phloem

Examples of phloem in the following topics:

• Transportation of Photosynthates in the Phloem

  • Phloem STEs have reduced cytoplasmic contents and are connected by sieve plates with pores that allow for pressure-driven bulk flow, or translocation, of phloem sap.
  • This flow of water increases water pressure inside the phloem, causing the bulk flow of phloem sap from source to sink.
  • Water diffuses from the phloem by osmosis and is then transpired or recycled via the xylem back into the phloem sap .
  • Phloem is comprised of cells called sieve-tube elements.
  • Phloem sap travels through perforations called sieve tube plates.

• Vascular Tissue: Xylem and Phloem

  • Xylem and phloem form the vascular system of plants to transport water and other substances throughout the plant.
  • The simplest arrangement of conductive cells shows a pattern of xylem at the center surrounded by phloem.
  • Together, xylem and phloem tissues form the vascular system of plants .
  • Phloem tissue is responsible for translocation, which is the transport of soluble organic substances, for example, sugar.
  • Xylem and phloem tissue make up the transport cells of stems.

• Plant Tissues and Organ Systems

  • It is made of two specialized conducting tissues: xylem and phloem.
  • Phloem tissue, which transports organic compounds from the site of photosynthesis to other parts of the plant, consists of four different cell types: sieve cells (which conduct photosynthates), companion cells, phloem parenchyma, and phloem fibers.
  • Unlike xylem-conducting cells, phloem-conducting cells are alive at maturity.
  • The xylem and phloem always lie adjacent to each other.
  • Phloem cells, which transport sugars and other organic compounds from photosynthetic tissue to the rest of the plant, are living.

• Stem Anatomy

  • The xylem and phloem that make up the vascular tissue of the stem are arranged in distinct strands called vascular bundles, which run up and down the length of the stem.
  • Phloem tissue is composed of sieve-tube cells, companion cells, phloem parenchyma, and phloem fibers.
  • Vascular tissue composed of xylem (red) and phloem tissue (green, between the xylem and cortex) surrounds the pith.
  • The xylem tissue is located toward the interior of the vascular bundle; phloem is located toward the exterior.
  • In (b) monocot stems, vascular bundles composed of xylem and phloem tissues are scattered throughout the ground tissue.

• Leaf Structure, Function, and Adaptation

  • Similar to the stem, the leaf contains vascular bundles composed of xylem and phloem .
  • The phloem transports the photosynthetic products from the leaf to the other parts of the plant.
  • A single vascular bundle, no matter how large or small, always contains both xylem and phloem tissues.
  • This scanning electron micrograph shows xylem and phloem in the leaf vascular bundle.

• Primary and Secondary Growth in Stems

  • The vascular cambium is located just outside the primary xylem and to the interior of the primary phloem.
  • The cells of the vascular cambium divide and form secondary xylem (tracheids and vessel elements) to the inside and secondary phloem (sieve elements and companion cells) to the outside.
  • The thickening of the stem that occurs in secondary growth is due to the formation of secondary phloem and secondary xylem by the vascular cambium, plus the action of cork cambium, which forms the tough outermost layer of the stem.
  • This supplies oxygen to the living- and metabolically-active cells of the cortex, xylem, and phloem.

• The Major Divisions of Land Plants

  • In contrast, vascular plants developed a network of cells, called xylem and phloem, that conduct water and solutes throughout the plant.

• Structural Adaptations for Land in Seedless Plants

  • The vascular system contains xylem and phloem tissues.
  • Xylem conducts water and minerals absorbed from the soil up to the shoot, while phloem transports food derived from photosynthesis throughout the entire plant.

• Meristems

  • Meristematic tissues are found in many locations, including near the tips of roots and stems (apical meristems), in the buds and nodes of stems, in the cambium between the xylem and phloem in dicotyledonous trees and shrubs, under the epidermis of dicotyledonous trees and shrubs (cork cambium), and in the pericycle of roots, producing branch roots.

• Intercellular Junctions

  • This transport primarily uses the vascular tissues (xylem and phloem); however, there are also structural modifications called plasmodesmata (singular: plasmodesma) that facilitate direct communication in plant cells.