Class 11 Biology Notes Chapter 1 (Chapter 1) – Examplar Problems (English) Book
Detailed Notes with MCQs of Chapter 1, 'The Living World', from your NCERT Exemplar. This chapter lays the foundation for understanding biological classification and diversity, which is crucial for various government exams. Pay close attention to the definitions and concepts.
Chapter 1: The Living World - Detailed Notes for Exam Preparation
1. What is 'Living'?
- Life is a unique, complex organization of molecules expressing itself through chemical reactions (metabolism) which lead to growth, development, responsiveness, adaptation, and reproduction.
- Key Characteristics of Living Organisms:
- Growth: Increase in mass and increase in the number of individuals are twin characteristics.
- Plants exhibit continuous growth throughout life.
- Animals grow up to a certain age.
- Non-living objects (e.g., mountains, boulders) can also grow by accretion (accumulation of material on the surface).
- Therefore, growth cannot be taken as a defining property of living organisms. Growth from inside is characteristic of living beings.
- Reproduction: Production of progeny possessing features more or less similar to those of parents.
- Modes: Asexual (spores, budding, fragmentation, true regeneration - e.g., Planaria) and Sexual.
- Many organisms do not reproduce (e.g., mules, sterile worker bees, infertile human couples).
- Therefore, reproduction also cannot be taken as an all-inclusive defining characteristic of living organisms.
- Metabolism: The sum total of all chemical reactions occurring in our body.
- Includes Anabolism (building up reactions) and Catabolism (breaking down reactions).
- Metabolic reactions can be demonstrated in vitro (outside the body in a test tube), but these isolated reactions are not living things, though they are living reactions.
- Metabolism is a defining feature of all living organisms without exception.
- Cellular Organisation: All living organisms are composed of cells. The cell is the fundamental structural and functional unit of life.
- Unicellular or Multicellular.
- Cellular organization of the body is the defining feature of life forms.
- Consciousness: Ability to sense their surroundings or environment and respond to these environmental stimuli (physical, chemical, biological).
- Plants respond to external factors like light, water, temperature, other organisms, pollutants, etc.
- Humans are unique in having self-consciousness.
- Consciousness is therefore a defining property of living organisms. (Even patients in a coma show metabolism and some level of response, even if not self-consciousness).
- Growth: Increase in mass and increase in the number of individuals are twin characteristics.
2. Diversity in the Living World (Biodiversity)
- Refers to the number and types of organisms present on Earth.
- Estimated number of species described: 1.7-1.8 million.
- Maximum diversity is found in tropical rainforests.
- Need for Classification: It is impossible to study all living organisms individually. Classification facilitates the systematic study of organisms. It helps in understanding the inter-relationships among different groups.
3. Taxonomy and Systematics
- Taxonomy: (Gr. taxis - arrangement, nomos - law) The science of identification, nomenclature (naming), and classification of organisms based on observable characteristics.
- Based on: External and internal structure, cell structure, development process, ecological information.
- Systematics: (Lat. systema - systematic arrangement) A broader field that includes taxonomy but also considers the evolutionary relationships (phylogeny) between organisms.
- Term coined by Linnaeus (Systema Naturae was the title of his publication).
- Aims to understand the diversity of organisms and their comparative and evolutionary relationships.
4. Taxonomic Categories (Taxonomic Hierarchy)
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Classification involves hierarchy of steps where each step represents a rank or category. All categories together constitute the taxonomic hierarchy.
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Each category, referred to as a unit of classification, represents a taxon (plural: taxa).
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Hierarchy is arranged in ascending or descending order. The basic unit is Species.
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Obligate Categories (Descending Order):
- Kingdom: Highest category (e.g., Animalia, Plantae). Assemblage of related Phyla/Divisions.
- Phylum (for animals) / Division (for plants): Assemblage of related Classes (e.g., Chordata, Angiospermae).
- Class: Assemblage of related Orders (e.g., Mammalia, Dicotyledonae).
- Order: Assemblage of related Families (e.g., Primata, Polymoniales). Identified based on aggregates of characters.
- Family: Group of related Genera with fewer similarities compared to genus and species (e.g., Hominidae, Solanaceae). Characterized based on vegetative and reproductive features (in plants).
- Genus: Group of related Species which has more characters in common compared to species of other genera (e.g., Panthera includes lion, leopard, tiger; Solanum includes potato, tomato, brinjal).
- Species: Group of individual organisms with fundamental similarities, capable of interbreeding to produce fertile offspring. Lowest category. (e.g., sapiens in Homo sapiens, tigris in Panthera tigris).
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Mnemonic (Example): Keep Pots Clean Or Family Gets Sick (Kingdom, Phylum, Class, Order, Family, Genus, Species)
5. Binomial Nomenclature
- System of providing scientific names to organisms with two components.
- Developed by Carolus Linnaeus (Father of Taxonomy).
- Universal Rules:
- Biological names are generally in Latin and written in italics.
