Transportation in Plants: The Basics
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Transportation in Plants: The Basics

An article covering the basics of the vascular tissues involved in transport in plants, but in a high level of detail. This article is designed to be a brief revision bite for any biology student of high school/senior school standard. This article covers the location and basic function of xylem and phloem tissues in the average plant.

Transport Tissues: Plants

There are 3 main ways in which plants transport materials within the organism, and the immediate surrounding areas.

  1. Active Transport - Active transport is an active process; this means it requires ATP (energy) to occur. This is because it moves materials against their concentration gradient (from low to high concentration).
  2. Diffusion - The passive (without energy) movement of molecules from high concentration to low concentration; down a concentration gradient.
  3. Osmosis - Passive movement of water particles down a water potential gradient (from high water potential to low water potential)

In larger, multicellular organisms, including large plants like trees, simple diffusion cannot provide all the nutrients needed for the plant to survive. This is because the surface area: volume ratio of the plant is not high enough. To overcome this plants have developed a transport system to transport water and sugars through the plant. The tissues involved in transport are called the xylem and phloem.

Water and minerals are transported in one direction; up the plant, from the roots to the leaves, to where it is needed for photosynthesis. They are transported in a vessel called the xylem. Sugars and other molecules are transported in all directions, as they are needed in respiring cells all over the organism. These are normally transported from the leaves where glucose was produced during photosynthesis to the respiring cell, or to the roots to be stored as starch in tubers or other such growths (e.g. potatoes). Both xylem and phloem are produced from non-differentiated cells called meristematic or cambium cells.

Arrangement of Vascular tissues within a plant

 Roots - Vascular bundle is located in the centre of the root, as this prevents vessels from breaking when the roots move around. The central core is called the stele. It consists of a cross shaped region of xylem with the phloem in 4 regions in the gaps between the 4 arms of the cross. Between the xylem and phloem is a region of cambium tissue which differentiates to form either tissue to replace any dead or damaged cells.

Stems - There are many separate oval shaped bundles of vascular tissue arranged on the outside of the stem. Each oval is divided into 3 sections; xylem, phloem and cambium. The inside half of the oval is xylem tissue, and the outer most half is phloem, and the cambium forms a thin band between them. Having the tissues arranged as such give the plant both strength and the flexibility to move in the wind without the plant snapping.

Leaves - In the main midrib of the plant is formed from vascular tissue, with xylem tissue on top, and phloem underneath.

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Comments (1)

Thanks for the education. This has been true source of knowledge.