NCERT Class 9 Science Chapter 12 Solutions – Diversity in Living Organisms
Looking for accurate and complete ncert class 9 science chapter 12 solutions for the new CBSE curriculum (2026-27)? You are in the right place! In this guide, we provide step-by-step, direct, and easy-to-understand solutions for all exercise questions from NCERT Exploration Class 9 Science Chapter 12: Diversity in Living Organisms.
These answers are crafted specifically to help students write clean, exam-ready answers in their notebooks without extra confusion or lengthy fluff.
Question 1
Meena and Hari observed an animal in their garden. Hari called it an insect while Meena said it was an earthworm. Choose the correct option which confirms that it is an insect:
(i) Bilateral symmetrical body (ii) Body with jointed legs
(iii) Cylindrical body (iv) Body with little segmentation
Correct Option: (ii) Body with jointed legs
Explanation: Insects belong to Phylum Arthropoda, which is fundamentally characterized by jointed appendages (legs) and segmented bodies, whereas earthworms belong to Phylum Annelida (cylindrical, segmented worms without jointed legs).
Question 2
Sponges represent one of the simplest animal body plans. Their bodies lack true tissues and organs. Which feature of sponge cells supports its classification under the animal kingdom?
(i) Absence of mitochondria (ii) Ability to photosynthesise
(iii) Presence of a cell membrane (iv) Presence of a cell wall
Correct Option: (iii) Presence of a cell membrane (and absence of rigid cell walls).
Explanation: Animal cells lack rigid cell walls (unlike plants and fungi) and possess flexible cell membranes, relying on heterotrophic nutrition.
Question 3
Observe two different animals in your immediate environment. What features help you distinguish between them? How do these features help place them into different groups?
For example, comparing a housefly (insect) and a pigeon (bird):
- Distinguishing features: Presence of exoskeleton, jointed legs, and wings in the fly versus feathers, beak, backbone (vertebral column), and internal skeleton in the pigeon.
- Taxonomic placement: The fly is placed in Phylum Arthropoda based on invertebrate jointed limbs, while the pigeon is placed in Vertebrata (Class Aves) due to its bony internal backbone.
Question 4
How would a scientist justify choosing cellular organisation as a more fundamental characteristic for the basis of classification rather than the presence of xylem and phloem?
Cellular organisation (prokaryotic vs. eukaryotic, unicellular vs. multicellular) is fundamental because every living organism is built of cells, determining its basic metabolic and structural framework. In contrast, vascular tissues (xylem and phloem) are specialized traits found only in a specific subgroup of plants (vascular plants/tracheophytes), making them too restricted for universal classification.
Question 5
You find an unlabeled slide of a single-celled organism that has a well-defined nucleus and multiple cilia. Which group would it most likely belong to? Give reasons.
- Group: Kingdom Protista (specifically ciliated protozoans like Paramecium).
- Reasons: It is unicellular with a well-defined nucleus (making it eukaryotic, ruling out Monera) and possesses cilia for locomotion, characteristic of aquatic protists.
Question 6
How does the diversity of organisms contribute to the balance and stability of an ecosystem?
Biodiversity ensures complex ecological food webs, nutrient cycling, pollination, and pest regulation. High diversity provides ecological redundancy; if one species declines, others can fulfill similar functions, preventing ecosystem collapse and maintaining overall stability.
Question 7
If all unicellular organisms were grouped into a single kingdom, what problems would arise?
Grouping all unicellular organisms together would place vastly different life forms into the same category—such as bacteria (prokaryotic, microscopic) alongside amoeba and yeast (eukaryotic). It would ignore fundamental evolutionary differences in cell structure, mode of nutrition, and genetics.
Question 8
Viruses were studied in earlier classes. Why are they not placed in any of the five kingdoms? Give reasons.
Viruses are considered borderline between living and non-living. They lack cellular machinery, cytoplasm, and organelles when outside a host cell. Because biological classification systems are built around cellular life, viruses do not fit into the five-kingdom system.
Question 9
If you were asked to revise the five kingdom classification, would you create a separate category for viruses or keep them outside the system? Justify your answer and explain what this indicates about the evolving nature of scientific classification.
