A-LevelBiologyTransport in plants9700/12 · Oct/Nov 2021 · Q271 Mark
Which sequence of events could lead to mass flow in a phloem sieve tube? 1 Sucrose moves into a sieve tube element. 2 Protons (H+) and sucrose molecules move into a companion cell through a co-transporter protein. 3 A very high hydrostatic pressure is produced. 4 The water potential of the sieve tube element decreases. 5 Protons (H+) are actively pumped out of a companion cell. 6 Water moves down a water potential gradient by osmosis.
A1→2→5→6→4→3
B3→1→2→5→6→4
C3→5→1→2→4→6
D5→2→1→4→6→3
✓ Correct answer
D: 5→2→1→4→6→3
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