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Lecture 11

Lecture 11 - Water and Fluid Transport I - Principles

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Biology 2601A/B
Graeme Taylor

LECTURE 11 – WATER AND FLUID TRANSPORT I: PRINCIPLES Osmoregulation  Balancing water and ions in the cells and the body to allow physiological function  Principles to cells to organisms Water  Highly polar o Hydrogen bonding o High heat of fusion and vaporization o Large thermal capacity o Cohesion and adhesion  The universal solvent for life  Water interacts with other molecules – it creates a “shell” of bound water around many macromolecules (like proteins)  Keeps ions dissociated Water in Cells  Determines cell volume in animals o Cell volume is often the bottom level of regulation of water and ion balance  Determines cell turgor in plants o The positive pressure (turgor pressure) in plant cells that keep them turgid Moving Water  Osmotic potential – based on solute concentration  In living cells, positive pressure – turgor pressure – tends to push water out of the cell and negative pressure – tension – is what pulls water in cell of xylem  Moving water requires the creation of a gradient, and some ion pumps only work in one direction  Water cannot be moved actively as there are no active water transporters in plants – moves down pressure gradient in which it is referred to as a water potential (Ψ) and measured in MPa  Water moves towards the lower water potential  In determining the osmotic potential (s ), it is calculated as follows: Ψ = -RTc where R is the s s gas constant, T is the temperature and s is the concentration of the solute  Increasing solute concentration lowers water potential. By osmosis, water will move through a selectively permeable membrane in the direction of the highest solute concentration  Thus, increasing solute concentratio
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