6. The plant tissues are grouped into broader categories, referred to as tissue systems. Elaborate on the kinds of tissue systems found in plants and their function.

 

6. The plant tissues are grouped into broader categories, referred to as tissue systems. Elaborate on the kinds of tissue systems found in plants and their function.

 answer:

A collection of cells performing a specific function is called tissue. Plant tissues can be grouped into plant tissue systems each performing specialized functions. A plant tissue system is defined as a functional unit, connecting all organs of a plant. Plant tissue system is also grouped into various tissues based on their functions.

Plant Tissues are categorized broadly into three tissue systems: the epidermis, ground tissue and the vascular tissue.

Classification of Plant Tissues – Based on its location in the Plant

1. Epidermal tissues – It covers the outside of a plant in a single layer of cells.
2. Ground tissues – It covers the interiors of a plant.
3. Vascular tissues – Transports water and dissolved substances inside the plant.

Classification of Plant Tissues – Based on the kind of cells they contain.

1. Meristematic – There are 3 major types in this.
2. Permanent – There are 2 major types under this named as Simple and Complex. Simple is further subdivided into 3 types named parenchyma, collenchyma, and sclerenchyma. The complex is further subdivided into 2 types named Xylem and Phloem.

Meristematic Tissues :

Meristematic tissue consists of actively dividing cells and leads to increase in length and thickness of the plant. The primary growth of a plant occurs only in certain, specific regions, such as in the tips of stems or roots. It is in these regions that meristematic tissues are present. Cells in these tissues are roughly spherical or polyhedral, to rectangular in shape, and have thin cell walls.

The growth in length and diameter of plants is carried out by this tissue. They are broadly classified as follows:

1. Apical Meristem – It is present at the apical portion of stems and roots. It is responsible for the growth in the length of the plants.
2. Lateral Meristem – It is present at the radial portion of the stems and roots. It is responsible for the growth in the thickness of the plants.
3. Intercalary Meristem – It is present at the internodes or the base of the leaves.

 Permanent Tissues :

Permanent tissues are a group of living or dead cells made by meristematic tissue that have lost their ability to divide and permanently have been placed at fixed positions in the plant body. Meristematic tissues which have a specific role lose their ability to divide. This process is called a cellular differentiation where a tissue takes up a permanent shape, size and function

There are 3 types of permanent tissues:

1. Simple permanent tissues
2. Complex permanent tissues

Simple Permanent tissues

A group of cells which are similar in origin; similar in structure and similar in function are called simple permanent tissue. They are of three types:

1. Parenchyma
2. Collenchyma
3. Sclerenchyma

• Parenchyma– These tissues are found in the soft parts of a plant such as the roots, stems, leaves, and flowers. The cells of this tissue are loosely packed and contain large intercellular spaces between them. Each cell has a vacuole at the center. The functions of parenchyma tissues are storage, photosynthesis, and to help the plant float on water.
• Collenchyma- Are similar to parenchyma cells with thicker cell walls. They are meant to provide mechanical support to the plant structure in parts such as petiole of the leaf.
• Sclerenchyma- The cells of this tissue are dead. They are rigid, contain thick and lignified secondary walls. Their main function is to provide strength and support to parts of the plant.

Complex Permanent Tissue

Unlike simple permanent cells which look the same and are made up of one type of cells, complex permanent tissues are made up of more than one type of cells. These different types of cells coordinate to perform a function. Xylem and Phloem are complex permanent tissues and are found in the vascular bundles in the plants.

Xylem- It consists of tracheids, vessels, xylem parenchyma and xylem fibres. Tracheids and vessels are hollow tube-like structures that help in conducting water and minerals. The xylem conducts only in one direction i.e vertically. The xylem parenchyma is responsible for storing the prepared food and assists in the conduction of water. Xylem fibres are supportive in function.

Phloem- It consists of four of elements: sieve tubes, companion cells, phloem fibres and the phloem parenchyma. Unlike the xylem, phloem conducts in both directions. It is responsible for transporting food from the leaves to the other parts of the plant. Phloem contains living tissues except for fibres that are dead tissues.

Functions of plant tissues

Plant tissues have different functions depending upon their structure and location

• Help provide mechanical strength to organs.
• They help in providing the elasticity and flexibility to the organs.
• They help the tissues to bend easily in various parts of a plant like- leaf, stem, and branches without damaging the plant
• The xylem and phloem tissues help in transportation of material throughout the plants
• They divide to produce new cells and help in the growth of the plants.
• They help in various cellular metabolisms like photosynthesis, regeneration, respiration, etc.