The Living World | CBSE Class 11 Biology Notes

This note covers the living world and the basics of taxonomy: the diversity of living organisms, identification and nomenclature, binomial nomenclature and its rules, classification and taxa, taxonomy and systematics, the taxonomic categories from species to kingdom, the placing of man, housefly, mango and wheat in the taxonomic hierarchy, the uses of taxonomy, and the life and work of Ernst Mayr.

What does biology study, and what question does the living world raise?

Biology is the science of life forms and living processes. The living world comprises an amazing diversity of living organisms, and the range of living types is itself a source of wonder.

Living organisms are found in extraordinary habitats: cold mountains, deciduous forests, oceans, fresh water lakes, deserts and hot springs.

The beauty of a galloping horse, of migrating birds, of the valley of flowers or of an attacking shark evokes awe and a deep sense of wonder.

The ecological conflict and cooperation among members of a population and among populations of a community, and even the molecular traffic inside a cell, also make us reflect deeply.

All of this makes us reflect on the question: what indeed is life? This question has two implicit questions within it.

• The technical question seeks to answer what living is, as opposed to the non-living.
• The philosophical question seeks to answer what the purpose of life is.

As scientists, biologists do not attempt to answer the second question. They try to reflect on the first: what is living?

How did human understanding of living things grow?

Early man could easily perceive the difference between inanimate matter and living organisms. Early man deified some inanimate matter, such as wind, sea and fire, and some of the animals and plants.

A common feature of all these inanimate and animate objects was the sense of awe or fear that they evoked.

The description of living organisms, including human beings, began much later in human history. Societies that indulged in an anthropocentric view of biology could register limited progress in biological knowledge.

Systematic and monumental description of life forms brought in, out of necessity, detailed systems of identification, nomenclature and classification.

The biggest spin-off of such studies was the recognition that living organisms share similarities both horizontally and vertically.

That all present-day living organisms are related to each other, and also to all organisms that ever lived on this earth, was a revelation. It humbled man and led to cultural movements for the conservation of biodiversity.

How diverse is the living world?

Look around and you will see a large variety of living organisms: potted plants, insects, birds, pets and other animals and plants. There are also several organisms that cannot be seen with the naked eye, yet they are all around us.

If the area of observation is increased, the range and variety of organisms seen also increases. A visit to a dense forest would probably show a much greater number and many more kinds of living organisms.

Each different kind of plant, animal or organism represents a species. The number of species that are known and described ranges between 1.7 and 1.8 million.

This refers to biodiversity, the number and types of organisms present on earth. As new areas, and even old ones, are explored, new organisms are continuously being identified.

Millions of plants and animals have been identified and described, but a large number still remains unknown.

The very range of organisms, in terms of size, colour, habitat, and physiological and morphological features, makes us seek the defining characteristics of living organisms.

To make the study of the kinds and diversity of organisms easier, biologists have evolved certain rules and principles for identification, nomenclature and classification. The branch of knowledge dealing with these aspects is taxonomy.

Why do living organisms need scientific names?

We know the plants and animals in our own area by their local names. These local names vary from place to place, even within a country.

Without some way of referring to the same organism in the same way, there would be confusion whenever people talked to each other about organisms.

So there is a need to standardise the naming of living organisms, so that a particular organism is known by the same name all over the world. This process is called nomenclature.

Nomenclature, or naming, is only possible when the organism is described correctly and we know to what organism the name is attached. This is identification. Naming therefore depends on correct identification.

Definition: Nomenclature is the standardised naming of living organisms so that a particular organism is known by the same name all over the world. Identification is describing the organism correctly, so that we know to what organism a name is attached.

Which codes govern scientific names?

A number of scientists have established procedures to assign a scientific name to each known organism, and these are acceptable to biologists all over the world.

What do scientific names guarantee?

• Each organism has only one name.
• The description of any organism enables people in any part of the world to arrive at the same name.
• Such a name has not been used for any other known organism.

