Recitation-03 - 9-24-07

Recitation-03 - 9-24-07 - Steve Suchora Recitation Biology...

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Steve Suchora 9/25/07 Recitation Biology 220 – Recitation 3 – 09/25/07 Plants and Water Transport: 1) Why are there no tall mosses? Because mosses do not have extensive root systems to the degree that plants like trees do. Since the concentration gradient between the roots (root hairs) and the soil allows for the passage of water into the root hairs and up to the center of the plant where it is distributed elsewhere, and mosses do not have root hairs, mosses will be unable to transport water great distances like other more complex plants can. In addition to root hairs, plants have a system of intercellular water transport; either Apoplastic movement, Transmembrane movement, or Symplastic movement. The water taken up by the root hairs is then transported to the center of the plant and sent elsewhere. This means of water transport is what allows for such dramatic growth in plants like trees (vascular transport system). Without it, all plants would be very short, like moss is. **** No vascular system. They have to rely on diffusion – really long time to go from point A to point B. 2) Under which conditions would you expect to find rapid water transport through the xylem? Under drought-like conditions, when the concentration gradient of water on the outside of the plant (cells) is significant and the concentration of water on the inside of the plant (cells) is low. Plants appear to wilt when their hydrostatic pressure has dropped (drought pressure). Soon, everything inside the cell will dry up if water is not attained. Therefore, when the cell(s) is exposed to water, the osmotic pressure on the outside of the cell will cause a great influx of water into the cell (the cell wants to take up water as quickly as possible in order to continue living). ** Transpiration is the process you need. If the air around a plant is really dry (little water) and a lot of water in leaves, we’re going to have an exchange of water with the dry air at high rate. There could be a lot of water in the soil or a lot of solute concentration in the roots. Really fast transpiration, really fast water transport. Water potential changes as water goes up the plant. 3) You discover that the potato tubers you stored in your kitchen cabinet have begun to sprout.
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a) Are the cells inside the tuber functioning as sugar sources or sugar sinks? Why? Translocation of Phloem Sap - Phloem transports products of photosynthesis throughout plant via TRANSLOCATION . -
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Recitation-03 - 9-24-07 - Steve Suchora Recitation Biology...

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