The Animal Kingdom is one diverse classification containing thousands of species, with thousands more waiting to be discovered. Each species would differ from the other, in terms of habitat, characteristics, hunting abilities, and much, much more. This diversity can be attributed to evolution – development of different defining characteristics that would set apart the large number of organisms from each other. The Animal Kingdom is truly one big melting pot of diverse beings. This however can be argued upon, for despite the hundreds of differences between the members of the group, there exists many more that would bind them as one.
This is fact became the gold standard of grouping these organisms into a single kingdom – the existence of several defining characteristics of the so-called “Animals”. Probably the most common factors of all animals is that they are heterotrophs, obtaining energy and other organic substances through ingestion (Johnson, 2008). Unlike those from the other kingdom, the Plant Kingdom, animals are incapable of producing their own energy source. They, for this are called consumers, feeding on the producers. Herbivores are those benefiting the most from plants, for they feed directly onto them.
The ruminants, such as cattle, are such organisms from the phylum Chordata that are capable of digesting plants. Their stomachs are specialized organs, having four chambers and a flora of bacteria that helps them degrade the plant material they take in (Schoenian, 2005). Other animals then obtain their energy from preying on other animals capable of digesting plants. Others still, obtained different skills in making plant material more edible, such as the humans do in cooking vegetables. Next is that all animals are multicellular (Johnson, 2008).
This means that organisms under this classification are composed of several cells, resulting to more complex body organization. Another term for this would be eukaryotes, meaning many nuclei, thus, many cells. As opposed to the prokaryotes that only have single cells, animals are much more complicated and the processes happening between each kind of cell is pretty difficult to deduce. Even the simplest of the animals, like the sponges of the phylum Porifera, are composed of several cells working together (Myers, 2001). Now, one might say that plants are also multicellular.
True, however there are a number of distinctive characteristics that would differentiate the two kingdoms. Aside from plants are autotrophs and animals are heterotrophs, the latter has no cell wall (Johnson, 2008). Plants, and some members of the prokaryotic groups such as bacteria have a cell wall covering the cell, just right outside the cell membrane. The cell wall adds protection for the plants, which would need a great deal of it in times of environmental stress, such as strong water and winds, and from predator attacks.
The cell wall also makes the plant structure rigid and stronger, pretty much like a defense from the outside world, and provides an area for signal transduction between cells to occur (Rader, 2009). Animals, on the other hand, don’t need the cell wall that much. For one thing, signals are attain through other means, like cell membrane junctions and receptor-signaling. The lack of cell wall also allows the animal to achieve a number of different cell types, thus tissues and different organ systems.
Specialized systems arise to muscle cells, nerves, and other which plants are not capable of making (Cartage, 2009). Another important thing the lack of cell wall gives is the less rigidity, and therefore the animals’ ability for motion which is, by the way, another characteristic of this kingdom. Motility, in a way or two, is described by all species of animals (Johnson, 2008). Movement may be as sophisticated as flying, such as that manifested by the birds of the class Aves and belonging to the phylum Chordata, or as simple as walking like we mammals do.
This motion is a result of evolution being bias to different organs and body structures such as the wings for the birds, the fins for the fishes, and the long legs for the kangaroos. Plants, on the other hand are generally considered stable; movement only observable in terms of growth and extension of parts, like the tendrils and the vines. Sponges, again from the phyla Porifera, may be plant-like in terms of motility, but one must remember that the young sponges and corals are once mobile, just like small jellyfishes under the sea (Myers, 2001).
The animal kingdom is also the most diverse of all, consisting of around 10 million living species (Johnson, 2008). And interestingly enough, a number of these can be mistaken as plants, such as the sponges (Porifera). Some might also be taken into as bacteria, being very small for the naked eye. Still others are very large that they can be viewed from a distance. The two major groups of the Animal Kingdom – vertebrates and invertebrates – may have presented a neat way of grouping the organisms, but the extent of the diversity results to several groupings, numbering to hundreds of orders and classes just for the invertebrates alone.
The vertebrates are still another issue, considering the rate of new species being discovered and produced through hybrid breeding. In line with this, animal diversity also extends to its habitat. The world, consisting of different biospheres, houses the million of animal species (Johnson, 2008). Most live in water, including microscopic animal organisms which prefer the environment due to less stress and energy usage in motility. But still, the waters can be divided into different habitats – freshwater, oceans, rivers, lakes – and one would normally find different species on different habitats.
The existence of different biospheres could have also contributed into the evolution of the different species. It is then like a give and take solution, while the habitat helped animals achieved diversity, the animals changed the habitat as well to better suit their needs. While invertebrates prefer the watery biomes, those from the phylum Chordata made the terrestrial area their home (Johnson, 2008). Other still, some might argue, prefers the air above, like the Aves class.
The result is sometimes specialized niches, on which some animals thrive better on locations just several meters apart (Blue Planet, 2009). Diversity is also contributed by the reproduction mechanism of the animals. This results to the fusion of two genomes – one from each parent. This gives several recombination chances for different genes to be expressed in the offspring. Also, sexual reproduction is prone to several mutations, which can give rise to even more diversity in the population (Reece, 2006).
Sexual reproduction is common for all, from Chordates to Arthropods, to the simple Poriferans. The resulting development is also similar for them. The fertilized zygote marks the start of embryonic development, followed by the actively dividing morula. A hollow space then takes place, forming the blastula. Gastrulation then occurs, where movement of the cells occur to correctly orient the different layers that would form the tissues and organs of the future animal (Reece, 2006). At this point, the gastrula development would differ depending on the organism (Johnson, 2008).
Finally, animals are composed of unique tissues, with function exclusively for animals only (Johnson, 2008). Some are mentioned above, such as that of the muscular tissues needed for movement. Others would include the nervous tissues for signals, the immunity-related tissues for body protection, and the organ systems for different access to the outside world. All of these contribute to the factors defining the Animal world. Though there are some exceptions to some of those listed in here, the majority falls to all of these and all animals are part in a way or another.
The Animal of Kingdom is truly a group which one can call unity in diversity – the millions of different species coming together as one with a set of defining characteristics. References: Blue Planet, 2009. Animals. Blue Planet Biomes Web. Retrieved February 20, 2009 from http://www. blueplanetbiomes. org/animals. htm Cartage. 2009. Animal Cell Structure. Cartage Organization. Retrieved February 21, 2009 from http://www. cartage. org. lb/en/themes/Sciences/Zoology/AnimalPhysiology/Anatomy/AnimalCellStructure/AnimalCellStructure. htm Johnson, G. B & Losos, J. B. 2008.
The Living World. New York: McGraw-Hill Myers, P. 2001. Porifera. Animal Diversity Web. Retrieved February 19, 2009 from http://animaldiversity. ummz. umich. edu/site/accounts/information/Porifera. html Rader, A. 2009. Cell Wall. Biology 4 Kids Website. Retrieved February 19, 2009 from http://www. biology4kids. com/files/cell_wall. html Reece, J. B. & Campbell, N. A. Biology. 2006. New York: Benjamin Cummings. Schoeninan, S. Ruminants. Sheep 101 Website. Retrieved February 20, 2009 from http://www. sheep101. info/cud. html