Water Transport in Plant Cells

Question 1

3 transport scales

Answer 1

1. local transport of water and solutes by individual cells (single-cell root hairs) by diffusion
2. short-distance transport of substances from cell to cell at levels of tissues/organs (roots)
3. long-distance transport within xylem at level of the whole plant

Question 2

Movement of water and solutes depend on what?

Answer 2

selective permeability of membranes

Question 3

what is selective permeability of membranes?

Answer 3

• control movement of solutes (nutrients, photosynthate) into and out of cells
• plant cell maintain internal environment

Question 4

what are the movement of water and solutes transport proteins?

Answer 4

1. passive transport
2. active transport

Question 5

What is passive transport ?

Answer 5

• facilitated diffusion
• osmosis

Question 6

Example of facilitated diffusion

Answer 6

channels/carriers

Question 7

Example of osmosis

Answer 7

aquaporins

Question 8

What is active transport?

Answer 8

-proton pumps
- secondary active transport

Question 9

What pumps do plants have?

Answer 9

proton pumps

Question 10

What does electrochemical gradient - proton motive force (pmf) do?

Answer 10

1. concentration gradient
2. charge gradient (membrane potential)

Question 11

What does proton pump do?

Answer 11

• pump actively move protons across membrane with ATP
• build a potential energy on one side of membrane

Question 12

What is potential energy used for?

Answer 12

• work of moving other substances across membrane

Question 13

What is the use of proton pumps?

Answer 13

1. cation uptake (K+, NH3+) using membrane potential (delta charge)
2. anion (Cl-, NO3-) uptake to facilitated proton diffusion using cotransport (symport protein)
3. neutral solute (sugar) uptake to facilitated proton diffusion using cotransport (symport protein)

Question 14

How does water move?

Answer 14

passively thru osmosis

Question 15

What does water energy have?

Answer 15

free energy - chemical potential

Question 16

chemical potential is usually referred to water potential

Question 17

What happens when water stick to substances?

Answer 17

• form hydrogen bonds to material (inorganic particles, organic molecules, ions) –> hydration shell
• do not move free = capacity decrease (less “free” water available)
• water potential of solution decreases

Question 18

What is water potential?

Answer 18

Ψw = Ψs + Ψp + Ψm

Question 19

What is Ψs?

Answer 19

solute (osmotic) potential
- add this = decrease free energy of water
- Ψs = always negative

Question 20

What is Ψp?

Answer 20

pressure (turgor) potential
- effect pressure on Ψw

• if water under pressure, both pressure potential + water potential increase

Question 21

What is Ψm?

Answer 21

matric potential
- adhesion of water like cell walls and soil particles
- can only decrease free energy of water
- Ψm = always negative

Question 22

how do plants survive?

Answer 22

balance water uptake and water loss

Question 23

how does water move from?

Answer 23

• from regions with high [free water], water potential is more +
• to regions with low [free water], water potential is -

thru osmosis

Question 24

how to measure water potential (Ψw)?

Answer 24

Ψw = Ψs + Ψp

Question 25

how to determine water movement?

Answer 25

higher (less negative) to lower (more negative)

Question 26

How does water potential affect plant?

Answer 26

- affects uptake - loss of water by plant cells

Question 27

what is turgid plant?

Answer 27

= rigid plant = cells have turgor pressure Ψp > 0 - equal water potential inside and outside cell

Question 28

What is flaccid plant?

Answer 28

= wilted plant = cells have no turgor pressure Ψp < 0 - extracellular fluid: higher on water potential, higher on pressure potential, higher osmotic potential - inside cell: lower on water potential, lower on pressure potential, lower on osmotic potential

Question 29

What is Ψw of distilled water?

Answer 29

0 MPa

Question 30

What happens to water transport in Turgid cells?

Answer 30

Water enters cell vacuole swells and pushes against cell wall

Question 31

What happens in water transport in flaccid cell?

Answer 31

water lost from cell vacuole shrinks and cell loses shape