1 / 13

Plant Circulation and Transport

Plant Circulation and Transport . Chapter 25. Xylem primary xylem apical meristems  procambium  primary xylem formed early in development herbaceous and woody plants transport of water secondary xylem formed later in development from vascular cambium

camden
Download Presentation

Plant Circulation and Transport

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Plant Circulation and Transport Chapter 25

  2. Xylem • primary xylem • apical meristemsprocambium primary xylem • formed early in development • herbaceous and woody plants • transport of water • secondary xylem • formed later in development from vascular cambium • woody plants only (annual rings in wood) • structural support; fair amount of transport • xylem is a complex tissue • tracheidsand vessel elements • transport of H2O • hollow and dead at maturity; only cell walls remain • stacked on top of each other, forming pipelines • parenchyma cells • storage of H2O and minerals • xylem fibers • provide structural support

  3. Fig. 24.6 Xylem structure

  4. how is H2O moved upwards in a plant? • many trees are very tall and H2O moves againstgravity • root pressure • H2O moves into plant’s roots from soil (osmosis) • H2O pressure in roots increases and pushes H2O up • not strong enough to account for rise of H2O in tall trees • strongest influence is in small plants in spring • cohesion-tension model • often begins with root pressure • plants only use a fraction of the H2O they absorb • most evaporates into the air and is lost • water moves up plants through transpiration • evaporation of water from plant parts exposed to air • H2O is pulled up by the drying power of air • top H2O molecules are evaporated off by transpiration • this E pulls up the rest of the water column • evaporation occurs through the stomata in leaves • water moves up a plant (roots  stems  leaves) • transpiration creates a negative pressure in xylem • extends downward from the leaves to roots • similar to sucking liquid up a straw

  5. The process of transpiration

  6. rate of transpiration • regulated by stomata and their guard cells • affected by env. factors • wind, heat, dryness • only works if H2O column is unbroken and narrow • cohesion and adhesion Fig. 25.12 Cohesion-tension model of xylem transport

  7. Phloem • transport in phloem is much slower than in xylem • primary phloem • apical meristemsprocambium primary phloem • formed early in development • herbaceous and woody plants • transport of nutrients (sugars) • secondary phloem • formed later in development from vascular cambium • found only in woody plants (part of the bark) • structural support; fair amount of transport • phloem is a complex tissue • sieve-tube members • transport nutrients • function as living cells, lack a nucleus and most organelles • stacked on top of each other, forming pipelines • companion cells • lie adjacent to sieve-tube members • continually nourish sieve-tube members  keeps them alive • one companion cell per sieve-tube member • parenchyma cells – storage of nutrients • phloem fibers – provide structural support

  8. Fig. 24.7 Phloem structure

  9. materials flowing through phloem • mainly sugars (sucrose) • small amounts of other materials • proteins, hormones, chemical defenses, lipids, wastes, etc. • phloem sap • how nutrients are moved within a plant • phloem sap moves from sources to sinks • sources • areas where sap is produced or stored • leavesand roots (winter only) • sinks • areas that require sap • all other areas of the plant • phloem sap moves primarily down from the leaves

  10. phloem sap moves through translocation • accomplished through a fluid pressure-flow mechanism • process • involves buildup of sap at sources  transported into phloem • phloem loading • involves release of sap at sinks  nutrients to tissues • phloem unloading • sap moves from high pressure at sources to low pressure at sinks • inflow of H2O from neighboring xylem cells assists the process • ATP needed for this is provided by companion cells • sieve-tube members, companion cells, and xylem all work together

  11. The process of translocation

  12. Translocation

  13. Fig. 25.15 Pressure-flow model of phloem transport (translocation)

More Related