NEET Biology The Living World and Taxonomy Notes

NEET Biology notes on Chapter 1, The Living World and Taxonomy, covering the characteristics of living things, levels of biological organisation, achievements of biologists from ancient times to the 21st century, branches and careers in biology, myths in biology, misuse of biology, and the taxonomy of species, nomenclature, classification systems, taxonomic categories and taxonomic aids.

CHAPTER 1: THE LIVING WORLD AND TAXONOMY

PART I: THE LIVING WORLD AT A GLANCE

Living and Non-Living

While going through the chapter, pay special attention to the following.
Terms and definitions: 1. Bioterrorism, 2. Amniocentesis, 3. Pasteurization, 4. Genome, 5. Palaeontology, 6. Serendipity.
Theories: 1. Theory of Pangenesis, 2. Theory of Germ plasm, 3. Cell theory, 4. Germ theory of diseases, 5. Theory of natural selection.
Differences: 1. Living and non-living, 2. Apiculture and sericulture, 3. Biomedical engineering and genetic engineering, 4. Anabolism and catabolism, 5. Bioinformatics and computer simulation, 6. Ectotherms and endotherms, 7. Homeostasis and haemostasis.
Books: 1. Philosophie Zoologique, 2. Micrographia, 3. Systema Naturae, 4. Origin of Species.
Biologists: 1. Alexander Fleming, 2. Watson and Crick, 3. N. E. Borlaug, 4. William Harvey, 5. Ian Wilmut, 6. H. G. Khorana, 7. Carolus Linnaeus, 8. Stanley Cohen.
Achievements of biologists up to the 19th century; important achievements in the 20th century; important achievements in the 21st century; biological study and its important branches; scope of biology; myths, disbeliefs or misconceptions in biology and their reality; misuse of biology; careers in biology; types of species; important terms; history of classification; basic categories of hierarchy; concept of species; types of classification; codes of nomenclature; taxonomic aids.

Check Point (p. 4)
1. Fill in the blanks with suitable words:
(a) ................ is known as the Darwin of 20th century.
(b) In unicellular organisms the ................ is synonymous with growth.
(c) The sum of all chemical reactions occurring in our body is called ................ .
(d) ................ is the only organism that is aware of one self.
(e) The number of species that are known and described ranges between ................ .
(f) ................ occurs in both living and non-livings, but in living it is from inside.
(g) The poikilotherms are also known as ................ animals.
(h) Tuna fish, though cold blooded, is ................ .
(i) A group of interbreeding individuals is called ................ .
(j) ................ is known as the father of zoology.

There is no clear-cut distinction between living and non-living things. Organisms like viruses are non-living by themselves but become active and multiply when they are inside living cells. They are neither plants nor animals, but they have hereditary material of their own. Prions do not even have hereditary material, and they propagate diseases like kuru and mad cow disease.

Living organisms occur in almost every habitat on earth, from cold mountains to hot springs. A wide range of living organisms can be found in fresh or marine water bodies and forests. Living forms, compared with non-living things, have some fundamental characteristics. They are defined as "self-replicating, self-evolving, self-regulating interactive systems capable of responding to external stimuli". All living organisms, past, present and future, are linked to one another by sharing a common genetic material.

Distinctive Characteristics of Living Forms

1. Growth
Increase in mass and increase in the number of individuals are twin characteristics of growth. Multicellular organisms grow by cell division. Animals grow up to a certain age, whereas plants grow throughout their life. Cell division also occurs to replace lost cells. Unicellular organisms also grow by cell division, but there it is a type of reproduction. In multicellular organisms, growth and reproduction are mutually exclusive events. Non-living things such as mountains, sand mounds and snow also grow in mass, but this growth is by accumulation of material on the surface, not from inside as in animals. So growth alone cannot be considered a defining property of living organisms unless it is well specified.

2. Reproduction
Living organisms reproduce asexually as well as sexually to multiply their number. Fungi reproduce asexually by spore formation. Lower organisms like Hydra and yeast reproduce by budding. In Planaria (flatworm), there is fragmentation and regeneration of lost parts. In unicellular forms, reproduction is synonymous with growth. Some living organisms do not reproduce, for example the mule, the worker honey bee and an infertile human, so reproduction, like growth, cannot be taken as a defining characteristic. Non-living objects, however, are not capable of reproducing or replicating themselves.

Fig. 1.1 (a) Budding in Hydra; (b) Fragmentation in Planaria

(a) Budding in Hydra: labels Parent and Bud; scale 0.5 mm. (b) Fragmentation in Planaria: the worm fragments into pieces, and each piece regenerates into a complete worm.