The basics of taxonomy, such as identification, naming and classification, are thus universally evolved under international codes.

Based on resemblances and distinct differences, each organism is identified and assigned a correct scientific or biological name of two words, under the binomial system of nomenclature.

How does binomial nomenclature work?

Biologists follow universally accepted principles to provide scientific names to known organisms. Each name has two components: the generic name and the specific epithet.

This system of providing a name with two components is called binomial nomenclature. It was given by Carolus Linnaeus and is practised by biologists all over the world. This two-word format was found convenient.

Take the mango. Its scientific name is written as Mangifera indica. In this name Mangifera represents the genus, while indica is a particular species, or the specific epithet.

What are the universal rules of nomenclature?

1. Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.
2. The first word in a biological name represents the genus, while the second component denotes the specific epithet.
3. Both words in a biological name, when handwritten, are separately underlined, or printed in italics, to indicate their Latin origin.
4. The first word, denoting the genus, starts with a capital letter, while the specific epithet starts with a small letter, as in Mangifera indica.

Where does the author's name go?

The name of the author appears after the specific epithet, that is, at the end of the biological name, and is written in an abbreviated form.

For example, Mangifera indica Linn. indicates that this species was first described by Linnaeus.

Write Mangifera indica Linn. on one line. Label the first word "generic name (genus): starts with a capital letter" and the second word "specific epithet: starts with a small letter".

Label the abbreviation Linn. "author: Linnaeus first described this species". Under the two Latin words, add "italics when printed; each word underlined separately when handwritten".

Which scientific names are used as examples?

Once a genus has been written out in full, it is often shortened to its capital initial when it is repeated, as in P. pardus for the leopard and P. tigris for the tiger.

What is classification, and what are taxa?

It is nearly impossible to study all living organisms, so some means has to be devised to make this possible. This process is classification.

Definition: Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.

We easily recognise groups such as plants, animals, dogs, cats or insects. The moment we use any of these terms, we associate certain characters with the organisms in that group.

When we think of a dog, each of us sees dogs and not cats. If we think of Alsatians, we again know exactly what we are talking about.

When we say mammals, we think of animals with external ears and body hair. In plants, the word wheat brings to mind wheat plants, not rice or any other plant.

So 'dogs', 'cats', 'mammals', 'wheat', 'rice', 'plants' and 'animals' are all convenient categories that we use to study organisms.

What is a taxon?

The scientific term for these categories is taxa (singular taxon). Taxa can indicate categories at very different levels.

'Plants' form a taxon, and 'wheat' is also a taxon. Similarly, 'animals', 'mammals' and 'dogs' are all taxa.

But a dog is a mammal and mammals are animals. So 'animals', 'mammals' and 'dogs' represent taxa at different levels.

Note: A taxon is not only a species. Any convenient category, from 'plants' or 'animals' down to 'wheat' or 'dogs', is a taxon; what differs is its level in the hierarchy.

Based on characteristics, all living organisms can be classified into different taxa. This process of classification is taxonomy.

What are taxonomy and systematics?

Several kinds of information about organisms are essential and form the basis of modern taxonomic studies:

• external and internal structure;
• the structure of the cell;
• the development process;
• ecological information about the organism.

Four processes are basic to taxonomy: characterisation, identification, classification and nomenclature.

How old is taxonomy?

Taxonomy is not something new. Human beings have always been interested in knowing more and more about the various kinds of organisms, particularly with reference to their own use.

In early days, human beings needed to find sources for their basic needs of food, clothing and shelter. Hence the earliest classifications were based on the 'uses' of various organisms.

What is systematics?

Human beings were, since long, interested not only in the different kinds of organisms and their diversities but also in the relationships among them. This branch of study was referred to as systematics.

The word systematics is derived from the Latin word 'systema', which means systematic arrangement of organisms. Linnaeus used Systema Naturae as the title of his publication.

