1. The building blocks of life
Cells
Chapter 3
Cell Passive Transport (Osmosis, Cell Tonicity) Slide
The building blocks of life

2. Water Balance of Cells Without Walls
Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water
Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water
Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water

3. Hypertonic solutions are those in which more solute (and hence lower water potential) is present. Hypotonic solutions are those with less solute (again read as higher water potential). Isotonic solutions have equal (iso-) concentrations of substances. Water potentials are thus equal, although there will still be equal amounts of water movement in and out of the cell, the net flow is zero.
Water relations and cell shape in blood cells Water relations in a plant cell.

4. Osmosis and tonicity

5. Keeping water balance
Cell survival depends on balancing water uptake & water loss
freshwater
balanced
saltwater

6. Keeping right amount of water in cell1
Freshwater
a cell in fresh water
high concentration of water around cell
cell gains water
example: Paramecium
problem: cells gain water, swell & can burst
water continually enters Paramecium cell
solution: contractile vacuole
pumps water out of cell
KABOOM!
No problem, here
freshwater

7. Keeping right amount of water in cell2
saltwater
Saltwater
a cell in salt water
low concentration of water around cell
cell loses water
example: shellfish
problem: cell loses water
in plants: plasmolysis
in animals: shrinking cell
solution: take up water
I’m shrinking, I’m shrinking!
I will survive!

8. Keeping right amount of water in cell3
Balanced conditions
no difference in concentration of water between cell & environment
cell in equilibrium
example: blood
problem: none
water flows across membrane equally, in both directions
volume of cell doesn’t change
balanced
That’s better!
I could be better…

9. Solute Concentration (a) Hypertonic surroundings (b) Isotonic
Hypotonic
surroundings
H2O
Animal
cell:
plasma
membrane
H2O
H2O
Plant
cell:
H2O
plasma
membrane
H2O
H2O
cell wall
wilted
turgid
Balanced water
movement
Net movement of
water out of cell
Net movement of
water into cell

10. Osmosis and Tonicity

11. Hypertonic-Isotonic-Hypotonic

14. Isotonic, Hypotonic, Hypertonic IV Solutions Made Easy | Fluid Electrolytes Nursing Students

15. Diffusion vs Osmosis
Passive diffusion is the net movement of gases or small uncharged polar molecules across a phospholipid bilayer membrane from an area of higher concentration to an area of lower concentration . Examples of gases that cross membranes by passive diffusion include N2, O2, and CO2; examples of small polar molecules include ethanol, H2O, and urea.
Osmosis is the diffusion of water across a membrane from an area of higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration). Osmosis is powered by the potential energy of a concentration gradient and does not require the expenditure of metabolic energy.
In an isotonic environment, both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate.
Simple diffusion
Osmosis
Passive transport
Active transport
Endocytosis
Exocytosis

16. Hypertonic-Hypotonic
If the environment is hypertonic, the water concentration is greater inside the cell while the solute concentration is higher outside (the interior of the cell is hypotonic to the surrounding hypertonic environment). Water goes out of the cell.
In an environment that is hypotonic, the water concentration is greater outside the cell and the solute concentration is higher inside (the interior of the cell is hypertonic to the hypotonic surroundings). Water goes into the cell.
Simple diffusion
Osmosis
Passive transport
Active transport
Endocytosis
Exocytosis

17. Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.
Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.
Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.