What makes up vascular tissue in plants

Such cells take on specific roles and lose their ability to divide further. They differentiate into three main tissue types: dermal, vascular, and ground tissue.

Each plant organ roots, stems, leaves contains all three tissue types:. Each plant organ contains all three tissue types. Koning, Ross E. Plant Basics. Plant Physiology Information Website. Reprinted with permission. Before we get into the details of plant tissues, this video provides an overview of plant organ structure and tissue function:.

Plant Cell Types Each plant tissue type is comprised of specialize cell types which carry out vastly different functions:. While these types of cells perform different functions and have different structures, they do share an important feature: all plant cells have primary cell walls, which are flexible and can expand as the cell grows and elongates. Some but not all plant cells also have a secondary cell wall, typically composed of lignin the substance that is the primary component of wood.

Secondary cell walls are inflexible and play an important role in plant structural support. The outer layer of tissue surrounding the entire plant is called the epidermis, usually comprised of a single layer of epidermal cells which provide protection and have other specialized adaptations in different plant organs. In the root, the epidermis aids in absorption of water and minerals. Root hairs , which are extensions of root epidermal cells, increase the surface area of the root, greatly contributing to the absorption of water and minerals.

A waxy substance is present on the walls of the endodermal cells. This waxy region, known as the Casparian strip , forces water and solutes to cross the plasma membranes of endodermal cells instead of slipping between the cells.

In fact, endodermis is a specialized type of ground tissue. This error is corrected below in the section about ground tissue. In the stem and leaves, epidermal cells are coated in a waxy substance called a cuticle which prevents water loss through evaporation. The cuticle is NOT present on root epidermis and is the same as the Casparian strip, which is present in the roots. To permit gas exchange for photosynthesis and respiration, the epidermis of the leaf and stem also contains openings known as stomata singular: stoma.

Two cells, known as guard cells , surround each leaf stoma, controlling its opening and closing and thus regulating the uptake of carbon dioxide and the release of oxygen and water vapor. Stems and leaves may also have trichomes , hair-like structures on the epidermal surface, that help to reduce transpiration the loss of water by aboveground plant parts , increase solar reflectance, and store compounds that defend the leaves against predation by herbivores.

Visualized at x with a scanning electron microscope, several stomata are clearly visible on a the surface of this sumac Rhus glabra leaf. At 5,x magnification, the guard cells of b a single stoma from lyre-leaved sand cress Arabidopsis lyrata have the appearance of lips that surround the opening. In this c light micrograph cross-section of an A. Wise; part c scale-bar data from Matt Russell. Trichomes give leaves a fuzzy appearance as in this a sundew Drosera sp. Leaf trichomes include b branched trichomes on the leaf of Arabidopsis lyrata and c multibranched trichomes on a mature Quercus marilandica leaf.

Wise; scale-bar data from Matt Russell. Just like in animals, vascular tissue transports substances throughout the plant body. But instead of a circulatory system which circulates by a pump the heart , vascular tissue in plants does not circulate substances in a loop, but instead transports from one extreme end of the plant to the other eg, water from roots to shoots. Vascular tissue in plants is made of two specialized conducting tissues: xylem , which conducts water, and phloem , which conducts sugars and other organic compounds.

A single vascular bundle always contains both xylem and phloem tissues. Unlike the animal circulatory system, where the vascular system is composed of tubes that are lined by a layer of cells, the vascular system in plants is made of cells — the substance water or sugars actually moves through individual cells to get from one end of the plant to the other.

Xylem tissue transports water and nutrients from the roots to different parts of the plant, and includes vessel elements and tracheids , both of which are tubular, elongated cells that conduct water. Tracheids are found in all types of vascular plants, but only angiosperms and a few other specific plants have vessel elements. Tracheids and vessel elements are arranged end-to-end, with perforations called pits between adjacent cells to allow free flow of water from one cell to the next.

They have secondary cell walls hardened with lignin , and provide structural support to the plant. Tracheids and vessel elements are both dead at functional maturity, meaning that they are actually dead when they carry out their job of transporting water throughout the plant body. Phloem tissue, which transports organic compounds from the site of photosynthesis to other parts of the plant, consists of sieve cells and companion cells. Sieve cells conduct sugars and other organic compounds, and are arranged end-to-end with pores called sieve plates between them to allow movement between cells.

They are alive at functional maturity, but lack a nucleus, ribosomes, or other cellular structures. Sieve cells are thus supported by companion cells, which lie adjacent to the sieve cells and provide metabolic support and regulation. The xylem and phloem are always next to each other. In stems, the xylem and the phloem form a structure called a vascular bundle ; in roots, this is termed the vascular stele or vascular cylinder.