The scope of systematics was later enlarged to include identification, nomenclature and classification. Systematics takes into account evolutionary relationships between organisms.

What is the taxonomic hierarchy?

Classification is not a single-step process. It involves a hierarchy of steps in which each step represents a rank or category.

Since the category is a part of the overall taxonomic arrangement, it is called the taxonomic category, and all the categories together constitute the taxonomic hierarchy.

Each category, referred to as a unit of classification, in fact represents a rank and is commonly termed a taxon (plural taxa).

How do insects illustrate a category?

Insects are a group of organisms sharing common features, such as three pairs of jointed legs. So insects are recognisable, concrete objects that can be classified, and they were given a rank or category.

Groups represent categories, and a category denotes a rank. Each rank or taxon represents a unit of classification.

These taxonomic groups or categories are distinct biological entities and not merely morphological aggregates.

What are the common categories?

Taxonomic studies of all known organisms have led to the development of common categories. In ascending order, they are:

1. Species, the lowest category
2. Genus
3. Family
4. Order
5. Class
6. Phylum, or Division for plants
7. Kingdom, the highest category

All organisms, including those in the plant and animal kingdoms, have species as the lowest category.

A single vertical column on a pale yellow panel lists the categories. From bottom to top they read: Species, Genus, Family, Order, Class, Phylum or Division, Kingdom.

An upward-pointing arrow joins each category to the one above it, so the column rises in rank from Species at the base to Kingdom at the top.

See Fig. 1.1 in your NCERT textbook

How is an organism placed in these categories?

The basic requirement is knowledge of the characters of an individual or group of organisms.

This knowledge helps in identifying similarities and dissimilarities among individuals of the same kind of organism, as well as among other kinds of organisms. The organism then occupies a place or position in the system of classification.

What are a species and a genus?

Species

Taxonomic studies consider a group of individual organisms with fundamental similarities as a species.

One should be able to distinguish one species from other, closely related species on the basis of distinct morphological differences.

Consider Mangifera indica (mango), Solanum tuberosum (potato) and Panthera leo (lion). The three names indica, tuberosum and leo represent the specific epithets.

The first words, Mangifera, Solanum and Panthera, are genera, and represent another, higher level of taxon or category.

Each genus may have one or more than one specific epithet, representing different organisms that have morphological similarities.

For example, Panthera has another specific epithet called tigris, and Solanum includes species such as nigrum and melongena.

Human beings belong to the species sapiens, which is grouped in the genus Homo. The scientific name for the human being is thus written as Homo sapiens.

Genus

A genus comprises a group of related species which has more characters in common in comparison to species of other genera. Genera are aggregates of closely related species.

Potato and brinjal are two different species, but both belong to the genus Solanum.

Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) have several common features and are all species of the genus Panthera.

This genus differs from another genus, Felis, which includes cats.

How are a family and an order defined?

Family

The next category, family, has a group of related genera, with still fewer similarities as compared to genus and species.

Families are characterised on the basis of both vegetative and reproductive features of plant species.

Among plants, three different genera, Solanum, Petunia and Datura, are placed in the family Solanaceae.

Among animals, the genus Panthera, comprising lion, tiger and leopard, is put along with the genus Felis (cats) in the family Felidae.

A cat and a dog show some similarities and some differences. They are separated into two different families, Felidae and Canidae respectively.

Order

Species, genus and family are based on a number of similar characters. Generally, order and the other higher taxonomic categories are identified on the basis of aggregates of characters.

An order, being a higher category, is the assemblage of families which exhibit a few similar characters. These similar characters are fewer than those shared by the different genera included in a family.

Plant families such as Convolvulaceae and Solanaceae are included in the order Polymoniales, mainly on the basis of floral characters.

The animal order Carnivora includes families such as Felidae and Canidae.

Draw two branching trees. In the plant tree, the order Polymoniales branches into the families Convolvulaceae and Solanaceae, and Solanaceae branches into the genera Solanum, Petunia and Datura.

