Water Distribution PDF

Volume Percent of Percent of 3 (1000 km ) T...

Volume Percent of Percent of 3 (1000 km ) Total Water Fresh Water Oceans, Seas, & Bays 1,338,000 96.5 - One estimate of global water Ice caps, Glaciers, & distribution: 24,064 1.74 68.7 Permanent Snow Groundwater 23,400 1.7 - http://earthobservatory.nasa.gov/Library/Water/ Fresh (10,530) (0.76) 30.1 Saline (12,870) (0.94) - Soil Moisture 16.5 0.001 0.05 Ground Ice & Permafrost 300 0.022 0.86 Lakes 176.4 0.013 - Fresh (91.0) (0.007).26 Saline (85.4) (0.006) - Atmosphere 12.9 0.001 0.04 Swamp Water 11.47 0.0008 0.03 Rivers 2.12 0.0002 0.006 Biological Water 1.12 0.0001 0.003 Total 1,385,984 100.0 100.0 Do not memorize this table. Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823.  Water Start with Global Water Trivia Since there are no major losses or gains of water from the biosphere, precipitation and evaporation must be equal on a global scale; -average of 90 cm precipitation or evaporation per year for Earth as a whole -28 cm of precipitation often used as one definition of “desert” -Regina averages 53.7 cm/year -Manaus, Brazil (Amazon basin) averages 228.6 cm/year Total evaporation for Earth is approximately 360,000 km3 of H2O per year; -approx. 72,000 km3 per year over land, rest over oceans -precipitation over land approx. 110,000 km3 per year → surplus of 38,000 km3 per year over the land Land is a net recipient of water from the oceans. Water is returned to ocean via runoff and by https://www2.whoi.edu/site/globalwatercycle/ percolation of groundwater.  Water Of the 72,000 km3 of total evaporation from land per year, approx. 65,000 km3 occurs through plants as transpiration; -transpiration = loss of water vapour (H2O(g)) from plants -majority of global transpiration is from forests Evaporation + Transpiration = Evapotranspiration https://www.usgs.gov/special-topic/water-science- school/science/evapotranspiration-and-water-cycle?  Water https://www.usgs.gov/special-topic/water-science- Climate is substantially affected by the water school/science/evapotranspiration-and-water-cycle? cycle; -clouds reflect radiation → cooling in daytime, but warming at night -H2O is also a greenhouse gas (polyatomic molecules absorb IR radiation, which is why CO2, CH4 and NO2, N2O are also greenhouse gases) Of water taken up by plants, ~99.7% transpired away; plants put a lot of H2O(g) into the atmosphere. Of the water that is transpired, the bulk is via stomates on leaves. ↳ adjustable pores Water cycle is substantially affected by vegetation due to transpiration; → vegetation has large effect on global climate By Ben Mills - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid= 3958545  Water Physiological Importance Constituent of protoplasm; -65 - 95% of FW of herbaceous plants -up to 50% of FW of woody plants (freshly chopped wood can be 50% water) Ozores-Hampton et al. (2005) http://edis.ifas.ufl.edu/ Medium for biochemical reactions; -reagent for in many biochemical reactions e.g. photosynthesis -solvent - movement of molecules within a cell and between different parts of the plant Maintenance of turgor i.e. cell rigidity (plant cells are under pressure). Temperature regulation e.g. evaporative cooling during photosynthesis; -leaves can temperature regulate to an extent  Water δ+ Structure of Water Water has a “bent” structure. O has higher affinity for electrons than H δ- (more electronegative) → distortion of δ+ δ- orbitals, leading to partial charges (δ-, δ+). Water is a polar molecule. · polar covalent bonds δ- δ- Modified from: Thebiologyprimer - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=32361523 δ+ δ+ By Ben Mills - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid= 3958545  Water to each other Attracted Partial charges → polar molecule. Polarity of water has 2 important - implications: 1) leads to H bonding - important implications for the movement of water in the plant (properties of cohesion, adhesion) 2) solvent for polar/charged solutes (i.e. most non-hydrocarbon molecules) Y → will dissolve amino acids, smallish carbohydrates, organic and inorganic ions dissolving → will not dissolve hydrophobic molecules e.g. lipids, fatty acids - important for membrane functioning Due to H bonding, H2O is a liquid at room temperature; unusual for a small molecule: Qwerter, public domain Water has polar covalent bonds containing H; → leads to H bonding H bonds In polar covalent bonds the two atoms in the bond have a moderate difference in electronegativity. Electrons are shared unequally, with O have a higher electronegativity than H.  