Patterns in Life: Diversity and ClassificationClass 9 Science NCERT Solutions
15 Solutions
Generated by KedovoAI
Solution 1 of 15
Q1Revise, Reflect, Refine
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
Solution
The correct option is (ii) Body with jointed legs.
Reasoning:
According to the chapter, the phylum Arthropoda, which includes insects, is characterized by having jointed appendages (legs). An earthworm belongs to the phylum Annelida and has a segmented body but lacks jointed legs. While both may have bilateral symmetry and segmented bodies, the presence of jointed legs is a defining structural feature of an insect that distinguishes it from an earthworm.
Q2Revise, Reflect, Refine
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
Solution
The correct option is (iii) Presence of a cell membrane.
Reasoning:
Sponges are classified under the animal kingdom because they are multicellular, heterotrophic eukaryotes. A key characteristic of animal cells is that they are enclosed by a cell membrane but lack a rigid cell wall, which is present in plants, fungi, and bacteria.
- (i) is incorrect; animal cells have mitochondria.
- (ii) is incorrect; animals are heterotrophic, not photosynthetic.
- (iv) is incorrect; animal cells do not have a cell wall. Therefore, the presence of a cell membrane (and the absence of a cell wall) is a feature consistent with an animal cell, supporting the sponge's classification in the animal kingdom.
Q3Revise, Reflect, Refine
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?
Solution
Let us consider two common animals: a crow and a dog.
Distinguishing Features:
- Body Covering: The crow's body is covered with feathers, while the dog's body is covered with hair (fur).
- Locomotion: The crow has wings and can fly, whereas the dog has four legs and walks or runs.
- Reproduction: The crow lays eggs (oviparous), while the dog gives birth to live young (viviparous).
- Mouth parts: The crow has a beak, while the dog has a jaw with teeth.
Placement into Different Groups:
These features help place them into different classes within the phylum Chordata (subphylum Vertebrata).
- Crow: The presence of feathers, wings for flight, and a beak are characteristic features of the class Aves (birds).
- Dog: The presence of hair on the body, giving birth to live young, and having mammary glands to feed them are characteristic features of the class Mammalia (mammals).
Q4Revise, Reflect, Refine
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?
Solution
A scientist would justify choosing cellular organisation as a more fundamental characteristic for classification because it represents a broader, more basic level of difference among all living organisms. The classification hierarchy proceeds from general to specific characteristics.
-
Universality: Cellular organisation—whether an organism is prokaryotic or eukaryotic, and unicellular or multicellular—is a characteristic that can be used to classify all known life forms. It is one of the first and most significant divergences in the history of life.
-
Specificity: The presence of xylem and phloem (vascular tissues) is a highly specialized feature. It is found only within the kingdom Plantae and, more specifically, only in certain groups like Pteridophytes, Gymnosperms, and Angiosperms. It is not present in algae, bryophytes, or any organism outside the plant kingdom.
Therefore, cellular organisation is used at a higher level of classification (e.g., separating Kingdom Monera from the other four kingdoms) because it is a fundamental characteristic shared or differing among vast groups of organisms. The presence of vascular tissue is a more specific trait used to differentiate groups at a lower level within a single kingdom.
Q5Revise, Reflect, Refine
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.
Solution
The organism would most likely belong to the Kingdom Protista.
Reasons:
- Single-celled Eukaryote: The presence of a well-defined nucleus indicates that the organism is a eukaryote. The five-kingdom classification places single-celled eukaryotic organisms primarily in the Kingdom Protista.
- Presence of Cilia: Cilia are hair-like structures used for movement. The presence of cilia is a common feature in many protists, such as Paramecium, which use them for locomotion and feeding.
Based on these characteristics—being a unicellular eukaryote with specialized structures for movement—the organism fits the description of a member of Kingdom Protista.
Q6Revise, Reflect, Refine
How does the diversity of organisms contribute to the balance and stability of an ecosystem?
Solution
The diversity of organisms, or biodiversity, is essential for the balance and stability of an ecosystem because each species plays a specific role, and their interactions create a resilient and functional natural system.