- The first word represents the Genus (starts with a capital letter).
- The second word represents the Specific epithet (starts with a small letter).
- When handwritten, both words are separately underlined. When printed, they are in italics.
- The name of the author (who first described the species) appears after the specific epithet, usually in an abbreviated form (e.g., Mangifera indica Linn.).
- Importance: Ensures each organism has only one unique scientific name across the world, avoiding confusion caused by local common names.
- Governing Bodies:
- ICBN: International Code for Botanical Nomenclature (for plants).
- ICZN: International Code for Zoological Nomenclature (for animals).
6. Taxonomical Aids
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Tools and procedures used to store and preserve information as well as specimens for identification and classification of organisms.
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Herbarium:
- Storehouse of collected plant specimens that are dried, pressed, and preserved on sheets.
- Sheets are arranged according to a universally accepted system of classification.
- Herbarium sheets carry a label providing: Date and place of collection, English, local, and botanical names, family, collector's name.
- Serve as quick referral systems in taxonomical studies.
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Botanical Gardens:
- Collections of living plants for reference.
- Plants are grown for identification purposes, and each plant is labelled with its botanical/scientific name and family.
- Famous examples: Kew (England), Indian Botanical Garden (Howrah), National Botanical Research Institute (Lucknow).
- Also used for ex-situ conservation of plants.
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Museum:
- Collections of preserved plant and animal specimens for study and reference.
- Specimens preserved in containers/jars in preservative solutions (e.g., formalin).
- Insects are preserved in insect boxes after collecting, killing, and pinning.
- Larger animals (birds, mammals) are usually stuffed and preserved (taxidermy).
- Often have collections of skeletons too.
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Zoological Parks (Zoos):
- Places where wild animals are kept in protected environments under human care, resembling their natural habitats.
- Enable us to learn about their food habits and behaviour.
- Also contribute to ex-situ conservation of threatened animals.
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Key:
- An analytical tool used for identification of plants and animals based on similarities and dissimilarities.
- Based on contrasting characters generally in a pair called a couplet.
- Each statement in the key is called a lead.
- Represents the choice made between two opposite options, resulting in acceptance of one and rejection of the other.
- Separate taxonomic keys are required for each taxonomic category (e.g., Family, Genus, Species).
- Keys are generally analytical in nature.
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Other Aids: Flora (actual account of habitat and distribution of plants in a given area), Manuals (information for identification of names of species in an area), Monographs (information on any one taxon), Catalogues (alphabetical list of species).
Multiple Choice Questions (MCQs)
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Which of the following is NOT a defining characteristic of living organisms?
a) Metabolism
b) Cellular organization
c) Growth
d) Consciousness -
The system of providing a scientific name with two components to an organism is called:
a) Taxonomy
b) Systematics
c) Binomial Nomenclature
d) Classification -
According to the rules of binomial nomenclature, when handwritten, the scientific name should be:
a) Italicized
b) Underlined together
c) Separately underlined
d) Written in bold -
Which taxonomic aid uses living plants for reference and identification?
a) Herbarium
b) Museum
c) Botanical Garden
d) Zoological Park -
A group of related genera with fewer similarities as compared to genus and species constitutes a:
a) Class
b) Order
c) Family
d) Phylum -
Systematics differs from taxonomy primarily by considering:
a) Only morphological features
b) Only nomenclature
c) Evolutionary relationships (phylogeny)
d) Habitat and distribution -
Select the correct sequence of taxonomic categories in ascending order:
a) Species -> Genus -> Family -> Order -> Class -> Phylum -> Kingdom
b) Species -> Family -> Genus -> Order -> Class -> Phylum -> Kingdom
c) Kingdom -> Phylum -> Class -> Order -> Family -> Genus -> Species
d) Genus -> Species -> Family -> Order -> Class -> Phylum -> Kingdom -
A taxonomic key is based on:
a) Detailed description of a single taxon
b) Contrasting characters in a pair called a couplet
c) Preserved specimens
d) Living organisms in their natural habitat -
ICZN stands for:
a) International Code for Zoological Nomenclature
b) International Congress of Zoological Names
c) International Code for Botanical Nomenclature
d) Indian Code for Zoological Nomenclature -
Which of the following serves as a quick referral system in taxonomical studies, using dried and pressed plant specimens?
a) Museum
b) Botanical Garden
c) Zoological Park
d) Herbarium
Answer Key for MCQs:
- c) Growth (as it also occurs in non-living things by accretion)
- c) Binomial Nomenclature
- c) Separately underlined
- c) Botanical Garden
- c) Family
- c) Evolutionary relationships (phylogeny)
- a) Species -> Genus -> Family -> Order -> Class -> Phylum -> Kingdom
- b) Contrasting characters in a pair called a couplet
- a) International Code for Zoological Nomenclature
- d) Herbarium
Study these notes thoroughly. Remember to correlate these concepts with the questions provided in your Exemplar book to understand how they are tested. Good luck with your preparation!