VII. Plant TransportA. Transport into the roots

1. Most minerals (solutes) and some water are actively transported into root hairs

(ATP)

2. These minerals are transported cell to cell toward the stele through plasmodesmata

3. Most water, on the other hand, is carried between cells, through the cell walls

4. Therefore the endodermis and Casparian strip control the entry of water and

solutes into the vascular cylinder (stele)

*Because of root organization all water and solutes must pass through a plasma membrane at some point, making selection of solutes possible

B. Transport of water (xylem sap)(2ft./min.)

1. Transpiration - evaporation from leaves

a. 99% of absorbed water is lost through evaporation (95% from stomata)

b. Why?

i. cooling of plant

ii. CO2 uptake

iii. adequate mineral supply to leaf

2. Root pressurea. Water potential is higher in soil than in root

due to mineral uptake (mineral are trapped in stele by endodermis)

b. Therefore water diffuses into stelec. Therefore water is forced up xylem in stele

3.Transpiration-cohesion-tension mechanism

C. Transport of food (translocation) - phloem sap (1m./hr.)- primarily sucrose

1. Source Sink- leaves - fruit- roots - roots

- shoot tip

2. Pressure-flow mechanisma. Sucrose is actively loaded into companion cell

(cotransport with proton (H+) pump) (ATP)b. Sucrose immediately diffuses into sieve tube

member through plasmodesmatac. Water diffuses into hypertonic sieve tube mem.d. Resulting pressure causes flow of sucrose

solution through sieve tube (bulk flow)e. At sink sucrose is actively transported out and

water follows osmotically

Companion cell

Sieve tube member

VIII. Stomata- most common on undersurface of leavesA. Guard cell structure

1. Inner cell wall thicker2. Unlike epidermal cells they have chloroplasts3. Radial microfibrils in cell walls, thus they can

only elongate

B. Factors affecting opening and closing of stomata1. Light and dark

2. CO2 concentration in leaf3. Circadian rhythm of plant itself

C. Steps in the process of stomatal opening are the following:

1. Blue-light receptors in guard cell membrane stimulate proton pump to pump out H+,

2. which makes the cytosol negatively charged,3. which causes K+ to diffuse in, [K+]4. which causes water to diffuse in osmotically, [H2O]5. which causes an increase in guard cell turgor, 6. which causes guard cell elongation,7. which causes stomatal opening.