Plant Physiology: Osmoregulation, Excretion, Gas Exchange, and Transport

Vocabulary flashcards covering plant osmoregulation, excretory adaptations, gas exchange, transpiration forces (TACT), and phloem translocation mechanism.

Excretion in Ebony Trees

The deposition of chemical waste into old, non-functional xylem at the centre of the trunk, resulting in dark heartwood.

Excretion in Conifer Trees

The active release of waste compounds through roots into the soil to act as chemical defense against competing plant species.

Osmotic Adjustment (Osmoregulation)

The physiological mechanism by which a plant maintains the appropriate balance of water and solutes in its body.

Hypotonic Situation

An environment with low solute concentration and high water concentration, causing water to enter the plant cell and make it turgid.

Hypertonic Situation

An environment with high solute concentration and low water concentration, causing water to leave the plant cell and make it flaccid.

Isotonic Situation

An environment where internal sap and external solvent concentrations are equal, resulting in no net movement of water across the cell membrane.

Hydrophytes

Plants adapted to water-rich environments featuring the highest transpiration rates, stomata on the upper leaf surface open day and night, and almost no leaf cuticle.

Mesophytes

Plants adapted to moderate water availability featuring stomata on the lower leaf surface open during the day and a thin leaf cuticle.

Xerophytes

Plants adapted to extreme dry conditions featuring the lowest transpiration rates, sunken stomata open at night, thick leaf cuticles, and water storage capacity in stems or roots (succulents).

Hydrogen Carbonate Indicator

A solution used to test carbon dioxide concentration changes; it turns yellow with increased $CO_2$ (acidic) and purple with decreased $CO_2$ (alkaline).

Homeostasis in Plants

The regulation and adaptation of plants to maintain internal stability across varying environmental temperatures, soil salinity, water levels, pathogens, and herbivores.

Excretophores

Leaves heavily loaded with pigmented waste products inside their vacuoles that turn yellow and fall off in autumn, effectively serving as waste disposal organs.

Chlorosis

The yellowing of plant leaves caused specifically by a lack of chlorophyll, distinct from waste accumulation in excretophores.

Transpiration Pull

A tension force driven by solar energy as water evaporates from leaves through stomata, pulling a continuous water column upward from roots to leaves through the xylem.

Adhesion (Xylem Transport)

The attraction between polar water molecules and cellulose in xylem cell walls, preventing the water column from falling when transpiration stops.

Cohesion (Xylem Transport)

The attraction between nearby polar water molecules via hydrogen bonding, holding the water column together as a continuous unit.

Translocation

The multidirectional transport of prepared food (organic solutes like sucrose) from source regions to sink regions through phloem tissue.

Sieve Tube Elements

Long, tube-like conducting cells in phloem that lack nuclei and function as channels for moving organic solutes.

Companion Cells

Nucleated cells adjacent to sieve tube elements that control sieve tube functions and actively load or unload sucrose using $ATP$.

Phloem Sap

The translocating fluid within phloem containing $10\text{--}25\%$ dry matter, which is predominantly sucrose alongside other organic compounds.

Pressure Flow Theory (Mass Flow Theory)

The mechanism of translocation where active sugar loading at a source draws water from xylem by osmosis, generating high hydrostatic pressure that pushes sap toward lower-pressure sinks.

Stomata

Tiny openings on leaf surfaces that regulate gas exchange and transpiration.

Lenticels

Small openings on stems that enable diffusion-driven gas exchange for internal plant tissues.