Q.Define metabolism.
Concept understanding — Characteristics of Life, Study Branches and Nomenclature
This concept ties together the basic criteria used to recognise something as "alive" with the vocabulary taxonomists use to name and study it.
Metabolism and growth are used together as the working definition of life: metabolism is the continuous set of chemical reactions (build-up and breakdown) occurring inside a cell, while growth in a living thing happens from the inside, by the addition of new cells and cytoplasm (intussusception), unlike the purely surface-deposition growth (accretion) seen in non-living objects such as crystals. Biogenesis — life only from pre-existing life — replaced the older belief in spontaneous generation.
Several specialised branches of biology feed evidence into classification: histology (microscopic tissue structure), embryology (development from egg to adult, a rich source of relationship evidence because early developmental patterns are conservative), ethology (behaviour), and palaeontology (fossil evidence of past life). Zoos contribute living reference material for morphology and behaviour, while museums and herbaria hold permanently preserved specimens using fluid preservation, dry preservation, or taxidermy.
Naming follows the binomial system (Genus + species) with an optional third, trinomial name for a subspecies; tautonymy is when the genus and species names are identical (allowed in zoology, not in botany); and the ICZN is the rulebook that keeps every animal name unique and stable worldwide.
[!TLDR] Metabolism is the sum of all chemical reactions occurring inside a living cell.
[!ANSWER] Metabolism is the sum total of all the biochemical reactions (both the breakdown of molecules for energy — catabolism, and the building of complex molecules — anabolism) that occur continuously inside a living cell or organism, for as long as it is alive.
[!ANSWER] Metabolism is the sum total of all the biochemical reactions (catabolism and anabolism) occurring inside a living cell or organism.
Every living cell is a site of uninterrupted chemical activity. Catabolic reactions break down complex molecules into simpler ones, releasing usable energy, while anabolic reactions use that energy to build up complex molecules (proteins, nucleic acids, lipids) needed for the cell's structure and function. This constant chemical turnover is a defining feature of a living system — it is present in every cell, at every moment the organism is alive, and it stops only at death.
Metabolism is used, along with growth, as one of the two working criteria for recognising life. However, it is worth noting that isolated enzymes taken out of a cell can also catalyse a biochemical reaction in a test tube (in vitro), so metabolism by itself is a necessary but not a fully sufficient test for "life" — it must be considered together with growth (see the next question) for a workable definition.
[!ANSWER] Metabolism is the sum total of all the biochemical reactions (catabolism and anabolism) occurring inside a living cell or organism — a continuous, uninterrupted process that stops only when the organism dies.
- Students often define metabolism only as "energy release", forgetting that anabolic (building-up) reactions are equally part of metabolism.
- Confusing metabolism (a process) with growth (a consequence/outcome) — the two are related but distinct criteria for life.
- CBSE 2025Set ANNUAL2 marksQ.What in meant by tautonymy? Give two examples.
›Reveal solutionSolution
Tautonymy is the use of the same word for both the genus and the species name of an animal, as in Naja naja and Rattus rattus.
Explanation:
- In binomial nomenclature every organism has a two-word scientific name - the first word is the genus and the second is the species.
- When the GENERIC name and the SPECIFIC name are exactly the same word, the condition is called TAUTONYMY.
- Tautonymy is permitted in zoological nomenclature (but not in botanical nomenclature).
Examples:
-
Naja naja (Indian cobra)
-
Rattus rattus (house rat)
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Axis axis (spotted deer)
✓Final answerTautonymy is the practice in which the generic and specific names of an organism are identical (the same word). Examples: Naja naja (Indian cobra) and Rattus rattus (house rat).
- CBSE 2024Set ANNUAL2 marksQ.What is meant by tautonymy? Give two examples.
›Reveal solutionSolution
Tautonymy means the genus name and the species (specific) epithet of a scientific binomial are the same word repeated twice.
In binomial nomenclature (Linnaean system), every organism is given a two-part Latinised name: the first word is the genus and the second the species (specific epithet). When both parts of this name are identical, the name is said to show tautonymy, and such a name is called a tautonym.
This convention is permitted under the International Code of Zoological Nomenclature (ICZN), so tautonyms are common among animal names, but they are not permitted under the International Code of Botanical Nomenclature (ICBN/ICN) - so no plant scientific name is ever a tautonym.
Examples:
- Naja naja - the Indian cobra.
- Rattus rattus - the common house rat.
(Other well-known examples include Bison bison, the American bison, and Gorilla gorilla, the western gorilla.)
✓Final answerTautonymy is when the generic and specific names in a binomial are identical, e.g. Naja naja (Indian cobra) and Rattus rattus (house rat) - allowed under the zoological code (ICZN), not under the botanical code.
- CBSE 2023Set ANNUAL2 marksQ.What is meant by tautonymy? Give two examples.
›Reveal solutionSolution
Tautonymy is the use of the same word for both the genus name and the species name of an animal, as in Naja naja and Rattus rattus.
Explanation:
- In binomial nomenclature every organism is given a two-word scientific name - the first word is the genus (generic name) and the second is the species (specific name).
- Usually these two words are different. When the GENERIC name and the SPECIFIC name are exactly the same word, the condition is called TAUTONYMY.
