Tissue
In the case of amoeba-like unicellular organisms, all functions are performed by organelles of that single cell. However, most of the organisms are multicellular. How are the various processes brought in their body?
Similarly, organization of the body of organisms follows a definite hierarchy. You have already studied cells and cell organelles in that hierarchy.
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‘A group of cells having the same origin, same structure and same function is called ‘tissue’. Millions of cells are present in the body of multicellular organisms.
These cells are divided into different groups and each group performs a definite function. For example, we can perform movements due contraction relaxation of muscles. Conducting tissues in plants transport water and food to all its parts. All functions of the body occur with full efficiency due to the specific organization of cells and their division of work.
Types Of Tissue
Simple tissue
Made up of only one type of cells. Ex. Epithelial tissue of animals, Meristematic tissue of plants
Complex Tissues
Made up of more than one type of cells Ex. Blood of animals, Xylem and phloem of plants
Tissue Information
Plants being sedentary, most of their tissues are of the type that give support. There are dead cells in some tissues and these do not need much attention. Growth of the plants occurs in specific parts of their body where the tissues contain dividing cells.
As animals have to move from place to place in search of food, shelter and partners, their energy needs are greater. Most of the tissues of animals are made up of living cells. Uniform growth occurs through out the body of an animal and they do not have different dividing and non-dividing tissue.
Animal Tissue
In the body of animal different organs come together to perform a specific function. Organs like the lungs and trachea. with the help of the contraction and relaxation of some muscles bring about the function of respiration. Different tissues perform different functions in the organs. Accordingly, tissues are classified into different types.
There are four main types of animal tissues, namely epithelial tissue, connective tissues, Muscular Tissue And Nervous tissues
Epithelial tissue
Protective coverings in the animal body are called epithelial tissues. Cells in this tissue are closely packed and form continuous layers. Any material that enters the body first encounters epithelial tissue.
Cells of epithelial tissue are separated from the cells of other underlying tissues by a fibrous membrane. The skin, mucous layer of the mouth cavity, inner surface of blood vessels, walls of the alveoli, etc. are made up of epithelial tissues.
Parts of Epithelial Tissues
- Squamous epithelium
- Stratified epithelium
- Glandular epithelium
- Columnar epithelium
- Ciliated Epithelium
- Cuboidal epithelium
Connective tissue
Tissues which join different parts of the body are called connective tissues. Cells in this type of tissue are loosely arranged with a ground substance in the free spaces in between. The ground substance may be solid, liquid like water or jelly-like.
Muscular Tissues
Muscle fibres and muscular tissues are formed from special type of contractile proteins due to which this contraction and relaxation is possible. Muscular tissues are made up of the long cells of muscle fibres.
Muscular movement occurs due to contraction and relaxation of the contractile proteins in these cells.
Nervous Cells
Cells of the nervous tissue are specially made to be come excited and to conduct that excitation form one part of body to other. The cell body which contents the cytoplasm and the nucleus is the main part of each nerve cell. Numerous, small, branched fibres called dendrites arise from the cell body. One of the fibres, however, is extremely long. It is called as the axon.
The length of a nerve cell may even be up to one meter. Many nerve cells are bound together with the help of connective tissue to form a nerve. Nervous tissue is present in the brain, spinal cord and the network of nerves spread all through the body.
In most animals, action in response to a stimules occurs due to the integrated functioning of nervous tissue and muscular tissue.
Meristematic tissue
As meristematic tissue is present in specific parts of a plant, growth occurs in those parts only. Cells of meristematic tissue contain thick cytoplasm, a conspicuous nucleus and a thin cell wall and are compactly packed together.
Vacuoles are usually absent in these cells. These cells are highly active. To bring about plant growth is the main function of meristematic tissue. According to the location, meristematic tissue is of three types as given below.
- Apical meristem : At the tip of the root and stem
- Intercalary meristem : At the base of the petiole of leaves and of branches.
- Lateral meristem : Lateral sides of root and stem
Permanent Tissue
After their growth is complete, new cells formed by division of meristematic tissue lose their ability to divide and start to perform a specific function at specific place.
Thus, they permanently acquire a specific structure, shape and location and perform a specific function. This is called as differentiation and permanent tissues are formed from these differentiated cells. There are two types of permanent tissues simple permanent and complex permanent tissue.
