Long Answer Questions (30) — Model Answers

1. 1. Explain the need for classification of living organisms and list any four benefits.
   Classification organises the vast diversity of living organisms into manageable groups based on similarities and differences. Benefits include: (1) Easier identification and naming of organisms; (2) Understanding evolutionary relationships and common ancestry; (3) Predicting characteristics of organisms placed in known groups; (4) Facilitating communication among scientists worldwide using standardized names and categories. A systematic classification also aids conservation efforts and biological research by providing a framework to study biodiversity.
2. 2. Describe the five-kingdom classification with one example and a key feature of each kingdom.
   The five-kingdom classification includes:
   Monera: Prokaryotic unicellular organisms lacking membrane-bound nucleus (e.g., Escherichia coli). Key feature: prokaryotic cell structure.
   Protista: Mostly unicellular eukaryotes (e.g., Amoeba, Paramecium). Key feature: true nucleus and organelles.
   Fungi: Eukaryotic, absorptive heterotrophs with chitin in cell walls (e.g., Rhizopus). Key feature: absorbative nutrition and spore production.
   Plantae: Multicellular autotrophs with cellulose cell walls (e.g., Hibiscus). Key feature: photosynthesis and organised tissues.
   Animalia: Multicellular heterotrophs without cell walls (e.g., Human). Key feature: specialised tissues and organs for varied functions. Each kingdom groups organisms sharing fundamental cellular and nutritional characteristics.
3. 3. Explain hierarchical classification and the major taxonomic ranks. Give a brief example using any familiar organism.
   Hierarchical classification arranges organisms into successive ranks from broad to specific: Kingdom, Phylum (Division in plants), Class, Order, Family, Genus, Species. Each lower rank represents organisms with increasing similarity. Example — Domestic dog: Kingdom: Animalia; Phylum: Chordata; Class: Mammalia; Order: Carnivora; Family: Canidae; Genus: Canis; Species: Canis lupus familiaris. This system helps place an organism in context relative to others and indicates relatedness.
4. 4. Describe the main distinguishing features of Monera and give two examples of organisms belonging to this kingdom.
   Monera consists of prokaryotic organisms characterised by absence of membrane-bound nucleus and organelles. They are unicellular, with genetic material in a nucleoid region, and cell walls typically containing peptidoglycan (in bacteria). Nutrition varies from autotrophic (photosynthetic cyanobacteria) to heterotrophic forms; reproduction is primarily asexual by binary fission. Examples: Escherichia coli (gut bacterium) and Nostoc (a cyanobacterium).
5. 5. Explain the characteristics and economic importance of fungi.
   Fungi are eukaryotic organisms with cell walls of chitin; they may be unicellular (yeast) or multicellular (mushrooms, molds). Nutrition is absorptive heterotrophy — they secrete enzymes to digest organic matter externally and absorb nutrients. Reproduction occurs both sexually and asexually via spores. Economic importance: beneficial fungi like Saccharomyces cerevisiae are used in baking and fermentation; Penicillium species produce antibiotics (penicillin); fungi decompose organic waste, recycling nutrients. Harmful effects include spoilage of food and plant diseases (e.g., rusts, smuts).
6. 6. Compare bryophytes and pteridophytes under five headings.
   Comparison:
   Presence of vascular tissue: Bryophytes: absent; Pteridophytes: present (xylem & phloem).
   Plant body: Bryophytes: thallus or small leafy forms (no true roots/stems); Pteridophytes: true roots, stems and leaves.
   Reproduction: Bryophytes: require water for gamete transfer; Pteridophytes: also require water for spores but have dominant sporophyte.
   Dominant generation: Bryophytes: gametophyte dominant; Pteridophytes: sporophyte dominant.
   Examples: Bryophytes: Funaria; Pteridophytes: Ferns (Pteris). These differences reflect adaptations to terrestrial life and complexity of vascular systems in pteridophytes.
7. 7. Write an essay on angiosperms highlighting their salient features and why they are considered the most advanced group of plants.
   Angiosperms (flowering plants) are the largest and most diverse group of plants. Salient features include presence of flowers as reproductive organs, seeds enclosed within fruits, double fertilisation resulting in endosperm formation, well-developed vascular tissues, and varied forms from herbs to trees. Flowers facilitate efficient pollination often with biotic agents (insects, birds), promoting cross-pollination and genetic diversity. Fruits protect seeds and aid dispersal by wind, water or animals. These innovations — enclosed seeds, specialized reproductive structures and efficient nutrient transport — have allowed angiosperms to colonise diverse habitats and become ecologically dominant, providing food, timber, medicines and habitat for many animals.
