1 / 17

Chapter 36

Chapter 36. Vascular System in Plants. Three ways water moves through root hairs. Apoplast: water moves through cell walls and never enter cells Symplast: water moves from one cell to another through the cytoplasm

zaina
Download Presentation

Chapter 36

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. Chapter 36 Vascular System in Plants

  2. Three ways water moves through root hairs • Apoplast: water moves through cell walls and never enter cells • Symplast: water moves from one cell to another through the cytoplasm • Transmembrane: water repeatedly moves back and forth from cell wall, crossing the membrane, and through the cytoplasm apoplastic symplastic

  3. Pathway of Water Movement • Root hairs use osmosis to soak up water • Water travels via apoplast or symplast through the cortex until it reaches the endodermis that lines the vascular cylinder (stele). • Endodermis has a “casparian strip”, a selectively waxy layer, which BLOCKS the apoplast pathway, so water MUST move into the stele via symplast (toregulate what minerals in the water can enter the stele) • Xylem within the stele transports water to shoots

  4. Transpiration • Definition: the loss of water vapor from leaves and aerial parts of a plant via stomata • Responsible for upward transport of water through the xylem due to: • pushing forces • pulling forces video

  5. Pushing Forces Endodermis accumlates ions in stele, causing these effects: a) Ψw ______________ in stele b) Water moves ____ stele, generating + pressure forcing water up the xylem (root pressure) c) Guttation is a result of root pressure -low transpiration rate at night -more water moves into stele than transpired -water droplets forced out at end of leaves by morning decreases into More solutes • Ψs • Ψw Ψw= 0

  6. Pulling Forces(transpiration, tension, cohesion mechanism) Transpiration: evaporation of water from stomata of leaves creates (-) pressure and develops tension Bulk Flow: Water moves up the xylem to replace the (-) pressure

  7. Pulling Forces(transpiration, tension, cohesion mechanism) Cohesion: Water molecules are hydrogen bonded to each other due to its polarity Water, therefore, moves up the xylem acting as one large polymer-like substance

  8. How is transpiration controlled by plants? There must be a compromise between photosynthesis and transpiration

  9. Pros: Transpiration can occur for PS Gas exchange for CR and PS can occur Cons: Plant risks dessication from excessive transpiration, leading to wilting The Great Debate!Pros and Cons of an Open Stomata

  10. Pros: Minimal dessication and minimal wilting Cons: No transpiration for PS No PS or CR can occur due to lack of gas exchange The Great Debate!Pros and Cons of a Closed Stomata

  11. Plants maintain a transpiration to PS ratio Ratio (in grams)= water loss CO2 assimilated for PS C3 plants  600:1 ratio C4 plants 300:1 ratio (greater CO2 assimilation rate) Goal = maximize PS rate w/ minimal transpiration

  12. When do plants open and close their stomata? Guard Cells guard cells close High temperatures  [CO2] is low  Night  Day  guard cells open guard cells close guard cells open

  13. How do guard cells open and close? K+ is pumped out of guard cells  ψw __________ inside, and water moves out of guard cells making them flacid and close K+ is pumped into guard cells  ψw ________ inside, and water moves into guard cells making them swell, turgid, and open decreases increases

  14. Translocation Definition: the transport of carbohydrates (CHO) in plants from: - the source (normally where CHO is produced) to - the sink (where CHO is used) ** storage organ (ex. bulb) can be a source or a sink video

  15. Translocation occurs in 2 steps • Sugar Loading • Pressure Flow

  16. Sugar Loading symplast CHO are moved from source to sieve-tube members • Symplast pathway or • Apoplast pathway - needs co-transport mechanism to move CHO from apoplast to cytoplasm of sieve tube apoplast H+ H+ H+ H+ Companion cell H+ ATP ADP ST members

  17. Pressure Flow Phloem (STmembers) xylem • CHO move from source to ST members by sugar loading mechanism • Ψ__________ in the phloem (STM), causing water from xylem to flow into the phloem • This increases pressure in the phloem. Increased pressure causes phloem sap to move to an area of less pressure • Carbohydrates move out towards sink • Ψ ____________ in phloem (STM) so water from phloem diffuses back out to xylem), decreasing pressure decreases source sink increases

More Related