david alercia
Bachelor of Biology
animalia It is characterized by being a group of multicellular and eukaryotic organisms, that is, its cells have a nucleus and organelles delimited by membranes. The simplest of all animals, marine sponges, are aggregations of poorly specialized cells. The rest of the existing animals have tissues, organs and organ systems. Likewise, all animals are heterotrophs, which means that they feed on other organisms for energy and nutrients. Neither is capable of photosynthesis.
Animals, among all types of living beings, are the closest to us, and the most familiar, so that oneself, in the biological order, is part of the kingdom animalia, which is one of the 5 kingdoms of the classical classification of living beings. It is an extensive group with a large number of different life forms: currently there are approximately 2 million species of living beings described, of which 1.5 million are animals. Despite the fact that the most familiar groups of animals for us are vertebrates (mammals, birds, reptiles, amphibians and fish), because we live with these species, either as pets, livestock or because they live in cities and we are used to seeing them ; The largest group of animals is that of invertebrates, and among them, insects.
Animals exist in all environments on Earth, from the depths of the ocean to about 8,000 meters in height (maximum height at which some birds can fly). In size, there are animals from just millimeters to the large vertebrates that inhabit today: whales, elephants, some crocodiles, snakes and sharks that can measure several tens of meters and weigh more than 1 ton. In the past, there were animals of gigantic proportions, such as dinosaurs and megamammals (mammoths, saber-toothed tigers, giant sloths, and other lesser-known forms) that inhabited the earth about 20,000 years ago.
Animal Characteristics
In addition to being multicellular, eukaryotic and heterotrophic, as the essential aspects that define animals, they have the ability to move (they can move from one place). Some, the simplest, simply let themselves be carried away by the currents of water or wind, but most can move at will. Animals have evolved various locomotion systems, including the skeletal and muscular system of vertebrates (the skeleton and muscles allow vertebrates to walk, run, swim, fly, or glide), the exoskeleton of insects, and even strange forms, as in snails, which “skate” on a track of mucus that its own body produces and lubricates the ground. Or even rarer, the aquifer system of starfish, which works by water pressure (like the pistons of doors that close by themselves), so work the “feet” of starfish, alternately filling and emptying to allow you to “walk”.
In general, they have the ability to react quickly to environmental stimuli, such as light, sound, heat, or cold. This is possible because animals have a nervous system, made up of a network of neurons and other tissues that form receptors for external stimuli such as eyes (light receptors), ears (sound receptors). There are animals with receptors that we ourselves do not have, so they have “extra senses” like the electric field receptors of sharks (which allows them to find prey even in complete darkness, only detecting the electric field produced by the body), the thermal radiation receptors of some snakes (which allow them to have infrared vision) or the sonar of dolphins and bats, which makes them orient themselves in total darkness through echolocation. In addition to these receptors, the nervous system also processes these signals and makes appropriate responses. Some of those responses are simple, like running away from a noxious stimulus, but others are more complex. Most animals have a central nervous system that is located in the brain and spinal cord and is responsible for receiving information from the environment, processing it, and developing appropriate responses. Sometimes these responses are involuntary, but in more complex animals, they involve decision making, learning, and memorization.
The size of the animals means that not all the cells are in direct contact with the air, therefore, they need a “system” that transfers the oxygen from the air to all the cells of the body and this is the function of the circulatory system, which It is made up of blood vessels and carries blood. Blood is liquid and can be of different colors: in vertebrates it is red, but in invertebrates it can be red, violet, blue or green. If the vessels rupture, the blood would spill until the death of the animal, so the blood can coagulate, that is, they form a “plug” of dried blood in the broken vessel, to seal it and prevent the loss of more blood . The circulatory systems also have pumps, whose job it is to pump blood through the vessels so that it travels throughout the body. These pumps are called hearts, and there can be more than one, worms have 5!
Animals also have a digestive system that allows them to digest and absorb food. Most animals have a digestive tube that extends from the mouth to the anus. This tube is made up of different organs, such as the mouth, stomach, and intestine, which work together to digest food. The ingested food circulates inside this tube and in the process, it is digested, which means that the ingested food is “broken down” into the simple molecules that constitute it and the intestine absorbs those nutrients, which are then distributed by the circulatory system. did the whole body.
Most animals reproduce sexually and are sexed, meaning they have two different sexes that reproduce by joining reproductive cells called gametes. However, some animals are asexual and can reproduce by budding or other forms of asexual reproduction.
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