8. 8. Describe the structure and mode of nutrition of Amoeba with a labelled diagram (brief description in words if diagram not possible).
   Amoeba is a unicellular protist with an irregular shape formed by pseudopodia (false feet). Key parts: cell membrane, ectoplasm and endoplasm, nucleus, contractile vacuole for osmoregulation, food vacuoles and pseudopodia used for movement and engulfing food. Mode of nutrition: holozoic — it engulfs food particles by phagocytosis, forming food vacuoles where enzymes digest the material. Contractile vacuole helps expel excess water. (Students should practise a neat labelled sketch showing nucleus, pseudopodia and contractile vacuole.)
9. 9. Explain the classification and distinguishing features of arthropods. Include examples of three major classes.
   Arthropoda is a large phylum characterised by segmented bodies, jointed appendages, exoskeleton made of chitin, and ecdysis (molting). They exhibit bilateral symmetry and varied body plans grouped into classes:
   Insecta: Three-part body (head, thorax, abdomen), three pairs of legs, usually two pairs of wings (e.g., butterfly).
   Arachnida: Two body segments (cephalothorax and abdomen), four pairs of legs, no antennae (e.g., spider).
   Crustacea: Mostly aquatic, biramous appendages, two pairs of antennae (e.g., crabs).
   Arthropods are ecologically important as pollinators, decomposers, pests, and as food sources.
10. 10. Discuss the life cycle of a fern emphasizing alternation of generations.
    Ferns exhibit alternation of generations between the multicellular diploid sporophyte and multicellular haploid gametophyte. The dominant sporophyte is the familiar frond-bearing plant that produces sporangia on the underside of fronds. Meiosis in sporangia produces haploid spores which disperse and germinate into a small, green, heart-shaped gametophyte (prothallus). The gametophyte bears antheridia (male) and archegonia (female) that produce gametes; water is required for sperm to swim to the egg for fertilisation. Fertilisation produces a diploid zygote that grows into a new sporophyte. This cycle demonstrates the alternation between gametophyte and sporophyte generations, showing adaptation to terrestrial life with a dominant sporophyte stage.
11. 11. Describe the structure and economic importance of bacteria.
    Bacteria are unicellular prokaryotes with a simple cell structure: cell wall (peptidoglycan), plasma membrane, cytoplasm, nucleoid region containing circular DNA, ribosomes and sometimes flagella for movement. They multiply rapidly by binary fission and exhibit varied metabolic modes (autotrophic, heterotrophic). Economic importance:
    Beneficial: Decomposition and nutrient cycling, nitrogen fixation (Rhizobium) enriching soil, use in fermentation (yogurt, cheese), production of antibiotics and biotechnology applications.
    Harmful: Pathogens causing diseases like tuberculosis and cholera. Understanding bacterial roles aids medicine, agriculture and industry.
12. 12. Explain the structural organisation of a typical flowering plant and relate each part to its function.
    A typical flowering plant has root, stem, leaf and flower:
    Root: anchors the plant, absorbs water and minerals, stores food.
    Stem: supports aerial parts, transports water and nutrients via xylem and phloem, stores food in some species.
    Leaf: site of photosynthesis, gas exchange through stomata, transpiration.
    Flower: reproductive organ producing male (stamen) and female (pistil) structures for pollination and seed formation. Each organ's structure is adapted to its physiological role, ensuring growth and reproduction.
13. 13. Discuss how classification helps in understanding evolutionary relationships among organisms.
    Classification groups organisms based on shared characteristics often reflecting common ancestry. By comparing morphological, anatomical, embryological and molecular traits, taxonomists infer evolutionary relationships and construct phylogenetic trees. Similarities in structural features, genetic sequences or developmental pathways suggest relatedness and divergence from common ancestors. Modern classification increasingly uses molecular data (DNA/RNA) to refine relationships, revealing evolutionary lineages and aiding our understanding of speciation and adaptive evolution.
14. 14. Write detailed notes on lichens and explain their ecological significance.
    Lichens are symbiotic associations between a fungus (mycobiont) and an alga or cyanobacterium (photobiont). The fungus provides structure, protection and absorbs moisture and minerals; the photobiont performs photosynthesis to supply organic nutrients. Lichens colonise harsh habitats (rocks, tree bark) and are pioneer species in ecological succession. Ecological significance: bioindicators of air quality (sensitive to pollutants), soil formation through rock weathering, providing food and habitat for organisms, and contributing to nitrogen fixation when cyanobacteria are photobionts.
15. 15. Compare the modes of nutrition in plants, animals and fungi with examples.
