CBSE Class 9 Science Notes on Tissues
Introduction to Tissues
Tissues are a group of cells that combine together to perform a particular function.
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Plant tissues are of various types and they are made up of similar types of cells. They are different from animal tissues since there are several differences between the animal and plant cell.
Animal tissues are made up of animal cells. These tissues are usually not rigid since the cells do not have cell walls.
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Meristematic tissues are seen in plants. They are primarily made up of rapidly dividing cells. They are the growing tissues of the plant.
Permanent tissues arise from the meristematic tissue and have structural and functional properties. Permanent tissue can be made up of either living or dead cells.
Differentiation is the process by which the meristematic tissues develop into different types of permanent tissues based on the location and requirement of the plant.
Apical meristem are present on the apex of the plant shoot and root. They are rapidly growing tissues and aid in increasing the height of the plant.
Lateral meristem are present on the lateral walls of the stem. They help in the horizontal growth of the plant and increasing the stem girth.
Intercalary meristem can be found between the nodes of the stem and the base of the leaf. They help in branching.
Simple permanent tissues
These are tissues that are made up of only one type of cells. They usually have structural role.
Complex permanent tissues
Complex permanent tissues are made by combination of different types of cells. These cells work together to perform a specific task.
Parenchyma tissues are made up of loosely packed cells with thin cell walls and large intercellular spaces. They are live cells and help in support and storage. Two types; Chlorenchyma and Arenchyma.
Collenchyma tissues are made up of live cells which have irregularly thickened corners and thus, have decreased intercellular spaces. They help in bending of various parts of the plant without breaking.
Sclerenchyma tissues make up the hard and stiff parts of the plant. They are made up of dead, long and narrow cells. They almost have no intercellular space as the walls are thickened due to the presence of lignin.
Phloem is made up of the following components – sieve tubes, companion cells, phloem parenchyma and phloem fibres. Phloem conducts food in both directions. Among all the components, phloem fibres are the only dead cells.
Xylem is made up of the following components. The vessels and tracheids – help in conduction of water and minerals from the soil. Xylem parenchyma helps in food storage and the xylem fibres provide mechanical support.
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Epithelial tissues are seen on the outer layer of a body or organ surface. They form the outermost protective layer of most of the animals.
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Squamous epithelium form an extremely thin and flat layer of tissues. They are semi-permeable and thus, perfect for gaseous exchange. They are present in the lining of oesophagus and mouth.
As the name suggests, they are cuboidal in shape and form the lining of salivary glands and kidney tubules. They provide mechanical support. They also form glandular epithelium when they form glands.
These tissues line the organs which help in absorption and secretion, such as lining of intestines. They are made up of elongated cells. When cilia is present on these cells, they form ciliated columnar epithelium like those present in the respiratory tract.
Stratified Squamous Epithelium
This kind of tissue is formed when multiple layers of squamous epithelium are arranged in a pattern. Our skin is made up of this kind of tissue.
These tissues make up our muscles which are responsible for almost all the movements that take place in the body.
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All the voluntary movements in our body is carried out by the striated or skeletal muscles. They are called skeletal because these tissues are mostly attached to the bones. They are long, cylindrical, unbranched with striations and are multinucleated.
Almost all the involuntary movements in the body are carried out by the smooth or striated muscles. They are long, smooth, spindle shaped and uninucleate. We can find them in places like alimentary canal and blood vessels.
Cardiac muscles make up our entire heart. These muscles are involuntary in nature and show rhythmic contractions and relaxations. Structurally they may look quite similar to striated muscles but they are branched, uninucleate and have intercalated discs.
These tissues help in connecting different parts of the body. Examples include, blood, bones, cartilages, tendons, ligaments, areolar tissues and adipose tissues.
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Nervous tissue makes up the entire brain, spinal cord and nerves of the body. They are responsible for all sensations, consciousness, memory and emotion.
These are the cells that form the entire nervous system. The cell consists of a cell body, axon and axon terminals.
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