Biology 15A

​Rivers of Life

•A plant relies on columns of water in its vascular tissues to transport nutrients.

•Xylem and phloem

–While these are both different from one another, they are both often called sap.

​Transpiration

the release of water through the stomata of the leaves of a plant​

​Rivers Flowing UPward

•Roots absorb water and minerals

–The root pressure caused by the incoming water will push the water and dissolved minerals up the xylem.

• If plant height relied on root pressure and capillary action alone, plants would be much shorter because they can only move water vertically short distances only.

​

​Rivers Flowing UPward

​•Properties of water

–Adhesion is an attraction between molecules of different substance

• Capillary action is when water rises up into a thin tube above the level of the rest of the water.

• Most of the force that moves the water up the xylem operates by pulling the water from the top​

–Strong hydrogen bonds

–Cohesion – substances stick together

•Cohesion-tension theory – water molecules in the leaves’ spongy mesophyll exit the leaf as water vapor through the stomata.

•Turgor pressure is what gives a plant rigidity. This is produced when water enters a plant cell's central vacuole

•Most of the water is released into the atmosphere as water vapor.

​Sweet Rivers

•Sugars need to reach every part of the plant.

–Move in the phloem

–Sinks and sources

​Sweet Rivers

​•According to the pressure-flow hypothesis, plants move sugars through the phloem from a high-pressure area to a low-pressure area.

•Phloem sap moves toward the sinks