NCERT Class 9 Science Chapter 12 Patterns in Life: Diversity and Classification

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NCERT Class 9 Science Chapter 12 Patterns in Life: Diversity and Classification

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Patterns in Life: Diversity and Classification

Chapter – 12

Pause And Ponder

1. If many organisms share common features, could they also share a common ancestry?

Ans: Yes. If many organisms share common features, they may have a common ancestry. Similar characteristics suggest that they have evolved from a common ancestor over a long period of time.

Pause And Ponder

1. How can a single-celled organism carry out all its life processes when billions of cells are required to perform similar functions in multicellular organisms like us?

Ans: A single-celled organism performs all its life processes within one cell. That single cell carries out functions such as nutrition, respiration, excretion, growth, reproduction, and response to stimuli. In multicellular organisms, these functions are divided among specialised cells, tissues, and organs.

Pause And Ponder

1. Which plant features reduce their dependence on water but still require moist conditions?

Ans: The development of roots, stems, and leaves, along with a waxy cuticle and stomata, reduces the dependence of plants on water. However, they still require moist conditions for reproduction because fertilisation depends on water.

2. Why do taller plants need specialised transport tissues?

Ans: Taller plants need specialised transport tissues (xylem and phloem) to transport water, minerals, and food efficiently to all parts of the plant.

3. How do seeds and fruits affect where and how plants can survive?

Ans: Seeds and fruits help in the dispersal of seeds to new places. This reduces competition for resources and enables plants to grow and survive in different environments.

Pause And Ponder

1. An earthworm (Annelida) and a beetle (Arthropoda), both have segmented bodies but the beetle has a hard external skeleton. How does the beetle’s external skeleton help it survive?

Ans: The beetle’s hard external skeleton (exoskeleton) protects its body from injury, prevents water loss, and provides support and attachment for muscles. This helps the beetle move efficiently and survive in different environments.

Pause And Ponder

1. Does the term ‘biodiversity’ relate only to the variety of organisms, or does it encompass other elements? 

Ans: Biodiversity includes not only the variety of organisms but also the diversity of their genes, ecosystems, and the interactions among them.

2. If you find a new organism in a pond, what features will you observe to classify it and why? 

Ans: I will observe its cell type, body structure, mode of nutrition, method of reproduction, and movement. These features help in identifying and classifying the organism into the correct group.

3. Why do genetic studies provide deep information about living beings? 

Ans: Genetic studies reveal the hereditary characteristics and evolutionary relationships among organisms, helping us understand their origin and classification.

4. How can changes in climate affect the biodiversity?

Ans: Climate change can alter habitats, reduce food and water availability, and cause the extinction or migration of species, leading to a decrease in biodiversity.

Revise, Reflect, Refine

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.

Ans: (ii) Body with jointed legs. 

Insects belong to the phylum Arthropoda, which is characterised by having jointed appendages (limbs) and a hard external skeleton. Earthworms, on the other hand, are annelids with cylindrical, segmented bodies but lack jointed legs.

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.

Ans: (iii) Presence of a cell membrane. 

Animals are multicellular, heterotrophic eukaryotes that lack a rigid cell wall, meaning their cells are only enclosed by a cell membrane. Sponges possess this feature, whereas they contain mitochondria (so i is false) and cannot photosynthesise (so ii is false).

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?

Ans: If we observe a housefly and a stray dog, we can distinguish them by their external and internal features. The housefly has a segmented body, jointed legs, and a hard external skeleton, which classifies it under the phylum Arthropoda (invertebrates). The dog has a backbone (internal skeleton), hair, and advanced organ systems, which places it under Vertebrata (Mammalia) within the phylum Chordata.

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?

Ans: Cellular organisation (whether an organism is prokaryotic or eukaryotic, unicellular or multicellular) is a highly fundamental characteristic because it applies to all living organisms across all five kingdoms (Monera, Protista, Fungi, Plantae, Animalia). In contrast, the presence of xylem and phloem (vascular tissues) is a specific structural feature that only applies to a subgroup within the plant kingdom (differentiating pteridophytes, gymnosperms, and angiosperms from simpler plants like bryophytes).

