D2.3 Water potential

Question 1

What is solvation

Answer 1

Combination of a solvent with molecules/ions of a solute.

Question 2

Properties of water as a solvent?

Answer 2

1) Polarity, partial charge of oxygen pole, partial charge on hydrogen pole.
2) polar solutes dissolve, attraction between partial charges on water and solutes
3) cations attracted to partial - oxygen pole
4) anions attracted to partial + h pole

Question 3

Why do water molecules form shells round many types of ions and charged molecules?

Answer 3

1) due to attractions between water and solutes. Form shell around ions with greater attraction in total than ionic bonds within.
2) prevents them from precipitating, clumps solutes together

Question 4

Cytoplasm

Answer 4

Complex mixture of dissolved substances where metabolic reactions occur.

Question 5

What happens when NaCl is dissolved in water?

Answer 5

1) bonds between Na and Cl ions break
2) H in water is attracted to anions
3) O in water attracted top cations
4) shell is formed around ions with greater attraction in total.

Question 6

Why do particles in a liquid move but cannot separate from each other?

Answer 6

1) Due to intermolecular forces of attraction, do not separate unless changing state to gas.

Question 7

When water changes position what happens to hydrogen bonds?

Answer 7

Repeatedly broken and formed. Many bonds exist, so strong overall attraction between molecules.

Question 8

How do solutions form?

Answer 8

Because of the intermolecular attractions between solutes+water are strong.

Question 9

How does solute-water attractions influence movement of water between solutions?

Answer 9

Attractions restrict movement of water molecules, so more viscous than pure water.

Question 10

What happens when water moves between two solutions?

Answer 10

Always movement in both directions, however more molecules move from less solute concentrated to more concentrated. Net movement of water

Question 11

What is osmosis?

Answer 11

passive net movement of water across a membrane, due to attractions between solutes and water.

Question 12

How to determine whether a solute is osmotically active?

Answer 12

If intermolecular attractions form between solute and water. E,g Na, K, Cl, glucose are osmotically active.

Question 13

Why is there movement from a hypotonic to hypertonic solution?

Answer 13

Has higher concentration of osmotically active solutes

Question 14

Why is there no net movement between two isotonic solutions?

Answer 14

No difference in concentrations of osmotically active solutes, equal no. of h2o molecules move between them, dynamic equilibrium.

Question 15

membranes are more permeable to?

Answer 15

Water, but much less permeable to solutes. Difference in solute conc between solution in and out cell results in movement of water across membrane. Membrane is semi permeable, not freely permeable to all particles.

Question 16

how can cells change how rapidly osmosis occurs?

Answer 16

changing permeability to water of the p membrane. Also can change direction of movement by lowering/raising conc of osmotically active solutes.

Question 17

what are the properties of a phospholipid membrane in animals and plants

Answer 17

thin, 5nm or less
liquid state, allows change of position, formation of vesicles by budding and diffusion of molecules
very low tensile strength
semi permeable

Question 18

Properties of a cellulose cell wall?

Answer 18

250nm to 5 nanometre/more
solid, changes of position limited, constituent (being a part of a whole) molecules of wall do not diffuse.
High tensile strength, more than steel
freely permeable, unless impregnated by waterproof material (cutin, lignin, suberin etc)

Question 19

What happens when animal cell bathed in hypotonic solution?

Answer 19

Water enters cell, osmosis, swelling occurs.
Cell bursts, lacks wall.

Question 20

why do high pressure due to entry of water build up inside plant cells?

Answer 20

Cell wall strong enough to prevent bursting.
Pressurized cell is said to be turgid/swollen.
Turgid plant tissue provides support due to strength under compression.

Question 21

if plants lose water what happens?

Answer 21

Pressure of cyto drops. If it drops to atmospheric, p membrane does no longer pushes against cell wall, cell is not turgid anymore

Question 22

what happens if plants lose even more water?

Answer 22

Plants become flaccid, leaves+stems bend downwards (wilting).
Seen in plants losing water by transpiration in hot weather, further water loss is avoided by closing stomata.

Question 23

What happens if plants bathed in hypertonic?

Answer 23

Loses water, cell wall permeable to water, does not move.
as vol of cyto decreases, membrane pulls away from cell wall, plasmolysis.
usually leads to death of cell.

Question 24

What are some medical applications of isotonic solutions?

Answer 24

normal saline, safely introduced in blood system (intravenous drip)
used to rinse wounds and skin abrasions
used to keep damaged skin areas moist prior to skin grafts (removal)
used as basis for eye drops
frozen to consistency of slush for cooling hearts, kidneys and other donor organs needed to be transported.

Question 25

What happens when human cells are placed in isotonic solutions?

Answer 25

water molecules pass in and out of membrane at same rate, cells healthy.

Question 26

what is water potential? Ψ (kPa or MPa)

Answer 26

measure of potential energy per unit volume. Helps understand movement of water in living systems, able to make predictions where net movement occurs

Question 27

What are two factors that influence water potential?

Answer 27

• rises/falls in hydrostatic pressure. Higher pressure, more potential (pressure potential Ψp) (positive or negative, greater/less than atmospheric_
• when solutes dissolve, potential energy decreases, higher sol concentration, lower potential energy. (solute potential Ψs)

Question 28

How does WP predict the direction in which there will be net movement of water molecules?

Answer 28

Water moves higher to lower water potential energy, minimizes its potential energy. Similar to rocks rolling done hills.

Question 29

What is the maximum value of water potential found in cells

Answer 29

0kPa.
otheravlues are egative, for e.g -200kPa leaf cells.

Question 30

formula for WP?

Answer 30

WP = Solute potential + pressure potential.

Question 31

what is the potential energy of water with no solutes dissolved?

Answer 31

Zero. as when solutes dissolve, potential energy is reduced.
impossible to hold less than 0 solutes so only values are 0 or negative.

Question 32

What are the effects of bathing plant tissue in a hypotonic solution?

Answer 32

at atmospheric pressure, Ψp = 0, so water and solute potential are equal and negative.
if water potential is more negative, net movement of water from solution to plant cells.
raise WP potential of plant tissue, as solute potential is less negative, and pressure potential more positive.
when tissue WP = Solution WP, net movement stops.

Question 33

What happens when plant tissue is bathed with more dilute hypotonic solution?

Answer 33

higher WP reached in tissue, if bathing solution is pure water, WP = 0.
plant tissue will reach this level.
Hydrostatic pressure of cells cannot rise higher, fully turgid.

Question 34

What happens when WP = 0?

Answer 34

Solute potential counterbalances pressure potential, numerical value is =, but sign is opposite.

Question 35

What happens when plant tissue is bathed with hypertonic solution?

Answer 35

SP of bathing solution is more negative than tissue
Pressure potential of bathing = zero
pressure potential in plants likely to be above zero initially.
thus solution has a higher water potential tahn solution so net movement out of tissue.

Question 36

What happens when water loss occurs inside cells?

Answer 36

Pressure reduced, when drops to atmospheric, pressures in bathing and cells are equal, cell becomes flaccid.
Solute concentration of cells rise due to water loss
if still higher than bathing, water continues to leave, cyto vol decrease
detachment of p membrane and cyto from cell wall
Plasmolysis.
when sol concentration is =. no net movement, thus water potential is equal.