BIOL1002 Lecture Notes - Lecture 2: Water Potential, Root Pressure, Xylem
6 Nov 2018
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Pla(cid:374)t (cid:454)(cid:455)le(cid:373) stru(cid:272)ture is opti(cid:373)ised to (cid:272)at(cid:272)h a (cid:862)free ride(cid:863) o(cid:374) the (cid:449)ater (cid:272)(cid:455)(cid:272)le. A(cid:374)(cid:455) theor(cid:455) of water transport must account for forces required to raise water to the tops of the tallest trees (100 m). That is, 1. 0 mpa gravity plus 1. 0 mpa frictional drag. Water could be propelled through the plant by either: a push from below (generated in the roots) or a pull from above (generated in the leaves). Os(cid:373)oti(cid:272) a(cid:272)(cid:272)u(cid:373)ulatio(cid:374) of (cid:449)ater i(cid:374) the (cid:454)(cid:455)le(cid:373) of roots can generates positive hydrostatic pressures of up to 0. 2 to 0. 4 mpa. Thus a push from below is not adequate to meet the pressure requirements. Transpiration is water loss via evaporation from the aerial parts of a plant. Transpiration occurs when: stomata are open, the air surrounding leaves is drier than the air inside leaves. Transpiration is the primary driving force of water movement through xylem tissue.
