D2.3 Water potential

Question 1

define:

solute
solvent
solution

Answer 1

solute: the substance that is dissolved in a solvent

solvent: a substance that dissolves other substances to create a solution

solution: a liquid mixture that consists of a solute dissolved in a solvent

Question 2

Define solvation

Answer 2

the combination of a solvent with the molecules or ions of a solute

Question 3

why is water able to dissolve charged and polar molecules?

Answer 3

because water has polarity, which allows it to form electrostatic interactions with other polar molecules and ions

• polar solutes dissolve due to attraction btwn the partial + and - charges on water molecules and solute molecules
• positively charged ions are attracted to the partial negative oxygen pole of water
• negatively charged ions are attracted to the partial positive hydrogen pole of water

Question 4

Outline the solvation of hydrophilic and hydrophobic substances.

Answer 4

The solvation of hydrophilic and hydrophobic substances in water is determined by whether the substance is polar or non-polar and can form hydrogen bonds with water

Question 5

Hydrophilic?

Answer 5

These substances are “water-loving” and dissolve easily in water

They include polar molecules + can form hydrogen bonds with water, allowing them to dissolve

Question 6

Hydrophobic?

Answer 6

These substances are “water-hating” and do not dissolve easily in water

They include non-polar molecules (ex. lipids) and CANNOT form hydrogen bonds with water, so they don’t dissolve and tend to join in groups instead

Question 7

Define osmolarity

Answer 7

the measure of the total concentration of solute particles in a solution

the measure of solute concentration per unit volume

Question 8

Define isotonic

Answer 8

isotonic solutions have the same concentration as the cytoplasm of the cell

look at photo

Question 9

Define hypotonic

Answer 9

hypotonic solutions have a lower concentration than the cytoplasm of the cell

Question 10

Define hypertonic

Answer 10

hypertonic solutions have a higher concentration than the cytoplasm of the cell

look at photo

Question 11

what is unit for concentration of a solute in a volume of solution?

Answer 11

moles per cubic decimeter

(mol dm⁻³)

Question 12

net movement of water in hypotonic solutions?

Answer 12

Water moves into the cell, causing it to swell or burst.

Hypotonic solutions have a lower solute concentration than the cell

Question 13

net movement of water in hypertonic solutions?

Answer 13

Water moves out of the cell, causing it to shrivel.

Hypertonic solutions have a higher solute concentration than the cell.

Question 14

net movement of water in isotonic solutions?

Answer 14

There is no net movement of water, so the cell’s size remains stable.

Isotonic solutions have the same solute concentration as the cell.

Question 15

what does the net movement of water depend on?

Answer 15

it depends on the solute concentration of each solution relative to the cell

Question 16

relative permeability of the plasma membrane compared to water and solutes?

Answer 16

The plasma membrane is more permeable to water compared to solutes

Question 17

What is the relative permeability of the plasma membrane to water?

Answer 17

The relative permeability of the plasma membrane to water is high, allowing water molecules to pass through easily

Question 18

What is the relative permeability of the plasma membrane to solute?

Answer 18

the relative permeability of plasma membrane to solute can vary because some solutes can pass through and some solutes need specific channels

Question 19

define osmosis

Answer 19

the movement of water particles from a high water potential to lower water potential through a partially permeable membrane

osmosis is a form of passive transport

Question 20

Explain what happens to cells when placed in:
- isotonic solutions

Answer 20

the cell does not change because it has reached equilibrium + water doesn’t move more in one direction than another

no net osmosis

Question 21

Explain what happens to cells when placed in:
- hypotonic solutions

Answer 21

cytolysis happens because water moves into the cell very quickly

in plant cells, the cell bursts and in animal cells, it becomes turgid (it doesn’t burst BC animal cells have a cell wall)

net osmosis into the cell

Question 22

Explain what happens to cells when placed in:
- hypertonic solutions

Answer 22

the cells crenate (they shrink).
both plant + animal cells undergo plasmolysis as water leaves the cell very quickly

net osmosis out of the cell

Question 23

what is plasmolysis?

