D2.3: Water Potential

Question 1

Identify solvent and solutes of a solution.

Answer 1

Solvent:
- Medium in which solutes dissolve through solvation

Solute:
- Substance that is dissolved in a solvent to form a solution

Question 2

Define solvation.

Answer 2

The interaction of a solvent with the dissolved solute

Question 3

Explain why water is able to dissolve charged and polar molecules.

Answer 3

• Polar molecules and charged ions dissolve in water as they are hydrophilic - they can form H bonds with water; partially positive charged H atom of a water molecule gets attracted to the negatively charged O atom of another water molecule (VV for negatively charged O atoms)
• Therefore, water molecules surrounding ions (solute) create hydration shells that separate and form a uniform distribution throughout the solution (process is called dissolution)

Question 4

Outline the solvation of hydrophilic and hydrophobic substances.​​

Answer 4

Hydrophilic:
- polar molecules (like water) are electrostatically attracted to ions; partially positive charged H atom of a water molecule gets attracted to the negatively charged O atom of another water molecule and VV for negatively charged O atoms.

Hydrophobic:
- Non-polar molecules (like lipids) are insoluble in water however they are attracted to other hydrophobic molecules thus, will clump together when exposed to water

Question 5

Define osmolarity, isotonic, hypotonic and hypertonic.

Answer 5

Osmolarity:
- a measure of the solute concentration

Isotonic:
- a solution having the same solute concentration as another solution

Hypotonic:
- a solution having lower solute concentration than another solution

Hypertonic:
- a solution having higher solute concentrations than another solution

Question 6

State the unit for concentration of a solute in a volume of solution.

Answer 6

mol dm^-3

Question 7

Outline the net movement of water between hypotonic, hypertonic and isotonic solutions.

Answer 7

Net movement of water in isotonic solutions:
- there is equal movement of water into and out of the cell

Net movement of water in hypotonic solutions:
- there is a net movement of water from the solution into the cell causing it to swell

Net movement of water in hypertonic solutions:
- there is a net movement of water out of the cell into the surrounding solution

Question 8

Compare the relative permeability of the plasma membrane to water and solutes.

Answer 8

Relative permeability of the plasma membrane to water:
- Not permeable to water; water moves freely by osmosis until a state of dynamic equilibrium

Relative permeability of the plasma membrane to solutes:
- Permeable to solutes; depends on its size and charge

Question 9

Define osmosis.

Answer 9

Movement of water molecules across a semi-permeable membrane from a region of higher water potential to a region of lower water potential

Question 10

State what form of transport is osmosis

Answer 10

passive transport

Question 11

Explain what happens to cells when placed in isotonic, hypotonic and hypertonic solutions.

Answer 11

Cells placed in isotonic solutions:
- this results in dynamic equilibrium - no change in shape or size of a cell

Cells placed in hypotonic solutions:
- LYSIS OCCURS IF ANIMAL CELL and too much water moves into the cell

Cells placed in hypertonic solutions:
- Leads to cell shrinking and becoming CRENATED IF ANIMAL CELL and PLASMOLYSED IF PLANT CELL

Question 12

Explain the change in mass and/or volume of plant tissues placed in either hypotonic or hypertonic solutions.

Question 13

Determine the concentration of solutes in a plant tissue given changes in plant tissue mass and/or length when placed in solutions of various tonicities.​

Question 14

State the effects of hypertonic and hypotonic solutions on cells without a cell wall.

Question 15

Explain why tissue fluid in multicellular organisms must be isotonic to the cells of the tissue.

Question 16

Outline the role of the contractile vacuole in freshwater unicellular organisms.​

Question 17

Describe the strength and permeability of a cell wall.

Question 18

Explain the effects of hypertonic and hypotonic solutions on cells with a cell wall with specific reference to turgor pressure and plasmolysis.

Question 19

State the effects of isotonic, hypertonic and hypotonic solutions on human cells.

Question 20

Outline the use of “normal saline” in medical procedures.

Question 21

Define water potential.

Question 22

State the symbol and unit for water potential.

Question 23

Outline factors that contribute to water potential in living systems.

Question 24

State that pure 20° water at standard atmospheric pressure as a water potential of 0kPa.

Question 25

Explain the movement of water from higher to lower water potential.

Question 26

Describe the impact of solute potential and pressure potential on the total water potential of cells with walls.

Question 27

Explain why solute potentials can only range from 0kPa downwards.

Question 28

State that pressure potentials are generally positive inside cells.

Question 29

State a cell type in which the pressure potential is negative. ​

Question 30

Explain the movement of water in plant cells bathed in a hypotonic solution in terms of solute and pressure potentials.

Question 31

Explain the movement of water in plant cells bathed in a hypertonic solution in terms of solute and pressure potentials.​