- Placement: Keeping them in a separate border category or sub-system is ideal since they are obligate intracellular parasites.
- Significance: This highlights that scientific classification is dynamic and continuously evolves as new biological entities and genetic insights are discovered.
Question 10
Viruses contain genetic material like living organisms but lack cellular organisation. Which features prevent them from fitting into the five kingdom system? What does this tell us about the limitations of classification systems?
Their complete lack of cell structure, metabolism, and independent reproduction prevents their inclusion. This reveals that human classification systems are human-made models designed for living cellular organisms and may struggle with anomalous entities bridging living and non-living worlds.
Question 11
Both pteridophytes and bryophytes lack flowers and seeds, yet they are placed in different groups. Explain this classification using their key features.
- Bryophytes: Non-vascular land plants lacking true roots, stems, leaves, and specialized vascular tissue (xylem/phloem).
- Pteridophytes: Vascular cryptogams possessing specialized vascular tissues (xylem and phloem) and true roots, stems, and leaves, justifying their placement in a more advanced plant group.
Question 12
In the classification hierarchy, which group—class or genus—has fewer members but more features in common? Explain your answer.
Genus has fewer members and more features in common. As we move down the taxonomic hierarchy (Kingdom → Phylum → Class → Order → Family → Genus → Species), organisms share a closer evolutionary ancestry and exhibit greater morphological similarity.
Question 13
A scientist discovers a new organism with locomotion and autotrophic nutrition. Which character(s) would help the scientist identify the organism belonging to Protista according to the five kingdom classification?
Its unicellular eukaryotic structure (presence of a true membrane-bound nucleus and organelles) along with locomotion (such as flagella or cilia) would place it in Kingdom Protista (e.g., unicellular algae like Chlamydomonas or euglenoids).
Question 14
A researcher identified a unicellular eukaryotic organism as fungi. What identification key would you suggest according to the five kingdom classification to keep a unicellular organism in the Kingdom Fungi?
The key features would be: presence of a chitinous cell wall and absorptive heterotrophic nutrition (saprophytic feeding on dead organic matter), which distinguishes unicellular fungi (like yeasts) from unicellular protists or bacteria.
Question 15
Case Study Analysis based on Organisms P, Q, R, S, and T from various environments (Pond, Soil, Animal tracts):
| Organism | Key Observations | Inferred Group / Kingdom |
|---|---|---|
| P | Microscopic, no true nucleus, rigid cell wall, extreme habitats | Monera (Archaebacteria) |
| Q | Multicellular, filamentous, cell wall (no chlorophyll), saprophytic | Fungi |
| R | Unicellular, true nucleus, flagella, mixotrophic (photo/hetero) | Protista |
| S | Multicellular, tissues, backbone present, aquatic respiration early on | Animalia (Vertebrata) |
| T | Acellular, genetic material, inactive outside host | Virus |
- (i) Kingdom Fungi: Organism Q (multicellular, filamentous, cell wall, saprophytic on dead organic matter).
- (ii) Kingdom Monera: Organism P (no true nucleus / prokaryotic).
- (iii) R vs Q criteria: Organism R is unicellular, eukaryotic, and mixotrophic with flagella (Protista), whereas Q is multicellular, filamentous, and purely saprophytic with chitinous walls (Fungi).
- (iv) Why S cannot be classified by nutrition alone: Organism S is multicellular with complex tissue differentiation and a backbone. Nutrition alone cannot capture anatomical complexity, embryology, and evolutionary backbone development.
- (v) Organism T (Virus): Lacks cellular organization entirely. This demonstrates the limitations of cell-based classification systems in categorizing non-cellular replicating entities.
- (vi) Classification based only on habitat: Organisms living in water (e.g., whales, fish, algae, amoeba) would be incorrectly grouped together. This would result in grouping prokaryotes, plants, and mammals together, completely obscuring true evolutionary relationships.
- (vii) Multicellular, eukaryotic, lacks chlorophyll, external absorption: It should be placed under Kingdom Fungi. Fungi secrete digestive enzymes externally and absorb digested nutrients across their cell walls, unlike animals that ingest food internally.
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Based on latest NCERT class 9 book.