    Plants: Autotrophic — produce organic food by photosynthesis using sunlight, CO2 and water (e.g., mango tree).
    Animals: Heterotrophic holozoic — ingest and internally digest food (e.g., cow, human).
    Fungi: Heterotrophic saprophytic or parasitic — absorb nutrients after external digestion by secreted enzymes (e.g., Rhizopus).
    These differences arise from structural adaptations: plants possess chloroplasts, animals have specialised digestive systems, fungi have hyphae and mycelium for absorption.
16. 16. Describe the general characteristics and examples of phylum Mollusca.
    Mollusca are soft-bodied animals often with a calcareous shell (external or internal). Key features include a muscular foot for movement, a visceral mass containing organs, and a mantle that secretes the shell. Many have a radula (tongue-like organ) for feeding. Classes include Gastropoda (snails), Bivalvia (clams), and Cephalopoda (octopus). Molluscs occupy marine, freshwater and terrestrial habitats and have economic importance as food (clams, oysters) and pearls, while some are pests or disease vectors.
17. 17. Explain the adaptations in plants that help them survive in different habitats (provide at least four examples).
    Adaptations include:
    Xerophytic adaptations: thick cuticle, reduced leaves or spines, deep roots to reduce water loss (e.g., cactus).
    Hydrophytic adaptations: aerenchyma for buoyancy, reduced cuticle and stomata on upper surface (e.g., water lily).
    Climbing plants: tendrils or adventitious roots to seek light (e.g., ivy).
    Salt-tolerant plants (halophytes): salt excretion mechanisms or succulent leaves to manage salinity (e.g., mangroves).
    These adaptations allow colonisation of varied niches by modifying morphology and physiology.
18. 18. Describe the circulatory system in earthworms and its significance.
    Earthworms have a closed circulatory system with blood enclosed in vessels. Major vessels include the dorsal blood vessel (pumping blood anteriorly), ventral blood vessel (transporting blood posteriorly), and five pairs of aortic arches (pseudo-hearts) that contract to circulate blood. Capillary-like networks supply body tissues with nutrients and oxygen. Significance: efficient transport of gases, nutrients and waste, aiding active burrowing lifestyle and supporting segmented body functions.
19. 19. Discuss the importance of binomial nomenclature and the rules for writing scientific names.
    Binomial nomenclature assigns each species a unique two-part Latinised name (Genus species), introduced by Linnaeus. Importance: universal communication avoiding regional common name confusion; provides information about relatedness (same genus indicates closer relation). Rules: genus name is capitalised and species name is lowercase; both are italicised or underlined when handwritten (e.g., Homo sapiens). The authority (name of describer) and year may follow for precision. This standardisation is essential in scientific literature and taxonomy.
20. 20. Explain how fungi are classified and provide examples of major groups with their characteristics.
    Fungi are classified based on reproductive structures and spore types. Major groups include:
    Zygomycota: produce zygospores (e.g., Rhizopus); often saprophytic.
    Ascomycota: sac fungi producing ascospores in asci (e.g., Saccharomyces, Penicillium).
    Basidiomycota: club fungi producing basidiospores on basidia (e.g., mushrooms, rusts).
    Deuteromycetes (imperfect fungi): sexual stage unknown (e.g., many antibiotic-producing species).
    Classification reflects life cycles and reproductive morphology, useful in understanding ecology and uses.
21. 21. Describe the major characteristics of phylum Chordata and the advantages they offer.
    Chordates possess, at some life stage, a notochord, dorsal hollow nerve cord, pharyngeal slits, endostyle (or thyroid) and post-anal tail. These features provide structural support (notochord), advanced nervous coordination (dorsal nerve cord), and adaptations for feeding and respiration (pharyngeal slits). In vertebrates, the notochord is replaced by a vertebral column, enabling larger body size, complex organ systems and adaptative diversity, facilitating locomotion, predation and varied ecological niches.
22. 22. Explain the role of microorganisms in nutrient cycling with specific examples.
    Microorganisms (bacteria, fungi, protozoa) decompose organic matter, breaking down complex molecules into simpler inorganic forms usable by plants. Example: decomp of leaf litter by fungi and bacteria releases minerals; nitrogen-fixing bacteria (Rhizobium) convert atmospheric N2 into ammonia for plant use; nitrifying bacteria convert ammonia to nitrates; denitrifying bacteria return nitrogen to atmosphere. These processes maintain soil fertility and ecosystem productivity by recycling essential elements.
23. 23. Discuss the structure and functions of xylem and phloem in higher plants.
    Xylem and phloem are vascular tissues for transport.