3. Metabolism
All living organisms are constantly making or breaking biomolecules. These conversions are due to chemical reactions, and the sum total of all such chemical reactions occurring in the body is called metabolism. Metabolic reactions can be anabolic (constructive) or catabolic (destructive).
Catabolism: energy is released by the breakdown of complex materials into simpler ones. Cellular respiration, the breaking down of glucose into carbon dioxide and water to release energy, is an example.
Anabolism: complex material is synthesised from simpler ones. Photosynthesis, in which glucose or starch is synthesised from carbon dioxide and water, is an example.
Each metabolic pathway in the cell is tightly regulated by enzymes, both activators and inhibitors. Non-living objects do not exhibit metabolism. Isolated metabolic reactions in vitro do not make things living.

4. Consciousness
All living organisms can sense their surroundings and respond to environmental stimuli. Stimuli can be physical, chemical or biological. From lower to higher organisms there are various types of sensory structures. Photoperiod affects seasonal breeders, both plants and animals. All organisms are aware of their surroundings. Human beings are the only organisms who are aware of themselves, and so have self-consciousness. Such self-consciousness is lacking in patients in coma and in brain-dead patients.

5. Cellular Organisation
All organisms, from prokaryotes to the most complex eukaryotes, have cellular organisation. The cell may be simple or highly specialised for its function. Such organisation is not shown by non-living objects, so cellular organisation of the body is the defining feature of all living forms. There is great diversity (biodiversity) in the number and types of organisms on earth.

6. Homeostasis
Homeostasis is the maintenance of constancy in internal conditions (steady state), different from the environment. All organisms maintain within narrow limits the levels of salts, glucose, carbon dioxide, oxygen, calcium, etc. in the intercellular matrix. Homeostasis is the fundamental property of living beings.
Connecting concept: homeostasis is different from haemostasis. In haemostasis, blood flow stops either by clotting or by constriction of blood vessels, or by other means.

Ectotherms and Endotherms
Most lower vertebrates (fishes, amphibians and reptiles) lose most of their heat energy to the environment. These vertebrates are called ectotherms. They depend on the environment for temperature regulation. At low ambient temperature their body temperature also drops, so they are called cold-blooded animals or poikilotherms.
Higher vertebrates, birds and mammals, have developed special devices to retard heat loss to the environment. Their body temperature remains nearly constant and is generally higher than the surroundings. These animals are called warm-blooded animals or homeotherms, and since they retain thermal energy in the body they are also called endotherms.
Connecting concept: some fishes, such as tuna and sword fish, have insulating devices to prevent heat loss and retain heat in the body. Such fishes, unlike others, are endotherms.
In mammals, when the surrounding temperature is low, the peripheral blood vessels constrict to prevent heat loss, and the blood is diverted to the deeper parts of the body. When the ambient temperature is higher, the superficial blood vessels dilate and a part of the heat is lost by radiation.
Sensory receptors (modified dendrites of neurons) perceive coldness (Krause end bulbs) and hotness (end bulbs of Ruffini). Information from these receptors reaches the hypothalamus, the thermoregulatory centre of the brain. Body temperature can be decreased by vasodilatation of superficial blood vessels and by sweating. Body temperature can be increased by vasoconstriction of superficial blood vessels and by shivering (contraction of skeletal muscles). Because the change in body temperature is in the reverse direction to the change in ambient temperature, this control system is called a negative feedback loop.

7. Adaptations
Adaptations are the results of natural selection that make organisms better suited to their environment. Adaptations may be structural, physiological or behavioural.
Examples: birds use wings for flight (volant adaptations); spiders design webs to trap flying insects, their prey; night-blooming flowers are white and emit scent to attract pollinating insects; some desert plants are leafless and conserve moisture; hummingbirds have extremely narrow and long beaks and, while hovering, suck nectar from flowers that have no landing platforms; certain orchids resemble the shape, colour and odour of the females of certain bees or flies, and male bees or flies attempt to copulate with them and transfer pollen from one flower to another.
Short-term adaptations persist for a short duration and disappear when the stimulus is removed, for example darkening of skin on sun exposure, rosy cheeks in hilly people, turning of shoots towards light, low metabolic rate in animals during hibernation, dormancy in seeds and geotropism in plants.
Long-term adaptations are permanent and persist even in the absence of the stimulus, for example beaks, claws and feathers in birds, the heel in human beings, use of the tail as a fifth limb in kangaroos, the opposable thumb in human beings, scent in night-blooming flowers, and the need for mammalian blood protein for egg laying in Anopheles mosquitoes.

Death
Organisms reproduce to compensate for death or loss of life. When organisms die, micro-organisms decompose the body. The elements that make up the body are freed and returned to the ecosystem. Such cycling of elements between living and non-living maintains the balance in nature.
Advantages of death:
1. It avoids overcrowding and maintains homeostasis.
2. It returns minerals to the soil and maintains balance.
3. Cellular death is essential for making the skin germ-proof.
4. Cellular death is essential for the metamorphosis of a tadpole.
Stages of death:
1. Clinical death: stoppage of heart beat and breathing.
2. Biological death: death of cells and tissues.
Removal of organs, if needed for transplantation, is done after clinical death but before biological death.

