Structural Organization in Animals

Animals are made up of large numbers of components. The structural organization in animals varies from animal to animal. There are different types of cells grouped together to form an organism.

                                         Cells   →  Tissues   →   Organs  →   Organ system

Cell

Cell

The cell is the smallest, structural and functional unit of an organism. The cell components are mainly involved in carrying out various life functions.
All unicellular organisms including bacteria are composed of a single cell and multicellular organisms, including animals, plants and humans are composed of millions to trillions of cells and cell organelles with their specialized functions.

Also refer: Cells

Tissues

Types of Tissues

Tissues are an integrated group of similar cells which perform similar functions together. These tissues are mainly involved in providing a basic framework in all animals.

Explore more about Tissues

There are four different types of tissues.

Epithelial tissue

This tissue is non-cellular basement membrane, with the absence of blood vessels. They are mainly involved in providing an outer covering and lining the internal surface of the body. In epithelial tissues, all cells are densely packed with the little intercellular matrix. Epithelial tissue is classified into the simple epithelium and compound epithelium.

Connective tissues

They are the most abundant and widely distributed tissues in the body of animals. All connective tissues apart from blood cells, secrete collagen or elastin (fibres of structural proteins) that provide strength, flexibility, and elasticity to the tissue. These tissues are called connective tissues because of their special function of linking and supporting other tissues in the body. There are three different types of connective tissues: Loose connective tissue, dense connective tissue, and specialized connective tissue.

Muscular tissues

These tissues are composed of long, tube-shaped fibres, which are structured in parallel arrays and are mainly composed of numerous fine fibrils, called myofibrils. Muscular tissues play a vital role in contraction, relaxation and other body movements. There are three different types of muscular tissues: skeletal muscles, smooth muscles, and cardiac muscles.

Nervous tissues

This tissue comprises of the neuron and neuroglial cells. Neuron, an excitable cell which is the main component of the neural system and neuroglia forms the rest of the neural system which makes up double the volume of neural tissue in our body. Nervous tissues have the greatest control over the body’s responsiveness to changing conditions.

The below table provides the complete details about tissue, origin and its functions.

Tissue Origin Function
 Epithelial  Ecto, Meso and Endoderm  Protection, absorption, secretion etc.
 Connective  Mesodermal  To connect, support, transport etc
 Muscular  Mesodermal  Locomotion and movement
 Nervous  Ectodermal  Control and coordination

Organ and Organ System

Collections of tissues form organs which in turn associate to form organ systems in the multicellular organisms.

Every organ is composed of one or more type of tissues. A group of organs working together to perform its function is called organ systems.

Excretory system, reproductive system, endocrine system, circulatory system, respiratory system are few examples of an organ system which functions together to keep an organism healthy and alive.

Also refer: Difference Between Tissues and Organs

For more information on cells, tissues, the structural organisation in animals and other related topics, explore BYJU’S Biology.

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