Water - Dissolution Shell of water Water Dissolves Salts and Small Polar Molecules - Dissolved molecules are surrounded by hydration shells (= solvation spheres). Crundell (2019) Chemical Engineering Science 205 https://www.mvschools.org/cms/lib03/CA01001212/Centricity DOI: 10.1016/j.ces.2019.04.050 /Domain/409/IonicCovalentImageBlank.pdf = Hydrogen Attracted cur of charges Dissolution of NaCl (a salt). Salts have full charges (+, -). Dissolution of sucrose (small polar molecule). Polar molecules have partial charges (δ-, δ+).  Water - Dissolution Water is attracted to cellulose, OpenStax Biology 2e but does not dissolve cellulose. Hydration shells (solvation spheres) around ions. Hubbe et al. (2013) BioResources 8:6556-6629. Part of a cellulose molecule. Cellulose is a large, polar molecule (too large to be dissolved). By NEUROtiker - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2951911 By Laghi.l - Own work based on: Cellulose strand.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=26213703  Water - Dissolution Salts (charged) and polar molecules are hydrophilic (= water-liking). Fats (= triglycerides) are non-polar and thus hydrophobic (= water-fearing). Phospholipids are amphipathic (partly hydrophilic and partly hydrophobic). Phospholipid bilayers are the basis for biological membranes. A phospholipid (left) and a phospholipid bilayer (right). https://chem.libretexts.org https://bio.libretexts.org  Water Movement Water Movement in a Plant/through a Plant When studying plant water relations, there are two mechanisms for the movement of water: of water Think Hough - moving pipe 1) bulk flow: mass movement of water in response to a pressure differential; -if you have a tube of H2O that has high pressure at one end, and low pressure at the other → mass movement of water from high to low pressure (down a ΔP) -like plumbing in a building → water flows 2) diffusion: net movement due to random kinetic activities or thermal motions L Slower than bulk flow By Hephaestos at en.wikipedia - Transferred from en.wikipedia to Commons by SreeBot., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16944545  Water Diffusion Must distinguish between diffusion of solutes and diffusion of H2O. First: solutes (despite the fact that this section is about water). Diffusion can occur in response to gradients of solute concentration (= gradients of chemical potential). Net diffusion of solutes occurs from areas of higher concentration to areas of lower concentration. Net of solute is down a [solute] gradient (down a ΔC of [solute]). higher concentration to lower concentration Diffusion of Solute: ΔC > 0 ΔC = 0 (equilibrium) By BruceBlaus - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=29452222  Water – Diffusion of Solute Diffusion of Solutes Rate of diffusion - Fick's Law of Diffusion: ΔC > 0 ΔC = 0, C1- C2 ΔC equilibrium J= = r r J – rate of diffusion C1, C2 – concentrations of the species of interest at two sites ΔC – concentration gradient r – resistance to diffusion (function of distance, diffusion coefficients of the species in question)  Water – Diffusion of Solute Diffusion of Solutes ΔC > 0 Rate of diffusion - Fick's Law: ΔC = 0, equilibrium C 1 - C2 ΔC J= = r r The larger the concentration gradient, the greater the rate of diffusion; -at equilibrium ΔC = 0 → no net movement (but still have gross movement) - J= 0 The larger the resistance, the lower the rate of diffusion. Diffusion of solute is from high solute concentration to low solute concentration; -another way of stating this: diffusion occurs from higher chemical potential to lower chemical potential High [solute] means high chemical potential for the solute. Chemical potential of the solute given the symbol µ.  Water – Diffusion of Solute Can calculate µ for any solute: µ = RT ln c (units: J/mol) We will not use this equation for any calculations. μ is the lower case R = gas constant = 8.314 J mol-1 K-1 version of the Greek = 0.008314 kg MPa mol-1 K-1 letter “mu” T – absolute temperature (K); 0K = -273°C c – concentration of the solute The higher the concentration of a substance, the greater its chemical potential (from the formula). In terms of diffusion, a molecule will move from areas of high µ (= high [solute]) to low µ (= low [solute]); → diffusion down a gradient of µ (higher µ → lower µ) For diffusion of solutes, Fick’s law is good enough; we won’t worry about µ, but µ is sort of (in a way) used to describe diffusion of liquid water (H2O(l))and water vapour (H2O(g)). (Fick’s Law of Diffusion will work for H2O(g) [= water vapour] and CO2; more about that later.)  