What features distinguish animals from other creatures? The question seems simple enough, but the answer requires an understanding of some of the more obscure characteristics of organisms, including multicellularity, heterotrophy, motility, and other complex concepts used by biologists. From snails and zebras to mongooses and sea anemones, what signs of living creatures are the same for at least most animals?
Multicellularity
If you're trying to distinguish a true animal from, say, a paramecium or an amoeba, it's not very difficult: animals are, by definition, multicellular creatures, although the number of cells varies greatly between species. For example, a roundworm, which is widely used in biology experiments, 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 that animals are notthe only multicellular organisms, they also include plants, fungi and even some types of algae.
Eukaryotic cell structure
Signs of living things 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-limited nuclei and other organelles and are exclusively unicellular. These include, for example, all bacteria.
In contrast, eukaryotic cells have well-defined nuclei and internal organelles (such as mitochondria) that can group together to form multicellular organisms. While 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 wide variety of tissues. One of the most remarkable things about animals is how specialized their cells are. As these organisms evolve, seemingly ordinary stem cells are actually not so simple. There are four broad biological categories: nervous, connective, muscle, and epithelial tissues (which build organs and blood vessels).
More advanced organisms exhibit even more specificlevels of differentiation. For example, the various organs of the human body are made up of cells from the liver, pancreas, and dozens of other types. The exception is sponges, which are technically animals but have little to no differentiated cells.
Sexual reproduction
Another sign of living beings is that most animals participate in sexual reproduction, combining their genetic information and producing offspring that carry the DNA of both parents. But even here there are exceptions. Some animals, including some species of sharks, are able to reproduce asexually.
The benefits of sexual reproduction are huge from an evolutionary point of view. The ability to test different combinations of genomes allows animals to quickly adapt to new ecosystems. Again, sexual reproduction is not limited to animals: this system is also used by various plants, fungi, and even some very promising bacteria.
Blastula stage
This is one of the most difficult to perceive signs of living beings. When a male's sperm meets a female's egg, the result is a single cell called a zygote. After the zygote goes through several rounds of division, it receives the name - morula. Only real animals reach the next stage - the formation of a blastula, a hollow ball of several cells. Only then can they differentiate intodifferent types of fabrics.
Movement (animals)
The first five signs of living beings are very difficult to show with the help of funny drawings. They are indeed 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 run, snails and snakes crawl - all animals are able to move at some stage in their life cycle. One of the studied signs of living beings of the surrounding world in grade 3 is movement. If there is movement, then the organism is alive.
This evolutionary innovation makes it easier for creatures to find new ecological niches, chase prey and avoid predators. Some animals, such as sponges and corals, are practically immobile in their 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. Some exceptions to the rule remain controversial, including carnivorous flycatchers and fast-growing bamboo trees.
Metabolism
Among the signs of living beings of the world studied by children (in the 3rd grade this sign will be called "nutrition"), it is worth noting the metabolism and energy. All organisms require organic carbon to support basic life processes, including growth, development, and reproduction. The ability to taste food, in scientific terms, is called heterotrophy. There are two ways to getcarbon: from the environment (as carbon dioxide, a freely available gas in the atmosphere) or by eating other carbon-rich organisms.
Living organisms that obtain carbon from the environment like plants are called autotrophs, and living organisms that obtain 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 energy sources in the form of food, light, and so on, is an important feature of living organisms.
Advanced nervous systems
This is another of the signs of living beings. Organisms, in particular animals, have advanced nervous systems. It is rather difficult to judge the intellectual level of plants and fungi. Of all organisms on Earth, only mammals are so advanced as to 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 vibrations in the water).
Of course, these senses entail the existence of at least a rudimentary nervous system, as in insects and starfish, as in the most advanced animals. Fully developed brains are perhaps one of the key features that really sets animals apart from the rest of nature.
Growth and development
Among the signs of living beings of the world studied in grade 3, there is such an item as growth. This is a property that means an increase in size and mass while maintaining the general features of the structure, and is accompanied by such a complex process as development.
Single chemical composition
Living beings consist of the same chemical elements, which include objects of inanimate nature. The difference lies in the unequal proportion. All life on Earth is 98 percent composed of elements such as carbon, oxygen, nitrogen and hydrogen.
Irritability
An integral feature that is inherent in all living organisms is the ability to respond to irritation. This sign is expressed by how 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 make up a single structural and functional organization.
Life has existed on planet Earth for approximately four billion years. The living creatures that live on our planet are incredibly diverse: from single-celled and tiny organisms invisible to the naked eye 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 thathelp to distinguish them from the bodies of inanimate nature.