- Tautonymy is allowed in zoological nomenclature (but not in botanical nomenclature).
Examples:
-
Naja naja (Indian cobra)
-
Rattus rattus (house rat)
-
Axis axis (spotted deer / chital)
✓Final answerTautonymy is the practice in which the generic name and the specific name of an organism are identical (the same word). Examples: Naja naja (Indian cobra) and Rattus rattus (house rat).
- CBSE 2022Set ANNUAL2 marksQ.What does ICZN stand for?
›Reveal solutionSolution
ICZN (International Code of Zoological Nomenclature) is the rule-book, maintained by the International Commission on Zoological Nomenclature, that standardises how animal species are scientifically named so that every animal has one valid, universally recognised name.
Taxonomists in different countries and languages describe new species independently. Without a shared set of rules, the same animal could end up with several different scientific names, or two different animals could accidentally be given the same name, causing confusion in research and communication. To prevent this, the International Commission on Zoological Nomenclature drew up a formal code — the International Code of Zoological Nomenclature (ICZN).
The ICZN lays down rules for:
- The correct formation of binomial/trinomial scientific names.
- The Principle of Priority — the first validly published name for a taxon takes precedence over later synonyms.
- What counts as valid publication of a new species description.
- Procedures for resolving naming disputes (homonyms and synonyms) through the Commission.
By following the ICZN, biologists anywhere in the world can be certain that a given scientific name refers to one, and only one, animal species.
✓Final answerICZN stands for the International Code of Zoological Nomenclature — the internationally accepted rules, administered by the International Commission on Zoological Nomenclature, that standardise the scientific naming of animals.
- CBSE 2022Set ANNUAL2 marksQ.What is meant by tautonymy? Give two examples.
›Reveal solutionSolution
Tautonymy means the genus name is repeated as the species name in a binomial — permitted under the zoological code but not the botanical code.
Under the binomial nomenclature system (Linnaeus), every scientific name has two parts: a genus name and a specific epithet, e.g. Homo sapiens. Tautonymy is the special case where both parts of the name are identical — the specific epithet simply repeats the generic name.
This is allowed under the International Code of Zoological Nomenclature (ICZN), so many well-known animals carry tautonymous names, but it is not permitted under the International Code of Nomenclature for algae, fungi and plants — no plant name may be a tautonym.
Two examples:
- Naja naja — the Indian cobra.
- Rattus rattus — the common house rat.
(Other valid examples include Bubo bubo, the Eurasian eagle-owl, and Vulpes vulpes, the red fox.)
✓Final answerTautonymy is when the generic and specific names of a binomial are identical, e.g. Naja naja (Indian cobra) and Rattus rattus (house rat) — allowed in zoological nomenclature but not botanical nomenclature.
- CBSE 2022Set ANNUAL2 marksQ.What is biogenesis?
›Reveal solutionSolution
Biogenesis states that life comes only from pre-existing life, disproving the older idea of spontaneous generation (abiogenesis of complex organisms from non-living matter).
Before the mid-19th century, many believed in spontaneous generation (abiogenesis) — the idea that living organisms such as maggots or microbes could arise directly from non-living matter (e.g. rotting meat, broth). This idea was progressively disproved:
- Francesco Redi (1668) showed that maggots appear on meat only when flies can lay eggs on it; meat in a sealed/gauze-covered jar (excluding flies) produced no maggots.
- Lazzaro Spallanzani further showed that boiled, sealed broth remained free of microorganisms.
- Louis Pasteur (1861), using his famous swan-necked flask experiments, conclusively demonstrated that microorganisms in broth arise only from microbes already present in the air/dust, not spontaneously from the broth itself — sterilised broth in a swan-necked flask (which excludes dust/microbes but allows air in) stayed sterile indefinitely, while broth in an open or straight-necked flask became contaminated.
These experiments established the principle of biogenesis — summed up in Latin as 'Omne vivum ex vivo' ('all life from life') — meaning every living organism originates from a pre-existing living organism (parent), never from non-living matter.
✓Final answerBiogenesis is the principle, established by Pasteur's experiments (building on Redi and Spallanzani), that life arises only from pre-existing life ('omne vivum ex vivo') and never spontaneously from non-living matter.
- CBSE 2020Set ANNUAL2 marksQ.What is meant by Tautonymy? Give two examples.
›Reveal solutionSolution
Tautonymy means the genus name and the species name of a binomial are identical words, e.g. Naja naja.
In binomial nomenclature every organism is given a two-part scientific name: the first word is the genus and the second is the specific epithet. When both words are exactly the same, the name is called a tautonym, and the phenomenon is called tautonymy.
Tautonymy is permitted under the International Code of Zoological Nomenclature (ICZN) but is not allowed under the International Code of Botanical Nomenclature (ICBN) — so true tautonyms occur only in animal names, never in plant names.
Examples:
-
Naja naja — the Indian cobra
-
Rattus rattus — the common house rat
(Other well-known examples include Bison bison, the American bison, and Gorilla gorilla, the western gorilla.)
✓Final answerTautonymy is when the genus and species names of a binomial are identical, e.g. Naja naja (cobra) and Rattus rattus (rat).
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