Chapter 12: Patterns in Life: Diversity and Classification
Biodiversity, why organisms are classified, the five kingdoms, plant and animal groups, hierarchy and binomial naming, fossils and threats to biodiversity.
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Biodiversity, endemic species and hotspots
Biodiversity is the immense variety of living organisms. Every organism plays a role in keeping nature stable: algae release most of our oxygen, fungi and bacteria decompose waste, birds, bees and bats pollinate flowers, plants capture sunlight to make food.
Humans depend on biodiversity for food, shelter, medicine and livelihood. Farmers conserved diverse crop varieties (drought tolerant, pest resistant); diversity reduces the risk of crop failure.
Endemic species are found naturally only in one region: Nilgiri tahr, Lion-tailed macaque, Nepenthes khasiana (pitcher plant), Neelakurinji in India.
Biodiversity hotspots: regions with many endemic species that have lost much habitat. Examples: Western Ghats, Indo-Burma (including North East India), Himalayas, Sundaland (including the Nicobar Islands).
Differences among individuals affected survival and reproduction; accumulated over generations they gave rise to new forms of life (evolution).
Why and how organisms are classified
Biological classification is the scientific system of grouping living organisms based on similarities and differences.
It makes study organised; shows similarities and differences and relationships; helps identify and name new organisms; supports conservation of organisms under threat; gives scientists a common system.
Criteria: external features, mode of nutrition (autotrophic or heterotrophic), internal structures, cell structure (unicellular or multicellular, prokaryote or eukaryote, cell wall), ecological role (producer, consumer, decomposer), reproduction, genetic (DNA) similarity.
The same organism can fit into different groups depending on the criterion. Similar features suggest common ancestors.
Case study: Pakke Tiger Reserve has nearly 300 bird species (India has about 1,300) and four hornbill species that nest only in large old trees.
Classification systems over time
Aristotle (4th century BCE): grouped animals by habitat (land, water, air) and external appearance. It relied only on easily visible features.
Linnaeus (1758): two kingdoms, Plantae and Animalia. Amoeba, Paramecium and bacteria did not fit.
Haeckel (1866): three kingdoms, added Protista for unicellular microscopic life.
Copeland (1938): four kingdoms, added Monera (bacteria have no true nucleus).
Whittaker (1969): five kingdoms, added Fungi (they do not move, are heterotrophic and absorb nutrients).
Classification keeps changing with new tools (microscopes, DNA studies): science is an ongoing process of reasoning. Carl Woese (1977) proposed the three domain system: Bacteria, Archaea, Eukarya.
Five kingdom classification
Basis: cell type (prokaryote or eukaryote), level of organisation (unicellular or multicellular), presence of cell wall, mode of nutrition, ecological role.
Monera: unicellular prokaryotes (bacteria, archaea, cyanobacteria). Bacteria are found everywhere; some are pathogens, many are useful (Lactobacillus, Rhizobium). Cyanobacteria are autotrophs; they added oxygen to the atmosphere about 2.5 billion years ago (stromatolites are their fossils).
Protista: unicellular eukaryotes, with no cell wall or a cellulose cell wall: Amoeba, Paramecium, Euglena. Some autotrophic, some heterotrophic; live in water or moist places.
Fungi: mostly multicellular eukaryotes with a cell wall of chitin; heterotrophic by absorption (saprophytes, parasites, symbionts); body of filaments (mycelium); reproduce by spores. Yeast is unicellular. Examples: mushrooms, Aspergillus, Penicillium. They are decomposers.
Plantae: multicellular autotrophic eukaryotes with a cellulose cell wall.
Animalia: multicellular heterotrophic eukaryotes without cell wall; most show locomotion and rapid response to stimuli.
Viruses are acellular (genetic material only, inactive outside a host), so they do not fit any of the five kingdoms.
Kingdom Plantae: five classes
Thallophyta (algae, e.g. Spirogyra): simple undifferentiated body (thallus), mostly aquatic. Cannot live on land.