-
Interdependence and Food Webs: Different organisms are linked through complex food webs. Plants (producers) capture energy from the sun, herbivores consume plants, carnivores consume herbivores, and decomposers (fungi, bacteria) recycle nutrients from dead organic matter back into the soil. The greater the diversity, the more pathways there are in the food web, making the ecosystem more stable. If one species declines, others can fill its role, preventing a total collapse.
-
Essential Ecological Roles: Specific groups of organisms perform vital functions. For example, microscopic algae produce a significant portion of the Earth's oxygen, bees and birds pollinate plants (essential for reproduction), and microorganisms maintain soil fertility.
-
Ecosystem Resilience: A diverse ecosystem is better able to withstand and recover from environmental stresses like climate change, disease, or pollution. For instance, a forest with many different tree species is less likely to be wiped out by a single disease than a monoculture forest.
In summary, every organism contributes to the overall health of the ecosystem. This interconnectedness ensures that energy flows, nutrients are cycled, and the system as a whole remains stable and productive.
Q7Revise, Reflect, Refine
If all unicellular organisms were grouped into a single kingdom, what problems would arise?
Solution
Grouping all unicellular organisms into a single kingdom would create significant problems because it would ignore a fundamental difference in cellular structure, making the classification system unscientific and less useful.
The main problem would be grouping prokaryotes and eukaryotes together.
-
Ignoring Fundamental Cell Structure: Bacteria (Kingdom Monera) are unicellular prokaryotes, meaning their cells lack a true, membrane-bound nucleus and other organelles. In contrast, organisms like Amoeba and Paramecium (Kingdom Protista) and yeast (Kingdom Fungi) are unicellular eukaryotes, with a well-defined nucleus and complex organelles. The prokaryote-eukaryote split represents one of the most significant evolutionary divergences in the history of life.
-
Loss of Evolutionary Relationships: Such a grouping would obscure the evolutionary relationships between organisms. Unicellular eukaryotes (like protists) are more closely related to multicellular eukaryotes (plants, animals, fungi) than they are to prokaryotes (bacteria). A classification system should reflect these relationships.
-
Contradiction of Classification Criteria: The five-kingdom system uses cell type (prokaryotic vs. eukaryotic) as a primary, high-level criterion. Lumping all unicellular organisms together would violate this fundamental principle and create a kingdom based solely on the number of cells, which is a less fundamental characteristic than the type of cell.
Q8Revise, Reflect, Refine
Viruses were studied in earlier classes. Why are they not placed in any of the five kingdoms? Give reasons.
Solution
Viruses are not placed in any of the five kingdoms because they do not fit the fundamental criteria used for classifying living organisms.
Reasons:
-
Acellular Nature: The five-kingdom classification system is for cellular life. Viruses are not cells; they are acellular particles consisting of genetic material (DNA or RNA) enclosed in a protein coat. They lack a cell membrane, cytoplasm, and organelles.
-
Lack of Independent Metabolism: Living organisms can carry out life processes such as respiration, nutrition, and excretion on their own. Viruses are metabolically inert outside a host cell. They cannot produce energy or synthesize proteins by themselves.
-
Dependence on a Host for Reproduction: Viruses can only reproduce by invading a living host cell and hijacking its cellular machinery to make more copies of themselves. They cannot grow or reproduce independently.
Because they exist on the borderline between living and non-living things and lack a cellular structure, they do not belong in any of the five kingdoms (Monera, Protista, Fungi, Plantae, or Animalia), all of which consist of cellular organisms.
Q9Revise, Reflect, Refine
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.
Solution
If asked to revise the five-kingdom classification, I would keep viruses outside the system rather than creating a separate kingdom for them.
Justification:
The five-kingdom classification is fundamentally based on organizing cellular life. The primary criteria include cell type (prokaryotic/eukaryotic), cell number (unicellular/multicellular), and mode of nutrition. Since viruses are acellular, creating a sixth kingdom for them would contradict the foundational principle of the entire system. They are better treated as a separate, unique category of biological entities that are not truly 'organisms' in the same sense as cellular life.
What this indicates about the evolving nature of scientific classification:
This situation perfectly illustrates that scientific classification is not a static, absolute set of rules but an evolving, human-made framework designed to organize our knowledge of the natural world.
- Science is a Process: As new discoveries are made (like viruses or archaea), existing systems are challenged. This forces scientists to refine, revise, or even replace old models.
