Vascular Tissue: Characteristics & Types

Vascular tissue is a form of plant tissue that transports water, nutrients, and other vital elements throughout the plant body. 

• It is an important mechanism that lets plants grow larger and more complex 
• By providing support and efficient resource distribution to various areas of the plant. 
• All higher plants have vascular tissue, including ferns, gymnosperms, and angiosperms.

Key terms: Vascular tissue, Xylem, Phloem, Transport system, Vascular bundles, Water conduction

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Vascular Tissue

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In plants, the vascular tissue system is made up of xylem and phloem. Phloem is a form of vascular tissue that conducts and stores food, whereas xylem is a type of vascular tissue that conducts and stores water. These two tissues work together to carry out numerous transportation tasks in plants.

• The vascular bundle is made up of a set of organised xylem and phloem components. 
• Phloem and xylem are referred to as closed vascular bundles when they lack cambium and as open vascular bundles when they do.
• The three basic categories of these vascular tissue bundles are radial, conjoint, and concentric.
• Gymnosperms have discrete clusters of vascular tissue called vascular bundles that are made up of vascular strands or cylinders.

Vascular Tissue

Radial bundles: The xylem and phloem independently make up the xylem bundles and phloem bundles in this type of vascular bundle. 

• These two varieties of bundles are placed in opposition to one another. 
• These both happen in various radii. The roots of plants have these types of bundles.

Conjoint bundles: As its name implies, this form of the vascular bundle contains both the xylem and phloem in a conjoined arrangement.

Concеntric bundlе: It rеfеr to thе arrangement of different typеs of vascular tissuеs (xylеm and phloеm) within a plant stеm.

• Thеsе tissuеs can be organized in a concеntric mannеr, with onе typе of tissuе surrounding thе othеr in distinct layеrs.
• This typе of vascular arrangеmеnt is oftеn found in monocot plant stеms. 

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Characteristics of Vascular Tissue

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The characteristics are mentioned below:

Specialised Transport System: Vascular tissue is a specialised transport system in higher plants. 

• It works like a network of interconnecting highways
• Allowing important components such as water, nutrients, and carbohydrates to travel efficiently to different regions of the plant.

Xylem and Phloem: Vascular tissue comprises two types of conducting tissues: xylem and phloem. 

• Water and various nutrients are transported from the roots to the rest of the plant by the xylem
• Whereas photosynthetic products, principally sugars, are transported to the rest of the plants from the leaves by phloem.

Vascular Bundles: Vascular bundles are cylindrical arrangements of the xylem and phloem 

• It is surrounded by supportive and protective structures that organise vascular tissue.
• These bundles can be found all over the plant, passing through the stem, leaves, and even the roots.

Efficient Water Conduction: Xylem comprises elongated, dead cells called vessel elements and tracheids that are specialised for water transport upward. 

• These cells' cell walls contain lignin, a complex polymer that reinforces and waterproofs the walls
• Allowing for efficient water conduction.

Nutrient Transport: Phloem is made up of specialised cells called sieve elements and companion cells that transport nutrients. 

• Sieve elements combine to form sieve tubes, elongated cells with perforated sieve plates that allow nutrients to pass through. 
• Companion cells offer metabolic support to sieve elements, ensuring that sugars and other chemicals are transported successfully.

Directional Transport: Vascular tissue provides for unidirectional substance movement. 

• Water and nutrients flow from the roots to the leaves in the xylem, while sugars move from the leaves to other parts of the plant
• Where they are needed for growth and energy storage in the phloem.

Plant Growth and Development: Vascular tissue is essential for growth and development. 

• New cells are added to the vascular tissue as the plant becomes larger due to the action of meristematic tissues, particularly the vascular cambium
• Which contributes to secondary growth in some plants.

Structural Support: The presence of lignin in the walls of xylem cells offers structural support to the plant, preventing it from collapsing under its own weight and environmental pressures.

Adaptability: Vascular tissue exhibits adaptability to environmental conditions. 

