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Lecture 68

BIOL 1010 Lecture 68: Lecture 68

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University of Manitoba
Biological Sciences
BIOL 1010
Emily A.Mc Kinnon

o78P Bio 1010 CHAPTER 23- Chapter 23: Nutrition in Plants 23.3: Transpiration As a plant grows upward toward sunlight, it needs to extract an increasing supply of water and dissolved mineral ions from the soil. Xylem tissue of angiosperms includes two types of conducting cells: Tracheid’s and vessel elements. Xylem sap, a solution of water and inorganic nutrients flows through the long, thin conduits formed by these dead cells from the roots to the tips of the leaves. The roots of the plants do exert a slight upward push on xylem sap. The root cells actively pump inorganic ions into the Xylem, and the roots endodermis holds the ions there. The ions accumulate in the Xylem, water tends to enter by osmosis, pushing Xylem sap upward ahead of it. This force is called root pressure, can push Xylem sap up a few meters. The pulling force is transpiration, which is loss of water from the leaves and other aerial parts of a plant by evaporation. Transpiration and its effect on water movement in a tree. Water molecules exit the leaf through stomata microscopic pores on the surface of the leaf. When the stomata are open, water diffuses out of the leaves because the surrounding air is usually drier than the inside of the leaf. Transpiration can pull Xylem sap up the tree because of two special properties of water: cohesion and adhesion. Both of these
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