Plant Biology: Transport and Adaptations

Flashcards on plant transport systems, water transport, transpiration, translocation, and plant adaptations based on lecture notes.

Herbaceous dicots

Soft tissues, short life cycles.

Woody arborescent dicots

Hard, lignified tissues, long life cycles.

Xylem

Transports water and mineral ions from roots to leaves; unidirectional, passive process (transpiration stream).

Phloem

Transports organic solutes like sugars and amino acids throughout the plant; bidirectional, active process.

Xylem composition

Non-living tissue made up of vessels, fibers, and parenchyma.

Xylem vessels

Long, hollow tubes formed by dead cells aligned end-to-end, facilitating water transport.

Xylem fibers

Provide mechanical strength in xylem.

Xylem parenchyma

Stores food and contains tannin, which deters herbivores in xylem.

Lignin

Strengthens cell walls and waterproofs vessels in xylem.

Pits

Areas without lignin in xylem, allowing lateral movement of water between vessels.

Phloem composition

Living tissue consisting of sieve tube elements, companion cells, fibers, and parenchyma.

Sieve tube elements

Aligned end-to-end with perforated sieve plates, facilitating flow of sap in phloem.

Companion cells

Adjacent to sieve tubes, containing nuclei and organelles to support sieve elements.

Root hair cells

Increase surface area for water absorption in roots.

Apoplast pathway

Water moves through cell walls and intercellular spaces.

Symplast pathway

Water moves through the cytoplasm of cells via plasmodesmata.

Vacuolar pathway

Water moves through the vacuoles and cytoplasm.

Casparian strip

A band of suberin in the endodermal cell walls that blocks the apoplast pathway, forcing water into the symplast pathway.

Cohesion

Water molecules stick together due to hydrogen bonding.

Adhesion

Water molecules adhere to the walls of xylem vessels.

Transpiration pull

Water evaporating from the leaves creates a negative pressure that pulls water upward through the xylem.

Transpiration

The evaporation of water from the mesophyll cells into the air spaces and then out through the stomata. Primary driving force for water movement.

Xylem vessels (adaptation)

Long, hollow tubes that facilitate efficient water transport.

Lignification (adaptation)

Strengthens xylem walls and prevents collapse under tension.

Stomatal regulation

Guard cells control the opening and closing of stomata to balance water loss and gas exchange.

Translocation

The movement of assimilates (primarily sucrose) through the phloem from sources to sinks. Facilitated by pressure flow mechanism.

Sources

Regions where assimilates are produced or released (e.g., green leaves, storage organs).

Sinks

Regions where assimilates are consumed or stored (e.g., roots, meristems, developing fruits).

Apoplast pathway (phloem loading)

Sucrose moves through cell walls (apoplast) to companion cells; H+ ions actively pumped out. Secondary active transport of sucrose.

Symplast pathway (phloem loading)

Sucrose moves from mesophyll cells into the cytoplasm of companion cells and sieve tube elements via plasmodesmata.

Xerophytes

Adapted to arid (dry) environments.

Hydrophytes

Adapted to aquatic or water-saturated environments.

Mesophytes

Adapted to environments with moderate water availability.

Thick waxy cuticle

Reduces water loss by evaporation from the leaf surface.

Sunken stomata

Stomata located in pits reduce air movement, creating a humid microclimate.

Reduced leaf area

Smaller leaves or spines decrease the surface area for water loss.

Hairy leaves (trichomes)

Trap a layer of moist air, reducing the water potential gradient.

Curled leaves

Leaves that roll inward trap moist air and reduce exposure to wind.

Succulent tissues

Specialized parenchyma cells store water in stems or leaves.

Deep or widespread root systems

Access water from deeper soil layers or a larger area.

Thin or no cuticle

Water loss is not a concern, thus a protective cuticle is unnecessary.

Stomata on upper leaf surfaces

In floating leaves