Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
Plant bio
Water and solute movement
| Question | Answer |
|---|---|
| How does water move? | Transpiration Water vapour pressure (deficit)/relative humidity Water potential Solute potential Turgor pressure (potential) Matrix potential Resistance Surface tension |
| Transpiration | Water movement through the plant Water (liquid) column is continuous from soil water to leaf tissues These continuities persist in growth & development Most water is lost as vapour/must be replaced Phase change at tissue/air space boundary |
| Transpiration and plant water potential | - plant in wet soil, stomata closed: water potential zero (high), atmosphere low - stomata opens: water potential inside falls as water vapour leaves - difference is proportional to resistance (sum of all) |
| Liquid flow resistances | Lack of resistance means flow is an instantaneous response to differences in water potential - resistance across xylem is greater than along leads to differences in water potential from one side to another |
| Stem resistances | Stem resistances are low Highest resistance in petioles – this isolates leaves from each other Resistances give rise to pressure differences |
| Water in xylem | - under tension - evidence of negative potentials in xylem |
| Absorption lag | Consider a plant transpiring, if you stop transpiration (by immersing leaves) what happens? - Plant carries on absorbing water, with a lag; but at diminishing rate, biphasic nature indicates different routes with different resistances |
| Water potential Ψ | the forces acting on water In plants, water moves from areas of +ve potential to -ve potential is less (more –ve): under hydrostatic tension, in osmotic solution or on adsorption to surface Cell water potential = pressure potential + osmotic potential |
| Water in cells and tissues | Consider cell, with overall water potential = -5.0 bar, osmotic potential Ψsap = -5 bar, pressure potential Ψp = 0 bar and cell wall with water potential Ψ= -1 bar water flows into cell (and hence vacuole) from cell wall with pressure of 4 bar |
| Causing Ψsap to increase (become less –ve) Thus, difference Ψcell vs Ψwall reduces, and Ψp (of cell) increases (becomes +ve) | |
| Water transport in xylem | Water movement through the xylem requires ten times less pressure than movement through living cells - simple low resistance pathway |
| Cohesion tension theory | Tension developed at the top of the tree pulls water through the xylem: requires cohesive properties of water to sustain large tensions in the xylem water columns |
| Water is brought to the leaves via the xylem of the leaf vascular bundle, branched into a very fine network of veins Most cells in a typical leaf are within 0.5 mm of a minor vein, water is drawn into the cells of the leaf and along the cell walls | |
| Evaporation | Water evaporation from the leaf air spaces generates a negative pressure in the xylem |
| Translocation in phloem | The phloem is the tissue that translocates the products of photosynthesis from mature leaves to areas of growth and storage, including the roots Sugar is translocated in phloem sieve elements |
| Pathways of translocation | Mature sieve elements are living cells highly specialised for translocation |
| Materials translocated in phloem | Sucrose, at rate 104 x that in other symplasts Amino acids Hormones Inorganic ions RNA |
| Phloem loading | - sugar from phloem to sink cells - from chloroplasts to sieve elements - occurs from mesophyll cells via the apoplast or the symplast (different companion cells are used) |
| Pressure flow model | - phloem translocation as a flow of solution driven by an osmotically generated pressure gradient between source and sink |
Created by:
rose.coo
Popular Ecology sets