- Models Have Limitations: The five-kingdom system is a useful model, but it has limitations. It cannot neatly categorize everything. The existence of entities like viruses highlights these boundaries.
- Progress through Change: The continuous process of questioning and revising classification systems based on new evidence (like genetic data leading to the three-domain system) is a hallmark of how science works. It is an ongoing quest for a more accurate understanding, not a search for a final, unchangeable truth.
Q10Revise, Reflect, Refine
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?
Solution
Features preventing viruses from fitting into the five-kingdom system:
The primary feature that prevents viruses from being classified in the five-kingdom system is their lack of cellular organisation (they are acellular). The system is designed to classify organisms made of one or more cells. Specifically, viruses lack:
- A cell membrane, cytoplasm, and organelles.
- The ability to carry out their own metabolic processes (like respiration or protein synthesis).
- The ability to reproduce independently without a host cell.
What this tells us about the limitations of classification systems:
The case of viruses reveals that classification systems are human-made tools with inherent limitations. They are designed to bring order to our understanding of nature, but nature is complex and does not always fit into neat boxes.
- Definitional Boundaries: It shows that even the definition of "life" can be ambiguous. Viruses challenge our criteria for what it means to be a living organism.
- Models are Not Reality: A classification system is a model, not a perfect representation of reality. When an entity does not fit, it highlights the model's limitations rather than a flaw in the entity itself.
- Necessity for Flexibility: It underscores the need for scientific frameworks to be flexible and open to revision as our knowledge expands and we encounter exceptions that challenge existing rules.
Q11Revise, Reflect, Refine
Both pteridophytes and bryophytes lack flowers and seeds, yet they are placed in different groups. Explain this classification using their key features.
Solution
Although both pteridophytes and bryophytes are seedless plants, they are placed in different groups because of significant differences in their body structure and the presence of a vascular system.
Bryophyta (e.g., Mosses):
- Plant Body: They have a simple, undifferentiated plant body. They lack true roots, stems, and leaves. Instead, they have root-like structures called rhizoids for anchorage.
- Vascular Tissue: They do not have a specialized vascular system (xylem and phloem) for transporting water and food. This limits their size and requires them to live in moist environments.
Pteridophyta (e.g., Ferns):
- Plant Body: They have a well-differentiated plant body with true roots, stems, and leaves. This is a major evolutionary advancement over bryophytes.
- Vascular Tissue: They are the first terrestrial plants to possess a specialized vascular system (xylem and phloem). This allows for efficient transport of water and nutrients, enabling them to grow much larger and live in a wider range of terrestrial habitats than bryophytes.
In conclusion, the classification separates them based on the evolutionary step of developing a differentiated body with a true vascular transport system, which is present in pteridophytes but absent in bryophytes.
Q12Revise, Reflect, Refine
In the classification hierarchy, which group-class or genus-has fewer members but more features in common? Explain your answer.
Solution
In the classification hierarchy, the genus has fewer members but more features in common.
Explanation:
The biological classification system is hierarchical, moving from broad categories to more specific ones:
Kingdom → Phylum → Class → Order → Family → Genus → Species
- As we move down this hierarchy, the groups become more specific and include fewer types of organisms. A class (e.g., Mammalia) is a large group containing many different orders, families, and genera (e.g., dogs, cats, monkeys, whales).
- A genus (e.g., Panthera) is a much smaller group, containing only very closely related species (e.g., Panthera tigris - tiger, and Panthera leo - lion).
Because the organisms in a genus are more closely related, they share a greater number of specific, common features than the organisms grouped together in a broader category like a class.
Q13Revise, Reflect, Refine
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?
Solution
To identify the organism as belonging to Protista, the most crucial character the scientist would need to confirm is its cellular organisation, specifically that it is a unicellular eukaryote.
Reasoning:
- Locomotion and Autotrophic Nutrition are not exclusive: While these features are found in some protists (like Euglena), they are not unique to the kingdom. Plants are autotrophic, and most animals exhibit locomotion.
- Unicellular Eukaryote is Key: The defining characteristic of the Kingdom Protista in the five-kingdom classification is that it is a group for eukaryotic organisms that do not fit into the other kingdoms, and it is composed predominantly of single-celled eukaryotes.
Therefore, observing that the organism is composed of a single cell with a well-defined, membrane-bound nucleus would be the definitive evidence to place it in the Kingdom Protista.