Water – Diffusion of Solute impermeable barrier gently pull out the barrier net sucrose diffusion, as there is a ΔC 1 mM sucrose 10 mM sucrose Sucrose (solute) diffusion down the ΔC (or Δµ). Net movement stops at equilibrium (ΔC = 0, or Δµ = 0); uniform [sucrose] throughout beaker. Gross movement continues at equilibrium; -sucrose molecules still moving around -water molecules still moving around  Water But, right now we are actually interested in the movement of water; -water also moves in response to gradients of chemical potential (just like solutes), but the formalism is slightly different (to be discussed very soon) Diffusion of H2O includes osmosis → the diffusion of a solvent such as water across a semi-permeable membrane separating two solutions of different concentrations (= different chemical potentials); → a special case of the diffusion of water → driving force is the same whether or not there is a membrane (but our examples will tend to have membranes) · lower concentration to higher concentrator In the diagram, the solute cannot pass through the selectively permeable membrane, but the water can. OpenStax Biology 2e  Diffusion of Solute and Water impermeable barrier gently pull out the barrier net water diffusion net sucrose diffusion Water and dissolved solutes 1 mM sucrose 10 mM sucrose diffuse in opposite directions. Sucrose (solute) diffusion down the ΔC (or Δµ). Water diffuses from lower [solute] to higher [solute]; -this is down Δμ for water (to be explained).  Water Water Potential (Ψ or Ψw) Ψ = Greek letter psi Water potential = the chemical potential of H2O. Water moves from higher Ψ to lower Ψ (down a ΔΨ) Or, a fuller definition of Ψ: Ψ is the chemical potential of H2O in a system, compared with the chemical potential of pure H2O at atmospheric pressure and the same temperature. Standard atmospheric pressure = 1 Atm = 0.1013 MPa By definition: Ψ of pure H2O at standard atmospheric pressure = 0 (this is defined, not derived) What about units for Ψ? -in theory, the units should be J mol-1 (like for µ); energy units -but - historically plant physiologists have used pressure units to discuss H2O movement -the pressure units that are are MPa -older textbooks and research articles used “Atm” as units  Water Pressure Units can Represent Energy Pressure units: MPa 1 MPa = 1 N m-2 N = units of force but, 1 J = 1 N m → 1 N = 1 J m-1 You won’t be asked to derive this. → 1 MPa = 1 J m-1 m-2 → 1 MPa = 1 J m-3 Simply keep in mind that although we are using pressure units (MPa), we are actually talking about potential energy. Take home message: energy/volume = pressure (force/area)  Water Movement of Water H2O, and all other molecules, move from areas of higher chemical potential to lower chemical potential (in the absence of a barrier); -in the case of H2O: high Ψ to low Ψ (= down a ΔΨ) -solutes: high µ to low µ (= down a Δµ) OpenStax Biology 2e When a substance is dissolved in water, the H2O loses some free energy; -has done work (is more “organized”, or has lower entropy) Dissolving a solute is doing work -potential energy has been measurement Hydration shells (solvation spheres) around ions. The diminished water is less random (more organized) if solutes are present. Take home message: dissolving a solute in H2O decreases the chemical potential (Ψ) of the H2O.  Water Effects of Solutes on Water Potential (Ψ) Dissolving a solute in H2O decreases the chemical potential (Ψ) of the H2O; -the water has become more ordered/organized (entropy decreases) Pure H2O at standard atmospheric pressure: Ψ = 0 MPa (by definition). H2O with any dissolved solute at atmospheric pressure: Ψ < 0 MPa; The greater [solute], the greater the depression of Ψ. Selectively permeable membrane. Water will diffuse from an area of lower [solute] to higher [solute]. By Kade Kneeland - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=79653442  Water [solute]o > [solute]i [solute]o = [solute]i [solute]o < [solute]i outside inside usual state bursting cell OpenStax Biology 2e equilibrium in danger of bursting Water relations of red blood cells: water will move, via osmosis, across the plasma membrane (a selectively permeable membrane) from higher to lower Ψ. Lower Ψ has a higher [solute]. Reb blood cells do not have a cell wall; if sufficient water moves in, they will burst due to the pressure increase.  