Living organism as an open system
Any living organism represents an open biological system. This means that its existence directly depends on the continuous exchange of matter and energy with the environment. This exchange is recognized as the primary and most important property of living things.
Two key components constantly enter the organism from the external environment:
- Substances that act as a universal building material.
- Energy, which is critically necessary for synthesizing own chemical compounds and performing any biological work.
Thanks to this continuous flow, all basic vital processes are ensured, including structural growth, organism development, and reproduction.
Essence and directions of metabolism
Chemical transformations constantly take place within a living system. The entire totality of metabolic reactions occurring in the body is called metabolism.
For ease of understanding, the unified metabolic process is conventionally divided into two opposite yet strictly interconnected directions:
- Anabolism (creative reactions).
- Catabolism (destructive reactions).
These two processes cannot exist without each other and occur in parallel in the body, forming a single cycle of metabolism and energy transformation.
Anabolism: plastic metabolism
Anabolism (also known as assimilation or plastic metabolism) is a set of endothermic biosynthetic reactions. Endothermicity means that these processes occur with the obligatory absorption and expenditure of energy.
Result of anabolism: formation of complex high-molecular-weight substances from simpler molecules. This is how the body builds its own tissues and stores nutrients.
Classic examples of plastic metabolism reactions are:
- Protein synthesis.
- Glycogen synthesis.
- Photosynthesis.
- Chemosynthesis.
Catabolism: energy metabolism
Catabolism (synonyms — dissimilation, energy metabolism) is the opposite of anabolism. It is a set of exothermic reactions, i.e., degradation and oxidation processes accompanied by energy release.
Result of catabolism: breakdown of large high-molecular-weight organic substances into simpler compounds. The energy released in the process is then used by the body for various needs, including supplying plastic metabolism.
Interconnection of anabolism and catabolism
Metabolism is a unified mechanism in which plastic and energy metabolisms are inextricably linked.
- Dependence of anabolism on catabolism: Biosynthesis reactions (creation of new substances) are absolutely impossible without energy. The body obtains this energy precisely during energy metabolism (degradation) reactions.
- Dependence of catabolism on anabolism: In turn, dissimilation (degradation) reactions cannot proceed spontaneously at the required rate—they require specific catalysts, which are enzymes. These protein enzymes are formed exclusively through plastic metabolism reactions.
Briefly: answers to topical questions
What processes belong to catabolic reactions in humans?
Catabolic reactions (energy metabolism, dissimilation) include processes of degradation and oxidation of high-molecular-weight substances into simpler ones. According to sources, the following catabolic processes occur in the body:
- Glycolysis (glucose breakdown);
- Glycogen breakdown;
- Lipolysis (fat breakdown);
- Proteolysis (protein breakdown);
- Ketogenesis;
- Krebs cycle (tricarboxylic acid cycle);
- Oxidative phosphorylation (respiratory chain).
What are the main stages of energy metabolism (catabolism) in the cell?
Energy metabolism in the cell is divided into the following main stages:
- Glycolysis — occurs in the cell cytoplasm;
- Krebs cycle (tricarboxylic acid cycle) — occurs in the mitochondrial matrix;
- Respiratory chain (electron transport chain) — takes place on the cristae of the inner mitochondrial membrane (oxygen stage).
In the form of which high-energy compounds is the energy released during catabolism stored?
According to sources, the energy released during catabolism is stored in the high-energy bonds of ATP. At certain stages, it is also temporarily concentrated in the high-energy anhydride bond of 1,3-bisphosphoglycerate; GTP (ATP) is formed in the citrate cycle.
Which human hormones predominantly stimulate anabolic processes?
According to sources, anabolic processes in the body are stimulated by:
- Insulin — the absorptive period is characterized by anabolic processes under the influence of insulin; it enhances glucose transport, glycolysis, glycogen synthesis, lipogenesis, and protein synthesis.
- Growth hormone (GH, somatotropin) — acts via somatomedins (IGFs), which are the main mediators of the anabolic action; enhances tissue growth and protein synthesis.
In which cell organelles do the main catabolic reactions with oxygen oxidation take place?
The main catabolic reactions with oxygen oxidation take place in mitochondria. Aerobic cellular respiration is localized in these semi-autonomous organelles. The Krebs cycle occurs in the mitochondrial matrix, and the respiratory chain enzymes ensuring oxidative phosphorylation and oxygen-based degradation of organic substances are located on the folds of the inner membrane (cristae).
What are the end products of carbohydrate and lipid catabolism in the body?
According to sources, during complete aerobic catabolism of carbohydrates, the end products are CO₂ and H₂O: during aerobic respiration, oxygen is consumed, while carbon dioxide and water are released. Under anaerobic conditions, lactate may form during glycolysis. For lipids, the sources directly name lipolysis and fatty acid oxidation, but the end products of their catabolism are not specified.
Class and exam questions
What is the main property of living organisms?
The primary property of living systems is the continuous exchange of matter and energy with the environment, characterizing organisms as open biological systems.
What is the difference between anabolism and catabolism?
Anabolism consists of endothermic reactions of biosynthesis of complex substances from simple ones with energy consumption. Catabolism consists of exothermic reactions of complex substance degradation with energy release.
How are plastic and energy metabolism interrelated?
Plastic metabolism reactions require energy, which is released during energy metabolism. At the same time, energy metabolism is impossible without enzymes synthesized during plastic metabolism.
Which processes belong to assimilation?
Assimilation (anabolism) includes biosynthetic reactions, for example: protein synthesis, glycogen synthesis, photosynthesis, and chemosynthesis.
What else to study on this topic
- Mechanisms of metabolic exchange with the environment
- Stages and significance of protein synthesis
- The role of glycogen in plastic metabolism
- Photosynthesis and chemosynthesis: similarities and differences
- The nature of enzymes and their role in dissimilation
- Energy storage during the breakdown of macromolecular substances
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