Transport in Plants and Transpiration

Vocabulary practice flashcards covering plant transport systems, xylem and phloem structure and function, the water uptake pathway, transpiration mechanisms, and experimental investigations.

Vascular Bundle

A group of transport vessels found throughout the roots, stems, and leaves of plants, composed of two primary transport tissues: xylem and phloem.

Vascular Tissue Arrangement in Dicotyledonous Plants

The organizational rule in dicotyledonous roots, stems, and leaves where xylem is always positioned on the inside and phloem is always positioned on the outside.

Xylem Tissue

A transport tissue composed of dead cells without end walls that forms a continuous hollow tube, conducting water and dissolved mineral ions in one direction from roots to leaves.

Xylem Adaptations

Specialized characteristics including lost end cross-walls forming an uninterrupted tube, dead cells emptied of cytoplasm and organelles to enable free water passage, and walls strengthened with lignin.

Lignin

A strengthening substance deposited in the cell walls of xylem vessels that causes the cells to die, hollows out the vessels, and reinforces the tubes against the pressure of water movement.

Phloem Tissue

A transport tissue composed of living cells that carries food materials, mainly sucrose and amino acids, in all directions throughout the plant via translocation.

Translocation

The biological process in which sucrose and amino acids synthesized in photosynthesising leaves are transported through phloem tissue to non-photosynthesising regions in all directions.

Root Hair Cells

Single-celled extensions of root epidermis cells that dramatically increase root surface area to absorb water by osmosis, mineral ions by active transport, and dissolved oxygen for respiration.

Pathway of Water from Soil to Leaf

The sequential route water follows through plant tissues: root hair cell $\rightarrow$ root cortex cells $\rightarrow$ xylem $\rightarrow$ leaf mesophyll cells.

Celery Dye Investigation

An experiment demonstrating water uptake and vascular transport by placing celery stalks in water stained with food dye, showing under cross-section that only the xylem vessels carry the colored solution.

Transpiration

The loss of water vapour from plant leaves caused by the evaporation of water from the surfaces of mesophyll cells, followed by the diffusion of water vapour through open stomata.

Cohesion (in Plants)

The force of attraction between identical molecules, specifically water molecules, creating cohesive tension that allows them to pull each other in an unbroken continuous column up the xylem.

Transpiration Stream

The unbroken flow of water travelling through xylem vessels from roots up through the stem to the leaves, driven by the transpiration pull generated by evaporation at leaf mesophyll cells.

Functions of Transpiration

The key physiological benefits of water movement through plants: transporting dissolved mineral ions, maintaining cell turgidity for mechanical support, providing water for photosynthesis, and cooling leaves through evaporative heat loss.

Wilting

The physical collapse of a plant occurring when the rate of water evaporation from the leaves exceeds water uptake from the soil, causing cells to lose turgor pressure so the cell walls can no longer support the shoot.

Potometer

A laboratory apparatus that measures the rate of transpiration from a cut leafy shoot by tracking the distance an air bubble moves along a capillary tube over a specified duration.

Environmental Factors Affecting Transpiration Rate

External variables that alter water loss from leafy shoots, including temperature (tested via cold and warm rooms), humidity (manipulated with a sprayed plastic bag), wind speed (simulated with a fan), and light intensity.