A group of cells having common origin, similar structure and performing a definite function is called a tissue. Tissues are found in plants and animals. Plants and animals are made up of many different kinds of tissues. For example, groups of bone cells form bone tissues and muscle cells form muscle tissue. Different types of tissues have distinctive architecture best suited for what they do. We will see that plant tissues are different from animal tissues in many ways.
Plant tissues can be grouped into two basic types: meristematic and permanent tissues.
Animal tissues can be grouped into four basic types: epithelial, muscular, connective and nervous tissues.
Parenchyma tissues are found in the soft parts of plant such the roots, stems, leaves and flowers. The cells in this tissue are loosely packed, as they contain large intercellular spaces between them. The cells consist of cytoplasm and nucleus that is surrounded by a cell wall. Each cell has a vacuole at the centre. The functions of parenchyma tissues are storage, photosynthesis, and also to help the plant float on water.
Sclerenchyma tissue consists of thick-walled, dead cells. These cells are long, narrow and have hard and extremely thick secondary walls due to the uniform distribution of lignin. Lignin deposition is so thick that the cell walls become strong, rigid and impermeable to water. There are no inter-cellular spaces between sclerenchyma cells. Nucleus is absent in the cell. The function of this tissue is to give protection and support to the plant.
Striated muscles cells are long and cylindrical fibres. The fibres are enclosed within a membrane called sarcolemma. These fibres are multinucleated, which means they have many nuclei. Each cell cytoplasm consists of many myofibrils. These are voluntary muscles.
The nervous tissue consists of the nerve cells and neurons. The large body of the nerve cell is called the cyton which contains the cell’s nucleus. The cell body branches out to form dendrons. Dendrons further branch out to form fibres called dendrites. There is also a single long fibre projecting from the cyton called axon. The neurons in the brain communicate with other nerve cells that reach throughout the body forming the body’s nervous system.