What is Animals?

Meaning and Definition of Animal

Based on experience, it is easy to recognize an animal and differentiate it from plant life forms . However, the distinction becomes more complex as one descends the evolutionary scale of the organization of the animal world.

Animals and plants

superficial observation allows to establish the clearest difference between an animal and a plant. Animals react to a series of stimuli in the environment and perceive light, sounds and smells directly and immediately.

Their relationship with the environment seems deeper and more active than that of plants , they grow and rise, therefore, they move; however, its movement is slower, almost imperceptible.

When we focus on the observation of less evolved animals , these differences seem to be progressively diluted. The sensory organs of a starfish are not recognizable and its form is not so definitely ” animal “.

Sponges are immobile and corals branch like trees. All the most familiar characteristics in animals seem to be absent in such beings: mobility, activity, responsiveness, etc. However, they are also animals .

The fundamental difference between the plant and animal kingdoms lies in the cellular characteristics and the type of nutrition. Plants are autotrophic organisms, that is, they feed on mineral substances, light and water.

For this they use photosynthesis , through which they produce organic molecules using sunlight. Animals are heterotrophic, since they have to feed on other living things to obtain nutrients .

Form and Organization

In the animal kingdom, beings of the most diverse shapes and sizes are integrated . There are microscopic animals, such as protozoa, which are unicellular , or rotifers, and others of gigantic dimensions, such as whales and sperm whales.

There are fixed and immobile marine forms , such as sponges, corals, crinoids and others that have great mobility and surprising speed.

Animal morphology is conditioned by the degree of adaptation to a given habitat. The spherical shapes of numerous aquatic protozoa, such as the radiolaria, reflect a type of life based on fluctuation.

The delicate webs of jellyfish favor their movement in the water; the elongated shape of the worms allows them to live and move underground, under the sea or inside other animals.

The many appendages of arthropods allow them to colonize all kinds of environments, etc. Also, the fusiform design of the fish facilitates its movement with a minimum of resistance in the water.

The thin and light body of the birds allows them to be held in the air; and the ends of mammals allow them to walk, jump and capture their prey.

Characteristics of an Animal

Integument and Skeletal System

As far as possible, the organism must be protected and isolated from the outside: for this purpose the so-called integuments are developed . Often the cells that make them up secrete special substances that harden and form an additional barrier, like a breastplate.

Such is the origin of the limestone skeletons of corals, the shells of molluscs or the quinine shells of insects and crustaceans. Vertebrates, the most highly evolved animals , also have protective external formations. Mention may be made, for example, of the scales of fish and reptiles , the feathers of birds, and the fur of mammals.

The skeletal system constitutes the support structure of the organism: in vertebrates, the skeleton is found inside the body, forming a set of articulated parts or bones that, in addition, serve as a support, fixation and lever for the muscles.

Breath of an Animal

In less evolved animals, oxygen enters cells by simple diffusion. As the structure of beings becomes more complex, the need for the development of conduits and devices to distribute oxygen throughout the body becomes evident. Aquatic animals breathe through gills through which dissolved oxygen enters the water.

Terrestrial animals , on the other hand, have tracheas, that is, systems of ducts, connected to the outside, which branch into ever thinner tubules until they reach the cells, as happens among insects.

In vertebrates, respiration is closely linked to the circulatory system . Red blood cells contain hemoglobin, a pigment that combines with oxygen and allows it to be transported to the ends of blood capillaries, being released there and then absorbed by the tissues.

Animal Circulatory System

Food, digested and absorbed by the animal, and oxygen are transported to the tissues through the circulatory system . This set is constituted, fundamentally, by a network of ducts or vessels through which a liquid composed of cells, proteins and other substances circulates.

In animals, the system opens and the vessels flow into holes or hemocoels, which bathe the viscera directly. In vertebrates and other groups, the system is closed, and blood is propelled through a muscular pumping organ , the heart.

Nutrition and Excretion

The ingested food must be broken down into its basic principles so that they can be assimilated by the animal organism. Such decomposition occurs in the digestive process.

As the evolutionary scale of animals increases, the digestive tract will progressively differentiate into a series of specialized cavities at different stages of food processing. Oral cavity, equipped with chewing parts, puffers, gizzards, stomach and intestines.

Through the process of excretion , assimilation residues and toxic substances are eliminated from the body. In vertebrates, this function belongs to the kidneys, organs in which blood is filtered to form urine.

Reproduction and Development of an Animal

Reproduction is the process that allows living beings to maintain their species over time. In the simplest animals, sexual reproduction coexists with asexual. The first, the reproductive cells, or gametes, of two individuals of the opposite sex unite to form a new being.

In the second, on the other hand, a part of the animal’s body separates and regenerates the organism. The egg that emerges from sexual intercourse undergoes an accelerated process of cell multiplication until it forms a homogeneous mass.

From which the cell envelopes that give rise to the different tissues and organs are wrapped. This process is called embryology.

Animal Communities

Many animals gather in more or less stable communities , to ensure their survival more efficiently than if they faced the environment alone.

In some groups, such as corals and bryozoans, the colonies are closely related. Certain insects, such as ants, termites and bees, give rise to true ” societies “, with a strict division of labor, so that the entire community acts as a superorganism.

Whose preservation are directed the activities of the individuals who are directed. Another form of relationship is gregariousness , whereby a certain number of animals of the same species share a territory. This is the case of herds of herbivores or schools of fish.

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