In the animal tree, the order Carnivora branches into the families Felidae and Canidae. Felidae branches into the genera Panthera and Felis, and Panthera branches into the species leo, pardus and tigris.

How are a class, a phylum and a kingdom defined?

Class

A class includes related orders. The order Primata, comprising monkey, gorilla and gibbon, is placed in the class Mammalia.

It is placed there along with the order Carnivora, which includes animals such as tiger, cat and dog. Class Mammalia has other orders also.

Phylum or division

Classes comprising animals such as fishes, amphibians, reptiles and birds, along with mammals, constitute the next higher category, called the phylum.

All these are included in the phylum Chordata, based on common features such as the presence of a notochord and a dorsal hollow neural system.

In the case of plants, classes with a few similar characters are assigned to a higher category called the division.

Kingdom

All animals belonging to various phyla are assigned to the highest category, called Kingdom Animalia, in the classification system of animals.

Kingdom Plantae, on the other hand, is distinct, and comprises all plants from the various divisions. These two groups are referred to as the animal and plant kingdoms.

How do shared characters change as we move up the hierarchy?

The taxonomic categories from species to kingdom are broad categories. Taxonomists have also developed sub-categories in this hierarchy, to allow a more sound and scientific placement of various taxa.

The basis of the arrangement is the number of characters that members share. As we go higher from species to kingdom, the number of common characteristics goes on decreasing.

The lower the taxon, the more are the characteristics that the members within the taxon share.

The higher the category, the greater is the difficulty of determining its relationship to other taxa at the same level. Hence the problem of classification becomes more complex.

1. At the species level, members have fundamental similarities and are distinguished from close relatives by distinct morphological differences.
2. At the genus level, related species have more characters in common than they have with species of other genera.
3. At the family level, related genera have still fewer similarities than those found in a genus or a species.
4. At the order level, families exhibit a few similar characters, and the category is identified from aggregates of characters.
5. At the phylum level, classes are grouped by common features, such as the notochord and dorsal hollow neural system of Chordata.

Draw seven boxes, one inside the other. Label the innermost box "Species: Panthera leo" and the boxes around it, working outwards, "Genus: Panthera", "Family: Felidae", "Order: Carnivora", "Class: Mammalia", "Phylum: Chordata" and "Kingdom: Animalia".

Add an arrow running from the inner box to the outer box, labelled "fewer common characteristics".

How are man, housefly, mango and wheat classified?

The hierarchy can be applied to common organisms such as the housefly, man, mango and wheat. The table shows the taxonomic categories to which each of them belongs.

Man and the housefly are animals, so both belong to Kingdom Animalia. Mango and wheat are plants, so both belong to Kingdom Plantae.

How do you trace mango through the hierarchy?

1. Species: Mangifera indica, with the specific epithet indica.
2. Genus: Mangifera.
3. Family: Anacardiaceae.
4. Order: Sapindales.
5. Class: Dicotyledonae.
6. Division: Angiospermae.
7. Kingdom: Plantae.

What does the comparison reveal?

Mango and wheat share the same division, Angiospermae, but belong to different classes: mango to Dicotyledonae and wheat to Monocotyledonae.

Their orders (Sapindales and Poales) and families (Anacardiaceae and Poaceae) also differ, as do their genera, Mangifera and Triticum.

Man and the housefly differ at every level shown, from genus up to phylum. Man is in the phylum Chordata, while the housefly is in the phylum Arthropoda, class Insecta, order Diptera and family Muscidae.

Man belongs to the family Hominidae in the order Primata, the same order that includes monkey, gorilla and gibbon.

For plants, the category above class is called a division, while for animals it is called a phylum. That is why the last column is headed "Phylum or Division".

Why is taxonomy useful?

Taxonomic studies of various species of plants and animals are useful in agriculture, forestry and industry. In general, they are useful for knowing our bio-resources and their diversity.

