Lecture 15 BIO 311D 2nd EditionOutline of Last Lecture I. ReviewII. How do plants exchange substances with their environment?III. Uptake into the rootsOutline of Current Lecture I. How do plants transport water up the xylem?II. What controls stomata opening?III. Design an experimentCurrent LectureI. How do plants transport water up the xylem?- What is the overall process of photosynthesis?- In what organs do plants take in what they need for photosynthesis and for cellular respiration?- Review: + K+: Passive ion channel protein: electrical charge + NO3-: symport+ Transport of water from soil to root to xylem, passive, depends on pressure flow going up to a point- Symplastic or apoplastic route - Casparian strip is a waxy belt around the wall of endodermis cells. Adaptive advantage: o Prevents “harmful” substances to go through, no passageway for things to go through; a selective barrier o Also acts as a “keeper”, makes it difficult for the water to flow back out the Casparian strip; retention - In the root cell is where it all starts, getting there by osmosis isn’t that smart- So the root cell must have a lower solute potential than in the ground a crucial part - Two things that predicts the movement of water: (1) Solute concentration (osmotic pressure), (2) Fluid (hydrostatic) pressure - Low water potential: tend to take up water | High water potential: water tends to leave water move a high potential area to a low potential area; move towards the most negative - Redwood tree and sequoia tree (very tall trees): how can water in the soil rise to the top of a talltree?- 90% of water taken into the tree’s roots is lost through the leaves- 100 gallons of water are transported up a large tree every hour - Water and dissolved solutes are moved around a plant through combined effects of solute concentration and fluid pressure- Amount of water loss depends on the weather - Major force: transpiration (evaporation out of leaf pores)Sunny dry day: transpiration rate goes upGloomy dark day: transpiration rate goes down - Forces that transport water up the xylem:- Transpiration (aka evaporation, creates an upward pull (tension)) - Cohesion: water sticking to water- Adhesion: water sticking to xylem walls- Vascular tissues: cells specialized for transport- What happens when there’s an air bubble trapped in a xylem vessel? Xylem has “pits”, holes in the wall. Through the pits, the water can go through to the nearby xylem vesselII. What controls stomata opening? - Guard cell function - Guard cells have highly specialized structure- Have chloroplast - When guard cells expand, stoma opens.- What makes guard cells expand? Taking in watero Bring in solutes through the proton pump - What’s the advantage of opening stomata in daylight?- For the process of photosynthesis- What’s the physiological mechanism for opening stomata in daylight?(1) Light receptor, (2) signal transduction, (3) proton pump, (4) K+ enters, (5) water enters, (6) guard cells expand and pore opens III. Design an experiment - To test one aspect of this system, the control of the stomata- Independent variable: amount of light - Dependent variable: stomata pore size in mm opening- Hypothesis: If there were an increase in the amount of light then the stomata pore size would have a larger opening. - Null hypothesis: If there were an increase in the amount of light then there would be no difference in the size of the stomata pore opening. - Two control variables: External pH and external osmotic
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