NCERT Exercises
1. Why are living organisms classified?
Living organisms are classified for several reasons:
- Easy Identification: It makes the identification of specific organisms easier.
- Study of Diversity: It is impossible to study millions of organisms individually. Classification groups them into categories, making study convenient.
- Understanding Relationships: It helps in understanding the evolutionary relationships and similarities between different organisms.
- Information Retrieval: It facilitates the collection and retrieval of information about specific groups.
2. Why are the classification systems changing every now and then?
Classification systems change because:
- New Discoveries: New species are constantly being discovered and described.
- Scientific Advancement: Improvement in tools and technology allows scientists to study organisms at a deeper level (e.g., molecular biology, DNA sequencing).
- Evolutionary Relationships: Modern classification aims to reflect evolutionary relationships (phylogeny), which leads to the rearrangement of groups as our understanding of these relationships improves.
3. What different criteria would you choose to classify people that you meet often?
To classify people we meet often, we can use observable and behavioural criteria such as:
- Physical appearance: Height, eye colour, hair texture, skin tone.
- Demographics: Age, gender.
- Relation: Family members, friends, classmates, colleagues.
- Profession: Doctors, teachers, engineers, etc.
- Mother tongue/Language spoken.
4. What do we learn from identification of individuals and populations?
Through identification, we learn:
- Variation: We can observe distinct morphological features that differentiate one individual or population from another.
- Similarities: It helps us identify common features shared by members of a population (species).
- Relationships: It helps in determining how closely related different populations are.
- It enables us to assign a scientific name to the organism.
5. Given below is the scientific name of Mango. Identify the correctly written name.
Options:
(a) Mangifera Indica
(b) Mangifera indica
Correct Answer: (b) Mangifera indica
Reason: According to the rules of binomial nomenclature, the biological name consists of two words. The first word (Genus) starts with a Capital letter, and the second word (specific epithet) starts with a small letter.
6. Define a taxon. Give some examples of taxa at different hierarchical levels.
Definition: A taxon (plural: taxa) represents a rank or category in the taxonomic hierarchy. It is a unit of classification containing a group of organisms sharing common characteristics.
Examples:
- Kingdom: Animalia (Taxon at Kingdom level)
- Phylum: Chordata (Taxon at Phylum level)
- Class: Mammalia (Taxon at Class level)
- Family: Felidae (Taxon at Family level)
- Genus: Panthera (Taxon at Genus level)
7. Can you identify the correct sequence of taxonomical categories?
Options:
(a) Species → Order → Phylum → Kingdom
(b) Genus → Species → Order → Kingdom
(c) Species → Genus → Order → Phylum
Answer: Both (a) and (c) represent correct sequences.
Explanation: The correct ascending hierarchy is:
Species → Genus → Family → Order → Class → Phylum → Kingdom.
- Sequence (a) is correct (ascending order), though it skips Genus and Family.
- Sequence (c) is correct (ascending order), though it skips Family and Class.
- Sequence (b) is incorrect because Species comes before Genus in ascending order (or Genus comes after Species), but the sequence lists Genus before Species.
8. 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.
General Definition: A species is a group of individual organisms with fundamental similarities that can interbreed to produce fertile offspring.
- In Higher Plants and Animals: The biological species concept applies. It is defined based on reproductive isolation. Members of the same species can breed among themselves but cannot breed with members of other species.
- In Bacteria: Bacteria reproduce asexually (fission), so the definition of interbreeding does not apply. Here, species are classified based on morphology, biochemical properties, and DNA similarities.
9. Define and understand the following terms:
- (i) Phylum: A taxonomic category higher than Class and lower than Kingdom. It consists of one or more related classes (e.g., Classes Mammalia, Aves, and Reptilia belong to Phylum Chordata).
- (ii) Class: A taxonomic category consisting of one or more related orders (e.g., Order Primata and Order Carnivora are in Class Mammalia).
- (iii) Family: A group of related genera with still less number of similarities as compared to genus and species (e.g., Genus Panthera and Genus Felis are in Family Felidae).
- (iv) Order: A higher category representing an assemblage of families which exhibit a few similar characters (e.g., Families Felidae and Canidae are in Order Carnivora).
- (v) Genus: A group of related species which has more characters in common in comparison to species of other genera (e.g., Panthera leo and Panthera tigris belong to Genus Panthera).
10. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Below is the classification of a Plant (Mango) and an Animal (Man) showing the hierarchy:
| Taxonomic Category | Plant Example: Mango | Animal Example: Man |
|---|---|---|
| Kingdom | Plantae | Animalia |
| Phylum / Division | Angiospermae | Chordata |
| Class | Dicotyledonae | Mammalia |
| Order | Sapindales | Primata |
| Family | Anacardiaceae | Hominidae |
| Genus | Mangifera | Homo |
| Species | Mangifera indica | Homo sapiens |