• For instance, during periods of drought or water scarcity, plants can regulate the opening and closing of stomata in leaves to control water loss 
• Through transpiration, which affects the water flow in the xylem.

Evolutionary Significance: The emergence of vascular tissue was an important milestone in the evolution of land plants. 

• The evolution of vascular tissue enabled plants to transition from aquatic to terrestrial settings
• Resulting in the diversification and extension of plant life on Earth.

Read More: Difference Between Monocot and Dicot System

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Types of Vascular Tissue

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The types are of Vascular Tissue:

Xylem

One of the two major forms of vascular tissue found in plants is xylem. It is in charge of transporting water, minerals, and dissolved nutrients from the roots to the plant's aerial parts, such as stems and leaves.

Xylem

The xylem is composed of several types of specialised cells:

Vessel Elements: Vessel elements are narrow, cylindrical chambers with perforated end walls known as perforation plates. 

• These plates allow water to flow efficiently from one vessel element to the next, generating continuous water-conducting tubes. 
• Angiosperms (flowering plants) and a few gymnosperms have vessel components.

Tracheids: Tracheids are tapering, long cells with overlapping ends. They feature pits in their cell walls and no perforation plates, allowing water to pass laterally between neighbouring tracheids. 

• Tracheids can be found in many vascular plants, including gymnosperms and ferns.
• The lignified cell walls of vessel components and tracheids provide strength to the plant's stems and branches
• Hence xylem is principally responsible for structural support.
• It is also essential in the ascent of water from the roots to the leaves against gravity, a process known as transpiration.

Phloem

Phloem is the other major type of vascular tissue in plants, and its primary function is the transport of photosynthates (sugars and other organic compounds) from the leaves to various parts of the plant.

Phloem

Phloem is composed of specialised cells:

1. Sieve Tube Elements: These are the phloem's major conducting cells. 

• Sieve tube elements are elongated cells with sieve plates at their ends. 
• The sieve plates include multiple pores that allow the sap to pass between adjacent cells. 
• These cells lack a nucleus and other organelles, allowing for efficient nutritional mass flow.

2. Companion Cells: Companion cells are closely related to sieve tube elements and supply them with metabolic assistance. They have a nucleus and other organelles that allow them to control the activity and metabolism of sieve tube elements.

Phloem is responsible for the translocation of sugars produced during photosynthesis from sources (areas of sugar production, usually leaves) to sinks (areas of sugar utilisation or storage, such as roots, fruits, and developing tissues). This transport occurs through a pressure-driven mechanism called the pressure flow hypothesis.

Read More: Polyembryony

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Uses of Vascular Tissue

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The uses of vascular tissues are:

• Water and Nutrient Transport: Vascular tissue transports water and nutrients throughout the plant
• Allowing it to grow, develop, and produce food through photosynthesis.
• Structural Integrity and Support: The lignified walls of xylem cells support and strengthen the plant, helping it to stand erect and retain structural integrity.
• Food Transport: Phloem transfers sugars and other organic molecules from the plant's leaves to other areas of the plant
• Maintaining a continual supply of energy for growth, flowering, and fruiting.
•  Wood Formation: Secondary development in the vascular cambium of many woody plants results in the formation of wood
• Which is a significant resource utilised in construction, furniture manufacturing, and other industries.
• Medicinal Uses: Some plants having specialised vascular tissues, such as medicinal herbs

Also Read:

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Things to Remember

• Vascular tissue distributes water, nutrients, and other necessary substances within plants.
• It promotes plant growth by efficiently allocating resources.
• The xylem and phloem are the two primary forms of vascular tissue.
• Water and minerals are transported by the xylem from roots to aerial portions.
• Sugars are transported from the leaves to other plant components by phloem.
• Vascular bundles coordinate the movement of the xylem and phloem throughout the plant.
• Xylem vessel components and tracheids enable water transfer.
• The sieve tube elements and partner cells of phloem aid in nutrition transfer.

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