Comparative Transport and Gas Exchange in Plants and Animals

Vocabulary practice flashcards covering transport mechanisms, vascular systems (xylem and phloem), and gas exchange adaptations across plants and diverse animal taxa (insects, fish, amphibians, birds, and mammals).

Cytoplasmic Streaming

The active circulation of cytoplasm within and between plant cells through plasmodesmata, which functions to move large molecules and organelles (such as chloroplasts) throughout the cell.

Plasmodesmata

Microscopic cytoplasmic channels traversing plant cell walls that connect neighboring cells and enable cell-to-cell transport and cytoplasmic streaming.

Transpiration-Cohesion-Tension Mechanism

The bulk water transport system in vascular plants where evaporation of water from leaf mesophyll creates negative pressure (tension) that pulls cohesive columns of water upward through xylem conduits from the roots without requiring metabolic energy (ATP).

Cohesion (Plant Water Transport)

The attractive force between molecules of the same substance; specifically, water molecules forming hydrogen bonds with one another to maintain an unbroken fluid column under tension in xylem tubes.

Adhesion (Plant Water Transport)

The attractive force between molecules of two different substances; specifically, water molecules adhering via hydrogen bonding to hydrophilic xylem cell wall components such as cellulose.

Capillary Action

The tendency of liquid to ascend a tube through the combined effects of cohesion, adhesion, and surface tension; it is most effective in narrow tubes, such as xylem elements with diameters ranging from $0.01\,\text{mm}$ to $0.5\,\text{mm}$.

Sugar Source

A plant organ that produces or releases more sugar than it consumes or stores, such as mature leaves photosynthesizing during the summer or a sprouting storage tuber in early spring.

Sugar Sink

A plant organ that consumes or stores more sugar than it produces, such as growing roots, developing shoot tips, fruits, or storage tubers during late summer and fall.

Pressure-Flow Model

The mechanism of organic material translocation where sucrose loading into sieve tubes decreases water potential, drawing water in from adjacent xylem vessels by osmosis; the resulting positive hydrostatic pressure drives sap flow to sink cells.

Stoma

A microscopic epidermal pore flanked by two guard cells, primarily located on the underside of plant leaves, that regulates gas exchange ($\text{CO}_2$ and $\text{O}_2$) and evaporative water loss.

Guard Cells

Specialized epidermal cells flanking a stoma that actively pump protons ($\text{H}^+$) out to create a voltage gradient, driving $\text{K}^+$ and osmotic water influx to become turgid and bow outward, opening the stomatal aperture.

Lenticels

Permanent, non-closing pores in the bark of woody stems, branches, and woody roots that facilitate gas exchange between internal living cells and the atmosphere.

Root Hairs

Elongated cellular extensions of young root epidermal cells that substantially expand surface area to optimize the uptake of water, dissolved minerals, and oxygen from soil air pockets.

Ventilation

The movement of a respiratory medium (air or water) over a specialized gas exchange surface to maintain concentration gradients required for diffusion.

Gastrovascular Cavity (Gas Exchange)

A central internal body chamber with a single opening found in cnidarians and flatworms that facilitates both digestion and gas exchange across internal cell layers in conjunction with the external body surface.

Tracheal System

The internal respiratory system of insects, composed of an extensive branching network of air-filled tubes that transports respiratory gases directly to body tissues independently of the circulatory system.

Tracheoles

The tiny, fluid-filled terminal branches of an insect tracheal system that interface directly with individual body cells to enable rapid gas diffusion.

Spiracles

External pore openings situated along the thorax and abdomen of insects that allow air to enter and exit the internal tracheal system.

Countercurrent Exchange (Fish Gills)

An arrangement where capillary blood flow across gill lamellae runs opposite to the unidirectional flow of water, maintaining an oxygen concentration gradient that extracts approximately $80\text{--}90\%$ of dissolved oxygen from the water.

Positive Pressure Breathing

The ventilation mechanism used by amphibians (such as frogs) in which air is drawn into the mouth by dropping the oral floor, and then forced into the lungs by closing the nostrils and elevating the mouth floor.

Parabronchi

Rigid, non-elastic microscopic parallel tubules within avian lungs through which air flows continuously in one direction while gas exchange occurs with surrounding blood capillaries.

Avian Air Sacs

A system of eight to nine bellows-like structures in birds that expand and contract to circulate air unidirectionally through the parabronchi across two complete respiratory cycles, without participating directly in gas exchange.

Negative Pressure Breathing

The inhalation mechanism utilized by mammals where contraction of the diaphragm and intercostal rib muscles increases lung volume, lowering internal pressure below atmospheric pressure to draw air in.

Alveoli

Microscopic, thin-walled, expandable terminal air sacs in mammalian lungs that are intimately enmeshed with capillaries, serving as the primary sites of oxygen and carbon dioxide exchange.