Class 11 Biology — New Syllabus 2025-26

THREE-DOMAIN SYSTEM OF CLASSIFICATION
Q1. Explain Three-Domain System of Classification. How is it different from the Five-Kingdom system?

Ans. Five-Kingdom Classification

• This system was proposed by American ecologist Robert Whittaker in 1969.
• According to this system all living organisms were classified into five kingdoms.
• Monera, Protista, Fungi, Plantae and Animalia.
• The kingdom Monera included all prokaryotes (organisms without a nucleus).
• The other four kingdoms included eukaryotes (organisms with a nucleus).

Three-Domain Classification

• An American microbiologist, Carl Woese in 1990 proposed the three domain system based on molecular and genetic studies. His three domain system provides a more accurate picture of evolutionary relationships of organisms.
• Woese discovered that prokaryotes are not all the same, they exist in two very different forms: 1. Bacteria 2. Archaea
• He introduced three domains instead of kingdoms:
  1. Domain Bacteria – True bacteria (prokaryotes)
  2. Domain Archaea – Ancient bacteria-like organisms (prokaryotes)
  3. Domain Eukarya – All eukaryotes (Protists, Fungi, Plants, Animals)

Key Differences

• The five-kingdom system grouped all prokaryotes into one kingdom (Monera).
• The three-domain system separates prokaryotes into two distinct domains: Bacteria and Archaea.
• Molecular evidences suggest Archaea are more closely related to eukaryotes than to bacteria. Which means Eukarya evolved from Archaea, after archaea split off from bacteria.

Q2. Describe distinguishing unique characteristics of Domain Archaea. Write their major groups.

In the five-kingdom system, this domain was included in kingdom Monera. The name Archaea comes from the Greek archaios ("ancient"). They are prokaryotes which diverged from bacteria in very ancient times.

★ Archaebacteria: Archaea were initially classified as a group of bacteria, and were called archaebacteria.

Size: Individual archaeans range from 0.1 μm to over 15 μm in diameter, some form aggregates or filaments up to 200 μm in length.

Morphology: They occur in various shapes, such as spherical, rod-shape, spiral, lobed, or rectangular.

Reproduction: Archaea reproduce asexually by binary or multiple fission, fragmentation, or budding. Mitosis and meiosis do not occur in archaea.

Archaea are unique because:

1. Cell Membrane — Archaean cell membrane contains lipids with ether-linkage between glycerol and fatty acid chains. The fatty acid chains are branched, making their membranes more resistant to extreme conditions. Bacteria and Eukarya have membrane lipids with fatty acids attached to glycerol by ester linkages, with unbranched fatty acid chains.

2. Cell Wall Composition — Archaea cell walls lack cellulose and peptidoglycan; instead they contain distinct polysaccharides and proteins (some archaea have pseudopeptidoglycan). Bacterial cell walls contain peptidoglycan, a polymer of sugars and amino acids. In Eukarya, cell walls (if present) are cellulose in plants or chitin in fungi.

3. Genetic Differences — Archaea share several genetic sequences and regulatory features with eukaryotes, highlighting their closer evolutionary relationship.

4. Metabolism — Archaea have unique metabolic processes like methanogenesis (production of methane), not found in bacteria or Eukarya. Bacteria exhibit photosynthesis, nitrogen fixation and fermentation. Eukarya metabolism is often more complex, including cellular respiration, photosynthesis, and fermentation.

Major Groups of Archaea

Methanogens (produce methane), Halobacteria (extremely saline environments), Thermococci (hot environments), Thaumarchaeota (nitrogen cycle).

Q3. Describe the general characteristics of Domain Bacteria.

In the five-kingdom system, this domain was included in kingdom Monera. They are the true bacteria, with several distinct characteristics differentiating them from Archaea and Eukarya.

• Cell Structure: Prokaryotic — lack a true nucleus and membrane-bound organelles.
• Cell Wall Composition: Composed of peptidoglycan (murein).
• Genetic Material: Single, circular chromosome in the nucleoid region.
• Plasmids: Small, circular DNA molecules transferable between bacteria, aiding genetic diversity.
• Reproduction: Asexually through binary fission.
• Nutritional Modes: Autotrophs and heterotrophs.
• Morphology: Cocci (spherical), bacilli (rod-shaped), spirilla (spiral), vibrios (comma-shaped).
• Arrangement: Singly, pairs (diplococci), chains (streptococci), clusters (staphylococci).
• Flagella, Pili and Fimbriae: Flagella for movement; pili and fimbriae for attachment and genetic exchange (conjugation).
• Respiration: Obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles or aerotolerant anaerobes; some ferment.
• Extremophiles: Thermophiles, halophiles, acidophiles.
• Pathogenicity & Symbiosis: Some cause disease; many live in mutualism or commensalism.