Water OpenStax Biology 2e [solute]o > [solute]i [solute]o = [solute]i [solute]o < [solute]i plasmolyzed cell plantcelsstate usual state > - cell wall prevents bursting Water relations of plant cells: water will move, via osmosis, across the plasma membrane (a selectively permeable membrane) from higher to lower Ψ. Lower Ψ has a higher [solute]. Plant cells do have a cell wall → no danger of bursting. In fact, plant cells are pressurized (internal pressure is greater than atmospheric pressure), Plant cells are said to exhibit turgor (they are rigid and pressurized).  Water So far have only examined the effect of solutes on Ψ; but in reality it’s more complicated than that: Components of Water Potential (Ψ) Three major components of Ψ, and they are additive: Ψ = ΨS + ΨP+ ΨM ΨS – solute potential (also known as osmotic potential, Ψπ) ΨP – pressure potential ΨM – matric (matrix) potential Solute Potential (ΨS) This is really what we have been talking about in our discussions about solutes in water; ΨS = the effect of solutes on water potential (Ψ). ΨS is always negative e.g. ΨS of seawater = -3.0 MPa ΨSmax = 0 MPa (= pure water; no solutes) Aside: the dissolving of solutes has only a minor effect on the volume of the water → the [water] is relatively unchanged; -the dissolving of solutes affects the chemical potential of the water, through the formation of hydration shells  Water ΨS is a measure of the effect the solute has on the chemical potential of the solvent (water) - not a measure of the chemical potential of the solute A version of the van't Hoff equation can be used to calculate ΨS: wont ask to calculate * You need to understand this equation, but you will ΨS = -ciRT not be asked to calculate ΨS on a test. c - [solute] expressed as molality units of molality = (mol solute)/(kg H2O) i - ionization constant = 1 for non-ionized molecules i = 1 for sucrose, glucose, mannitol i = 1.8 for NaCl (i ≠ 2 due to ion pairing) R - universal gas constant = 0.008314 kg MPa mol-1 K-1 T - temperature in K (0K = -273°C) This is an empirical relationship.  Water Use of van't Hoff equation only justified for dilute, ideal solutions. Molality and molarity are almost the same thing, especially for dilute solutions. At 4°C, 1 kg of water has a volume of 1 L (maximum density of water is at 4°C); → mol/kg (molality) is almost the same thing as mol/L (molarity) Examples of sugar solutions (i = 1 for sugars): → plug various concentration into the van’t Hoff equation: You need to understand this equation, but on a ΨS = -ciRT test you will not be asked to calculate ΨS. temperature = 25°C = 298 K This is the largest/greatest ΨS value. 0 mmolal: ΨS = 0 MPa 1 mmolal: ΨS = -(0.001 molal)(1)(.008314)(298) = -0.002478 MPa 10 mmolal: ΨS = -0.02478 MPa 100 mmolal: ΨS = -0.2478 MPa This is the smallest/lowest ΨS value. Water diffuses down ΔΨS (equivalent to lower [solute] → higher [solute]).  Water Other properties of water affected by addition of solute: 1) Addition of a solute to water will also result in an increase in the boiling point, and also results in a depression in the freezing point (1.86°C per molal) = “freezing point depression” (Δf) The relationship between Δf and ΨS turns out to be linear(ish): -a 1 molal solution has a ΨS of -2.269 MPa at 0°C Freezing point depression osmometer; -instrument that estimates ΨS by measuring Δf Freezing point depression caused by solutes. By AstroImager001 - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curi d=12778398  Water - Raoult’s Law 2) Effects on the RH of the air space above the solution Solutes depress the partial (vapour) pressure (PH2O) of water above a solution. Modified from https://www.pasco.com/products/lab- Beakers with lids: supplies/glassware/se-7288 PH2O = Pmax H2O PH2O < Pmax H2O RH = 100% RH < 100% H2O + solute pure H2O The depression of PH2O above the solution can used as a measure of the ΨS of the solution; → instruments called “thermocouple psychrometers” are used for this purpose  Water Summary of what we just talked about Add solutes to a solution, and three things change. Kramer PJ (1983) Water Relations of Plants. Academic Press.  Water Section Summary (so far) Ψ = ΨS + Ψ P + ΨM. Ψ is the water potential, which is the chemical potential of water (units of MPa). ΨS is the solute potential = the effects of solute on Ψ. Adding solute to a solution decreases ΨS (but only ΨS). van’t Hoff equation: ΨS = -ciRT From the van’t Hoff equation, ΨSmax = 0 MPa (= pure water, where c = 0 molal). The greater the value of c (i.e. the greater the [solute]) the more negative the value of Ψ S. Water moves down a gradient of ΔΨ, from higher Ψ to lower Ψ; Moving down a gradient of ΔΨ explains osmosis. Assuming no pressure differences (next section), water and solutes diffuse in opposite directions.