2.8 Tonicity And Osmoregulation

Question 1

What is tonicity?

Answer 1

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

Question 2

What does tonicity depend on?

Answer 2

Depends on the concentration of solute that CANNOT pass through the cell membrane

Question 3

Cells can be in three types of solutions. What are they?

Answer 3

Isotonic, hypertonic, hypotonic

Question 4

What is Osmoregulation? (2)

Answer 4

• cells must be able to regulate their solute concentrations and maintain water balance
• animal cells will react differently than cells with cell walls, like plants, fungi, and some protists

Question 5

What does it mean when a cell is inside an isotonic solution? (3)

Answer 5

• The concentration of non-penetrating solutes inside the cell is equal to that outside the cell
• so the cell immersed in an isotonic solution have no net movement of water
• water diffuses in the cell at the same rate water moves out of the cell

Question 6

What does the cell immersed in a hypertonic solution mean? (4)

Answer 6

• The concentration of non-penetrating solute is higher outside of the cell
• water will move to the extra cellular fluid
• The cell will lose water to the extracellular surroundings
• The cell will travel and die (plasmolyze)

Question 7

What is plasmolysis?

Answer 7

• vacuole shrinks and the plasma membrane pulls away from the cell

Question 8

What does it mean when a cell is immersed in a hypotonic solution? (4)

Answer 8

• The concentration of non-penetrating solute is lower outside of the cell than inside the cell
• The cell will gain water
• animal cells will swell and lyse
• plant cells work optimaly

Question 9

when a cell is immersed in a hypotonic solution, why do animal cells lyse, wild plant cells do not?

Answer 9

Animal cells have no central vacuole to hold extra water, which is why they swell

Question 10

What is water potential? (2)

Answer 10

A physical property that predicts the direction water will flow
- includes the effect of solute concentration and osmotic pressure

Question 11

Which way does water flow in? (4)

Answer 11

• From hypo to hyper
• From high water potential to areas of low water potential
• From low solute to areas of high solute concentration
• From high pressure to areas of low pressure (ex. Toothpaste)

Question 12

What is the WATER POTENTIAL formula, and what does each symbol mean?

Answer 12

Ψ = ΨS + ΨP

• ΨS is solute potential (osmotic potential)
• ΨP is pressure potential

Question 13

In terms of solute potential, what does an increase in solute cause? (3)

Answer 13

• causes binding to more free water
  — this reduces water potential
• expressed as a negative number bc it can pull more water towards in (think salt pulls more water)

Question 14

What is pure water’s solute potential?

Answer 14

0 MPa

Question 15

What is pressure potential?

Answer 15

• The physical pressure on a solution
• can be positive or negative relative to atmospheric pressure
• “open air” means ΨP is 0 MPa

Question 16

What is the formula for solute potential? What does each symbol mean?

Answer 16

ΨS = - iCRT
-i is ionization constant
C is molar concentration
R is pressure constant (0.0831 Lbars/ mol k)
T is temp in kelvin (273+)

Question 17

What is an ionization constant?

Answer 17

• Number of particles formed
• if no ions are formed, the ionization constant is 1 (sucrose)
• salt has an ionization constant of 2

Question 18

Why does salt have an ionization constant of (-) two?

Answer 18

Because when one mole of NaCl ionizes in H2O, u have 1 M Na+ and 1 M of Cl-, therefore 2

Question 19

What is the main rule of water potential?

Answer 19

High water potential goes to low water potential (search 57 in book)

Question 20

Why does high solute concentration pull water towards it? (2)

Answer 20

• Salt has attractive forces that move water towards it

- this creates more space for water to move into the new system