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Biology 162 Plant and Animal Water Balance

by: Jenn Guzman

Biology 162 Plant and Animal Water Balance Biology 162

Jenn Guzman
Cal Poly
GPA 3.3

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About this Document

These are lecture notes from week 2 and 3 of lecture that cover Water Balance in Plants and Animals.
Intro to Organismal Form and Function
Dr. Taylor, Dr. Ritter
Class Notes
Water Balance, Electrolytes, Bio 162, Biology, Dr. Taylor, Dr. Ritter, week 3, notes, plants, animals
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This 3 page Class Notes was uploaded by Jenn Guzman on Thursday April 14, 2016. The Class Notes belongs to Biology 162 at California Polytechnic State University San Luis Obispo taught by Dr. Taylor, Dr. Ritter in Spring 2016. Since its upload, it has received 22 views. For similar materials see Intro to Organismal Form and Function in Biological Sciences at California Polytechnic State University San Luis Obispo.


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Date Created: 04/14/16
Week Of: Monday, April 11, 2016 Plant and Animal Water Balance Week III Lecture, Dr. Taylor & Dr. Ritter Important Review Terms Terms I. Plant Water Balance (Lecture Wednesday 4/13 with Chapter 38) A. Water loss in plants takes place when stomata are open for gas exchange. Leaves can lose up to 100% of their water in one hour. They retain less than 1% of the water they absorb from their roots. 1. Transpiration is the diffusion of water vapor from a leaf. But, water is a strange molecule due to its polarity. It sticks to other molecules (adhesion) and sticks to other molecules of itself (cohesion). B. Water potential (Y) is a result of adding Pressure Potential (Yp) to Solute Potential (Ys). Ys can be zero, indicating pure water, or negative. Yp can be positive or negative, negative values denoting tension. 1. Water always flow from areas of high Water Potential to areas of low Water Potential. In plants, the highest water potentials are located in the roots while the lowest areas of water potential are up in the leaves and atmosphere. 2. Turgor pressure is the pressure exerted on cell wall via water entering the cell. C. Cohesion-Tension Theory of Xylem Water Transport 1. Transpiration and cohesion work together to drive a force that propels the flow of water upwards. The presence of xylem cells to which water adheres to allows for resistance to gravity. D. Pressure-Flow Theory of Phloem Sugar Transport 1. Translocation is the movement of sugars by bulk flow throughout a plant from sources (tissue where sugar enters the phloem) to sinks (tissue where sugar exits the phloem). This Pressure- Flow theory states that events at source tissues and sink tissues create a pressure potential gradient in phloem: differences between turgor pressure in the phloem near source tissues and turgor pressure in the phloem near 1 Week Of: Monday, April 11, 2016 sink tissues generate the necessary force. The water in phloem sap moves down this pressure gradient and sugar molecules are carried along by bulk flow. II. Animal Water Balance (Lecture Monday 4/11 with Chapter 43) A. Dehydration results in lost water content and concentrated ion content. The cell is hypertonic to the environment. “Overhydration” is also known as hypotonic hydration, in which the cells intake large volumes of water and risk bursting. The cell is hypotonic to the surrounding environment. B. Water only moves by diffusion, a term known as osmosis. 1. Water moves from area of high water concentration to low water concentration. In regards to ion content, water moves from areas of low osmolarity to areas of high osmolarity. 2. It moves across semipermeable membranes. 3. Free water is water that is not otherwise blinded to a dissolved ion. C. Forms of Passive Transport Direct diffusion occurs when small, non polar molecules across semi permeable 1. membranes. 2. Facilitated diffusion occurs with the help of transmembrane proteins allowing for the diffusion of molecules that otherwise cannot simply diffuse across membranes. Channel proteins allow for the passive movement of water (polar molecules). Carrier proteins allow large, non polar molecules like glucose to passively diffuse across membranes. D. Methods of Active Transport 1. Active transport occurs when molecules are moved against their electrochemical gradient. Primary active transport expends a source of energy (ATP) to move ions against their gradients. Secondary active transport can occur only once this occurs. 2 Week Of: Monday, April 11, 2016 Cotransporters can use the energy in the electrochemical gradient cross a cell membrane to transport a different solute against its gradient. A symporter moves solutes in the same direction. An antiporter moves solutes in opposite directions. E. Marine Fishes are osmoregulators: they actively regulate their osmolarity and water concentrations. The problem they face is losing large amounts of water by osmosis into the hypertonic surrounding ocean. They also bring in large amounts of electrolytes. Their solution is to lose electrolytes through active transport out. 1. Sharks maintain their osmolarity across four distinct steps. a) 3Na+ are pumped out, 2K+ are pumped in the epithelial cells via the Sodium-Potassium Pump. b) Sodium-Potassium-Chloride pump brings in ions through its symporter properties. c) Chloride diffuses into the lumen, Potassium diffuses into the extracellular fluid d) Sodium diffuses between epithelial cells into the lumen F. Freshwater Fish face issues with having gills with a higher osmolarity than the surrounding water. They gain too much water via osmosis and lose electrolytes by diffusion. They solve this issue by actively transporting electrolytes not their system. G. Terrestrial animals lose water in urine as well as electrolytes into the environment. As a result, they are forced to gain metabolic water, and replace water and electrolytes by eating and drinking in large volumes. 1. The kidney regulates water loss. The nephrons act as the functional unit of the kidney that filter out water, wastes, ions, and nutrients out of the blood. Wastes are expelled into the environment. Water, ions, and nutrients are reabsorbed into the blood. The loop of henle establishes and maintains the osmotic gradient in the fluid in the medulla. 3


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