Why are living organisms classified?

It is nearly impossible to study all living organisms one by one. Grouping them into convenient categories, based on easily observable characters, makes their study possible.

Once an organism is placed in a group, we can associate certain characters with it at once. Calling an animal a mammal, for instance, brings to mind an animal with external ears and body hair.

The detailed study of organisms through identification, nomenclature and classification also brought out the similarities that organisms share horizontally and vertically, and revealed that all present-day organisms are related to each other and to all organisms that ever lived on earth.

Why do classification systems change?

New organisms are continuously being identified as new areas, and even old ones, are explored. Each new organism has to be identified, named and given a place in the hierarchy.

Modern taxonomy also draws on many kinds of information: external and internal structure, cell structure, development process and ecological information. Systematics also takes evolutionary relationships into account.

As knowledge of these features and relationships grows, the placement of taxa can be revised, and so classification systems change from time to time.

Who was Ernst Mayr?

Ernst Mayr (1904 to 2005) was the Harvard University evolutionary biologist who has been called 'The Darwin of the 20th century'. He was one of the 100 greatest scientists of all time.

He was born on 5 July 1904 in Kempten, Germany. He joined Harvard's Faculty of Arts and Sciences in 1953 and retired in 1975, assuming the title Alexander Agassiz Professor of Zoology Emeritus.

Throughout his nearly 80-year career, his research spanned ornithology, taxonomy, zoogeography, evolution, systematics, and the history and philosophy of biology.

He almost single-handedly made the origin of species diversity the central question of evolutionary biology that it is today. He also pioneered the currently accepted definition of a biological species.

Mayr was awarded the three prizes widely regarded as the triple crown of biology.

Mayr died at the age of 100 in February 2005.

Glossary

• Biology — The science of life forms and living processes, which includes the study of the amazing diversity of living organisms.
• Biodiversity — The number and types of organisms present on earth; between 1.7 and 1.8 million species are known and described.
• Identification — Describing an organism correctly, so that we know to what organism a name is attached; naming is possible only after it.
• Nomenclature — The standardised naming of living organisms, so that a particular organism is known by the same name all over the world.
• Binomial nomenclature — The naming system given by Carolus Linnaeus, in which each scientific name has two components: the generic name and the specific epithet.
• Specific epithet — The second word of a scientific name, which starts with a small letter, such as indica in Mangifera indica.
• ICBN — The International Code for Botanical Nomenclature, which provides the agreed principles and criteria on which the scientific names of plants are based.
• Classification — The process by which anything is grouped into convenient categories based on some easily observable characters.
• Taxon — A unit of classification that represents a rank or category, such as plants, mammals or wheat; the plural is taxa.
• Taxonomy — The classification of organisms into taxa based on characteristics; characterisation, identification, classification and nomenclature are basic to it.
• Systematics — The study of the kinds and diversity of organisms and the relationships among them, including evolutionary relationships; from the Latin 'systema'.
• Taxonomic hierarchy — All the taxonomic categories taken together, arranged as ranks from species, the lowest, to kingdom, the highest.
• Genus — A group of related species that has more characters in common than with species of other genera, such as Panthera.
• Family — A group of related genera, characterised in plants by vegetative and reproductive features, such as Solanaceae or Felidae.
• Division — The plant category above class, to which classes with a few similar characters are assigned, such as Angiospermae.

