People sometimes wonder why animals make such an important part of our lives. Animals provide companionship, therapy, food, and many other essential services. Many people consider animals to be a significant part of their families because of the emotional connection they have with pets and children. While it is true that humans depend on animals for companionship, many animals throughout history have provided those emotional bonds as well.
Animals are multicellular organisms, meaning they have multiple cell walls. Multicellular organisms are different from simple cells. Humans and animals share many of the same characteristics, but animals are very different. The sponges that contain mucus in our bodies are a perfect example of multicellular organisms. The sponges are constantly being produced, though, so we do not actually “feel” them. In fact, we cannot “touch” the sponges as we cannot feel the cells in our bodies.
Because of their multiscellular organization, animals are classified into three main classifications: Bacteria, protozoa, and vertebrates. Bacteria, which includes all known types of bacteria and viruses, are the most common of all the animals in the animal kingdom. Many bacteria live in feces and other secretions. These bacteria belong to the classifications of aerobic microorganisms, which include several varieties of eukaryotes (single-celled animals), and protozoa, which includes sea animals such as snails and salamanders.
A variety of viruses also belong to the bacteria, protozoa, and aerobic microorganism categories. Some viruses are part of the hereditary architecture of some animals including humans and animals including horses. Human tumors and other diseases that affect animals including dogs have been identified as resulting from viral infection.
The third main classification is that of eukaryotic animals. Eukaryotic animals have a nucleus, a cell wall, a ribosome, a protein coat, and metalloprotein complexes (which can code for specific functionalities). Compared to bacterial or viral organisms, eukaryotic animals do not require a plasmid, as they utilize a genetic material called a transposon to generate DNA. Unlike plants and animals that use plastics to create DNA, eukaryotes use a transposon only to insert genetic information within the host genome. Animals such as mice, birds, and humans are eukaryotic in nature.
There are three primary types of cells in animals: eukaryotic (or prokaryotic), protoplastic (or metacentric), and metalloplastic (or metacarpal). Eukaryote cells divide into two different daughter clones that reproduce sexually. Metabolic pathways exist in all animals, but metacentrics reproduce mostly by means of a process called replication. The metapleural cells reproduce sexually by means of a sexual pheromone. Although animals do not fit neatly into any of these three major biological kingdom categories, there are many parallels between all three.