Biological Organisation

Biological organisation starts at the sub-microscopic molecular level and ends with the ecosystem and the biosphere. The atom is the lowest unit at the molecular level, whereas the cell is the lowest unit at the organism level. The levels of organisation are:
Sub-microscopic level: atoms, then molecules.
Microscopic level: cells, then tissues, then organs.
Visible level: organism, then species (a group of interbreeding individuals), then community (populations of different species), then ecosystem (interaction between living and non-living components), then biome, then biosphere (lithosphere + hydrosphere + atmosphere).

[Figure: Levels of biological organisation shown as a stack, from bottom to top: Atoms, Molecules, Cells, Tissues, Organs, Organism, Species, Community, Ecosystem, Biome, Biosphere (Lithosphere + Hydrosphere + Atmosphere).]

Important Achievements Made by Scientists/Biologists up to the 19th Century

1. Aristotle (384 BC - 322 BC): a Greek philosopher and student of Plato. He classified organisms into a hierarchy based on complexity of structure and function, called Scala Naturae (the ladder of life). He wrote Historia Animalium and De Generatione Animalium. He is known as the father of biology, zoology and embryology.
2. Andreas Vesalius (1514-1564): a Belgian scientist known as the father of anatomy. He wrote De Humani Corporis Fabrica (the structure of the human body).
3. William Harvey (1578-1657): a British scientist who discovered blood circulation. His monograph was named Anatomical Exercise on the Motion of the Heart and Blood. He is known as the father of blood circulation. He also studied reproduction and development in the chick.
4. Robert Hooke (1635-1703): a British scientist who first coined the term cellulae (cell) in 1665 by observing a slice of cork under a self-made simple microscope. His book was Micrographia.
5. Antony van Leeuwenhoek (1632-1723): a Dutch cloth merchant who turned into a scientist. He invented a simple microscope and studied living cells. He drew the diagram of bacteria and studied Euglena, sperms, blood corpuscles and the compound eyes of insects.
6. Carolus Linnaeus (1707-1778): a Swedish naturalist. He published Species Plantarum (6000 species of plants) and Systema Naturae (4000 species of animals) in 1758. He reported binomial nomenclature in Philosophia Botanica in 1751 for naming plants and animals.
7. Georges Leopold Cuvier (1769-1832): a French palaeontologist. He rejected Aristotle's Scala Naturae, studied fossils and laid the foundation of palaeontology. He is known as the father of modern palaeontology. He also studied comparative anatomy.
8. Jean Baptiste Lamarck (1744-1829): a French naturalist. He was the first to discard the idea of fixity of species. He is known as the father of evolutionary theories. He wrote Philosophie Zoologique in 1809. He introduced the term "biology" along with Treviranus.
9. Robert Brown (1773-1858): discovered Brownian movement in cytoplasm (1828) and the nucleus in the cell.
10. Matthias Schleiden (1804-1881): a German botanist who proposed the cell theory in 1838 on the basis of his study of plant tissues.
11. Theodor Schwann (1810-1882): a German zoologist who strengthened the cell theory in 1839 by his study of animal tissues.
12. O. Hertwig (1875): studied the fusion of nuclei during fertilisation. He proposed the protoplasmic theory to elaborate Schultze's hypothesis that protoplasm is the physical basis of life. He coined the term cytology.
13. Charles Robert Darwin (1809-1882): a British naturalist. His book The Origin of Species by Means of Natural Selection was published in 1859. He is called the Newton of biology. He proposed the theory of pangenesis to explain inheritance in On the Variation of Animals and Plants under Domestication (1868).
14. Rudolf C. Virchow (1858): proposed "Omnis cellula e cellula", meaning new cells arise from pre-existing cells. He also suggested that disease is the pathological condition of cells.
15. Louis Pasteur (1822-1895): a French scientist who proved that fermentation is caused by living organisms (yeast and bacteria). He established the germ theory of diseases. He discovered a vaccine against anthrax (caused by Bacillus anthracis in cattle). He discarded the spontaneous theory of origin of life. He proposed pasteurization for sterilisation (killing of germs).
16. Ernst Haeckel: introduced two kingdoms, Monera and Protista. He also coined and fully defined the term "ecology".
17. Gregor Johann Mendel (1822-1884): an Austrian monk who discovered the principles of inheritance from his work on Pisum sativum, published in 1866. He is known as the father of genetics.
18. August Weismann (1834-1914): a German biologist who rejected Lamarck's concept of inheritance of acquired characters and Darwin's theory of pangenesis, with the discovery of the theory of germ plasm in 1892.

