PLANT TISSUES

Tissues

  • Definition: A tissue is a group of cells that are similar in structure and work together to perform a specific function. All living organisms are made of cells. In unicellular organisms like Amoeba, a single cell performs all functions. In multicellular organisms like humans, different groups of cells, or tissues, specialize in specific tasks.

  • Utility in Multicellular Organisms: Tissues provide a defined structure, offer mechanical strength, and allow for a division of labor, meaning different parts of the organism can perform different jobs efficiently.

Plant Tissues

Plant tissues are groups of specialized cells in plants. They are broadly divided into two main types:

  1. Meristematic Tissues: These are dividing tissues responsible for plant growth.

  2. Permanent Tissues: These are mature tissues that have lost the ability to divide and have taken on specific roles.

Meristematic Tissues

  • Characteristics: These tissues consist of continuously dividing cells that are very active, have thin cellulose walls, dense cytoplasm, prominent nuclei, and few or no vacuoles. They are responsible for increasing the length and girth of the plant.

  • Types based on location:

    • Apical Meristem: Found at the tips of stems and roots. It is responsible for increasing the height of the plant (primary growth).

    • Lateral Meristem: Located beneath the bark. It increases the diameter and girth of the plant (secondary growth).

    • Intercalary Meristem: Found at the base of leaves and internodes. It helps in increasing the length of organs like leaves.

Permanent Tissues

These tissues are fully grown and have lost the ability to divide. They are formed through a process called differentiation.

Simple Permanent Tissues

These are made of only one type of cell.

  • Parenchyma: The most common simple tissue. It consists of living, rounded, and loosely arranged cells with thin walls. It serves to store food, fill spaces between other tissues (packing tissue), and store waste products.

  • Collenchyma: Consists of living, elongated cells with generally no intercellular spaces. It provides mechanical support and elasticity, allowing parts of the plant to bend without breaking. It is found below the epidermis in stems and leaves.

  • Sclerenchyma: Composed of dead cells with greatly thickened walls due to lignin. These cells are closely packed and provide strength, rigidity, and flexibility to the plant. The husk of a coconut is made of this tissue.

Protective Tissues

  • Epidermis: The outermost single layer of cells covering the entire plant. It protects the plant from water loss and infection. It contains small pores called stomata for gas exchange.

  • Cork (Phellem): A protective, dead, water-resistant tissue found in the outer bark of woody plants. It contains a waxy substance called Suberin, which makes it impervious to water and gases.

Complex Permanent Tissues

These tissues consist of more than one type of cell that work together to perform a common function, primarily transport. They are also known as vascular tissues.

  • Xylem: Transports water and minerals vertically through the plant. It is composed of tracheids, vessels, xylem parenchyma (stores food), and xylem fibres (provide support).

  • Phloem: Transports food from the leaves to other parts of the plant. (The text mentions it but does not provide further details).