Major Groups of Bacteria

Proteobacteria (E. coli, Rhizobium, H. pylori), Firmicutes (Bacillus subtilis, Lactobacillus, Clostridium botulinum), Actinobacteria (Streptomyces, M. tuberculosis), Cyanobacteria (Anabaena, Spirulina), Spirochaetes (Treponema pallidum), Acidobacteria (Acidobacterium), Aquificae (Aquifex pyrophilus).

Q4. Explain the general characteristics of Domain Eukarya.

The domain Eukarya encompasses all organisms with eukaryotic cells, fundamentally different from the prokaryotic cells of Bacteria and Archaea.

• Cell Structure: True nucleus enclosed by nuclear membrane; membrane-bound organelles (mitochondria, chloroplasts, ER, Golgi, lysosomes, peroxisomes); cytoskeleton (microtubules, microfilaments, intermediate filaments) for structural support, movement, and intracellular transport.
• Genetic Material: Multiple linear chromosomes with histone proteins.
• Reproduction: Mostly sexual (meiosis + fertilization); some asexual via mitosis.
• Complex Cellular Organization: Cells differentiate into specialized tissues/organs.
• Evolutionary Relationships: Originated via endosymbiosis (aerobic bacteria → mitochondria; cyanobacteria → chloroplasts).

TAXONOMIC HIERARCHY
Q5. Elaborate the hierarchical system for the classification of living organisms.

Classification is organized into a hierarchical system of taxa (singular: taxon), from Domain down to Species:

1. Domain — highest level; three domains: Archaea, Bacteria, Eukarya.

2. Kingdom — groups life sharing fundamental characteristics e.g. Animalia, Plantae, Fungi, Protista within Eukarya.

3. Phylum — organisms share a basic body plan e.g. phylum Chordata (notochord).

4. Class — more specific common traits e.g. class Mammalia (hair, mammary glands).

5. Order — shared characteristics and evolutionary history e.g. order Primates (large brains, opposable thumbs).

6. Family — even more closely related e.g. family Hominidae.

7. Genus — very closely related, visually similar species e.g. genus Homo.

8. Species — most specific; single interbreeding type e.g. Homo sapiens.

SALIENT FEATURES OF KINGDOMS OF DOMAIN EUKARYA
Q6. What are the salient features of kingdoms of domain Eukarya?

Eukarya consists of kingdoms Protista, Fungi, Plantae and Animalia — all with complex eukaryotic cells containing a nucleus and other membrane-bound organelles.

1. Kingdom Protista

Eukaryotes which are unicellular, colonial, filamentous or simple multicellular (no specialized multicellular sex organs).

Major Groups: Protozoa (animal-like, unicellular, heterotrophic — Paramecium, Amoeba, Plasmodium, Trypanosoma); Algae (plant-like, cellulose walls, chlorophyll, autotrophs — Euglena, diatoms, dinoflagellates, red/green/brown algae); Fungi-like protists (Myxomycota — slime molds, Oomycota — water molds, saprophytic, hyphae-like structure).

2. Kingdom Fungi

Eukaryotic, heterotrophic, uni/multicellular; cell wall of chitin; absorb food rather than ingest.

Major Groups: Zygomycota (aseptate hyphae e.g. Rhizopus), Ascomycota (largest group — molds, morels, truffles, yeasts), Basidiomycota (septate hyphae — mushrooms, toadstools, puffballs, rusts, smuts). ~100,000 known species; most Ascomycetes found in lichens, some in mycorrhizae.

3. Kingdom Plantae

Eukaryotic, multicellular, cellulose cell walls, autotrophic (photosynthesis), develop from embryos.

Major Groups: Non-vascular (bryophytes — liverworts, hornworts, mosses); Vascular (tracheophytes) — seedless (ferns) and seed plants: Gymnosperms (naked seeds e.g. Pine, Spruce) and Angiosperms (flowering, most diverse — 235,000 species; Monocots e.g. grass, corn and Dicots e.g. rose, sunflower).

4. Kingdom Animalia

Eukaryotic, multicellular, heterotrophic; develop from embryos; ingest food and digest it within their bodies e.g. mammals, birds, reptiles.

Q7. Table showing distinguishing characteristics of kingdoms of Three Domains

Basic Terminologies related to Kingdom Animalia

Animals (metazoa) are subclassified into: Parazoa (phylum Porifera — lack tissues organized into organs, indeterminate/asymmetrical shape) and Eumetazoa (tissues organized into organs/organ systems — includes radially symmetrical Grade Radiata (phylum Cnidaria) and bilaterally symmetrical Grade Bilateria).