Important Achievements Made by Scientists/Biologists in the 20th Century

1. Hugo de Vries (1900): a Dutch geneticist who rediscovered Mendel's laws with Tschermak (Austrian) and Correns (German). He also proposed the theory of mutation.
2. Walter Sutton (1904): an American geneticist who discovered the chromosomal basis of heredity.
3. William Bateson (1909): a British biologist who introduced the term "genetics" and discovered linkage.
4. T. H. Morgan (1910): an American geneticist who discovered sex-linked inheritance and described linkage and crossing over.
5. Alexander Fleming (1928): a Scottish bacteriologist who discovered penicillin, an antibiotic from Penicillium notatum, which contaminated a culture of Staphylococcus bacteria. Penicillin was the first antibiotic used in the Second World War.
6. Oswald Theodore Avery (1944): an American bacteriologist who discovered that genes are composed of DNA.
7. James Watson and Francis Crick (1953): discovered the double helical structure of DNA.
8. H. G. Khorana, Robert Holley and Marshall Nirenberg (1968): Khorana synthesised a string of nucleotides in the laboratory (the first man-made gene). The three scientists shared the Nobel Prize for their work on the genetic code and protein synthesis.
9. Norman E. Borlaug (1970): associated with the Green Revolution and won the Nobel Prize.
10. Stanley Cohen and Herbert Boyer (1973): American biochemists who discovered recombinant DNA (rDNA) technology, a breakthrough for modern biotechnology.
11. Ian Wilmut and Campbell (1996): Scottish embryologists who produced the first live clone of a sheep, named Dolly.
12. Human Genome Project: launched in 1990 by the US Department of Energy and the National Institutes of Health. In 2001 they identified all the approximately 25,000 to 30,000 (3 × 10⁴) genes in human DNA, which consists of 3 billion (3 × 10⁹) base pairs.

Important Achievements Made by Scientists/Biologists in the 21st Century

1. Paul C. Lauterbur (American) and Sir Peter Mansfield (British), 2003: made discoveries concerning MRI and were awarded the Nobel Prize in Physiology or Medicine.
2. Barry J. Marshall and J. Robin Warren (Australians), 2005: discovered the role of Helicobacter pylori in gastritis and peptic ulcer. Nobel Prize in Physiology or Medicine.
3. Andrew Z. Fire and Craig C. Mello (Americans), 2006: discovered RNA interference (gene silencing by double-stranded RNA). Nobel Prize in Physiology or Medicine.
4. Harald zur Hausen (German), Françoise Barré-Sinoussi and Luc Montagnier (French), 2008: made discoveries regarding human papilloma virus and human immunodeficiency virus. Nobel Prize in Physiology or Medicine.
5. Osamu Shimomura (Japanese), Martin Chalfie and Roger Y. Tsien (Americans), 2008: discovered the green fluorescent protein. Nobel Prize in Chemistry.
6. Venkatraman Ramakrishnan (Indian), Thomas A. Steitz (American) and Ada E. Yonath (Israeli), 2009: studied the structure and functions of ribosomes. Nobel Prize in Chemistry.
7. Bruce A. Beutler (American), Jules A. Hoffmann (Luxembourger) and Ralph M. Steinman (Canadian), 2011: made important discoveries regarding innate and adaptive immunity. Nobel Prize in Physiology or Medicine.

Biological Study and Its Important Branches

Biology is divided into two main branches, zoology and botany. The science of microbiology was created by the invention of the microscope in the 16th century. Many animals and plants are arranged or classified on the basis of evolutionary relationships. International codes of classification exist for animals, plants and bacteria.

