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The word ‘animal’ is derived from the Latin word animalis which means ‘having breath’. The Kingdom Animalia is characterized by eukaryotic and heterotrophic organisms. They are multicellular and lack cell wall. Animals are eukaryotic, multicellular and heterotrophic organisms. They have multiple cells with mitochondria and they depend on other organisms for food. Habitat – Most of the animals inhabit seas, fewer are seen in fresh water and even fewer on land.
There are around 9 to 10 million animal species that inhabit the earth. Only 800,000 species are identified. Biologists recognize 36 phyla in the animal’s kingdom. Size – The sizes of animals ranges from a few celled organism like the mesozoans to animals weighing many tons like the blue whale. Animal bodies – Bodies of animals are made of cells organized into tissues which perform specific functions. in most animals tissue are organized into complex organs, which form organ systems.
Cell structure – The animal cell contains organelles like the nucleus, mitochondria, Golgi complex, ribosomes, endoplasmic reticulum, lysosomes, vacuoles, centrioles, cytoskeleton. Animals are made up of many organ systems, that aids in performing specific functions that are necessary for the survival of the organism. Organ systems are skeletal system, muscular system, digestive system, respiratory system, circulatory system, excretory system, reproductive system, immune system and the endocrine system.
Body symmetry – Most of the animals are bilaterally symmetrical, while primitive animals are asymmetrical and cnidarians and echinoderms are radially symmetrical. Locomotion – Most animals have the ability to move, they show rapid movement when compared to plants and other organisms. Respiration – It is a gaseous exchange of taking in oxygen and giving out carbon dioxide. This process takes place in organs of respiration like the lungs, gills, book gills and book lungs and some animals skin is also used for respiration.
Digestion – Animals ingest food, and digestion takes place in the internal cavity like the digestive system in animals, in primitive animals vacuoles are for digestion. Nervous system – Sensory mechanism and the coordination of the organ systems is carried on by the nervous system. In animals the nervous system comprises of nerve ganglions, or brain, spinal cords and nerves. Circulatory system – The distribution of nutrients, exchange of gases and removal of wastes takes place in the circulatory system. This system comprises of the heart, blood vessels and the blood. Excretory system – Removal of wastes from kidneys. Skeletal system – support and protection is provided by the skeletal system.
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