Topic 7: Tonicity & Osmoregulation

Tonicity

the ability of an extracellular solution to cause a cell to gain or lose water.

Osmoregulation

cells must be able to regulate their solute concentrations and maintain water balance.

Cells immersed in an isotonic solution have ___ net movement of water.

no; water diffuses into the cell at the same rate water moves out of the cell.

What happens to animal and plant cells when placed in a hypertonic solution?

Plant Cell: Plasmolysis - vacuole shrinks and the plasma membrane pulls away from the cell wall. 

Animal Cell: shrivels and dies

What happens to animal and plant cell when placed in a hypotonic solution?

Plant Cells: work optimally/maintain turgor pressure

Animal Cells: swell and lyse

Water Potential

a physical property that predicts the direction water will flow

-includes the effects of solute concentration and physical pressure

How does water flow in terms of potential?

Water will flow from areas of:

High water potential to low water potential

Low solute to high solute

High pressure to low pressure

What unit is water potential measured in?

bars

What is the solute potential of pure water?

0 MPa

What is the pressure potential of “open air”? (object sitting on table)

0 MPa

What is the ionization constant of sucrose/glucose?

1

What is the ionization constant of NaCl

2

Why would it be bad to administer distilled water into a patient’s bloodstream?

Distilled water is hypotonic, so when injected into the bloodstream, it dilutes the plasma making it much less concentrated than the fluid inside red blood cells.

How would red blood cells react to the introduction of distilled water?

The cells swell & burst, cytolysis (specifically hemolysis) due to water entering. This releases hemoglobin into the blood leading to kidney failure, seizures, brain swelling, or death. 

How does water entering/exiting plant cells affect turgor pressure?

Water entering (not too much) maintains turgor pressure

Water leaving lowers turgor pressure