5. You find an unlabelled 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.

Ans: It would most likely belong to the kingdom Protista. The kingdom Protista includes single-celled (unicellular) eukaryotic organisms, meaning they possess a well-defined, membrane-bound nucleus. Paramecium is a classic example of a ciliated protist.

6. How does the diversity of organisms contribute to the balance and stability of an ecosystem?

Ans: Biodiversity is essential for ecosystem stability because every organism plays a specific ecological role (as producers, consumers, or decomposers). For instance, microscopic algae produce oxygen, fungi and bacteria decompose waste to make soil fertile, and animals pollinate flowers and disperse seeds. This rich diversity establishes interconnected food webs, reduces the risk of species collapse, and strengthens environmental resilience.

7. If all unicellular organisms were grouped into a single kingdom, what problems would arise?

Ans: Grouping all unicellular organisms together would create scientific confusion because it ignores a massive evolutionary difference: the presence or absence of a true, membrane-bound nucleus. Bacteria are prokaryotes without a true nucleus, while organisms like Amoeba are eukaryotes with a true nucleus. Combining them would violate the fundamental criteria of cell type used in biological classification.

8. Viruses were studied in earlier classes. Why are they not placed in any of the five kingdoms? Give reasons.

Ans: Viruses are not placed in any of the five kingdoms because they lack cellular organisation (they are acellular). While they contain genetic material, they cannot function or reproduce independently and remain completely inactive outside of a living host cell. The five-kingdom system is strictly based on cellular life forms.

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.

Ans: Viruses should be kept outside the traditional cellular domains or placed in a completely separate, non-cellular category. This is because the entire five-kingdom classification is founded on the structural features of cells (prokaryotic vs. eukaryotic). This limitation indicates that scientific classification is an evolving and ongoing process of reasoning. As we make new discoveries that don’t fit existing frameworks, classification systems must be modified or expanded to accommodate new knowledge.

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?

Ans: The primary feature preventing viruses from fitting in is their acellular nature and their inability to perform life processes outside a host cell. This tells us that classification systems have limitations; they are artificial frameworks built upon our current understanding of biology and are designed specifically for typical cellular organisms, making them inadequate for borderline entities like viruses.

11. Both pteridophytes and bryophytes lack flowers and seeds, yet they are placed in different groups. Explain this classification using their key features.

Ans: Although both lack flowers and seeds, they are placed in different groups because of major structural differences in their plant bodies. Bryophytes (like mosses) possess a simpler body design without true roots, stems, leaves, or vascular tissues (xylem and phloem). In contrast, Pteridophytes (like ferns) have evolved to possess true roots, stems, leaves, and a specialised vascular system (xylem and phloem) to transport water and food.

12. In the classification hierarchy, which group — class or genus — has fewer members but more features in common? Explain your answer.

Ans: The genus has fewer members but more features in common. The biological classification hierarchy is arranged from broad groups to highly specific ones: Kingdom → Phylum → Class → Order → Family → Genus → Species. As we move down the hierarchy from class to genus, the group size becomes smaller, and the organisms within it are more closely related, thereby sharing many more specific common features.

13. A scientist discovers a new organism with the characteristic features of locomotion and autotrophic nutrition. Which character(s) would help the scientist identify the organism belonging to Protista according to the five kingdom classification?

Ans: To belong to Protista, the newly discovered organism must be unicellular and eukaryotic (possessing a true, membrane-bound nucleus). In the kingdom Protista, there are already organisms like Euglena or Chlamydomonas that are single-celled, have a true nucleus, show locomotion, and can be autotrophic.

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?

