Animals are multicellular, non-bacterial eukaryotic organisms in the Kingdom Animalia. With few exceptions, all animals breathe air, digest animal matter, can move, reproduce sexually, and secrete waste material. All vertebrates (all animals with a backbone) have the ability to move about on two legs, although most animals do not have eyelids or a tail. All mammals give birth to live babies that must remain underdeveloped until they reach adulthood. The term animal is usually used to refer to any of the above mentioned animals.
The study of animal science involves studying the behavior, anatomy, physiology, ecology and genetic structure of animals. Many people think that animal science is simply research on how animals behave. The truth is that animal science is much more than this. It is actually an entire branch of zoology, meaning “Zoology” is the study of animal life. Some animal scientists work in laboratories only, but others do research in zoos and other wildlife centers.
An animal cell is made up of a nucleus (which forms the center of a cell), a proenzyme (which produces enzymes), a receptor, and a germ-free outer membrane. There are two types of cells: the nucleus that make up the nucleus of an individual animal cell, and a non-nucleus cell that surrounds the nucleus. Every living animal possesses at least one non-nucleus cell. Nucleus cells can be either proenzyme-producing or non-proenzyme cells.
Animal experiments are used to understand the function of particular organs, breed of animal, physiological mechanisms, natural history and relationships among organisms. For example, researchers use animal experiments to learn more about the structure and dynamics of the lymph system in animals, to study the effect of infection on the immune system of an animal species, how an organ functions under a variety of disease conditions, and how different animals cope with stress. They also study the effect of diet, nutrition, environment and lifestyle on the well being and health of an animal.
An animal can undergo many different kinds of alterations, depending on the demands of its species. Most animals experience a change in reproductive capability when they are confronted with challenges or difficulties in their environment. In this case, they may either undergo a metamorphosis or undergo an asexual reproduction process. In metamorphosis, the animals undergo different physical changes: the tissues become thicker and more resilient, muscles grow stronger, hair growth occurs, eyes develop, and so on. In an asexual reproduction process, the animals’ organs reproduce sexually instead of simultaneously, as in a fertilization process.
All animals possess nervous system and all animals have gastro-intestinal tract. The nervous system enables animals to feel fear, pain, or anxiety and to move their limbs. Gastro-intestinal tract is used by all animals for digestion, thus, all animals possess digestive tract.