The study of different levels of organization of animate or living things enables us to gain insights into the complexities of their structure and functioning. The five levels of organization in multicellular organisms in sequence are the cells, tissues, organ, systems, and organisms.
The cell is considered to be the basic unit of life. It is also known as the building block of life. The two basic types of cells are prokaryotic and eukaryotic. Prokaryotic cells are smaller and simpler in form. Eukaryotic cells are more specialized in their structure than the prokaryotic cells.
A tissue is a group of cells which are similar in shape and in size and perform the same function. The cells which form a tissue need not be identical but have the same origin. The different types of animal tissues which form organs are the nervous, muscle, connective and epithelial tissues, blood tissue, and skeletal tissue. Plant tissues include photosynthetic tissue (palisade and spongy mesophylls), epidermal tissue, strengthening tissue (collenchyma, parenchyma, and sclerenchyma), and conducting tissue (xylem and phloem).
| Name of tissue in plants | Components | Some function(s) |
|---|---|---|
| Palisade tissue | Cells with chloroplasts | Produces food |
| Epidermal tissue | Sheets of cells | Covers the surface of plants |
| Collenchyma, parenchyma, and sclerenchyma tissue | Bundles of tough fibres | Provides support for the plant |
| Xylem tissue | Tubular cells | Transport water and food substances |
| Name of tissue in animals | Components | Some function(s) |
|---|---|---|
| Nerve tissue | Cells with long extensions | Transmit and co-ordinates messages |
| Muscle tissue | Bundles of elongated cells | Contracts, bringing about movements |
| Skeletal Tissue | Hard and tough material containing living cells | Provides support and permits movement |
| Epithelial Tissue | Continuous layers of cells | Covers internal and external surfaces |
An organ consists of a number of different tissues which are grouped together to perform a specific function.
The various organs of animals include the lungs, brain, liver, etc. Roots, stems, and leaves are different organs of plants.
Organs could be classified on the basis of the functions they perform. For example, in case of animals, tongue, ears, eyes, skin, and nose form the sensory organs. Flowers and seeds are the reproductive organs in plants.