Which of the following statements, A to D, correctly explains the relationship between structure and transport mechanisms in plant vascular tissues?
The evaporation of water from the surface of spongy mesophyll cells into the sub-stomatal air spaces increases the water potential of these cells, driving the pull of water from the xylem.
In phloem loading, hydrogen ions (H+H^+H+) are actively transported from companion cells into the sieve tube elements to drive the co-transport of sucrose.
The active accumulation of sucrose in sieve tube elements at the source lowers their water potential, leading to water entry by osmosis and generating a high hydrostatic pressure.
Lignification of the cell walls in mature xylem vessels provides structural support to prevent the tubes from bursting under high positive pressure during active transpiration.
28 exam-style questions on OCR A A Level Biology Transport in plants. Each one has a worked solution and a mark scheme showing where the marks go.