Biology - D2.3 Water Potential

Solution

a homogeneous mixture of a solvent and a solute

Solvent

a substance in a which a solute is dissolved to form a solution

Solute

dissolves in a solvent to form a solution

the solute is present in a smaller quantity than the solvent

Solvation

• Solvation describes the interaction between a solvent and a solute.

• The solute particles interact with the solvent through various intermolecular forces such as hydrogen bonding.

Polar Molecules

• when bond dipoles don’t cancel out

• When polar molecules dissolves in water, hydrogen bonds form between water molecules and the other polar molecules.

Hydrogen Bonds

• occurs when Hydrogen is bonded to Nitrogen, Fluorine, or Oxygen

• Water molecules form hydrogen bonds with other charged particles.

Osmosis

• Osmosis is the passive movement of water molecules from a hypotonic solution (low solute concentration) to a hypertonic solution  (high solute concentration) through a partially permeable membrane.

• Water molecules move from a hypotonic solution to a hypertonic solution.

• Osmosis can also be defined using water potential.

• Osmosis is the passive movement of water particles from a region of high water potential to a region of low water potential through a partially permeable membrane.

• Water will have a high water potential, if there is low solute concentration.

• Water will have a low water potential, if there is a high solute concentration.

• There will be a net movement of water until the water potential energy is equal in both systems.

Hypertonic Solution

• has a higher concentration of solutes compared to another solution.

• when cells are placed into a hypertonic solution relative to the cytoplasm of the cells, Water will move out of the cytoplasm, which is hypotonic, to the hypertonic solution surrounding the cells.

Hypotonic Solution

• has a lower concentration of solutes compared to another solution.

• when cells are placed into a hypotonic solution relative to the cytoplasm of the cells, water will move from the hypotonic solution surrounding the cells into the hypertonic cytoplasm.

Isotonic Solution

• has the same concentration of solutes compared to another solution.

• when cells are placed into an isotonic solution relative to the cytoplasm of the cells, there will be no net movement of water as the cytoplasm and solution are isotonic.

  • There is a dynamic equilibrium, as the number of water particles entering and exiting the cell are equal.

Standard Deviation

• Standard deviation or standard error can be calculated to determine the range of values, which is an indication of the reliability of the data collected.

  • Calculated standard deviation or standard error values can be used to construct error bars on graphs.

  • Error bars can be used to determine if there is likely to be a significant difference between data points on a graph.

• idk how to calc it

Standard Error

• Standard error could be shown graphically as error bars.

• same thing as standard deviation

Crenation

• The loss of water from an animal cell is known as crenation.

• the animal cell shrinks and dies

Cytolysis

• The bursting of an animal cell is known as cytolysis.

• the cell swells as water goes in and bursts

Contractile Vacuole

• Many unicellular organisms without cell walls remove excess  water from the cell using a contractile vacuole to prevent cytolysis.

• This is osmoregulation, a form of homeostasis.

Osmoregulation

• Osmoregulation is maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations.

• it’s a form of homeostasis

Plasmolysis

• Plant Cells in a Hypertonic Solution

• There is a net movement of water out of a cell surrounded by a hypertonic solution.

• If the cell has a cell wall, the plasma membrane and cytoplasm shrink and detach from the cell wall.

• This is known as plasmolysis, and leads to cell death.

Turgor Pressure

• when a plant cell is in a hypotonic solution, water moves into the cell vacuole

• The vacuole pushes the cytoplasm and plasma membrane against the cell wall, creating turgor pressure.

• Water continues to move into the cell until turgor pressure equals the pressure exerted by the cell wall. The cell is then fully turgid.

Turgid

• when water moves into the cell until turgor pressure equals the pressure exerted by the cell wall. The cell is then fully turgid.

Flaccid

• A plant cell will become flaccid in an isotonic solution. 

• it looses water, which results in turgor pressure going down and the cell becoming flaccid

Intravenous Fluids

• Intravenous fluids are fluids directly administered into a person's vein.

• needs to be isotonic with the inside of the body

  • Isotonic fluids are used, as they have the same concentration as blood plasma and tissue fluid.

  • Using isotonic fluids prevents excessive movement of water in or out of cells

• Isotonic intravenous fluids are used to support hydration, nutrition, replace lost fluids and administer medications.

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Water Potential

• Water potential is the potential energy of water (with something dissolved in it)  per unit volume, relative to pure water. 

• Water potential determines how freely water particles can move in a solution.

• Water potential is the pressure exerted by water particles on a membrane.

• It is impossible to measure the absolute quantity of the potential energy of water, so values relative to pure water at atmospheric pressure and 20°C are used. 

  • The units are kiloPascals (kPa).

  • Pure water at 20°C has a water potential of 0 kPa.

• Water potential is determined by the pressure potential and solute potential in cells with walls. 

• Water Potential (ψw) = Solute Potential (ψs) + Pressure Potential (ψp.)

Solute Potential

• a component of water potential that measures how dissolved solutes reduce the free energy of water, causing water to move toward areas of higher solute concentration

• The solute potential of pure water is 0 kPa.

• As solute is added to water, the solute potential decreases. Increasing the solute concentration of a solution, decreases the solution’s solute potential.

• solute potentials can range from zero downwards

Pressure Potential

• the physical pressure (hydrostatic pressure) exerted on water within a system, such as a plant cell, influencing its total water potential

• Pressure potential results from the turgor pressure exerted by a cell wall on water in a cell.

• Pressure potentials are usually positive, but may be negative in xylem vessels with the sap being transported under pressure.

plant tissue bathed in a hypotonic solution:

• If the solution outside the cell is hypotonic, then  it will have a relatively high water potential due to having a low solute concentration.

• The hypertonic cytoplasm of cells in the tissue has a relatively low water potential.

• Water will move into the cell by osmosis moving from the high water potential outside the cell to a low water potential inside the cell.

• As water moves into the cell, the pressure potential increases, because water is pushed against the cell wall which increases turgor pressure.

• There will continue to be a net movement of water into the cell until the water potential inside the cell equals the water potential outside the cell.

Tissue bathed in a hypertonic solution:

• If the solution outside the cell is hypertonic, then  it will have a relatively low solute potential due to having a high solute concentration.

• The hypotonic cytoplasm of cells in the tissue has a relatively low solute potential.

• Water will move out of the cells by osmosis, moving from the high water potential in the cytoplasm of the cells, to the low water potential of the fluid surrounding the cells.

• As water leaves the cell by osmosis the pressure potential decreases. The plasma membrane and cytoplasm no longer push against the cell wall.

• Osmosis will continue until the water potential inside the plant tissues’ cells and the solution surrounding them have the same water potential.