D2.3 Water potential

Describe in details the step of the solvation with water as the solvent.

1) Hydrogen bonds form between polar solute and polar water molecules

2) Slightly positively charged H atom of water attracted to negative ions

3) Slightly negatively charged O atom of water attracted to positive ions

4) Water molecule surround charged ions using “hydration shells”

5) Solute particles separated and surrounded by water → solvation

What is tonicity?

it refers to the ability of an extracellular solution to make water move in or out of cell

state and describe the three types of extracellular solution

1) hypertonic solution

• high solute concentration outside cell than inside → water moves out

2) hypotonic solution

• low solute concentration outside cell than inside cell → water moves in

3) isotonic solution

• equal solute concentration outside and inside cell → water moves in/out in equilibrium (no net movement)

What are some effects of animals lacking a cell wall?

• Can swell and burst (lysis) in a hypotonic environment (water moves into cell)

  ● Can shrink and crenate in a hypertonic environment (water moves out of cell)

  ● Isotonic tissue fluid in multicellular organisms needs to be maintained to

  prevent harmful changes and maintain proper functioning

  ● Freshwater organisms like the Paramecium or Amoeba live in a hypotonic

  environments

  ○ have contractile vacuoles to constantly expel water to prevent bursting

What are the effects of plant cells having a cell wall?

• Water moves into plant cells in a hypotonic environment

  ○ Causes increase in internal pressure called turgor pressure against the rigid cell walls

  ○ Cell walls prevent bursting and allow plant cells to maintain a “turgid” shape

  ● Water moves out of plant cells in a hypertonic environment

  ○ Plasmolysis: cell membranes shrink

  away from cell walls

  ○ Lose turgor pressure and cell shrinks

what are the medical applications of isotonic solutions?

Organ transplantation

● Organ needs to be bathed in a fluid that is isotonic to the cytoplasm of organ’s

cells

● Prevent loss or gain of water → reduce risk of damage for a successful

transplant

Intravenous (IV) fluids

● Replace lost fluids, administer drugs, blood transfusion

● More rapid and direct absorption into circulatory system if fluid is isotonic to

blood/tissue fluid

What is water potential?

water potential

• the potential energy (energy stored in a system) of water per unit volume of water

  • values are relative to pure water (water potential of 0) at atmospheric pressure and 20c

  • measured in kPa

  • water moves from high water potential to low water potential

what is the law of water potential?

Ѱw = Ѱs + ѰP

Ѱw = water potential

Ѱs = solute potential (the effect of solutes on water particles → reduces water’s

ability to move freely)

● Always a negative value (decreases Ѱw)

Ѱp = pressure potential (positive Ѱp is exerted outwards from a cell while a

negative Ѱp is the loss of pressure from water)

● Generally positive inside cells (increases Ѱw)

What happens to plant tissues in hypotonic solutions?

● Solute potential of tissue is more negative than solution

● Water moves from less negative to more negative potential

● Influx of water increase pressure potential

What happens to plant tissues in hypertonic solutions?

● Solute potential of solution is more negative than tissue

● Water moves from less negative to more negative potential

● Efflux of water decreases pressure potential