Terminology (Biology)

Terms and Their Definitions (Biology) Part - ITissue: A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.Meristematic Tissue: These are the dividing tissue in plants that are located in the regions where the growth of the plant occurs.Apical Meristem: The meristematic tissue that is present at the growing tips of stems and roots and increases the length of the stem and the root is the apical meristem.Lateral Meristem (Cambium): These are the meristamatic tissue that is responsible for the increase in the girth of the stem or root.Intercalary Meristem: The meristematic tissue that is present at the base of the leaves or internodes (on either side of the node) on twigs is intercalary meristem.Permanent Tissue: The cells of meristematic tissue that take up a specific role and lose their ability to divide form permanent tissue.Simple Permanent Tissue: Different types of tissues that are all made up of one type of cells which look like each other are called simple permanent tissue. Parenchyma (Tissue): This is a type of permanent tissue formed by few layers of cells that form a basic packing tissue. This tissue provides support to plants and stores food. It consists of relatively unspecialised cells with thin cell walls. The cells are live and are usually loosely packed.Chlorenchyma (Tissue): Parenchyma that contains chlorophyll and performs photosynthesis is called chlorenchyma.10. Aerenchyma: Parenchyma in aquatic plants has large cavities to give buoyancy to the plants and help them to float in water. Such a parenchyma is called aerenchyma.Collenchyma (Tissue): This is the permanent tissue that gives flexibility in plants. It allows easy bending in various parts of a plant (leaf, stem) and also provides mechanical support to plants. It is found in leaf stalks below the epidermis. The cells of this tissue are living, elongated and irregularly thickened at the corners. Sclerenchyma (Tissue): The permanent tissue which makes the plant hard and stiff is the sclerenchyma. It is seen in the husk of a coconut. The cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin (a chemical substance which hardens them). This tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts and provides strength to the plant parts.Epidermis: The outermost layer of cells is called epidermis. The entire surface of a plant has epidermis to protect all the parts of the plant. Epidermal cells of the roots have long hair-like structures to increase the total absorptive surface area and thus help in the absorption of water and minerals from the soil. Epidermal cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface to protect it from loss of water, mechanical injury and invasion by parasitic fungi. Cells of epidermal tissue are a continuous layer without intercellular spaces as these have a protective role to play. Most epidermal cells are relatively flat. In some xerophytes (desert plants) epidermis has a thick waxy coating of cutin (chemical substance with water-proof quality) on its outer surface to protect it from loss of water through transpiration.Stomata: These are the small pores present here and there in the epidermis of the leaf. Stomata are enclosed by two kidney-shaped cells called the guard cells. These help in the exchange of gases and transpiration (loss of water in the form of water vapour).Cork (bark of the tree): The outer protective tissue undergoes certain changes, as the plant grows older. The epidermis is replaced by a strip of secondary meristem. Cells on the outside are cut off from this layer and thus form the several-layer thick cork or the bark of the tree. Cells of cork are dead and compactly arranged without intercellular spaces. They have a chemical called suberin in their walls that makes them impervious to gases and water. Complex Permanent Tissue: The tissues that are made up of more than one type of cells that coordinate to perform a common function are called complex permanent tissue. Xylem and phloem are the examples.Xylem: These are the conducting tissue (complex permanent tissue) that consists of tracheids, vessels xylem parenchyma and xylem fibres. The cells have thick walls, and many of them are dead cells. Tracheids and vessels are tubular structures and help in the transport of water and minerals vertically. The parenchyma stores food and helps in the sideways conduction of water. Fibres are mainly supportive in function.Phloem: These are the conducting tissue (complex permanent tissue) made up of four types of elements: sieve tubes, companion cells, phloem fibres and the phloem parenchyma Sieve tubes are tubular cells with perforated walls. Phloem transports food from leaves to other parts of the plant. Unlike xylem, materials can move in both directions in phloem. Except for phloem fibres, phloem cells are living cells. By: Kalyani Chivukula