Common errors and misconceptions

• Misconception: The scientific name of mango may be written as Mangifera Indica. Correct: The genus starts with a capital letter and the specific epithet with a small letter, so the correct form is Mangifera indica.
• Misconception: Identification and nomenclature mean the same thing. Correct: Identification is describing the organism correctly and knowing to what organism a name is attached; nomenclature is standardising its name. Naming is possible only after identification.
• Misconception: Genus is the lowest taxonomic category. Correct: All organisms, including plants and animals, have species as the lowest category; genus is the next higher one.
• Misconception: Members of a higher category share more characters than members of a lower one. Correct: Going from species to kingdom, the number of common characteristics decreases; the lower the taxon, the more characters its members share.
• Misconception: A taxon means a species. Correct: Taxa can be at very different levels; 'plants', 'wheat', 'animals', 'mammals' and 'dogs' are all taxa.
• Misconception: Plants and animals use the same name for every category. Correct: In plants, classes are grouped into a division rather than a phylum; mango and wheat are in the division Angiospermae.
• Misconception: The author's name is written before the genus. Correct: It appears at the end, after the specific epithet, in an abbreviated form, as in Mangifera indica Linn.
• Misconception: The cat and the dog belong to the same family. Correct: They are separated into two families, Felidae and Canidae, which are both included in the order Carnivora.

Exam-style questions with model answers

Q1. Which is the correctly written scientific name of mango: Mangifera Indica or Mangifera indica? Give a reason. [1 mark]

1. Mangifera indica is correct. The first word, the genus, starts with a capital letter, and the specific epithet starts with a small letter; both words are printed in italics or, when handwritten, separately underlined.

Q2. Why are living organisms classified? [2 marks]

1. It is nearly impossible to study all living organisms individually. Classification groups them into convenient categories based on easily observable characters, which makes their study possible.
2. Placing an organism in a group lets us associate certain characters with it at once; calling an animal a mammal brings to mind an animal with external ears and body hair.

Q3. Distinguish between identification and nomenclature. [2 marks]

1. Identification is describing an organism correctly, so that we know to what organism a name is attached.
2. Nomenclature is standardising the naming of organisms so that a particular organism is known by the same name all over the world. Nomenclature is possible only after correct identification.

Q4. Define a taxon. Give some examples of taxa at different hierarchical levels. [3 marks]

1. A taxon (plural taxa) is a unit of classification: a category that represents a rank in the taxonomic hierarchy.
2. Taxa can be at very different levels. 'Animals', 'mammals' and 'dogs' are all taxa, but a dog is a mammal and mammals are animals, so these are taxa at different levels. Similarly, 'plants' and 'wheat' are taxa at different levels.
3. For the lion, the taxa at successive levels are Panthera leo (species), Panthera (genus), Felidae (family), Carnivora (order), Mammalia (class), Chordata (phylum) and Animalia (kingdom).

Q5. State the universal rules of binomial nomenclature, taking mango as the example. [4 marks]

1. Each name has two components, the generic name and the specific epithet. In Mangifera indica, Mangifera is the genus and indica the specific epithet.
2. Biological names are generally in Latin and written in italics; they are Latinised or derived from Latin irrespective of their origin.
3. When handwritten, both words are separately underlined; when printed, they are in italics, to indicate their Latin origin.
4. The genus starts with a capital letter and the specific epithet with a small letter.
5. The author's name appears after the specific epithet in an abbreviated form, as in Mangifera indica Linn., showing that Linnaeus first described the species.

Q6. How does systematics differ from taxonomy? [3 marks]

1. Taxonomy is the process of classifying organisms into taxa based on their characteristics; characterisation, identification, classification and nomenclature are basic to it.
2. Systematics is the study of the kinds and diversity of organisms and also of the relationships among them. The word comes from the Latin 'systema', systematic arrangement of organisms, and Linnaeus titled his publication Systema Naturae.
3. The scope of systematics was later enlarged to include identification, nomenclature and classification, and it takes into account evolutionary relationships between organisms.

Q7. Why are classification systems changing every now and then? [3 marks]

1. New organisms are continuously being identified as new areas, and even old ones, are explored, and each has to be identified, named and placed in the hierarchy.
2. Modern taxonomy is based on many kinds of information: external and internal structure, cell structure, development process and ecological information. Systematics also takes evolutionary relationships into account.
3. As knowledge of these features and relationships grows, the placement of taxa is revised, so classification systems change from time to time.

