporation (transpiration) creating negative pressure (tension) in the xylem, not condensation. This makes the statement inaccurate.
Option b: It describes tension placed on water by evaporation at a plant's surface, pulling a constant stream of water from the soil. This aligns with the core idea of the Cohesion-Tension Theory: transpiration at the leaf surface generates a tensile force that is transmitted down the water column through cohesive forces between water molecules, drawing water upward from the soil through the xylem. The mechanism involves negative pressure created by evaporation, and a continuous pool of water is maintained by cohesion, so this framing is correct.
Option c: It claims tension is placed on water by evaporation at a plant's surface but pulls water from the leaves. While evaporation drives the tension, the water column is pulled from the soil upward through the plant, not from the leaves themselves. Leaves are the site of transpiration and water loss, not the source of the water being pulled from the soil, so this wording misidentifies the source of the water.
Option d: It asserts that evaporation-driven tension pulls water from the atmosphere. Water movement in the Cohesion-Tension Theory originates in the soil as the water is pulled up through the plant due to transpiration at the leaves, not directly from the atmosphere. The atmosphere provides the evaporative pull, but the actual water source and ascent involve soil-to-leaf transfer within the plant, so this description is inaccurate.
In summary, the statement that best captures the Cohesion-Tension Theory is the one describing evaporation at the plant surface generating tension that pulls water upward from the soil through the xylem, sustained by cohesion among water molecules.

BIO 181 (001&002) FALL 2025 4G. Self-Check - Plant Transport (LO 4G.1, 4G.2, 4G.3, 4G.4)

Which of the following describes the Cohesion-Tension Theory in plants?

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