D2.3 Water Potential

Question 1

Identify solvent and solutes of a solution.

Answer 1

Solvent: the liquid in which a solute dissolves (ex.water-universal solvent)
Solute: substance that dissolves in a solvent
Solution: the mixture of the solute(s) in a solvent

Question 2

Define solvation.

Answer 2

The process of which solvent molecules surround and interact with solute ions or molecules. (substances dissolving process)

Question 3

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

Answer 3

• Polar molecules can dissolve in water since they are HYDROPHILIC and can form HYDROGEN bonds with water
  (positive charge of hydrogen atom is attracted to negatively charged regions of solute)
• Charged Ions can dissolve since they are also HYDROPHILIC and water is electrostatically attracted
  (positive charge of water attracts to negative charge of anion)
  (negative charge of water attracts a positive charge of cation)

Question 4

Outline the solvation of hydrophilic and hydrophobic substances.​​

Answer 4

Hydrophilic:
-dissolve in water because of hydrogen bonds with water or electrostatic attraction
Hydrophobic:
-cannot attract water
-clump together when exposed to water
-all lipids are hydrophobic

Question 5

osmolarity

Answer 5

the number of particles of solute per liter of solution (osmol/L)

Question 6

isotonic

Answer 6

isotonic solution - no net movement of water will take place.

Question 7

hypotonic

Answer 7

hypotonic solutions- there is a net movement of water from the solution into the body

Question 8

hypertonic

Answer 8

hypertonic solution - the net movement of water will be out of the cell and into the solution

Question 9

How does water move? (solute concentration)

Answer 9

Water moves from LESS concentrated to MORE concentrated solutions

Question 10

Osmosis

Answer 10

diffusion of water across a semipermeable membrane

Question 11

osmosis is a form of ______ transport.

Answer 11

passive

Question 12

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

Answer 12

The plasma membrane is more permeable to water compared to solutes

Question 13

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

Answer 13

isotonic - no net movement of water; stay the same
hypertonic - water leaves cell; shrivel/shrink in size
hypotonic - water enters cell; bulge/grow bigger

Question 14

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

Answer 14

Osmosis will occur based on solute concentration (measured in molarity) differences between the potatoes and solution

Question 15

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.​

Answer 15

-Water naturally moves into the plant roots because the roots are hypertonic in comparison with the nearby soil.
-Solution with higher molarity causes the potato(plant) to shrink; water moves out
-Solution with lower molarity causes water to move into the potato which creates an increase in mass

Question 16

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

Answer 16

• Red blood cells don’t have a cell wall so they will burst in a hypotonic solution.
  -When placed in a hypertonic solution, a cell without a cell wall will lose water to the environment, shrivel, which leads to crenation (abnormal notches on the surface of the cell.)

Question 17

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

Answer 17

-hypertonic solutions, water will leave the cell causing it to shrivel (crenation)
-In hypotonic solutions, water will enter the cell causing it to swell and potentially burst (lysis)
-Therefore, for multicellular organisms it is important that tissue fluid remains isotonic to prevent harmful changes.

Question 18

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

Answer 18

Amoeba- contain contractile vacuole that collect excess water and pump it out. Regulate the water concentration in comparison with the solutes inside the cell.Helps the cell main homeostasis with regulation on movement of water and other substances across the membrane.

Question 19

Describe the strength and permeability of a cell wall.

Answer 19

Cell walls provide strength and shape to cells and contribute to their permeability. Mainly composed of cellulose in plant cells, they resist compression and maintain structural integrity by allowing balanced movement of water.

Question 20

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

Answer 20

Plant cells - designed to take in large amounts of water; stabilized and supported by their cell wall. Cells with a cell wall will swell when placed in a hypotonic solution, but once the cell is turgid (firm), the tough cell wall prevents any more water from entering.
When a water vacuole is completely full with water it puts turgor pressure on the plant cell wall. When all the cells have this pressure it allows the plant to stand upright and compete for light energy.
Plasmolysis - plant cells don’t have water. They are dehydrated. Not enough turgor pressure causes a plant to bend over or wilt.

Question 21

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

Answer 21

If a cell is placed in a hypertonic solution; water will leave the cell, and the cell will shrink.
In an isotonic environment, there is no net water movement, so there is no change in the size of the cell.
When a cell is placed in a hypotonic environment, water will enter the cell, and the cell will swell.

Question 22

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

Answer 22

It is a solution that is a mixture of salt and water that you can use to rinse your sinuses, clean wounds, flush your eyes and more.
-It’s for management and treatment of dehydration
-It can transport an heart organ that is used for transplant to another location since saline is an isotonic situation
- it can enter nutrients into the bloodstream when vitals are low

Question 23

How is water potential calulated?

Answer 23

Adding solute potential (Ψs) to pressure potential (Ψp)

Question 24

Define water potential.
State the symbol and unit for water potential.

Answer 24

A sample of water and the energy within it that has the potential to move. (symbol Ψ psi - pascals (Pa) or kilopascals -kPa)

Question 25

Pure 20° water at standard atmospheric pressure as a water potential of ___.

Answer 25

0kPA

Question 26

Outline factors that contribute to water potential in living systems.

Answer 26

Water potential is affected by factors such as pressure, gravity, and matric potentials. The higher the pressure potential (Ψp), the more potential energy in a system.

Question 27

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

Answer 27

If there are differing water potentials across a membrane. For example one side has 50 kPa while the other side has 25 kPa. Water will move from 50 to 25 until the potentials even out.

Question 28

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

Answer 28

The combined effect of increased solute potential (more negative) and increased pressure potential (more positive) may result in a net increase in water potential.

Question 29

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

Answer 29

All solutions have a lower water potential than pure water.

Question 30

Pressure potentials are generally _______ inside cells.

Answer 30

positive

Question 31

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

Answer 31

It is negative in the case of xylem vessels. It is also known as wall pressure or turgor pressure.

Question 32

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

Answer 32

Water potential: water moves towards the more negative number (kPa).
HYPOTONIC-
-Increase in solute potential since the movement of water dilutes the solute.
-Increase pressure potential; more molecules exist is the same space
HYPERTONIC-
-solute potential decrease since there is more negative water potential outside the cell. (plasmolyzed state)
-pressure potential decrease since the cell is losing water