D2.3 - Water Potential

How is water bonded

Tow hydrogen, one carbon, covalently bonded.

The O is more electronegative, shared electron pair closer to O

H bonds form between water molecules.

What happens when attraction between water and ions is stronger than between opposite charged ions

water can dissolve substances

What happens when water molecules surround ions

• create hydration shells

  • leads to seperation of solute particles and uniform distribution

Covalent compounds in water

eg glucose and oxygen, can dissolve in water due to intermolecular interactions

Solute substances

made of solutes

Solvent

substance that dissolves

Solution

Homogenous mixture

What happens if regions are separated by selectively permeable membrane

• H20 can move across

  • move by osmosis, until both have equal concentration

    • dynamic equilibrium

Hypertonic

High solute concentration

Hypotonic

Lower solute concentration

Isotonic

Same solute concentration

Osmosis

movement of water across a selectively permeable membrane from lower to higher concentration

What happens when cell is in hypertonic

Water moves out of cell, it shrinks

• crenated (animal cell)

• Plasmolysis (plant cell)

Cell in hypotonic

water moves in, cell swells, it can burst

How to measure isotonic solute concentration - plant tissue

• percentage change of tissue mass

• length of plant tissue

Plant cell in hypertonic

• loses water, osmosis

  • loss of length and mass

Plant cell in hypotonic

• gains water

• increase in length and mass

Hypotonic without a cell wall

• can reach a point where is bursts

Hypertonic without cell wall

shrink, can affect cell structure and function, cause damage

How do cells prevent excessive water intake

• contractile vacuoles

  • actively expel water

e.g. paramecium and amoeba

what does kidney do to prevent harmful changes

• vital role in maintaining isotonic fluids

affect of hypotonic solution with cell wall

• plants have cell wall

• as water enters, leads to increasing internal pressure, known as turgor pressure

• cell referred to as turgid

Turgor pressure

exerted by cytoplasm on cell wall

Cell with wall in hypertonic

• Cell membrane shrinks away from cell wall

  • plasmolysis

• loses turgor pressure

plasmolysis

when membrane shrinks away from cell wall

how can isotonic fluids be given

• intravenously, through the veins

  • allows rapid and direct absorption of medications, fluids or nutrients into circulatory system

what is water potential

water potential is measure of potential energy of water per unit volume of water, relative to potential energy of pure water at standard conditions

Standard conditions of water

0 kPa, highest possible water potential

What happens as water potential becomes more negative

harder for water to move

What is water potential influences by

Solute and pressure potential

Solute potential

Attraction of water molecules to solute particles

• decrease as solute concentration increase

Pressure potential

physical pressure exerted on a system

What can pressure potential be

• positive

  • exerted outwards from a cell

    • e.g. root

  • + water potential

• negative

  • e.g. suction of water in xylem

  • negative, - , decreases water potential

How does water move - WP

Water moves from higher WP, to lower WP, until eq. achieved

WP in hypotonic

Solute potential of tissue more negative than solute potential of solution

• water moves in, less negative solute potential to more negative solute potential

  • causes turgor pressure, pushes cell membrane against wall

• PP is +, pressure in cell increase

Why cant animal cells generate pressure potential

Animals cells don’t have cell wall, cant generate pressure potential, no + pressure potentials

WP in hypertonic

• solute potential of solution more negative than of tissue

  • water moves out of tissue, less negative SP to more negative SP

• volume of cell decreases, cell membrane detaches from wall

  • PP negative, pressure inside cell lower than outside

Solute and pressure potential, both negative, water potential = negative