Animal Cells and Their Structure


Animal Cells and Their Structure

When we speak of animals, we typically refer to four things: cats, dogs, fishes, and birds. All four have lived in mankind’s environment since their beginning. Animals are multicellular, multiregular organisms in the living kingdom Animalia. With few exceptions, all animals breath oxygen, can reproduce fully, eat organic matter, move, and live in groups. Although some taxonomists class all animals under a single kingdom, such as mammal, which includes all the mammals and reptiles including humans, birds, and fish, each kingdom has a number of different classes that are composed of distinct kinds of animals.

Plants are animals too, although they are much less complex than animals. Plants are made up of a single layer of epidermal cells that are connected by process of diffusion. Animals on the other hand are multi-celled, which means that each cell is coated with more than one cell wall, and has an extensive internal environment of blood vessels, nerves, lymph nodes, muscles, organs, and a thick coating of body tissues. In comparison to plants, animals only have a single celled placenta, and the inner environment of their body is relatively simple because it consists mostly of water.

The word ‘animal’ is used to refer to any creature not requiring muscular action for walking, swimming, digesting, breathing, secreting or producing milk, driving out waste products, or secreting fat stores. Herbivores, omnivores, protists, and eusocial insects are some examples of animal beings. These include all vertebrates, which include all fish, amphibians, birds, mammals, reptiles, mollusks, crustaceans, and alligators. The term ‘plant’ refers to any multicellular organism that is alive, including all algae, plants, fungi, protista, invertebrates, and molds.

Virtually all animals belong to at least two major categories. Herbivores eat plants and many animal species such as salamanders and snails. Omnivores eat animal and plant materials together. Protists eat both animal and plant materials, along with enzymes, vitamins, and other food supplies. Eusocial insect species are known as colonies of insects that are capable of feeding off of other insects, which belong to other insect species.

The body of an animal is covered with many layers of tissue, including the epidermis, dermis, epidermal layers, subcutaneous layers, the immune system, blood, and various other elements. Organ tissues make up the body of an animal. Animal cells are enclosed in a thick layer of extracellular matrix. Extracellular matrix surrounds all animal cells except for blood, which has a protective covering called the endomembrane. The body of an animal can be composed of several types of cells and the cellular makeup may vary considerably depending upon the type of organism.

Insects are unique in that most insects are eusocial, which means that they live together in groups of a few hundred insects. Unlike vertebrates, most insects are diploid in nature, which means that they have a very long tail. All animals have a nervous system, although the nerves of arachnids and moths are simpler than those of mammals. Most animals have a liver and kidneys, although mammals and birds do not.

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