Branches and their study:
Aquaculture: production of useful fauna and flora, such as algae, fishes, prawns and pearl oysters, at commercial level using small and large water bodies.
Biochemistry: the study of the chemistry of biological processes in living organisms; also called physiological chemistry or biological chemistry.
Biophysics: application of the tools, techniques, methods and principles of physics to the study of biological processes.
Cell biology: the study of the life processes of cells and their correlation with cell structure; it depends mainly on biochemical techniques.
Cryopreservation (cryobiology): preservation of living forms at very low temperature, or the effect of low temperature on living forms.
Cytology: the study of the structure and composition of cells.
Demography: statistical study of population dynamics.
Dysteleology: the study of rudimentary organs.
Ecology: the study of the relationship of organisms to their physical environment and to one another. Auto-ecology studies individual organisms or a single species; synecology studies groups of organisms.
Embryology: the study of individual development (ontogeny) from egg to hatching or birth. Developmental biology covers development up to sexual maturity or adulthood.
Entomology: the study of insects.
Ethnology: the study of human races.
Ethology: the study of animal behaviour in relation to body functioning, ecology and evolutionary aspects.
Evolutionary biology: the study of changes in living organisms with the passage of time.
Exobiology: the search for life outside the earth, within the solar system.
Fisheries: rearing, harvesting and marketing of commercially important aquatic fauna. Important fisheries are molluscan, crustacean, sponge and estuarine fisheries; inland fisheries are in fresh water.
Genetics: the study of the mechanism of inheritance and maintenance of hereditary characters.
Gerontology: the scientific study of ageing or senescence. Its foundation was laid by Vladimir Korenchevsky.
Histology: the study of the structural organisation of living beings at the tissue level. The microtechnique used for histology has these steps: 1. fixation of tissue (to maintain cell architecture or stabilise proteins); 2. dehydration (removal of water to prevent decomposition); 3. paraffin embedding; 4. slicing or sectioning with a microtome; 5. dewaxing; 6. staining; 7. mounting.
Ichthyology: biological study of fishes.
Karyology: the study of the cell nucleus (karyosome).
Limnology: the study of fresh water bodies (ecosystems), especially lakes.
Marine biology: the study of ocean (marine) animals and plants and their ecological relationships.
Molecular biology: the study of the molecular organisation (inorganic and organic molecules) in the cells of organisms. The term was first given by the British scientist W. T. Astbury (1898-1961).
Morphology: the study of body structure. Internal morphology is also called anatomy.
Myrmecology: the scientific study of ants.
Oncology: the study of cancer.
Ophidology (serpentology): the study of snakes. The study of lizards is called saurology.
Palaeontology: the study of fossils, which are preserved remains or traces of organisms that lived in the past and are now extinct.
Phylogeny: the study of evolutionary development or racial history of a group.
Physiology: the study of the functions of body systems of animals and plants, covering vital activities at the cellular, tissue and organ level.
Pisciculture: rearing and management of fishes at commercial level.
Serology: the study of antigens, antibodies and serum.
Splanchnology: the study of visceral organs, which lie beneath the splanchnic mesoderm.
Systematics: the study of the diversity and evolutionary relationships of organisms, based on comparative study of different fields of biology.
Taxonomy: the scientific study of the principles and procedures of classification.

(The other branches of biology have been discussed chapter wise with running text.)

Check Point (p. 9)
1. Can you differentiate between:
(a) Ethology and Ethnology
(b) Physiotherapy and Occupational therapy
(c) Biotechnology and Biomedical engineering
(d) Silviculture and Sericulture
(e) Homeostasis and Haemostasis

Scope of Biology

1. Food storage, cancer, population explosion, poverty, AIDS and global warming are burning issues related to human welfare.
2. Study of medicinal plants has helped in the production of quinine, penicillin, nux vomica, antibiotics and other drugs for serving mankind.
3. Study of classification, life history, vectors and diseases has helped in combating human miseries.
4. Knowledge of genetics has helped to minimise hereditary diseases and genetic disorders.
5. New courses and specialisations have emerged, such as horticulture, jute technology, fisheries, tea technology, apiculture, sericulture, poultry farming and aquaculture. These can help develop the national economy.
6. Genetically modified (GM) crops are being developed to solve the problem of food shortage.
7. Direction of biotechnology, conservation of biodiversity, maintenance of the environment and human welfare are in the hands of biologists. Biodiversity, including wildlife, is immensely important for human existence.

Myths, Disbeliefs or Misconceptions in Biology and Their Reality

Misuse of Biology

1. Amniocentesis: amniotic fluid contains foetal skin cells and amniocytes of the amniotic membrane. These cells are cultured for chromosomal study to detect foetal abnormality. The technique is now also used for sex identification of the embryo or foetus (between 1½ and 2½ months), and the foetus is aborted if it is found to be female. This is a misuse of a biological technique.
2. Bioweapons: development of antibiotic-resistant micro-organisms. Spores of the anthrax bacterium (Bacillus anthracis) have been produced and stored to keep them viable for long periods and used as a weapon of bioterrorism. Other similar diseases on an epidemic or endemic scale include plague and smallpox.

Careers in Biology

1. Professional Courses

2. Vocational Courses

PART II: TAXONOMY

While going through the chapter pay special attention to the following.
Terms and definitions: 1. Species, 2. Binomial nomenclature, 3. Allochronic species, 4. Biosystematics, 5. Taxon, 6. Sibling species, 7. Cladogram.
Differences: 1. Sympatric and allopatric species, 2. Monotypic and Polytypic species, 3. Taxonomy and Systematics, 4. α and β-taxonomy, 5. Phenetics and Cladistics, 6. Typological and Biological species, 7. Periodical and Manual.
Taxonomists / Biologists: 1. Carolus Linnaeus, 2. Whittaker, 3. John Ray, 4. Julian Huxley.
Books: 1. Historia Animalium, 2. Systema Naturae, 3. Susruta Samhita, 4. Historia Plantarum.

More than 1.2 million animal species, and more than 0.5 million plant species have been identified and described so far.

The purpose of biological classification is to name and remember the organisms.

Species – It is the basic unit of classification. According to the 'Biological concept of species', a species can be defined as a group of natural populations whose members can interbreed among themselves and are reproductively isolated from other such groups.

