Transport in Plants Vocabulary

Vocabulary flashcards covering plant tissue anatomy, transport pathways, xylem and phloem structures, transpiration, translocation, and plant adaptations from the lecture notes.

Source

A plant tissue or site where food substances (such as sugars) are synthesized, e.g., leaves.

Sink

A plant tissue or site where food substances are transported and consumed or stored, e.g., roots, stems, meristems, flowers, fruits, and tubers.

Palisade Mesophyll

Leaf tissue consisting of 1–2 layers of regularly packed, cylindrical cells with a large central vacuole and high chloroplast density.

Spongy Mesophyll

Leaf tissue consisting of multiple layers of loosely and irregularly arranged, polygonal cells with large air spaces, low chloroplast density, and a thicker region compared to palisade mesophyll.

Xylem Vessel Element

A dead cell with lignified cell walls, removed end walls, no protoplasm, and cellulose-containing pits in side walls, stacked end-to-end to form a xylem vessel.

Lignin

A hydrophobic polymer present in xylem cell walls that prevents water loss, provides structural support, and prevents xylem vessels from collapsing under tension.

Pits

Non-lignified regions in xylem vessel walls containing cellulose that allow lateral movement of water into adjacent tissues and permit air bubbles to pass laterally.

Sieve Tube Element

A living cell in phloem tissue with thin cell walls, scanty cytoplasm containing few organelles, no nucleus, and end walls forming perforated sieve plates.

Sieve Plates

Perforated end walls separating neighbouring sieve tube elements that contain sieve pores to enable the flow of phloem sap and prevent sieve tubes from bursting under pressure.

Companion Cells

Metabolic cells associated with sieve tube elements via plasmodesmata, containing a nucleus and numerous mitochondria to produce ATP required for translocation.

Phloem Sap

The fluid flowing through phloem sieve tubes, composed of sucrose, amino acids, plant hormones (e.g., auxins), mineral ions ($NO_3^-$, $Mg^{2+}$, $PO_4^{3-}$, $K^+$), ATP, and water.

Transpiration

The evaporation of water from mesophyll cell walls into intercellular air spaces followed by the diffusion of water vapour down a water potential gradient into the external atmosphere via stomata.

Apoplast Pathway

The movement of water from one cell to another through cellulose cell walls, driven primarily by transpiration pull.

Symplast Pathway

The movement of water between adjacent cells across cell surface membranes and cytoplasm connected by plasmodesmata, driven primarily by osmosis.

Suberin

A waxy, hydrophobic substance deposited within the cell walls of endodermal cells to form the Casparian strip.

Casparian Strip

A hydrophobic band of suberin in endodermal cell walls that blocks the apoplast pathway, forcing water to pass through the cytoplasm via cell membranes to filter out soluble toxins and unwanted ions.

Cohesion-Tension Model

The mechanism of water transport in which tension generated by transpiration pull draws water upward from roots in a continuous column maintained by cohesive and adhesive forces among water molecules.

Mycorrhiza

A mutualistic association between plant roots and certain fungi that provides an increased surface area for absorption of water and mineral ions in exchange for plant nutrients.

Assimilation

The range of processes through which a plant converts inorganic nutrients into organic substances, such as sugars, amino acids, and fatty acids.

Active Loading of Sucrose

The process wherein $H^+$ ATPase actively pumps $H^+$ ions out of companion cells, which then return alongside sucrose via a $H^+$ sucrose cotransporter protein before sucrose diffuses into sieve tube elements via plasmodesmata.

Translocation

An active, bidirectional transport mechanism involving mass flow that transfers assimilates from source tissues to sink tissues through phloem vessels.

Xerophytes

Plants adapted to survive in regions where the water supply is deficient.

Mesophytes

Plants adapted to survive in regions where the water supply is adequate.

Hydrophytes

Plants adapted to survive in regions where the water supply is abundant.

Guard Cells

Epidermal cells with unequally thickened cell walls and radial cellulose microfibrils that regulate stomatal opening and closing through changes in turgidity driven by $K^+$ ion movement and osmosis.