Plant Tissues

Plant Tissues Plant tissues are collections of similar cells that serve a specific purpose by functioning together. Unlike that of tissues present in animals, the major organs of plants (roots, stems and leaves) are all composed of the same three tissues (epidermis, vascular and ground tissues)

Types of Plant Tissues Meristematic Tissues – embryonic tissue that will give rise to more specialized kinds when mature Dermal Tissues – outer layer that covers the plant body. It permits the exchange of matter between the plant and the environment. Vascular Tissues – complex tissue system responsible for water and nutrient transport Ground Tissues – constitutes majority of the plant body, contains three types of cells: parenchyma, collenchyma and sclerenchyma. It functions for metabolism, storage and support activities.

Meristematic Tissue Cells in a meristematic tissue (also called meristem) are active in growing and dividing and can be considered as embryonic tissues Two types Apical meristem – spical meristeems occur at the tips of roots and shoots. These are the root apical meristem (RAM) and shoot apical meristem (SAM). They are responsible for the length-wise extension of the plant body, which is known as primary growth. Apical meristems give rise to primary tissues Lateral meristem – lateral meristems are responsible for the outward expansion of plants, known as secondary growth. They produce the secondary tissues which constitute the secondary plant body. Lateral meristems are called cambia (singular, cambium). Many plants lack lateral meristems. These is only produced by the vascular cambium). These plants are said to be herbaceous.

Ground Tissue Three types: Parenchyma – the progenitor of all other cells and the most common component of ground tissues. They perform virtually all the metabolic activities of plant cells Examples: chlorenchyma cells – contains chrloroplasts and are specialized for photosynthesis; aerenchyma cells contain large intracellular air spaces and function in gas exchange

Collenchyma Collenchyma cells are living at maturity. They usually occur as discrete strands or as continuous cylinders beneath the epidermis in stems and petioles. They also border veins in dicots. They are relatively long, with nonlignified primary walls which allow them to stretch. N dicot

Sclerenchyma Sclerenchyma cells are non living and lack protoplasts at maturity. They may be found in all parts of both the primary and secondary plant body. They have thick, lignified secondary walls. They provide strength and support in parts that have cease elongating. There are two types: fibers – long slender cells which occur in strands or bundles; and sclereids – vary in shape, often branched, and may occur singly or in groups in ground tissues throughout the plant. They make up the seed coat of seeds, shells of nuts, and give the pears its gritty texture. Their function is primarily for protection.

Vascular Tissues A complex tissue system produced from procambium in primary growth and from vascular cambium in secondary growth. It functions for the conduction of water and some minerals throughout the plant, support for the plant, and for some food storage. There are two types: xylem (a complex tissue and one of the major components of the vascular tissue) and phloem (the principal food conducting tissue in vascular plants and consists of elongated cells

Surface Tissues The epidermis is the outermost layer of the primary plant body. In organs that undergo secondary growth, the epidermis is eventually replaced by the periderm. In leaves and stems the epidermis contain several types of special cells: Guard cells – sausage-shaped cells that occur in pairs on leaf surfaces Trichomes – hair-like projections (major function is secretion and absorption Periderm – replaces the epidermis in stems and roots that undergo secondary growth. It forms the “bark” with the phloem. Function is for protection.