Check Point (p. 13)
1. Can you differentiate between:
(a) Sibling and sympatric species
(b) Allochronic and synchronic species
(c) Taxonomy and Systematics
(d) Phenetics and Cladistics
(e) Natural and artificial system of classification
(f) Chemotaxonomy and Biochemical taxonomy

Types of Species and Classification

1. Morphological/Typological/Taxonomic species and Biological species: taxonomic species are identified on the basis of morphological characters, while biological species are identified on the basis of interbreeding. The term biological species is not applicable to fossils or asexually reproducing organisms.
2. Static species and Non-static species: species were thought to be unchangeable (static) before Lamarck. After Lamarck, species were considered non-static or dynamic.
3. Monotypic species and Polytypic species: monotypic species contain only one subspecies, while polytypic species contain many subspecies.
4. Allochronic and Synchronic species: allochronic species belong to different time periods, whereas synchronic species belong to the same time period.
5. Allopatric and Sympatric species: allopatric species occur in different geographical areas, whereas sympatric species occur in the same geographical area.
Sibling species or cryptic species: two different species which are morphologically identical or indistinguishable but are reproductively isolated, e.g. Drosophila pseudoobscura and D. persimilis.

Important Terms

Nomenclature: the process of giving scientific names (not vernacular or local names) to organisms.
Classification: the process of grouping animals and plants into convenient categories on the basis of certain observable traits.
Identification: determination of the correct position of an organism in the classification.
Taxonomy: the study of the process of classification.
Systematics: includes the identification, nomenclature and classification of organisms based on various parameters.
New systematics: systematic studies considering evolutionary relationships, including other branches such as molecular biology, cytology, genetics and biochemistry.

History of Classification

Hippocrates (460-377 BC): classified animals into various groups such as insects, fishes and birds.
Aristotle (384-322 BC): wrote Historia Animalium. Known as the father of zoology and biology. He classified animals on the basis of red blood into Anaima (animals without red blood) and Enaima (animals with red blood). Enaima was further divided into ovipara and vivipara.
Theophrastus (370-285 BC): a Greek naturalist and pupil of Aristotle. Known as the father of botany. He classified plants into trees, shrubs, under-shrubs and herbs, and described about 500 plants in Historia Plantarum.
John Ray (1686): a British botanist. He described 1800 plant and animal species in Historia Generalis Plantarum. He introduced the terms species, genus and family.
Carolus Linnaeus: a Swedish naturalist and father of taxonomy. He coined the terms "class" and "systematics". The term taxonomy was given by A. P. de Candolle. He published Systema Naturae, Genera Plantarum and Species Plantarum (1753). In Species Plantarum he classified 4000 species of plants on the basis of sexual characters (artificial system of classification). He proposed the Linnaean hierarchy with five taxa: class, order, genus, species and varieties.
Linnaeus's principles of binomial nomenclature were given in Philosophia Botanica (1751) and finally in Species Plantarum (1753) for plants, and in the 10th edition of Systema Naturae (1758) for animals. The law of priority for nomenclature is therefore applicable from 1753 for plants and from 1758 for animals.
Lamarck and Treviranus: introduced the term "Biology".
Cuvier: father of modern palaeontology. He also introduced the term "Phylum".
Ernst Haeckel (1868): suggested two new kingdoms, Monera and Protista.
Julian Huxley: introduced the term "New-systematics".
Ernst Mayr (1940): proposed the biological concept of species, on the basis of interbreeding.
Turrill: introduced the terms alpha-taxonomy and beta-taxonomy for classical systematics and new systematics respectively.
Copeland (1956): suggested four kingdoms: Monera, Protista, Animalia and Plantae.
Whittaker (1969): introduced the five-kingdom classification: Monera, Protista, Animalia, Plantae and Fungi.
Carl Woese et al.: created three monophyletic domains above kingdom level, Archaea, Bacteria and Eukarya, and introduced a six-kingdom classification on the basis of sequences of ribosomal RNA genes. Domain Archaea included the kingdom Archaebacteria. Domain Bacteria included the kingdom Bacteria. Domain Eukarya included four kingdoms: Protista, Animalia, Plantae and Fungi.

Check Point (p. 15)
1. Answer the followings:
(a) What is the basic unit of classification?
(b) Who coined the term Phylum?
(c) Who introduced 5-kingdom classification. Can you name 5-kingdoms?
(d) Name the taxon above kingdom level.
(e) Who wrote Historia Plantarum?
(f) Who is father of Taxonomy?
(g) For which organisms the Biological concept of species cannot be applied.
(h) What is holotype?

Basic Categories of Taxonomic Hierarchy

There are seven basic categories of hierarchy: 1. Kingdom, 2. Phylum (in animals) or Division (in plants), 3. Class, 4. Order, 5. Family, 6. Genus, 7. Species.
Other subcategories also exist, such as subphylum, subclass, suborder, subfamily and subspecies. The category (taxon) cohort is used by palaeontologists between class and order. Tribe has recently been introduced between subfamily and genus.