This light micrograph shows a cross section of a squash Curcurbita maxima stem. Each teardrop-shaped vascular bundle consists of large xylem vessels toward the inside and smaller phloem cells toward the outside. Xylem cells, which transport water and nutrients from the roots to the rest of the plant, are dead at functional maturity. Phloem cells, which transport sugars and other organic compounds from photosynthetic tissue to the rest of the plant, are living. The vascular bundles are encased in ground tissue and surrounded by dermal tissue.

Ground tissue cells include parenchyma, photosynthesis in the leaves, and storage in the roots , collenchyma shoot support in areas of active growth , and schlerenchyma shoot support in areas where growth has ceased.

Parenchyma are the most abundant and versatile cell type in plants. They have primary cell walls which are thin and flexible, and most lack a secondary cell wall. Parenchyma cells are totipotent, meaning they can divide and differentiate into all cell types of the plant, and are the cells responsible for rooting a cut stem. Most of the tissue in leaves is comprised of parenchyma cells, which are the sites of photosynthesis, and parenchyma cells in the leaves contain large quantities of chloroplasts for phytosynthesis.

In roots, parenchyma are sites of sugar or starch storage, and are called pith in the root center or cortex in the root periphery. Xylem is the tissue responsible for supporting the plant as well as for the storage and long-distance transport of water and nutrients, including the transfer of water-soluble growth factors from the organs of synthesis to the target organs.

The tissue consists of vessel elements, conducting cells, known as tracheids, and supportive filler tissue, called parenchyma. These cells are joined end-to-end to form long tubes. Vessels and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at the ends. It is the thick walls of the tracheids that provide support for the plant and allow it to achieve impressive heights. Tall plants have a selective advantage by being able to reach unfiltered sunlight and disperse their spores or seeds further away, thus expanding their range.

By growing higher than other plants, tall trees cast their shadow on shorter plants and limit competition for water and precious nutrients in the soil.

The tracheids do not have end openings like the vessels do, but their ends overlap with each other, with pairs of pits present. Dermal tissue, for example, is a simple tissue that covers the outer surface of the plant and controls gas exchange. Vascular tissue is an example of a complex tissue, and is made of two specialized conducting tissues: xylem and phloem. Xylem tissue transports water and nutrients from the roots to different parts of the plant, and includes three different cell types: vessel elements and tracheids both of which conduct water , and xylem parenchyma.

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 Figure 1.

In stems, the xylem and the phloem form a structure called a vascular bundle ; in roots, this is termed the vascular stele or vascular cylinder. Like the rest of the plant, the stem has three tissue systems: dermal, vascular, and ground tissue.

The dermal tissue of the stem consists primarily of epidermis , a single layer of cells covering and protecting the underlying tissue.

Woody plants have a tough, waterproof outer layer of cork cells commonly known as bark , which further protects the plant from damage. Epidermal cells are the most numerous and least differentiated of the cells in the epidermis.

The epidermis of a leaf also contains openings known as stomata, through which the exchange of gases takes place Figure 2. Two cells, known as guard cells , surround each leaf stoma, controlling its opening and closing and thus regulating the uptake of carbon dioxide and the release of oxygen and water vapor.

Trichomes are hair-like structures on the epidermal surface. They help to reduce transpiration the loss of water by aboveground plant parts , increase solar reflectance, and store compounds that defend the leaves against predation by herbivores.

Figure 2. Openings called stomata singular: stoma allow a plant to take up carbon dioxide and release oxygen and water vapor. The a colorized scanning-electron micrograph shows a closed stoma of a dicot.

Each stoma is flanked by two guard cells that regulate its b opening and closing. The c guard cells sit within the layer of epidermal cells credit a: modification of work by Louisa Howard, Rippel Electron Microscope Facility, Dartmouth College; credit b: modification of work by June Kwak, University of Maryland; scale-bar data from Matt Russell. 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.

When the stem is viewed in cross section, the vascular bundles of dicot stems are arranged in a ring. In plants with stems that live for more than one year, the individual bundles grow together and produce the characteristic growth rings. In monocot stems, the vascular bundles are randomly scattered throughout the ground tissue Figure 3.

Figure 3. In a dicot stems, vascular bundles are arranged around the periphery of the ground tissue. The xylem tissue is located toward the interior of the vascular bundle, and phloem is located toward the exterior.

Sclerenchyma fibers cap the vascular bundles. In b monocot stems, vascular bundles composed of xylem and phloem tissues are scattered throughout the ground tissue.