Revision: Tissue and Tissue System Botany HSC Science Class 11 Tamil Nadu Board of Secondary Education

Meristematic tissue is a group of cells that constantly divide and produce cells indefinitely throughout the life of the plant.

Permanent tissue refers to a group of cells which temporarily or permanently cease to divide and thus assume permanent form and function

• Meristematic tissue consists of cells that can divide and is restricted to specialised regions of the plant.
• Apical meristem is found at the root and shoot tips, is a primary meristem and increases the length of the plant.
• Intercalary meristem is found between mature tissues, is a primary meristem and helps form branches and flowers.
• Lateral meristem is found in mature regions, is a secondary meristem and is responsible for secondary growth (e.g. vascular cambium, cork cambium).
• Axillary bud is present in the axils of leaves and is responsible for forming branches or flowers.

• Tissue variation in plants depends on their location in the plant body, and the structure and function of each tissue is related to where it is found.
• Plants have three main tissue systems: epidermal tissue system, ground (fundamental) tissue system and vascular (conducting) tissue system.
• These three systems are classified based on their structure and location, and each serves a specific purpose in plant anatomy.

• Epidermal tissue is the outermost covering of the plant body, made up of epidermal cells, stomata, trichomes and root hairs.
• Epidermis is a single layer of compactly arranged parenchymatous cells covered with a waxy cuticle (absent in roots) to prevent water loss.
• Stomata regulate transpiration and gaseous exchange; each stoma has two bean-shaped guard cells (dumb-bell shaped in grasses).
• Stomatal apparatus = stomatal aperture + guard cells + subsidiary cells.
• Root hairs are unicellular extensions of epidermal cells that absorb water and minerals from the soil.
• Trichomes are stem hairs that may be branched, unbranched or secretory, and help prevent water loss.

• Vascular bundles = Xylem + Phloem together, and they form the vascular tissue system.
• Open vascular bundles are found in dicot stems where cambium is present between xylem and phloem, allowing the formation of secondary tissues.
• Closed vascular bundles are found in monocot stems where cambium is absent, so no secondary growth takes place.
• Radial bundles have xylem and phloem placed on different radii (alternating with each other) and are found in roots.
• Conjoint bundles have xylem and phloem on the same radius, with phloem always on the outer side of xylem, and are found in stems and leaves.