Please remember that:
i. two generic names in any kingdom cannot be the same;
ii. all organisms, in either the plant or animal kingdom, have species as the lowest category.

The term "taxon" is used to refer to any rank or level or category of the classification. Dogs, Carnivora, Mammals and Animals are all taxa at different levels of hierarchy. The term taxon for animals was given by Adolf Meyer (1926).

Species: the lowest category in the basic taxonomic hierarchy, and has the maximum common characteristics with other species under the same genus. In genus Panthera there are several species, such as tigris, pardus and leo.
Genus: an aggregate or group of closely related species. The generic names of Panthera, Felis, Homo and Canis are common examples. A genus has more common characteristics with other genera than the higher ranks.
Family: a group of closely related genera, with fewer common characteristics than a species or genus. Cats and dogs belong to families Felidae and Canidae respectively. The suffixes used for family, subfamily and tribe in animals are -idae, -inae and -ini respectively.
Order: a higher taxon and an assemblage of families having similar characteristics. Common characteristics are fewer than at family or genus level. Common mammalian orders are Primates (monkey, gorilla, human), Carnivora, Rodentia and Cetacea (whale and dolphin).
Class: a group of related orders. Lizards, birds and cattle belong to the classes Reptilia, Aves and Mammalia respectively.
Phylum: classes with similar features are grouped into a phylum in animals and a division in plants. Phyla share very few common characteristics with other phyla. Common characteristics of phylum Chordata are a dorsal tubular nervous system, a notochord and pharyngeal gill slits at some stage of the life cycle. Other phyla include Annelida, Arthropoda and Mollusca.
Kingdom: phyla are grouped into still broader categories called kingdoms, such as the animal kingdom and the plant kingdom.

As we move from lower to higher rank (species to kingdom), the number of common characteristics decreases. The lower the taxon, the more common characteristics it has; the higher the taxon, the fewer common features it has.

[Figure: vertical arrow diagram, bottom to top: Species → Genus → Family → Order → Class → Phylum or Division → Kingdom.]

Taxonomic categories of common animals

Rules of Nomenclature

1. In binomial nomenclature each scientific name has two components: i. the generic name (genus) and ii. the specific name or epithet (species).
2. The generic name begins with a capital letter, whereas the specific name begins with a small letter.
3. Both names are underlined separately if handwritten, or printed in italics, to indicate their Latin origin. Examples: Amoeba proteus, Panthera tigris, Homo sapiens, Pavo cristatus.
4. The first (generic) name is usually a noun, whereas the second (species) name is usually an adjective.
5. The scientific name is generally followed by the name (full or abbreviated) of the person who first described the species. Example: Homo sapiens Linnaeus 1758.
If the species is transferred to another genus after its first publication, or its generic name is changed, the first author's name is given in brackets. Example: Panthera leo (Linnaeus), because Linnaeus assigned the species leo to the genus Felis.
If the specific name is given in honour of a person, it ends in "i" if the person is male, or "ae" if the person is female. Example: Lumbricus friendi (after Mr R. H. Friend).
Tautonym: a binomial name in which the genus and species names are the same, e.g. Gorilla gorilla.
Trinomial nomenclature: includes genus, species and subspecies, and is applicable to animals only. Botanists do not recognise the subspecies level.

Concept of Species

1. Typological species concept
It is a simpler and widely accepted concept. All individuals of a species match the "type specimen" very closely. The type specimen used for nomenclature in this system is called the holotype. Other types of specimen are: paratype, isotype and lectotype. The isotype is a copy of the holotype. The paratype is cited with the original description but is neither the holotype nor the isotype. The lectotype is a specimen selected from the original material in the absence of a holotype.

2. Biological species concept
It is based on the interbreeding of members. It is not applicable to fossils or asexually reproducing organisms, as they cannot interbreed.

Types of Classification

1. Artificial system of classification: all taxonomists from Aristotle to Linnaeus classified organisms on the basis of external observable (morphological) characters such as floral structure (number of stamens), root modification and leaf venation. No weightage was given to natural or phylogenetic relationships. This system is based on one or a few superficial similarities and is arbitrary. It may also be based on the habit and habitat of organisms.
2. Natural system of classification: uses more characters and is based on natural affinities, using homology and comparative study. Bentham and Hooker used this system for angiosperms.
3. Numerical taxonomy (phenetics) or quantitative taxonomy: uses numerical methods to evaluate similarities and differences between species. It uses the maximum number of characters, giving equal importance and weightage to all of them. Sophisticated calculating machines and computers are used for statistical analysis. It was first attempted by Adanson (1763), so it is also known as the Adansonian system. Phenetics is considered a better classification because it uses a large number of comparative features.
4. Phylogenetic classification (cladistics): based on evolutionary relationships, using morphological characters and the origin and evolution of organisms. The family tree in this system is called a cladogram. This system led to the emergence of new systematics and biosystematics. It was proposed by Hutchinson. Adolf Engler and K. Prantl, both German botanists, published a phylogenetic system of classification in plants, considering monocots to be more primitive than dicot angiosperms. They published twenty volumes of classification (from algae to angiosperms) in Die Natuerlichen Pflanzenfamilien.
5. Karyotaxonomy: uses information such as chromosome number, structure, size and shape, and the behaviour of chromosomes during meiosis.
6. Chemotaxonomy: based on chemical products, particularly secondary metabolites. Various plant families have been identified on the basis of raphides (crystals of calcium oxalate).
7. Experimental taxonomy: relationships are determined on the basis of genetics, breeding experiments and the effect of captivity.
8. Biochemical taxonomy: based on the biochemistry of various chemicals such as hormones and pheromones.