Q14Revise, Reflect, Refine
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?
Solution
To justify placing a unicellular eukaryotic organism in the Kingdom Fungi, the key identification feature to check would be the composition of its cell wall.
Identification Key: The cell wall should be made of chitin.
Reasoning:
According to the five-kingdom classification, the Kingdom Fungi includes heterotrophic eukaryotes that have a cell wall made of a tough, complex sugar called chitin. While most fungi are multicellular (like mushrooms and moulds), there are exceptions like yeast, which is unicellular.
- Protista: Some unicellular eukaryotes have cell walls, but they are typically made of cellulose (if present).
- Fungi: The presence of a chitin cell wall is a defining characteristic of the entire fungal kingdom.
Therefore, even if the organism is unicellular, confirming its cell wall is made of chitin would be the definitive key to classify it as a fungus (like yeast) rather than a protist.
Q15Revise, Reflect, Refine
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.
Organisms 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.
(ii)
Which organism would be placed in the Kingdom Monera? Mention one characteristic that justifies this placement.
(iii)
Organisms R and Q are both eukaryotic, yet they are placed in different kingdoms. Analyse the criteria that separate them.
(iv)
Explain why organism S cannot be classified using the mode of nutrition alone.
(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?
(vi)
If classification were based only on habitat, which organisms might be incorrectly grouped together? Explain the scientific consequences of such a classification.
(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.
Solution
(i)
Organism Q clearly belongs to the Kingdom Fungi. The key observation supporting this is that it is a heterotroph with a saprophytic mode of nutrition, as indicated by "grows on dead organic matter". Additionally, its filamentous body is characteristic of moulds, which are fungi.
(ii)
Organism P would be placed in the Kingdom Monera. The characteristic that justifies this placement is that it has "no true nucleus", which means it is a prokaryote. Kingdom Monera is the only kingdom for prokaryotic organisms.
(iii)
Organisms R and Q are separated by two main criteria:
1. Level of Organisation: Organism R is unicellular, while Organism Q is multicellular (and filamentous). This difference in body complexity is a key criterion.
2. Mode of Nutrition: Organism Q is strictly heterotrophic (saprophytic). Organism R is mixotrophic—it can be autotrophic (photosynthesis in light) and heterotrophic (in the absence of light). The ability to photosynthesise places R outside the Fungi kingdom.
Based on these differences, R is placed in Protista and Q is placed in Fungi.
(iv)
Organism S is a vertebrate (presence of a backbone), placing it in Kingdom Animalia. All animals are heterotrophic. If we used only the mode of nutrition (heterotrophic) to classify it, it would be grouped with all fungi (like Q) and many protists. This would ignore its far more defining characteristics, such as being multicellular with well-differentiated tissues and possessing a backbone, which clearly separate it from these simpler organisms. Classification requires considering a combination of fundamental features, not just one.
(v)
Organism T lacks a cellular structure (it is "acellular"). The five-kingdom classification is based entirely on cellular organisms. This reveals the limitation that such classification systems are models designed by humans to organize living things, and they may not be able to categorize entities like viruses (which T represents) that exist at the boundary of living and non-living.
(vi)
If classification were based only on habitat, organisms found in aquatic or moist environments could be incorrectly grouped. For example, Organism R (a protist from a pond), Organism S (an amphibian/fish, aquatic in early life), and Organism P (a bacterium that can survive high salinity) might all be found in water. Grouping them together would be scientifically meaningless, as it would ignore fundamental differences in their cell type (prokaryote vs. eukaryote), body plan (unicellular vs. multicellular), and evolutionary history.
(vii)
The new organism should be placed under the Kingdom Fungi.
Justification: The key criteria here are the mode of nutrition and cell structure.
- Mode of Nutrition: The organism absorbs nutrients externally. This absorptive heterotrophic nutrition is the hallmark of the Kingdom Fungi. In contrast, animals are typically ingestive heterotrophs (they ingest food and digest it internally).
- Cell Wall: Although not stated, fungi possess a cell wall (made of chitin), while animals do not. The absorptive mode of nutrition is a strong indicator that it is a fungus.
Therefore, based on its absorptive nutrition, it fits the description of a fungus far better than an animal.