How does water reach the top of a tall tree?

Transpiration from leaf surfaces creates tension in the continuous water columns of the xylem; because water molecules cohere strongly, this tension pulls water upward from the roots, requiring no pump.

What are plant hormones?

Plant hormones are signaling molecules, active at very low concentrations, that regulate growth and development; major classes include auxin, cytokinin, gibberellin, abscisic acid, and ethylene.

Plant Physiology

Plant physiology explains how plants function as living systems — how they take up and move water and nutrients, sense their environment, and coordinate growth through hormonal signals.

Definition

Plant physiology is the study of the functions and processes of plants, including transport, nutrition, water relations, and the hormonal and environmental regulation of growth.

Scope

This area covers the functional processes of plants other than core energy metabolism: water relations and long-distance transport, mineral nutrition and uptake, and the hormones and signaling networks that integrate growth and development.

Sub-topics

Core questions

How do plants move water and solutes over long distances without a pump?
Which mineral nutrients do plants require, and how are they acquired and assimilated?
How do hormones coordinate growth, development, and responses to the environment?

Key theories

Cohesion–tension theory of water transport: Water is pulled up the xylem under tension generated by transpiration from the leaves, held together by the cohesion of water molecules, allowing ascent to the tops of tall trees without metabolic energy.
Hormonal regulation of development: A small set of hormones — auxin, cytokinin, gibberellin, abscisic acid, ethylene, and others — act in concert to control cell division, elongation, differentiation, and environmental responses.

Clinical relevance

Plant physiology underpins agriculture and food security: water-use efficiency, nutrient management and fertilization, and hormone-based growth regulators all derive from understanding how plants transport, feed, and signal.

History

Quantitative plant physiology began with Hales's eighteenth-century measurements of sap flow and Sachs's nineteenth-century work on nutrition and growth; Went's isolation of auxin in the early twentieth century launched the modern study of plant hormones.

Key figures

Stephen Hales
Frits Went
Julius von Sachs

Seminal works

taiz2015
buchanan2015

Frequently asked questions

How does water reach the top of a tall tree?: Transpiration from leaf surfaces creates tension in the continuous water columns of the xylem; because water molecules cohere strongly, this tension pulls water upward from the roots, requiring no pump.
What are plant hormones?: Plant hormones are signaling molecules, active at very low concentrations, that regulate growth and development; major classes include auxin, cytokinin, gibberellin, abscisic acid, and ethylene.