Diploblastic animals: body of two cell layers (ectoderm, endoderm); lesser specialization, sac-like digestive system, no CNS. Triploblastic animals: body of three layers (ectoderm, mesoderm, endoderm); greater specialization, specialized organ systems, blood vascular system present in most.

Triploblastic animals may be acoelomate, pseudocoelomate or coelomate:

• Acoelomates (Platyhelminthes): no body cavity; mesoderm forms a loose tissue (parenchyma/mesenchyma) filling space around organs.
• Pseudocoelomates (Aschelminthes): pseudocoelom (false body cavity) — not lined by coelomic epithelium, develops from blastocoel, bounded externally by muscles, internally by intestinal cuticle.
• Coelomates: true coelom lined by mesoderm (outer parietal + inner visceral layers), filled with coelomic fluid — e.g. animals from annelids to chordates.

Coelomates are further divided into: Protostomes (blastopore becomes mouth; coelom via schizocoely — Aschelminthes, Annelida, Mollusca, Arthropoda) and Deuterostomes (mouth forms away from blastopore, which becomes anus; coelom via enterocoely — Echinodermata, Hemichordata, Chordata).

CLASSIFICATION OF KINGDOM ANIMALIA
Q8. Discuss the general characteristics of Phylum Porifera.

Phylum Porifera (literal meaning: pore bearing) contains sponges.

1. Habitat: Mostly marine (Leucosolenia, Euplectella - Venus flower basket); Spongilla is a common freshwater sponge.

2. Level of Organization: No tissue-level organization; mostly asymmetrical, some radially symmetrical.

3. Nervous System: Absent.

4. Water Flow System: Numerous pores (ostia) let water in; a larger osculum lets water out.

5. Body Structure: Outer pinacoderm (pinacocytes); middle jelly-like mesohyle (amoeboid cells); inner choanoderm (choanocytes/collar cells) lining the spongocoel. Skeleton of calcium carbonate or silica needles (spicules).

6. Reproduction: Mostly asexual (budding, regeneration); some form gemmules (resistant capsules) — released on parent's death, amoeboid cells emerge to form a new sponge in favourable conditions.

Q9. Describe the general characteristics of Phylum Cnidaria.

1. Habitat: Almost all marine (few freshwater e.g. hydra, jellyfish); most colonial (obelia, corals) and sessile (hydra, coral); some motile (jellyfish).

2. Symmetry: Radially symmetrical, diploblastic.

3. Body Structure: Epidermis (ectoderm) + gastrodermis (endoderm), with jelly-like mesoglea between containing amoeboid cells.

4. Defense System: Cnidocytes contain nematocysts for defense and prey capture.

5. Digestive System: Sac-type — single opening (mouth = anus), gastrovascular cavity, mouth surrounded by tentacles.

6. Nervous System: Nerve net; no CNS, respiratory, excretory or transport systems.

7. Body Forms: Polyps (cylindrical, attached at aboral end, asexual) and Medusae (umbrella-like, free-swimming, sexual).

Q10. Describe the general characteristics of Phylum Platyhelminthes.

"Flatworms" — unsegmented, soft, dorsoventrally compressed.

1. Habitat: Free-living (planaria) or endoparasitic (liver fluke, tapeworm, blood-fluke).

2. Body Organization: Triploblastic. Tapeworms are segmented.

3. Body Cavity: Acoelomate — parenchyma fills space between body wall and organs.

4. Symmetry: Bilateral.

5. Excretory System: Protonephridia with flame cells; waste exits via nephridiopore.

6–7. Respiratory/Circulatory/Nervous: No respiratory/circulatory systems; nerve net with cerebral ganglia and longitudinal cords.

8. Eyespots: Most free-living flatworms have two simple eyespots anteriorly.

9. Reproduction: Asexual fission; sexual reproducers are hermaphrodites.

Q11. Outline the general characteristics of Phylum Nematoda.

"Thread-like" roundworms. ★ Aschelminthes — pseudocoelomates classified in seven phyla, of which Nematoda is representative.

1. Habitat: Free-living (Caenorhabditis elegans) or parasitic (ascaris, hookworm, pinworm, whipworm).

2. Body Organization: Triploblastic, bilateral, unsegmented; pseudocoelomate (false cavity filled with fluid).

3. Digestive System: Tube-like, mouth (anterior) and anus (posterior).

4. Excretory System: Protonephridia + two excretory canals uniting anteriorly into a single canal opening via nephridiopore (ventral).

