Exercises
Why are living organisms classified?
Answer
Classification of living organisms is necessary because:
(i) There is an enormous diversity of living organisms – more than a million species have been identified. Classification helps us study this diversity in an organised way.
(ii) It helps in identifying, naming and placing organisms in a systematic order, making study convenient.
(iii) Classification reveals relationships between different groups of organisms and helps us understand their evolutionary history.
(iv) It helps in locating and understanding organisms for various purposes – medical, agricultural, industrial and ecological.
Why are the classification systems changing every now and then?
Answer
Classification systems keep changing because:
(i) New information about organisms keeps emerging through research in biochemistry, molecular biology, genetics and electron microscopy, which reveals new relationships not visible from external features alone.
(ii) As scientific tools improve, criteria used for classification also improve – for example, DNA sequencing has changed many traditional groupings.
(iii) Scientists discover new species regularly, requiring revision of existing classifications.
(iv) Different scientists emphasise different characteristics (morphological, physiological, evolutionary), leading to varied and evolving systems over time.
What different criteria would you choose to classify people that you meet often?
Answer
People we meet often can be classified using various criteria:
(i) By physical appearance – height, body build, skin colour, hair type.
(ii) By gender – male or female.
(iii) By age group – children, teenagers, adults, elderly.
(iv) By language spoken or regional background.
(v) By profession or occupation – teacher, doctor, farmer.
(vi) By relationship – family, friends, colleagues.
This illustrates that classification depends on the purpose and criteria chosen by the observer.
What do we learn from identification of individuals and populations?
Answer
Identification of individuals and populations helps us:
(i) Recognise similarities and differences among organisms, which forms the basis for grouping them.
(ii) Understand the range of variation within a species (population-level variation).
(iii) Know the geographic distribution and ecological preferences of organisms.
(iv) Track changes in populations over time – useful in conservation and ecological studies.
(v) Assign scientific names accurately, maintaining consistency in biological communication worldwide.
Given below is the scientific name of Mango. Identify the correctly written name.
Answer
Mangifera Indica
Mangifera indica
Ans. The correctly written scientific name is Mangifera indica. In binomial nomenclature, the genus name starts with a capital letter (Mangifera) while the specific epithet is written entirely in lowercase (indica). Both words are either italicised (in print) or underlined (when handwritten).
Define a taxon. Give some examples of taxa at different hierarchical levels.
Answer
A taxon (plural: taxa) is any unit or category used in the classification of organisms. It represents a group of organisms at a definite level in the taxonomic hierarchy.
Examples of taxa at different hierarchical levels:
• Species – Panthera leo (Lion)
• Genus – Panthera (includes lions, tigers, leopards)
• Family – Felidae (all cats)
• Order – Carnivora (meat-eating mammals)
• Class – Mammalia (all mammals)
• Phylum – Chordata (animals with notochord)
• Kingdom – Animalia (all animals)
Can you identify the correct sequence of taxonomical categories?
(a) Species → Order → Phylum → Kingdom
(b) Genus → Species → Order → Kingdom
(c) Species → Genus → Order → Phylum
Answer
Option (c) is the correct sequence: Species
⇒ Genus
⇒ Order
⇒ Phylum. This represents an ascending order from the most specific to broader categories. The complete correct hierarchy (ascending) is: Species
⇒ Genus
⇒ Family
⇒ Order
⇒ Class
⇒ Phylum
⇒ Kingdom.
Try to collect all the currently accepted meanings for the word 'species'. Discuss with your teacher the meaning of species in case of higher plants and animals on one hand, and bacteria on the other hand.
Answer
The term species has various interpretations:
(i) Biological species concept (Mayr): A species is a group of naturally interbreeding populations that are reproductively isolated from other such groups. This is the most widely accepted definition for higher plants and animals.
(ii) Morphological (typological) species concept: Organisms that share similar morphological features are grouped as a species.
(iii) Phylogenetic species concept: A species is the smallest monophyletic group (sharing a common ancestor).
For higher plants and animals, the biological species concept works well – interbreeding and reproductive isolation are clear criteria.
For bacteria, the biological species concept is difficult to apply because bacteria reproduce asexually (binary fission) and undergo horizontal gene transfer. Hence, bacterial species are often defined by morphological, biochemical, and genetic similarity (e.g., DNA-DNA hybridisation ≥70% similarity is used).
Q9. Define and understand the following terms
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Ans.
(i) Phylum: A taxonomic category above class and below kingdom. It groups organisms with a common body plan or a common fundamental feature. Example: Phylum Chordata includes all animals with a notochord. In plants, the equivalent rank is called Division.
(ii) Class: A taxonomic category above order and below phylum. It groups related orders together. Example: Class Mammalia includes all mammals (orders Carnivora, Primates, etc.).
(iii) Family: A taxonomic category above genus and below order. It groups closely related genera. Example: Family Felidae includes lions, tigers, cheetahs.
(iv) Order: A category above family and below class. It groups related families. Example: Order Carnivora includes families Felidae (cats), Canidae (dogs), etc.
(v) Genus: A category above species and below family. It includes closely related species that share many common characters. Example: Genus Panthera includes P. leo (lion), P. tigris (tiger), P. pardus (leopard).
Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Answer
The taxonomical hierarchy (from highest to lowest rank) with examples:
Plant example – Wheat (Triticum aestivum):
Kingdom: Plantae
⇒ Division: Angiosperms
⇒ Class: Monocotyledonae
⇒ Order: Poales
⇒ Family: Poaceae
⇒ Genus: Triticum
⇒ Species: T. aestivum
Animal example – Housefly (Musca domestica):
Kingdom: Animalia
⇒ Phylum: Arthropoda
⇒ Class: Insecta
⇒ Order: Diptera
⇒ Family: Muscidae
⇒ Genus: Musca
⇒ Species: M. domestica
This hierarchy shows that each higher rank includes more diverse forms, while lower ranks have organisms that are more similar to each other.
Important Extra Questions
What is binomial nomenclature? Who proposed it?
Answer
Binomial nomenclature is the system of giving every organism a scientific name consisting of two words: the genus name (capitalised) and the species epithet (lowercase). It was proposed by Carolus Linnaeus. For example, the scientific name of humans is Homo sapiens.
What is a herbarium? What is its significance?
Answer
A herbarium is a store-house of collected, dried, pressed and preserved plant specimens mounted on sheets. These sheets are arranged according to a universally accepted classification system. It serves as a quick reference in taxonomic studies, helps in identification of newly collected specimens, and acts as a permanent repository of taxonomic data.
Distinguish between nomenclature and classification.
Answer
Nomenclature is the process of assigning a specific scientific name to a known organism, following the International Code of Nomenclature. Classification is the process of arranging organisms into groups based on similarities and differences. Nomenclature requires that organisms be correctly identified and classified first; classification precedes nomenclature.
What is ICZN? What role does it play?
Answer
ICZN stands for International Code of Zoological Nomenclature. It is a body that sets and maintains the rules and standards for the scientific naming of animals. It ensures that each animal species has a unique, universally accepted scientific name. The equivalent body for plants is the International Code of Botanical Nomenclature (ICBN), now called the International Code of Nomenclature for algae, fungi and plants (ICN).
What is meant by 'taxonomic key'? How is it useful?
Answer
A taxonomic key is an analytical tool used to identify organisms based on contrasting characters (usually presented as pairs). Each step in the key offers two choices, and by selecting the correct one for the organism in question, one eventually arrives at the correct identification. Keys are available for different taxonomic levels (families, genera, species). They help biologists quickly and accurately identify an unknown organism in the field or laboratory.