Population systematics and biosystematics are new branches of classification. Biosystematics is the classification of organisms based on evolutionary history and phylogeny, considering various parameters in totality, from all fields of biology.

Codes of Nomenclature

1. International Code of Botanical Nomenclature (ICBN)
2. International Code of Zoological Nomenclature (ICZN)
3. International Code of Bacteriological Nomenclature
4. International Code of Viral Nomenclature (not based on binomial nomenclature)
5. International Code of Nomenclature for Cultivated Plants

The International Code of Zoological Nomenclature was adopted in 1964 and was published in two languages, English and French.

Taxonomic Aids

Taxonomic studies of animals, plants and microorganisms help in knowing our bio-resources and their diversity. Biologists have established procedures and techniques to store and preserve information and specimens. The important taxonomic aids are: 1. Herbarium, 2. Botanical gardens, 3. Zoological parks, 4. Biological museums, 5. Keys, 6. Manuals, 7. Flora, 8. Monograph, 9. Periodicals and catalogues.

1. Herbarium: a store house of dead, dried, pressed and preserved plant specimens on paper sheets, called herbarium sheets. The sheets, along with a description of the specimen, are arranged according to a standard system of classification and stored for future use. Each sheet carries a label with the date and place of collection, English, local and botanical names, family and collector's name. Herbarium sheets serve as quick reference for taxonomic studies.
2. Botanical gardens: have a collection of living plants for identification and taxonomic studies. Each plant is labelled with its botanical name and family. Famous Indian botanical gardens are the Indian Botanical Garden, Howrah, and the National Botanical Research Institute, Lucknow. The world famous botanical garden is at Kew, England.
3. Zoological parks (zoos): wild animals are kept in a protected environment under human care. As far as possible, conditions similar to their natural environment are provided. Zoos help us learn about the food habits and behaviour of animals in captivity.
4. Biological museums: have collections of preserved animal and plant specimens for study and reference. They are generally set up in educational institutes such as schools and colleges. Specimens may be preserved dry or in preservative solution in jars or containers. Insects are preserved in insect boxes after collecting, killing and pinning. Larger animals such as mammals and birds are stuffed and chemically treated for long-term preservation. Museums also have collections of animal skeletons.
5. Keys: a device or scheme used for identification of animals and plants. Keys are generally analytic in nature, and separate keys are required for separate taxa. There are two types:
(a) Indented key or yoked key: provides a sequence of choices between two or more characters. The user has to make the correct choice of statement or character for identification.
(b) Bracketed key: has one pair of contrasting statements for identification. Each statement in the key is called a lead. The numbers on the right indicate the next choice of paired contrasting statements. Example:
(1) Pinna present - - - go to (2)
(1) Pinna absent - - - go to (3)
(2) Flies - - - Bat
(2) Does not fly - - - Cat/Dog
(3) Limbs present - - - Frog
(3) Limbs absent - - - Go to (4)
(4) Gills present - - - Fish
(4) Gills absent - - - Snake

6. Manuals: contain information for the identification of names of species found in an area. They also provide information about keys and descriptions of families, genera and species.
7. Flora: contains an actual account of the habitat and distribution of plants of a given area. It is an index to the plant species found in a particular area.
8. Monograph (memoir): gives comprehensive information on one family or genus at a given time.
9. Periodicals and catalogues: provide information about new additions and update the records. Catalogues are also a means of recording information for taxonomy.

Check Point (p. 19)
1. Fill in the blanks:
(a) In Bracketed key ................ pair/s of contrasting characters are used.
(b) ................ on Pheretima posthuma was written by Dr. K. N. Behl.
(c) Indented key is also known as ................ .
(d) In place of phylum, ................ is used, in plants.
(e) The taxon ................ is used in Trinomial and not binomial, system of classification.
(f) The world famous botanical garden is at ................ .
(g) In animals the suffix used for family is ................ .
(h) The ................ is the taxon between family and class.
(i) The international code of zoological nomenclature was published in two languages, i.e. ................ .
(j) The term 'taxon' for animals was given by ................ .