Plant Transport Chapter 36

Overview of Transport Water leaves the plant via transpiration Oxygen leaves the plant through leaves Sugars move down into other plant parts from leaves through phloem tissues Carbon dioxide enters plant through stomata Water enters the plant through roots and travels through xylem

Vascular Tissue: Xylem Xylem: carries water and minerals Made up of tracheids and vessel elements Dead at maturity

Xylem tissue One-way transport only Walls of cells reinforced with lignin Tracheids made of sclerenchyma cells: thickened cell walls

Fluid Movement in Xylem Root pressure forces water into xylem while transpiration pulls it up: cohesion- tension theory Adhesion: water sticks to cellulose walls Cohesion: water sticks to itself

Vascular Tissue: Phloem Phloem: carries sugar from leaves to rest of plant Made up of sieve tube members and companion cells Alive at maturity

Phloem tissue Two-way transport possible Consist of thin-walled parenchyma cells Sieve plates have plasmodesmata

Vascular Cylinder: Stele Arrangement of vascular bundles differs in monocot and dicot plants

Lateral transport in plants Symplast: substances travel through cells via plasmodesmata Apoplast: substances travel between cell walls

Lateral transport in roots Symplast Apoplast: fluids must pass through a living cell to get to stele Casparian strip: waxy coating forces water into stele

Transpiration Water exits the stomates of leaves due to differences in water potential, coupled with root pressure Photosynthesis- transpiration compromise In leaf: High  Outside leaf: low 

Factors Affecting Transpiration Wind: faster winds increase rate of transpiration Humidity: high humidity slows transpiration rate Temperature: increased temp increases rate of transpiration

Transpiration

Guard cells accumulate K+ ions   inside cells becomes negative Water rushes in,cells swell and stoma opens Trigger: low CO2 in leaf, blue light receptors Behavior of Guard Cells: Open

Behavior of Guard Cells: Closed Guard cells lose K+   inside guard cells becomes less negative Water exits, stoma closes as guard cells become flaccid

Translocation The movement of photosynthetic products from leaves to other parts of the plant via phloem tissues

How it happens Carbohydrates are made in mesophyll cells Sugars actively transported by bundle sheath cells to vascular bundle, composed of companion cells and sieve tube members

A Closer Look Symplast transport from mesophyll to bundle sheath and parenchyma cells Companion cells act as transfer cells mesophyll Bundle sheath cell Companion cell Sieve tube member

Bulk Transport in Phloem xylem phloem source sink Water flows into xylem via root pressure and transpiration flow

Bulk Transport in Phloem xylem phloem source sink Phloem sap flows from high pressure to low pressure; from source to sink

Bulk Transport in Phloem xylem phloem source sink In source cells, sucrose enters sieve tube member,  becomes negative

Bulk Transport in Phloem xylem phloem source sink Sink cells remove sucrose, so water pressure in sieve tube members decreases