Water Transport in Plant Cells Flashcards
3 transport scales
- local transport of water and solutes by individual cells (single-cell root hairs) by diffusion
- short-distance transport of substances from cell to cell at levels of tissues/organs (roots)
- long-distance transport within xylem at level of the whole plant
Movement of water and solutes depend on what?
selective permeability of membranes
what is selective permeability of membranes?
- control movement of solutes (nutrients, photosynthate) into and out of cells
- plant cell maintain internal environment
what are the movement of water and solutes transport proteins?
- passive transport
- active transport
What is passive transport ?
- facilitated diffusion
- osmosis
Example of facilitated diffusion
channels/carriers
Example of osmosis
aquaporins
What is active transport?
-proton pumps
- secondary active transport
What pumps do plants have?
proton pumps
What does electrochemical gradient - proton motive force (pmf) do?
- concentration gradient
- charge gradient (membrane potential)
What does proton pump do?
- pump actively move protons across membrane with ATP
- build a potential energy on one side of membrane
What is potential energy used for?
- work of moving other substances across membrane
What is the use of proton pumps?
- cation uptake (K+, NH3+) using membrane potential (delta charge)
- anion (Cl-, NO3-) uptake to facilitated proton diffusion using cotransport (symport protein)
- neutral solute (sugar) uptake to facilitated proton diffusion using cotransport (symport protein)
How does water move?
passively thru osmosis
What does water energy have?
free energy - chemical potential
chemical potential is usually referred to water potential
What happens when water stick to substances?
- 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
What is water potential?
Ψw = Ψs + Ψp + Ψm
What is Ψs?
solute (osmotic) potential
- add this = decrease free energy of water
- Ψs = always negative
What is Ψp?
pressure (turgor) potential
- effect pressure on Ψw
- if water under pressure, both pressure potential + water potential increase
What is Ψm?
matric potential
- adhesion of water like cell walls and soil particles
- can only decrease free energy of water
- Ψm = always negative
how do plants survive?
balance water uptake and water loss
how does water move from?
- from regions with high [free water], water potential is more +
- to regions with low [free water], water potential is -
thru osmosis
how to measure water potential (Ψw)?
Ψw = Ψs + Ψp
how to determine water movement?
higher (less negative) to lower (more negative)
How does water potential affect plant?
- affects uptake
- loss of water by plant cells
what is turgid plant?
= rigid plant
= cells have turgor pressure
Ψp > 0
- equal water potential inside and outside cell
What is flaccid plant?
= 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
What is Ψw of distilled water?
0 MPa
What happens to water transport in Turgid cells?
Water enters cell
vacuole swells and pushes against cell wall
What happens in water transport in flaccid cell?
water lost from cell
vacuole shrinks and cell loses shape