Answer 23

it is the shrinking of protoplasm away form the cell wall of a plant of bacterium

(it is often due to water loss via osmosis, causing gaps btwn the cell wall and plasma membrane)

Question 24

what happens to a plant tissue’s mass/volume if put in a hypotonic solution?

Answer 24

water is absorbed = increase in mass/volume = swollen

Question 25

what happens to a plant tissue’s mass/volume if put in a hypertonic solution?

Answer 25

water is lost = decrease in mass/volume = dehydrated

Question 26

what is the concentration of solute if hypotonic?

Answer 26

lower than solution

Question 27

what is the concentration of solute if hypertonic?

Answer 27

higher than solution

Question 28

what is the concentration of solute if isotonic?

Answer 28

balanced with solution

Question 29

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 29

• If plant tissue decreases in mass and length SIGNIFICANTLY, it was in a hypertonic solution
  –>
  plasmolysed BC of osmosis and is pretty shriveled
• If the plant cell content has shrunken a little bit, it is flaccid and was in isotonic solution
  –>
  Cell appears limp/flaccid
• If plant cell appears slightly swollen, it was in hypotonic solution

Question 30

what happens to a cell with no cell wall placed in a hypertonic solution?

Answer 30

cell will shrink and lead to crenation

AREA of plasma membrane DOES NOT CHANGE, so cell develops indentations (these are called crenations)

Question 31

what happens to a cell with no cell wall placed in a hypotonic solution?

Answer 31

cell will burst and lead to cytolysis

Question 32

plasma membranes are made of?

Answer 32

made of phospholipids

it is thin + has very low tensile strength

Question 33

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

Answer 33

it must be isotonic to maintain osmotic balance

An isotonic environment prevents water movement that could cause cells to shrink or swell, ensuring a stable cell volume

This balance facilitates:
- nutrient exchange
- waste removal
- cellular processes

*isotonic tissue fluid = essential for the proper functioning and health of cells in a multicellular organism

Question 34

Outline the role of the contractile vacuole in freshwater unicellular organisms

Answer 34

The contractile vacuole expels excess water that continuously enters the cell due to the hypotonic environment of freshwater

The vacuole collects and pumps out water, preventing the cell from swelling and potentially bursting.

Through rhythmic contractions, it maintains the cell’s internal osmotic balance

Question 35

Describe the strength and permeability of a cell wall

Answer 35

The cell wall is composed of cellulose

It has high tensile strength, stronger than steel

It is freely permeable unless impregnated w/ a waterproof material

Question 36

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

Answer 36

In cells with a cell wall:

• hypertonic solutions cause water to move out of the cell, leading to plasmolysis where the cell membrane shrinks away from the cell wall, resulting in a loss of turgor pressure

Hypotonic solutions:

• cause water to enter the cell, increasing turgor pressure and inducing a firm, turgid state

Turgid is the healthy state for plants

Question 37

State the effects of isotonic solutions on human cells

Answer 37

will help to keep the cell alive

Question 38

State the effects of hypertonic solutions on human cells

Answer 38

cell will lose water and lead to crenation and die

Question 39

State the effects of hypotonic solutions on human cells

Answer 39

cell will gain water and lead to cytolysis and burst

Question 40

Outline the use of “normal saline” in medical procedures

Answer 40

Normal saline is a 0.9% solution of sodium chloride, which is isotonic with blood

during organ transplants, the organs are bathed in normal saline so that cells will not shrink

Question 41

Explain the difference in function between carrier proteins and channel proteins

Answer 41

Carrier proteins allow both passive and active transport through them

Channel proteins allow only passive transport

Question 42

Describe what happens to a protein when it enters the Golgi apparatus

Answer 42

It is then modified and packaged into a vesicle

Question 43

Explain what facilitated diffusion is

Answer 43

The movement of particles down the concentration gradient through protein channels

Question 44

Explain why water only diffuses slowly through plasma membranes

Answer 44

Water is small so can diffuse straight through the phospholipid bilayer.

However. it is polar, which means it diffuses through slowly

Question 45

Explain how molecules are actively transported

Answer 45

Through channel proteins, against the concentration gradient, with the use ATP

Question 46

Answer 46

from left to right

Water molecules always move from a region of high water potential to a region of low (more negative) water potential

pure water = 0 kpa