Ans: The primary identification key would be the composition of its cell wall and its mode of nutrition. If the unicellular eukaryotic organism has a cell wall made of chitin and exhibits a heterotrophic (saprophytic or parasitic) mode of nutrition rather than autotrophic, it strictly belongs in the Kingdom Fungi. Yeast is the prime example of a unicellular fungus classified this way.

15. During a long-term ecological study, students examined organisms collected from three different environments — a freshwater pond, damp soil near decaying logs and the digestive tract of animals. Instead of naming organisms directly, scientists recorded only structural, cellular and nutritional features as given in the table below.

Organism	Key Observations
P	Microscopic; no true nucleus; rigid cell covering; survives high salinity and temperature
Q	Multicellular; filamentous body; cell wall present; no chlorophyll; grows on dead organic matter
R	Unicellular; true nucleus; contractile vacuole present; moves using flagella; shows photosynthesis in light but heterotrophic in the absence of light.
S	Multicellular; well-differentiated tissues; backbone present; aquatic respiration during early life stage
T	Acellular; contains genetic material; remains inactive outside a host cell

The students realised that some organisms fit neatly into Whittaker’s five kingdom classification, while others challenged the very basis of this classification. 

Based on the case study, answer the following questions — 

(i) Identify one organism that clearly belongs to the Kingdom Fungi. State one observation that supports your answer. 

Ans: Organism Q belongs to Fungi. This is supported by the observation that it is multicellular with a filamentous body (mycelium), possesses a cell wall, lacks chlorophyll, and grows on dead organic matter (saprophytic nutrition).

(ii) Which organism would be placed in the Kingdom Monera? Mention one characteristic that justifies this placement. 

Ans: Organism P belongs to Monera. This placement is justified because it is microscopic and has “no true nucleus”, meaning it is a prokaryote.

(iii) Organisms R and Q are both eukaryotic, yet they are placed in different kingdoms. Analyse the criteria that separate them. 

Ans: They are separated primarily by their level of organisation and nutrition. Organism R is unicellular and placed in Protista. Organism Q is multicellular with a filamentous body, lacks chlorophyll entirely, and relies strictly on decaying matter, which firmly places it in Fungi.

(iv) Explain why organism S cannot be classified using the mode of nutrition alone. 

Ans: Organism S is heterotrophic, but mode of nutrition alone cannot classify it because Fungi, many Protists, and most Monerans are also heterotrophic. Organism S must be classified as an Animal (specifically a vertebrate) because it is multicellular, possesses well-differentiated tissues, and has a distinct backbone.

(v) Organism T does not fit into any of the five kingdoms. Which fundamental characteristic used in classification does it lack and what does this reveal about the limitations of classification systems? 

Ans: Organism T (a virus) lacks cellular organisation (it is acellular). This reveals that our rigid biological classification systems are inherently limited because they are strictly designed to categorise cellular life forms, struggling to place unique, border-line entities like viruses.

(vi) If classification were based only on habitat, which organisms might be incorrectly grouped together? Explain the scientific consequences of such a classification. 

Ans: Organisms like P (bacteria) and Q (fungi) might be grouped together as “soil dwellers,” or organisms like S (vertebrate) and R (protist) as “aquatic”. The scientific consequence is massive confusion, as completely unrelated organisms (prokaryotes with eukaryotes, or unicellular with complex multicellular vertebrates) would be clustered together, entirely failing to show their true evolutionary relationships or biological functions.

(vii) Imagine scientists discover a new organism that is multicellular, eukaryotic, lacks chlorophyll and absorbs nutrients from a host externally. Should it be placed under fungi or animalia? Justify your reasoning using classification criteria.

Ans: It should be placed under Fungi. According to the criteria, organisms that are multicellular, eukaryotic, heterotrophic (lacking chlorophyll), and obtain nutrients by absorbing them externally from a host (often via filaments) belong to Kingdom Fungi. In contrast, while Animalia are also multicellular and heterotrophic, they typically ingest their food internally rather than absorbing it externally, and their cells strictly lack cell walls.