Vascular tissue

Cross section of celery showing vascular bundles

Vascular tissue in a bramble leaf under polarized light

Diagram of vascular tissue

Vascular tissue is a complex conducting tissue found in vascular plants. The primary components of vascular tissue are the xylem and phloem, which transport water, nutrients, and sugars throughout the plant. Vascular tissue is essential for the plant's ability to grow larger and transport resources efficiently.

Structure

Vascular tissue is organized into vascular bundles, which are distributed throughout the plant. Each bundle contains both xylem and phloem tissues. The xylem is responsible for the transport of water and dissolved minerals from the roots to the rest of the plant, while the phloem distributes the sugars produced by photosynthesis in the leaves to other parts of the plant.

Xylem

The xylem is composed of various cell types, including tracheids, vessel elements, and parenchyma cells. Tracheids and vessel elements are elongated cells that form tubes for water transport. These cells are dead at maturity, allowing for efficient water movement.

Phloem

The phloem consists of sieve tube elements, companion cells, and parenchyma cells. Sieve tube elements are living cells that form channels for the transport of sugars and other organic compounds. Companion cells assist in the maintenance and function of sieve tube elements.

Function

Vascular tissue plays a crucial role in the plant's ability to transport water, nutrients, and sugars. The xylem's water transport is driven by transpiration, a process where water evaporates from the leaves, creating a negative pressure that pulls water upward from the roots. The phloem's transport of sugars is driven by a pressure flow mechanism, where sugars are actively transported into sieve tubes, creating a pressure gradient that moves the sugars to areas of lower concentration.

Evolution

Vascular tissue is a key innovation in the evolution of land plants, allowing them to grow taller and colonize a variety of terrestrial environments. The development of vascular tissue enabled plants to overcome the limitations of diffusion for nutrient and water transport, leading to the diversification of plant forms and the establishment of complex ecosystems.

Related pages

• Xylem
• Phloem
• Transpiration
• Photosynthesis

References

• Raven, P. H., Evert, R. F., & Eichhorn, S. E. (2005). Biology of Plants. W.H. Freeman and Company.
• Taiz, L., & Zeiger, E. (2010). Plant Physiology. Sinauer Associates.