Final answer:
Osmosis is the mechanism involved in soil-water uptake by roots, facilitating the movement of water into the plant through root hairs and its eventual exit through transpiration at the stomata.
Step-by-step explanation:
The mechanism involved in soil-water uptake by the roots is osmosis. Osmosis is the process by which water moves from an area of high water potential (such as moist soil) to an area of low water potential (such as the root hairs of a plant), driven by the differential in concentration. Water enters the plants through the root hairs due to the negative water potential present there, and then it is drawn up the plant's vascular system, which includes the xylem, through cohesion and adhesion forces. Eventually, the water exits the plant through the stomata in the leaves in a process called transpiration. This process is crucial not only for the plant's water uptake but also plays a role in nutrient transport and temperature regulation within the plant.
Transpiration also factors significantly in the biosphere as the evaporated water from the leaf surfaces returns back to the atmosphere. It is important to note that during periods of drought, plants can adjust their transpiration rates by closing stomata to conserve water, and in extreme cases, shedding leaves. The main water source for land plants is the soil, and even under drought conditions, plants must efficiently manage water uptake and loss to survive.