BSCI 207 Lecture 19: BSCI207 - Lecture 19 - Plant Circulation Continued
26 Jan 2016
School
Department
Course
Professor
Document Summary
Bsci207 - lecture 19 - plant circulation continued. When you have high potassium concentration in guard cells: h2o flows in by osmosis. Low potassium in guard cells: h2o flows out by osmosis. Stomata can open and close quickly not only in light level, but also co2 concentration and water loss. Over longer term, plants can change number of stomata in response to environmental conditions. Typically, stomata open during the day and close at night. Photosynthesis occurs during the day (light energy), so stomata open b/c gas exchange occurs. Reverse pattern seen in cam plants, which typically grow in arid conditions. Even in sun, stomata may close on a hot, windy day. Bulk flow of water from roots to leaves mediated by continuous water potential gradient. Tension (pulling from above) on xylem accounts for most of flow. Osmotic contribution (pushing from below) is limited to roots, contributes little to flow in tall plants.
