The main signs of living beings

What traits distinguish animals from other creatures? The question seems simple enough, but the answer requires understanding some of the more obscure characteristics of organisms, including multicellularity, heterotrophy, mobility and other complex concepts used by biologists. What signs of living beings are one, at least for most animals, from snails and zebras to mongooses and sea anemones?

Multicellularity

If you are trying to distinguish a true animal from, say, paramecia or amoeba, it is not very difficult: animals are by definition multicellular creatures, although the number of cells varies greatly in species. For example, a roundworm, which is widely used in experiments on biology, consists of exactly 1 031 cells, no more and no less, while a person literally consists of trillions of cells. However, it is important to note the fact that animals are not the only multicellular organisms, they include plants, mushrooms and even some species of algae.

Eukaryotic cell structure

Signs of living beings include the eukaryotic structure of cells. Perhaps the most important split in the history of life on Earth is what happens between their two vast species. Prokaryotic organisms do not have membrane-bound nuclei and other organelles and are exclusively unicellular. These include, for example, all bacteria.

In eukaryotic cells, on the contrary, there are clearly defined nuclei and internal organelles (such as mitochondria) that can group together to form multicellular organisms. Although all animals are eukaryotes, not all eukaryotes are animals: this extremely diverse family also includes plants, fungi and tiny marine proto-animals, known as protists.

Specialized fabrics

Another sign of living beings is the presence of a large variety of tissues. One of the most remarkable features of animals is how specialized their cells are. As these organisms evolve, the seemingly ordinary stem cells are not really that simple. There are four broad biological categories: nerve, connective, muscle and epithelial tissues (which build organs and blood vessels).

More advanced organisms exhibit even more specific levels of differentiation. For example, various organs of the human body consist of cells of the liver, pancreas and dozens of other species. Exceptions are sponges, which are technically animals, but practically do not have differentiated cells.

Sexual reproduction

Another sign of living beings is that most animals participate in sexual reproduction, combining their genetic information and producing offspring carrying the DNA of both parents. But here there are also no exceptions. Some animals, including some types of sharks, are able to reproduce themselves asexually-like.

The benefits of sexual reproduction are enormous from an evolutionary point of view. The ability to test different combinations of genomes allows animals to adapt quickly to new ecosystems. Again, sexual reproduction is not limited to animals: this system is also used by various plants, mushrooms and even some very promising bacteria.

Stage of blastula

This is one of the most difficult to perceive signs of living beings. When the male sperm meets the female egg, the result is a single cell called a zygote. After the zygote passes several rounds of division, it gets the name - morula. Only real animals reach the next stage - the formation of a blastula, a hollow ball of several cells. Only in this case they can differentiate into different types of tissues.

Movement (animals)

The first five signs of living beings with the help of funny drawings show very difficult. They really are quite complex if you explain them, for example, to a child. What can not be said about the next sign. Fish swim, birds fly, wolves flee, snails and snakes crawl - all animals are able to move at a certain stage of the life cycle. One of the studied signs of living beings of the surrounding world in the third class is the movement. If there is movement, then the organism is alive.

This evolutionary innovation allows creatures to find new ecological niches easier, pursue prey and avoid predators. Some animals, such as sponges and corals, are practically immobile in the adult stage, but their larvae are able to move before they take root on the seabed. This is one of the key features that distinguishes animals from plants and fungi. Disputable there is an opinion about some exceptions to the rules, including carnivorous flycatchers and fast-growing bamboo trees.

Metabolism

Among the characteristics of living things that are studied by children in the world around them (in the third grade this feature will be called "food"), it is worth noting the metabolism and energy. All organisms need organic carbon to support the basic processes of life, including growth, development and reproduction. The ability to taste food, in scientific terms, is called heterotrophy. There are two ways of obtaining carbon: from the environment (in the form of carbon dioxide, freely available gas in the atmosphere) or by eating other, carbon-rich organisms.

Living organisms that receive carbon from the environment like plants are called autotrophs, and living organisms that receive carbon by ingesting other living organisms, such as animals, are called heterotrophs. However, animals are not the only heterotrophs in the world. All fungi, many bacteria and even some plants are at least partially heterotrophic. The use of external sources of energy in the form of food, light, and so on, is an important sign of living organisms.

Advanced Nervous System

This is another sign of living beings. Organisms, in particular animals, have advanced nervous systems. The intellectual level of plants and fungi is difficult to judge. Of all the organisms on Earth, only mammals are so developed that they have more or less acute senses of sight, hearing, taste and touch (not to mention the echolocation of dolphins and bats or the ability of some fish and sharks to sense magnetic fluctuations in the water).

Of course, these feelings entail the existence, at least, of a rudimentary nervous system, both in insects and sea stars, and in the most advanced animals. A fully developed brain is perhaps one of the key features that really distinguishes animals from the rest of nature.

Growth and development

Among the characters of the living world that are studied in the 3rd class, there is such an item as growth. This property, which means increasing the size and mass while maintaining the common features of the structure, and is accompanied by such a complex process as development.

Unified chemical composition

Living beings consist of the same chemical elements as include objects of inanimate nature. The difference is in the unequal proportional relationship. All living things on Earth are 98 percent composed of elements such as carbon, oxygen, nitrogen and hydrogen.

Irritability

An inherent feature that is inherent in all living organisms is the ability to respond to irritation. This sign is expressed by how the creatures react to external sources of influence.

Discreteness

The common property of living matter is its discreteness. This means that any biological system includes separate interacting elements, which together constitute a single structural and functional organization.

On Earth, life exists about four billion years. The living beings that live on our planet are incredibly diverse: from unicellular and invisible tiny organisms to unarmed eyes to giant trees, up to 90 meters, and massive animals weighing up to 150 tons. Despite all the biological diversity, there are a number of signs that help distinguish them from the bodies of inanimate nature.