Bryophyta (moss, Marchantia): first on land but need moisture; rhizoids; no vascular tissue; need water for reproduction (amphibians of the plant kingdom).
Pteridophyta (ferns): true roots, stems and leaves; vascular tissue (xylem carries water, phloem carries food); no seeds; need water for reproduction.
Gymnosperms (pine, cycads): naked seeds on cones; needle-like leaves reduce water loss; water not needed for fertilisation.
Angiosperms (flowering plants): flowers, fruits and seeds; seeds enclosed in fruits; most complex and most diverse group.
Lichens are symbiotic associations of an alga and a fungus and are bioindicators of air quality.
Kingdom Animalia: invertebrates
Animals with no notochord are non-chordata (invertebrates). The notochord is a flexible rod-shaped structure.
Porifera (sponges): pores, cellular level, fixed, aquatic, no tissues.
Cnidaria (Hydra, jellyfish, corals): tissue level, tentacles, a single opening.
Platyhelminthes (flatworms): bilateral symmetry, organ level, single opening; parasitic forms have hooks and suckers.
Nematoda (roundworms): cylindrical, organ system level, two openings (mouth and anus).
Annelida (earthworm): segmented, body cavity, organ systems.
Arthropoda (insects, crabs, spiders): jointed appendages, segmented body, hard exoskeleton (protection, less water loss).
Protochordates (e.g. Amphioxus) have a notochord at least once in life: a primitive type of chordate.
Vertebrates have a vertebral column (backbone) that supports the body and protects the brain and spinal cord. Five groups: fish, amphibians, reptiles, birds, mammals.
Adaptations: fins and gills in fish; feathers and hollow bones in birds; fat storage in camels; thick fur in polar bears; mammary glands in mammals.
Hierarchy and binomial nomenclature
Hierarchy from broad to specific: Kingdom → Phylum → Class → Order → Family → Genus → Species. Lower levels have fewer organisms with more features in common; each is part of the group above, like a postal address.
Tiger: Animalia, Chordata, Mammalia, Carnivora, Felidae, Panthera, P. tigris. Pea: Plantae, Magnoliophyta, Magnoliopsida, Fabales, Fabaceae, Pisum, P. sativum.
Binomial nomenclature (Linnaeus, 18th century): two parts, genus and species, in Latin form. Rules: genus begins with a capital letter, species in small letters; italics when printed, underlined when handwritten. Examples: Panthera tigris, Mangifera indica.
A species is a group of similar individuals that can interbreed and produce offspring.
Fossils and threats to biodiversity
Fossils are preserved remains of plants and animals in layers of rocks, sand and mud. Older layers contain simpler organisms; newer layers show more complex forms. Birbal Sahni studied fossil plants.
Biodiversity is under threat from pollution, deforestation, overuse of resources and climate change. When one species disappears, those that depend on it may decline too.
Forests with rich biodiversity act as barriers: mangroves reduced damage in the 1999 Odisha super cyclone; diversity lowers tick-borne disease risk (Kyasanur Forest Disease in the Western Ghats); soil microorganisms and mangroves break down or trap pollutants.
Examples: the Purple Frog (Nasikabatrachus sahyadrensis) of the Western Ghats; the Sangai deer of Manipur on phumdis (floating grasslands).
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NCERT Q&A
Answers to the Pause and Ponder questions and the Revise, Reflect, Refine exercises. Numerical working is in the Numericals tab.
Pause and Ponder
PAUSE AND PONDER 1
If many organisms share common features, could they also share a common ancestry?
Answer: Yes. Similar features in organisms suggest that they have evolved from common ancestors. The more features they share (including similarity in DNA), the more closely related they are likely to be.
PAUSE AND PONDER 2
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?
Answer: A single cell has all the organelles it needs, so one cell takes in food, respires, excretes, responds and reproduces. In a multicellular organism, these jobs are divided among specialised cells, tissues and organs, and the body is far larger, so many cells are needed.
PAUSE AND PONDER 3
Which features reduce the dependence of pteridophytes on water but still require moist conditions?
