Key Characteristics of the Animalia Kingdom
- Animals are eukaryotic and multicellular (with mitochondria) organisms.
- Animals are heterotrophic, obtaining their energy by consuming energy-releasing food substances.
- Animals typically reproduce sexually.
- 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.
- 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, tissues 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 cells that do not have cell walls.
- 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.
- 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.
- Reproductive system - Most animals reproduce sexually, by the fusion of haploid cells like the eggs and the sperms.
- Glands of the endocrine system help in control and coordination of the body system.
- Animals are able to respond quickly to external stimuli as a result of nerve cells, muscle or contractile tissue, or both.
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