Q8. Illustrate the taxonomic hierarchy with suitable examples of a plant and an animal. [5 marks]

1. The taxonomic hierarchy is the arrangement of categories in ascending order: species, genus, family, order, class, phylum (division in plants) and kingdom. Species is the lowest category and kingdom the highest.
2. Plant example, mango: species Mangifera indica; genus Mangifera; family Anacardiaceae; order Sapindales; class Dicotyledonae; division Angiospermae; kingdom Plantae.
3. Animal example, man: species Homo sapiens; genus Homo; family Hominidae; order Primata; class Mammalia; phylum Chordata; kingdom Animalia.
4. As we go higher from species to kingdom, the number of common characteristics goes on decreasing. The lower the taxon, the more characteristics its members share.
5. The higher the category, the greater the difficulty of determining its relationship to other taxa at the same level, so classification becomes more complex.

Q9. Define the following terms with one example each: (i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus. [5 marks]

1. Phylum: the category made of related classes. Fishes, amphibians, reptiles, birds and mammals are placed in the phylum Chordata because they share a notochord and a dorsal hollow neural system. In plants the equivalent category is the division.
2. Class: a category that includes related orders. The orders Primata and Carnivora are placed in the class Mammalia.
3. Family: a group of related genera with still fewer similarities than genus and species. Solanum, Petunia and Datura are in the family Solanaceae.
4. Order: an assemblage of families which exhibit a few similar characters. Felidae and Canidae are included in the order Carnivora.
5. Genus: a group of related species with more characters in common than with species of other genera. Lion, leopard and tiger are species of the genus Panthera.

Key takeaways

• The living world is rich in variety: between 1.7 and 1.8 million species are known and described, and new organisms are still being identified.
• Nomenclature gives each organism the same name all over the world, and it is possible only after correct identification; ICBN covers plants and ICZN covers animals.
• Binomial nomenclature, given by Carolus Linnaeus, uses a generic name and a specific epithet, as in Mangifera indica; the names are generally in Latin and printed in italics.
• Classification groups organisms into convenient categories called taxa, based on easily observable characters; classifying organisms into taxa based on characteristics is taxonomy.
• Characterisation, identification, classification and nomenclature are basic to taxonomy, while systematics also studies the relationships, including evolutionary relationships, between organisms.
• In ascending order the categories are species, genus, family, order, class, phylum (division in plants) and kingdom, with species the lowest for all organisms.
• Going up from species to kingdom, the number of common characteristics decreases, and determining relationships between taxa at the same level becomes harder.
• Taxonomic studies are useful in agriculture, forestry and industry, and in general for knowing our bio-resources and their diversity.

Test yourself

How many species are known and described?

The number of species that are known and described ranges between 1.7 and 1.8 million, and new organisms are continuously being identified.

Which code provides the rules for naming animals?

Animal taxonomists have evolved the International Code of Zoological Nomenclature (ICZN). Plant names follow the International Code for Botanical Nomenclature (ICBN).

What does "Linn." at the end of Mangifera indica Linn. show?

It is the abbreviated name of the author, written after the specific epithet. It shows that the species was first described by Linnaeus.

What were the earliest classifications based on?

They were based on the 'uses' of various organisms, because early human beings needed sources for their basic needs of food, clothing and shelter.

Which common features place fishes, amphibians, reptiles, birds and mammals in one phylum?

They all have a notochord and a dorsal hollow neural system, so they are included in the phylum Chordata.

Name three genera placed in the family Solanaceae.

Solanum, Petunia and Datura are three different genera placed in the family Solanaceae.

In which families are the cat and the dog placed, and which order includes both families?

The cat is in the family Felidae and the dog in the family Canidae. Both families are included in the order Carnivora.

Who has been called 'The Darwin of the 20th century'?

Ernst Mayr, the Harvard University evolutionary biologist who pioneered the currently accepted definition of a biological species, has been called 'The Darwin of the 20th century'.