5. Nervous System: Nerve ring around pharynx attached to four longitudinal nerve cords.

6. Sense Organ: Sensory papillae (hair-like) on lips.

7–8. Respiratory/Circulatory/Reproduction: No defined respiratory/circulatory systems; unisexual (separate testes/ovaries).

Q12. Describe the general characteristics of Phylum Mollusca.

"Soft bodied" molluscs, un-segmented.

1. Habitat: Widely distributed; aquatic (mussels, octopus, oyster) or moist places (land snail).

2. Body Organization: Triploblastic, bilateral, true coelom; protostomes.

3. Body Structure: Head, visceral mass (digestion/excretion/reproduction organs), foot.

4. Mantle Cavity: Epithelial envelope (mantle) around visceral mass; secretes calcareous shell in most.

5. Radula: Rasping tongue-like organ (absent in bivalves).

6. Circulatory: Open type (except cephalopods) — single ventricle, two auricles.

7–8. Digestive/Excretory: Tube-like gut (mouth+anus); paired nephridia discharge into mantle cavity.

9. Respiratory: Gills.

10. Nervous: Three pairs of ganglia (head, visceral mass, foot).

11–12. Locomotion/Classes: Muscular foot; Class Gastropoda (slug, garden snail), Class Bivalvia (mussel, oyster), Class Cephalopoda (octopus, cuttlefish).

Q13. Describe the general characteristics of Phylum Annelida.

"Little rings" — segmented worms.

1. Habitat: Marine (nereis), freshwater (leech), damp soil (earthworm); some ectoparasitic (leeches).

2. Body organization: Bilateral, triploblastic, protostome coelomates.

3. Metameric Segmentation: Body divided into similar segments separated by septa, each with its own circulatory, excretory, neural elements.

4. Setae: Chitinous bristles for anchoring during movement (absent in leeches).

5. Digestive System: Tube-like, divided into distinct parts (simplified in parasitic forms).

6. Excretory System: Ciliated, funnel-shaped metanephridia, one pair per segment.

7. Circulatory System: Closed type; pulsating blood vessels (pseudohearts); haemoglobin dissolved in plasma.

8. Respiratory: Through skin.

9. Nervous System: Cerebral ganglion (brain), double ventral nerve cord, ganglia per segment.

10. Receptors: Tactile, chemoreceptors, balance, photoreceptors; some have well-developed eyes.

11. Reproduction: Mostly hermaphrodite (earthworm, leech); some unisexual (nereis).

Q14. Elaborate the general characteristics of Phylum Arthropoda.

"Jointed legs" — insects, crustaceans, spiders, scorpions, centipedes; found in every habitat.

1–2. Habitat/Symmetry: Triploblastic, bilateral, protostome coelomates; coelom reduced to reproductive/excretory systems.

3. Jointed Appendages: Modified for running, swimming, capturing prey, respiration, reproduction, mouthparts.

4. Body Structure: Segmented; fused into tagmata — head, thorax, abdomen.

5. Exoskeleton & Ecdysis: Chitin exoskeleton, shed periodically (ecdysis/molting, driven by hormone ecdysone) to allow growth.

6. Circulatory: Open type; blood (haemolymph) in hemocoel, colourless (no haemoglobin).

7. Respiratory: Tracheal tubes opening via spiracles; aquatic forms use gills.

8. Digestive: Tube-like, with mouth, esophagus, crop, gizzard, mesenteron, ileum, colon, rectum, anus.

9. Excretory: Malpighian tubules; excrete solid uric acid crystals.

10. Nervous: Well-developed CNS, three fused cerebral ganglia, double ventral nerve cord; compound eyes, antennae.

11. Reproductive: Unisexual, egg-laying.

12. Classes: Crustacea (crayfish, crab), Insecta (fly, butterfly), Arachnida (spider, mite, scorpion), Myriapoda (centipede, millipede).

Q15. Explain the general characteristics of Phylum Echinodermata.

"Spiny skinned" — exclusively marine (cake urchin, sea star, sea urchin, brittle star, sea cucumber).

1–2. Organization: Triploblastic, deuterostome coelomates; larvae bilateral, adults radially symmetrical (5 or multiples of 5 around oral-aboral axis).

3. Skeleton: Calcareous endoskeleton (ossicles) from mesoderm; forms spines.

4–5. Water-Vascular System & Tube Feet: Ring canal around mouth ↔ madreporite; radial canals → lateral canals → tube feet (locomotion via water pressure).

