D 2.3 - WATER POTENTIAL

• What is solvation?

  combination of a solvent with the molecules or ions of a solute
• what are the properties of water as a solvent


  polarity and ability to form hydrogen bonds
• polar solutes


  dissolve due to attraction between the partial positive and negative charges on water molecules and solute molecules
• positively charged ions


  attracted to the partial negative oxygen pole of water
• negatively charged ions

  attracted to the partial positive hydrogen pole of water
• describe the structure of cytoplasm (what it contains)

  complex mixture of dissolved substances in which the chemical reactions of metabolism occur
• describe how sodium chloride dissolves when placed in water

  ionic bonds between sodium and chloride ions are broken when sodium chloride dissolves in water; sodium attracted to oxygen in water; chloride attracted to hydrogen in water
• describe movement of a liquid


  liquid particles can move but they do not separate from each other completely, due to intermolecular attraction, unless changing state
• how do hydrogen bonds change in water

  continuously broken and made, however, water has multiple bonds being made thus there is a strong overall attraction
• what is the bonding like in solutes

  intermolecular attractions between solutes and water are even stronger - helping form solutions
• how are solutions formed

  When a solute dissolves in a solvent
• how does the addition of a solute effect water

  restricts water molecules movement, so is more viscous than pure water
• if water can move between two solutions


  there is always movement in both directions
• Define osmosis

  net movement of water from an area of low water potential (high solute conc) to high water potential (low solute conc) through a partially permeable membrane
• What is osmosis?

  net movement of water across a membrane due to the attractions between solutes and water
• what does it mean to be osmotically active

  solutes that cannot pass through the membrane.
• when are solutes osmotically active


  if intermolecular attractions form between them and water
• examples of osmotically active substances


  sodium ion, potassium ions, chloride ions and glucose
• Hypertonic


  Having a higher concentration of solute than another solution. (more salt solution than other solutions)
• hypotonic

  Having a lower concentration of solute than another solution (lower salt solution than other solutions)
• Isotonic

  when two solutions have equal concentration of solutes across a semipermeable membrane
• What is dynamic equilibrium?

  where there is no difference between the concentrations of osmotically active solutes; equal numbers of water molecules between them
• what is concentration

  the amount of a substance in a given volume
• in a cell, what separates intracellular side from the extracellular side

  plasma membrane
• plasma membrane permeability


  very permeable to water but much less permeable to solutes
• why are plasma membranes semi permeable

  because they are not freely permeable to all particles
• what kind of process is osmosis

  passive process
• how can cells regulate the speed at which osmosis takes place

  changing the permeability to water of their plasma membrane; change direction of movement (only by raising or lowering the concentration of osmotically active solutes inside the cell)
• describe how root cells absorb water

  because the cytoplasm of the cells is hypertonic compared with water in the soil
• what is plasma membrane of plants and animals made of

  phospholipids
• what is the cell wall of plants made of

  cellulose
• what is the thickness of the plasma membrane

  thin - 5nm or less
• what is the thickness of cell walls in plants

  thicker - 250nm to 5um
• what is the state of the plasma membranes

  liquid allowing changes of positions such as formation of vesicles by budding and diffusion of molecules into membrane
• state of cell wall in plants

  solid, thus changes of positions are limited and constituent molecules of the wall do not diffuse
• plasma membrane tensile strength

  very low - easily torn
• cell walls tensile strenght

  high - stronger than steel
• permeability of cell walls

  freely permeable unless impregnated with a waterproof material (e.g. cutin, lignin or suberin)
• if an animal cell is places in a hypotonic solution

  water enters the cell by osmosis making it swell (as it lacks cell wall support thus cell bursts)
• what would you see when a small droplet of blood wat placed in pure water

  blood cells swell up to form spherical shape and bursts leaving a ruptures plasma membrane called red cell ghost