Scientific definitions of life
In biology, there are several approaches to understanding what living matter represents.
Historically important is the materialistic definition formulated by Friedrich Engels more than a century ago. According to this concept, life is viewed as a special mode of existence of protein bodies. The main criterion of the living here is the process of constant self-renewal of the chemical components that make up these bodies.
Modern science uses a more complex definition proposed by the biophysicist M.V. Volkenstein. In his interpretation, living organisms on Earth are open, self-regulating, and self-replicating systems. Their fundamental structural basis relies on biopolymers—complex molecules of proteins and nucleic acids.
Chemical unity and discreteness
Despite the colossal external diversity, all living beings obey common principles of organization.
- Unity of chemical composition. Living and inanimate nature consist of the same chemical elements. The key difference lies in their quantitative ratio. In biological objects, four organogen elements absolutely dominate: carbon (C), oxygen (O), nitrogen (N), and hydrogen (H). Together they make up about 98% of the entire organism's mass.
- Discreteness. This universal property of matter is clearly manifested in biology. Any biological system (whether an individual organism, population, species, or an entire biogeocoenosis) is not a solid monolith. It always consists of separate, isolated, yet closely interacting parts. It is precisely the coordinated work of these discrete units that ensures the integrity of the system.
Energy and functional support
To maintain their structure and activity, organisms must continuously interact with the environment.
- Metabolism and energy exchange. Any organism is an open system through which energy and material flows constantly pass. The process includes the absorption of necessary components from the outside and the obligatory excretion of metabolic products. This condition is absolutely critical: it is precisely exchange with the environment that guarantees the constancy of the structure and chemical composition of the organism. The cessation of this exchange inevitably leads to the cessation of life.
- Self-regulation. Closely related to metabolism. This is the ability of a system to autonomously maintain the intensity of physiological processes and chemical composition at a stable level. In science, this phenomenon is designated by the term homeostasis (from the Greek roots homoios — similar, alike, and stasis — state, immobility).
- Irritability. The property of any living system to adequately respond to internal changes or external influences (stimuli). Irritability serves as the primary basis for the organism's adjustment (adaptation) to constantly changing environmental conditions.
Reproduction, development, and evolution
The lifespan of any individual creature is limited in time. For life not to disappear, mechanisms for preserving and changing information exist.
- Self-reproduction (reproduction). The mechanism solving the problem of the temporal limitation of life. It ensures the continuity of generations and the preservation of the species. It is based on the synthesis of new structures using the matrix of genetic information encoded in the sequence of DNA nucleotides.
- Heredity. The ability to transmit anatomical and physiological traits and development specifics to offspring. This function directly relies on the chemical stability and structural constancy of DNA molecules.
- Variability. The property opposite to heredity. It is expressed in the ability to acquire completely new traits during individual development under the influence of environmental factors. Variability plays a crucial evolutionary role: it supplies diverse material for natural selection. The most adapted individuals survive, which in the long run leads to the formation of new species and forms of life.
- Growth and development. These processes are strictly subordinate to the genetic program. The development of living matter is realized in two forms. Ontogeny (individual development) encompasses the manifestation of all inherent properties during the life of a single individual. Phylogeny (historical development) describes global processes: the progressive complication of the biosphere, the emergence of new species, and the formation of modern biodiversity.
Briefly: answers to topical questions
By means of what specific physiological mechanisms is homeostasis maintained in the organism?
Homeostasis is maintained through a complex of physiological regulatory mechanisms aimed at preserving the constancy of the internal environment. Three main ways of regulating the organism's functions are distinguished:
- Nervous — rapid and direct influence on organs through the nervous system.
- Humoral — slow influence through substances circulating in body fluids (hormones, mediators, cytokines, etc.). The main mechanism of hormonal regulation is negative feedback.
- Neurohumoral — a combination of nervous and humoral pathways.
In addition, homeostasis is maintained with the participation of:
- Cellular mechanisms (for example, the $Na^+/K^+$-pump for ion homeostasis).
- Excretory organs (the kidneys begin to perform a homeostatic function immediately after birth).
- Behavioral functional systems that ensure active interaction with the environment (consumption and excretion of substances) to restore balance.
What are the main levels of organization of living matter distinguished in biology?
Biology distinguishes a hierarchical system of structural levels of organization of living matter, where each preceding level forms subsystems within subsequent ones. The classification of levels includes:
- Microsystems: molecular (macromolecular), subcellular (ultrastructural), cellular (cytological).
- Mesosystems: tissue (histological), organ, organismal (anatomical).
- Macrosystems: population-species, biogeocoenotic, biosphere.
At each new level of organization, emergent properties arise (new qualities absent in the components separately).
What forms of reproduction of living organisms exist?
There are two main modes of reproduction in living organisms: asexual and sexual.
- Asexual reproduction: in sources for protozoa, it is indicated that it is carried out by mitotic division of nuclei; forms include cell division into two and multiple cell division (schizogony).
- Sexual reproduction occurs with the formation of sex cells (gametes) and is characterized by the combination of traits of two parents in the offspring and the appearance of new combinations of genetic material. Sources for protozoa indicate two pathways of sexual reproduction:
- Copulation — the fusion of nuclei and cytoplasm of gametes from parent organisms with the formation of a zygote.
- Conjugation — the exchange of genetic information enclosed in nuclei without the fusion of cytoplasm of two individuals.
In many species, life cycles include an alternation of asexual and sexual reproduction. Parthenogenesis is also mentioned as an exception to the necessity of two individuals participating in sexual reproduction.
Class and exam questions
Why are living organisms called open systems?
Because their existence is impossible without continuous two-way exchange with the environment: they constantly absorb necessary substances and energy from the outside and then excrete the products of their vital activity back.
What is the difference between ontogeny and phylogeny?
Ontogeny is the individual development of a specific organism from conception to the end of life, while phylogeny is the historical development of species on the scale of the entire duration of life on Earth.
How does the chemical composition of living organisms differ from non-living objects?
They do not differ in their set of elements; the difference lies in their ratio. In living systems, 98% of the mass comes from just four organogens: carbon, oxygen, nitrogen, and hydrogen.
What else to study on this topic
- Structure and functions of nucleic acids (DNA and RNA)
- Mechanisms of homeostasis maintenance
- The role of variability in the process of natural selection
- Levels of organization of biological systems
- Main stages of the phylogeny of the animal kingdom
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