The Cell Cycle

Page
5

Water and minerals can travel through a plant by three routes:

Transmembrane route: out of one cell, across a cell wall, and into another cell

Symplastic route: via the continuum of cytosol

Apoplastic route: via the cell walls and extracellular spaces

Water and Mineral Short Distance Transport

Slide 30

Bulk Flow in Long-Distance Transport -Vessels Xylem and Phloem

Efficient long distance transport of fluid requires bulk flow, the movement of a fluid driven by pressure.

Water and solutes move together through tracheids and vessel elements of xylem, and sieve-tube elements of phloem.

Efficient movement is possible because mature tracheids and vessel elements have no cytoplasm, and sieve-tube elements have few organelles in their cytoplasm.

Slide 31

Absorption of Water and Minerals by Root Cells

Most water and mineral absorption occurs near root tips, where the epidermis is permeable to water and root hairs are located.

Root hairs account for much of the surface area of roots.

After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals.

Slide 32

Transport of Water and Minerals into the Xylem

The endodermis is the innermost layer of cells in the root cortex.

It surrounds the vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue.

Slide 33

Water can cross the cortex via the symplast or apoplast.

The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder.

Slide 34

Transport of water and minerals from root hairs to the xylem

Pathway along apoplast

Casparian strip

Endodermal cell

Pathway through symplast

Casparian strip

Plasma membrane

Apoplastic route

Symplastic route

Root hair

Epidermis

Cortex

Endodermis

Vessels (xylem)

Stele (vascular cylinder)

Slide 35

Transport of water and minerals from root hairs to the xylem

Casparian strip

Plasma membrane

Apoplastic route

Symplastic route

Root hair

Epidermis

Cortex

Endodermis

Vessels (xylem)

Stele (vascular cylinder)

Slide 36