As we know that our body consists of very small structures that is cell and tissue.
We consider the cell as a structural and functional unit of life.
It is because a cell is building block of our body and all the life processes happens inside the cell.
Unicellular organisms consists of a single cell. All life processes like growth, digestion, transportation, reproduction, recreation, movement, nutrition, etc. Occur in the same cell.
But multicellular organisms have a group of cells for special functions.
The group of cells having a similar structure and function is called a tissue.
They are mainly classified into the following two ways,
A. Animal tissue
Animal tissues consist of animal cells. Usually, all the animal tissues consists of living cells.
They have the capacity of increasing their number by their division.
The tissues usually lack a cell wall and plastids.
On the basis of their structure and function, we can figure out them into the following four types,
1. Muscle tissue
This tissue is made of different types of muscles found in the body of animals.
The cells of this tissue are elongated and elastic in nature.
They have one or many nuclei in a single cell.
They have intercellular space. Muscular tissues may be striated, unstriated or cardiac.
The tissue is mainly concerned with movement occurred in our body.
About all the life processes are conducted by this type of tissue.
The tissue which connects or bond different tissues and organs is connective tissue.
It has a nonliving matrix in the intercellular space.
The matrix may be hard, soft or fluid.
The tissue also has fibres. The tissue forms the framework of our body, conduct movement by the coordination with muscles and protect the delicate organs like heart, lungs, livers, brain, spinal cord, etc. Examples of the tissue are bone, blood, lymph, etc.
3. Nervous tissue
The tissue is made up of neurons. Neurons are the longest cells which consist of cyclon(cell body) and fibers like dendrites and axons. The network of the neurons is spread all over the body which gives us sensation.
4. Epithelial tissue
The tissue which forms the covering of organs and lining or cavities is called epithelial tissue.
It also forms the lining of ducts. The tissue has the following characteristics,
1. The cells are arranged on a basement membrane.
2. The tissue does not have intercellular space and vacuoles.
3. The tissue forms the covering of organs and lining of cavities and blood tubes.
4. The cells of this tissue may be arranged in a single layer or in many layers.
The function of epithelial tissue
The major functions of this tissue are as the following.
Types of epithelial tissue
On the basis of function and structure of epithelial tissue, it has the following types,
a. Squamous or pavement epithelium
The epithelium consists of flat cells and the arrangement of the cell is in a tile-like formation on the basement membrane. The arrangement of cell is in a single layer. It forms a lining of cavities such as the mouth, the blood vessels, the heart, and the lungs. It also forms the outer layer of the skin. The major function of this tissue is to provide protection and conduct the diffusion process.
b. Cuboidal epithelium
This epithelium contains a single layer of cuboidal cells. Each cell has a spherical nucleus at the central part. The glands consist of tissue and it also forms the lining of the ducts of glands and the lining of the kidney tubules. It also forms germin epithelium that forms reproductive cells.
C. Columnar epithelium
The epithelium consists of elongated cells arranged on the basement membrane. The nuclei are also elongate and consist near the base of the cell. They usually form the lining of the stomach and intestine and help in the absorption of food. Some columnar cells are special for sensory reception inside the nose, the ears, and the tongue. Columnar epithelium cells of duodenum produce mucus which keeps the inner surface of the digestive system smooth.
d. Ciliated epithelium
It is a modified columnar epithelium. It has cilia st its free margin. The cilia are a hairy structure that beats in a particular direction and helps the materials to move in that direction. The epithelium is found in the nose. The uterus and the fallopian tubes.
e. Glandular epithelium
It is also a modified columnar epithelium and sometimes cuboidal epithelium. The epithelium has goblet cells that produce milk, sweat was, mucus, hormones, and enzymes. The tissue forms the inner lining of glands.
f. Stratified epithelium
It is also called as compound epithelium as it is made of many layers of cells. The cells close to the basement membrane form a germinal layer from new cells. When we push the cells upward they die and gradually change into horny cells. They form our skin, mouth, cavity, etc.
B. Plant tissue
Plant tissue consists of plant cells. Some of the plant tissues consist of dead cells. All the plant tissues don’t have the capability of cell division. Each tissue has a cell wall and plastid.
The tissues further divided into the following two types,
a. Meristematic tissue
Meristematic tissue has the capacity of cell division. The tissue is responsible for the growth of a plant. The tissue consists of the cells of different shapes. Cells have a thin cell wall and dense cytoplasm. The arrangement of the cell is end to end and they have no plastid. There is no intercellular space in this tissue.
Types of meristematic tissues
On the basis of the location at which meristematic tissues consists, they are in the form of three types.
a. Apical meristem
This type of meristematic tissue consists at the tip of a shoot. It is responsible for the height of a plant. If we cut the tip of a stem, it does not grow tall. It is because the tissues responsible for the height of the plant are already break out from the plant.
b. Lateral meristem
Lateral meristem is at the lateral sides of a stem. They are responsible for the thickness of the stem.
c. Intercalary meristem
This meristem is found in between the permanent tissue at the internodes of a stem and at the base of a leaf. It is responsible for the growth of the axis of the internodes.
b. Permanent meristem
This tissue does not have the capacity of cell division and its cells are different in shapes.
It has the following sub-categories,