Answer: Pteridophytes have true roots, stems and leaves and vascular tissue (xylem and phloem) that carry water and food through the plant, so they are not limited to a thin body in water. They still need water for reproduction, so they need moist conditions.
PAUSE AND PONDER 4
Why do taller plants need specialised transport tissues?
Answer: Water and minerals must be carried from the roots to the top and food from the leaves to all parts over long distances, which simple diffusion cannot do. Xylem and phloem transport water and food throughout the plant.
PAUSE AND PONDER 5
How do seeds and fruits affect where and how plants can survive?
Answer: Seeds protect the embryo and contain stored food, and fruits help to spread seeds to new places by wind, water and animals. This lets plants live in many kinds of environments, including dry places, and reproduce without needing water for fertilisation (as in gymnosperms and angiosperms).
PAUSE AND PONDER 6
An earthworm and a beetle both have segmented bodies but the beetle has a hard external skeleton. How does the beetle's external skeleton help it survive?
Answer: The hard external covering (exoskeleton) protects the body, reduces water loss and supports powerful muscles, so the beetle can live in dry and exposed environments.
PAUSE AND PONDER 7
Does the term "biodiversity" relate only to the variety of organisms, or does it encompass other elements?
Answer: It covers more than the variety of species. It includes the variety within species (such as crop varieties), the habitats and ecosystems in which they live, and their interactions and ecological roles such as food webs, pollination and decomposition.
PAUSE AND PONDER 8
If you find a new organism in a pond, what features will you observe to classify it and why?
Answer: Observe its cell type (prokaryote or eukaryote, presence of a nucleus), whether it is unicellular or multicellular, the presence and type of cell wall, its mode of nutrition (autotrophic or heterotrophic), and its movement and body structure. These are the criteria used in the five kingdom classification, so they place it in a kingdom.
PAUSE AND PONDER 9
Why do genetic studies provide deep information about living beings?
Answer: Every cell has DNA which carries the instructions for growth and function. Organisms with similar DNA are considered to have common ancestry, so DNA comparison shows relationships that visible features cannot, and led to the three domain system.
PAUSE AND PONDER 10
How can changes in climate affect biodiversity?
Answer: Climate change alters temperature and rainfall, so habitats change. Species that cannot adapt or move may decline or disappear, and other species that depend on them also decrease, so biodiversity falls.
Revise, Reflect, Refine
QUESTION 1
Hari called an animal an insect and Meena said it was an earthworm. Which option confirms it is an insect? (i) Bilateral symmetrical body (ii) Body with jointed legs (iii) Cylindrical body (iv) Body with little segmentation
Answer: (ii) Body with jointed legs. Insects are arthropods with jointed appendages and a hard exoskeleton, while an earthworm is cylindrical and segmented.
QUESTION 2
Which feature of sponge cells supports their 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
Answer: (iii) Presence of a cell membrane. Sponges are multicellular and heterotrophic and their cells have no cell wall; of the given options only the cell membrane is a true feature of their cells.
QUESTION 3
Observe two different animals in your surroundings. What features help you distinguish between them? How do these features help place them into different groups?
Answer: Example: a cat and a fish. The cat has a backbone, hair and mammary glands and lives on land (mammal); the fish has a backbone, fins, gills and lives in water (fish). Both are vertebrates in Chordata, but differences in body covering, breathing organs and reproduction place them in different classes.
QUESTION 4
How would a scientist justify choosing cellular organisation as a more fundamental characteristic than the presence of xylem and phloem?
Answer: Cellular organisation (prokaryote or eukaryote, unicellular or multicellular, cell wall) applies to all living organisms, so it can divide them into the kingdoms. Xylem and phloem occur only in some plants (pteridophytes onwards) and are absent from animals, fungi and protists, so they can only separate groups within the plant kingdom.
QUESTION 5
A single-celled organism has a well-defined nucleus and multiple cilia. Which group does it most likely belong to?
Answer: Protista. It is unicellular and has a true nucleus (eukaryote), and cilia are used for movement, as in Paramecium.