    Xylem: composed of tracheids, vessels, xylem fibres and xylem parenchyma; conducts water and dissolved minerals from roots to aerial parts; provides mechanical support.
    Phloem: includes sieve tube elements, companion cells, phloem fibres and parenchyma; translocates organic solutes (sugars) from source (leaves) to sink (growing tissues, storage organs).
    Together, they form a transport system vital for plant growth, nutrient distribution, and physiological integration.
24. 24. Explain the significance of structural adaptations in animals with two examples.
    Structural adaptations enhance survival in specific environments. Examples:
    Birds: hollow bones and wings for flight; beaks adapted to feeding habits (e.g., hooked beak in raptors).
    Fish: streamlined body and fins for efficient swimming; gills for aquatic respiration.
    Such adaptations enable efficient locomotion, feeding, defense and reproduction in respective habitats, demonstrating the link between form and function.
25. 25. Describe how viruses are different from cellular organisms and give two examples of viral diseases.
    Viruses are acellular infectious agents composed of nucleic acid (DNA or RNA) enclosed in a protein coat (capsid); some have lipid envelopes. They lack cellular organisation, metabolic machinery and cannot reproduce independently—requiring host cells for replication. They may integrate into host genomes or cause cell lysis. Examples of viral diseases: Influenza (caused by influenza virus) and AIDS (caused by HIV). Understanding their acellular nature is crucial in virology and disease control.
26. 26. Explain the evolutionary significance of homologous and analogous organs with examples.
    Homologous organs arise from common ancestry and have similar structural plan despite different functions—indicating divergent evolution (e.g., forelimbs of human, wing of bat, flipper of whale). Analogous organs perform similar functions but have different structural origins—indicating convergent evolution (e.g., wings of insects and birds). Homology helps infer phylogenetic relationships, while analogy shows adaptive solutions to similar environmental pressures.
27. 27. Discuss the main features and examples of poriferans and their ecological role.
    Porifera (sponges) are sessile aquatic animals with porous bodies and canal systems allowing water flow for filter feeding. Body composed of choanocytes (collar cells) that drive water current and capture food particles; support provided by spicules and spongin. Reproduction can be sexual (formation of larvae) or asexual (budding). Ecologically, sponges filter large volumes of water, maintain water clarity, and provide habitat for other organisms; they are also indicators of environmental changes in aquatic ecosystems.
28. 28. Provide a detailed answer on how molecular data has influenced modern classification systems.
    Molecular data (DNA/RNA sequences, protein comparisons) have revolutionised classification by providing objective, quantifiable measures of relatedness. Molecular phylogenetics uncovers genetic similarities and differences, leading to reclassification of organisms (e.g., splitting groups previously united by morphology). It helps resolve relationships among microorganisms and cryptic species, traces evolutionary timelines via molecular clocks, and supports cladistics—grouping by common ancestry. Molecular evidence complements morphology and has led to robust, often revised taxonomies reflecting evolutionary history more accurately.
29. 29. Explain the roles of various plant groups (algae, bryophytes, pteridophytes, gymnosperms, angiosperms) in ecosystems and human use.
    Algae: primary producers in aquatic ecosystems, produce oxygen and form base of food webs; some used as food supplements (seaweed).
    Bryophytes: colonise moist habitats, contribute to soil formation and moisture retention; used in horticulture (peat moss).
    Pteridophytes: important in soil formation and as pioneer species; some used as ornamental plants.
    Gymnosperms: timber and resins (e.g., pines), adapted to cold/dry habitats.
    Angiosperms: provide food, medicine, fibres, fuel and ecological services (habitat, pollination).
    Together they maintain ecosystem productivity and resources essential for humans.
30. 30. As a student preparing for board exams, outline an effective study plan to master this chapter and score well in classification questions.
    Study plan: (1) Read NCERT thoroughly and highlight definitions, examples and diagrams. (2) Make comparative tables (kingdoms, plant groups, animal phyla) summarising key features and examples for quick recall. (3) Practice labelled diagrams (Amoeba, leaf, flowering parts, life cycle of fern) and write stepwise answers. (4) Solve NCERT exercises and previous year board questions under timed conditions. (5) Use flashcards for important terms and perform short daily revisions. (6) Attempt at least 5 long answer questions weekly and get feedback on structure and content. Consistent practice, clarity of key concepts, and neat diagrams will help achieve high marks.

This set of 30 long answer questions is aligned with NCERT Class 9 — Chapter 13: Diversity in Living Organisms. Use it for thorough revision and exam practice. Copy the HTML directly into the WordPress editor (Text/HTML mode) for immediate use.