Download Monocots, Dicots, Plant cells and Transpiration pull. 4. One

Monocots, Dicots, Plant cells and Transpiration pull.
4. One structural response of plants is a “skeleton” to support the weight of the plant or
the growth of branches in response to wind.
One physiological response is closing of stomata if there is a water deficiency.
Monocotyledonae
Dicotylendonae
1. One cotyledon (seed leaf)
2. Leaves have parallel veins.
3. Vascular bundles are spread out.
4. Roots are fibrous.
5. Floral parts in multiples of 3.
6. Orchids, bamboo, grasses (wheat,corn)
Lilies, palms.
Two cotyledons.
Leaves have netlike veins.
Vascular bundles are in rings.
Roots are tap roots with lateral roots.
Floral parts in multiples of 4 or 5.
Roses, beans, sunflowers, maples, oaks.
Parts of an Angiosperm (flowering plants).
See figure in text book.
5. Structure of Xylem cells.
Tracheids
1. Dead when functional.
2. Long, thin with tapering ends.
3. Thick walls.
4. Pits in thinner regions.
5. Water transport through pits.
Vessel elements
Dead when functional.
Wide, short, less tapered.
Thin walls.
End walls are perforated ( plates).
Water transport through plates.
How does water move up the plant?
Night time
Less transpiration
Root cells still pumping minerals into the xylem
Accumulation of minerals in the stele (vascular tissue region)
Lowers water potential in this region
Water flows in from the root cortex
Positive pressure that pushes fluid up xylem = root pressure.
This is not the main mechanism moving xylem sap up the plant.
Transpiration-cohesion-tension mechanism.
a) Transpiration provides the pull up the xylem.
b) Cohesion transmits the upward pull along the length of the xylem to the roots.
Transpiration is water loss from the leaves which results in evaporation of the water layer
form the mesophyll cells.
Cohesion (H-bonds in water) leads to an increase in the surface tension of the water film.
Remaining water goes into the pores of the cell walls by adhesion to the cell walls.
These two phenomena result in a pull on the water which forms a meniscus.
This creates a negative pressure and since water goes from high to low pressure it moves
up the xylem.
Differences in solute concentration and pressure drive the microscopic transport from cell
to cell.
Osmosis is movement of water only.
Bulk flow moves water, minerals and other dissolved solutes and no energy is spent.
The sun drives transpiration and this causes the movement of sap up the xylem.