QUESTION 6
How does the diversity of organisms contribute to the balance and stability of an ecosystem?
Answer: Each organism has a role: producers make food, consumers feed on them and decomposers recycle nutrients; pollinators and seed dispersers help plants. Many different species make food webs strong, so if one species declines, others can fill its role and the ecosystem stays stable.
QUESTION 7
If all unicellular organisms were grouped into a single kingdom, what problems would arise?
Answer: Very different organisms would be put together: prokaryotes without a nucleus (bacteria) with eukaryotes with a nucleus (Amoeba, yeast); autotrophs with heterotrophs; organisms with cell walls of different kinds. The grouping would hide real differences and relationships and would be of little use.
QUESTION 8
Why are viruses not placed in any of the five kingdoms?
Answer: Viruses are acellular: they have genetic material but no cellular organisation, and they remain inactive outside a host. The five kingdoms are based on cell type, level of organisation and nutrition, which do not apply to viruses.
QUESTION 9
Would you create a separate category for viruses or keep them outside the system? What does this indicate about the evolving nature of classification?
Answer: Either choice can be justified. Keeping viruses outside the five kingdoms is reasonable because they are not cellular and cannot carry out life processes on their own; a separate category could also be made to include them in the system. This shows that classification is a human-made system that changes as new knowledge and tools appear.
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?
Answer: They have no cells, no cytoplasm or organelles, no mode of nutrition and cannot reproduce or show life processes outside a host. So the criteria of cell type, nutrition and level of organisation cannot be applied. Classification systems depend on the criteria chosen and some organisms do not fit neatly.
QUESTION 11
Pteridophytes and bryophytes lack flowers and seeds, yet are in different groups. Explain using key features.
Answer: Pteridophytes have true roots, stems and leaves and vascular tissue (xylem and phloem) to transport water and food. Bryophytes have rhizoids and only simple stem-like and leaf-like parts, with no vascular tissue, so they remain small and need moist places.
QUESTION 12
Which group, class or genus, has fewer members but more features in common?
Answer: Genus. In the hierarchy, lower groups (species, genus, family) contain fewer organisms that share more features, while higher groups (class, phylum, kingdom) contain more members that share fewer features.
QUESTION 13
A new organism has locomotion and autotrophic nutrition. Which characters would help identify it as belonging to Protista?
Answer: It should be unicellular and have a true nucleus (eukaryote) with a cell wall of cellulose or none. Moving by flagella or cilia together with photosynthesis suggests a protist such as Euglena; plants do not move and animals are not autotrophic.
QUESTION 14
A unicellular eukaryote was identified as a fungus. What identification key would you suggest to keep it in Kingdom Fungi?
Answer: Check for a cell wall made of chitin (protists have cellulose or no wall) and for heterotrophic nutrition by absorption from dead organic matter (saprophytic), with reproduction by spores or budding, as in yeast.
QUESTION 15
Case study of organisms P, Q, R, S, T: (i) one organism of Fungi; (ii) one in Monera; (iii) why R and Q differ; (iv) why S cannot be classified by nutrition alone; (v) T and the limits of classification; (vi) habitat-only classification; (vii) multicellular eukaryote without chlorophyll absorbing nutrients from a host.
Answer: (i) Q: multicellular, filamentous, cell wall present, no chlorophyll, grows on dead organic matter. (ii) P: no true nucleus (prokaryote). (iii) R is unicellular (Protista; flagella, can photosynthesise or feed), while Q is multicellular with a cell wall and absorptive nutrition (Fungi): level of organisation, cell wall and nutrition separate them. (iv) S is a multicellular animal with a backbone; nutrition alone does not place it, since fungi and some protists are also heterotrophic. Cellular organisation and the backbone are also needed. (v) T lacks cellular organisation, which is the basic criterion; this shows classification systems have limits. (vi) Bats and birds (both fly), or fish and whales (both aquatic), would be grouped together although they differ greatly in structure and descent, hiding true relationships. (vii) Fungi, because it absorbs nutrients externally rather than ingesting food; this can be confirmed by a chitin cell wall and spores.