Biology 3.1.3 How water moves up the stem

Question	Answer
What are the three mechanisms that keep water moving up the stem?	Root pressure Transpiration pull (cohesion and tension) Capillary action
Explain root pressure	When water and mineral ions move into the root hair cells, the cells become turgid and increases in pressure, as a result water moves to adjacent cells with less pressure, forcing water out of the roots and up the stem
What three factors effect root pressure?	Metabolic poison, temperature and O2 concentration
How effective is root pressure?	Not very, it can't get water all up the plant, just a bit
Explain the transpiration pull	Water molecules are attracted to each other by cohesive forces, which forms a long column of water up the stem. As water is lost at the top of the plant via transpiration, tension is created, which pulls more water up the plant. Furthermore, as the water molecules are attracted to each other, the whole column moves up, creating tension in the column
What prevents the xylem from collapsing?	Lignin
Explain capillary action	Adhesive forces between the water molecules and the narrow xylem vessel move water up the xylem against the force of gravity.
What makes capillary action effective with xylem vessels?	The xylem vessels are very narrow, so there is a greater proportion of water in contact with the walls, resulting in greater adhesive forces
What does water pass through to get into the xylem vessel?	Pits

Resource summary

	Created by Sam Gunnell about 5 years ago