Lecture 16 BIO 311D 2nd EditionOutline of Last Lecture I. How do plants transport water up the xylem?II. What controls stomata opening?III. Design an experimentOutline of Current Lecture I. Stomata experiment, what do we learn?II. Phloem loading and unloading, how?Current LectureI. Stomata experiment, what do we learn?- Which would lead to expansion of guard cell (and opening stomata)?K+ ions flow into guard cells These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. Phloem loading and unloading, how?- Plants use phloem tissue to move sugar solutions from source to sinkA. Which type of phloem cell is specialized for transport of sugar solutions?- How can cells spend ATP to move water against its concentration gradient?- Phloem loading move sugar into phloem tissue at a high concentration- Phloem loading is an active process using proton pumps to create a H+ ion gradient and a co-transport protein (proton-sucrose symport) to move sucrose into a cell against its concentration gradient - Need a high concentration of H+ on the outside, this is done through a proton pump- Movement through the symport is powered through the H+ gradient B. So, how could sugars be unloaded from phloem?- Think of some ways to maximize transport of sugar from a phloem cell into sink cell - Through the plasmodesmata (does not required ATP), a sucrose-membrane transport protein (go down it’s gradient) 1. Transpiration pulls water up xylem vessels2. Source cells load sucrose into phloem sieve tubes, reducing their water potential3. So water is taken up from xylem vessels by osmosis4. Internal pressure differences drive the sap down the sieve tube to sink cells5. Sucrose is unloaded into sink cells6. And water moves back to xylem
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