6. Digestive: Tube-like — mouth, oesophagus, stomach, intestine, rectum, anus.

7. Respiratory/Excretory: No specialized organs.

8. Nervous: Poorly developed — nerve net, nerve ring, radial nerves.

9. Reproduction: Asexual (body division + regeneration) and unisexual. ★ Many echinoderms (especially sea stars, brittle stars) can drop and regenerate body parts.

Q16. Outline the four major characteristics of Chordata, also describe their major groups.

Chordates are bilateral, triploblastic, deuterostome coelomates, with four unique characteristics present at some developmental stage:

1. Notochord — rod-like semi-rigid body of vacuolated cells; extends between gut and dorsal nerve cord; retained throughout life in lower chordates, replaced by vertebral column in vertebrates.

2. Pharyngeal slits — series of openings in pharynx wall; develop into gills (Amphioxus, fishes), functional temporarily (amphibians), or modified (reptiles/birds/mammals — e.g. Eustachian tube).

3. Tubular nerve cord — dorsal to notochord, expands anteriorly as brain.

4. Post-anal tail — posterior to anus; retained in some, degenerates in others during development.

Classification

Phylum Chordata includes: Invertebrate Chordates — Subphylum Urochordata (notochord/nerve cord only in free-swimming larvae e.g. sea squirts) and Subphylum Cephalochordata (notochord persists throughout life e.g. Amphioxus); and Vertebrates — possess vertebral column and cranium, divided into seven classes in two groups (Pisces & Tetrapoda).

CLASSIFICATION OF VERTEBRATES
Q17. Describe the basic characteristics of group Pisces.

• Habitat: Aquatic vertebrates — freshwater or marine.
• Streamlined body: fusiform, reduces water resistance.
• Scales: placoid, cycloid or ctenoid.
• Skeleton: cartilaginous (sharks/rays) or bony (most fish).
• Respiration: gills, often covered by operculum in bony fish.
• Circulatory: closed, two-chambered heart, single/incomplete circulation.
• Fins: paired and unpaired, for locomotion/balance/direction.
• Reproduction: mostly oviparous, some viviparous; fertilization external (bony fish) or internal (cartilaginous fish).
• Ectothermic.

Q18. Describe the common traits of Class Amphibia.

First class of tetrapods.

• Skeleton: Bony; cervical vertebra allows skull to nod.
• Skin: Smooth, moist — gas exchange, thermoregulation, water absorption/storage.
• Heart: Three-chambered, double-circuit (2 atria, 1 ventricle).
• Respiration: Gills (larval), lungs + skin (adult).
• Ectotherms: Poikilothermic, hibernate in winter.
• Examples: Salamander/newts (tailed), frogs/toads (tail-less), caecilians (legless).
• Reproduction: Unisexual, usually external fertilization.

Q19. Discuss the common characteristics of reptiles.

• Amniotic Eggs: First group with amniotic eggs.
• Extra-embryonic membranes: amnion, allantois, chorion — protect from drying, nourish embryo, enable land development.
• Food: Yolk (food supply) and albumin (nutrients/water).
• Shell: Leathery calcareous, gas-permeable but not water-permeable.

• Skin: Dry, scaly.
• Endoskeleton: Harder than amphibians; atlas & axis vertebrae allow more head movement.
• Heart: Ventricle incompletely partitioned.
• Thermoregulation: Ectothermic, poikilothermic.
• Fertilization: Internal, oviparous.
• Examples: Lizards, snakes, tuatara, crocodiles.

Q20. Explain in detail the specific traits which belong to all Aves (birds).

1. Feathers — flight surfaces, lift, steering, heat/water conservation.
2. Thermoregulation — endotherms, homeotherms.
3. Body Plan — streamlined; forelimbs = wings; light bones; keel on sternum for flight muscles.
4. Digestive System — crop (storage), gizzard (crushing food, no teeth).
5. Heart — four-chambered, right aortic arch.
6. Nervous System — well developed; vision & hearing key senses.
7. Respiration — nares → pharynx → trachea → syrinx (voice) → bronchi → air sacs → parabronchi in lungs.
8. Bills — replace teeth, modified per diet.
9. Fertilization — internal, external development (oviparous).
10. Amniotic eggs — yolk + albumin, leathery shell.
11. Running birds (lost flight) — ostrich, kiwi, rhea, cassowary, emu.
12. Flying birds — pigeon, parrot, crow, eagle, robin.

Q21. How are mammals the most advanced class of Chordata?

1. Mammary glands — nourish young with milk; functional in females; hair on body.
2. Skin — sebaceous (oil) & sudoriferous (sweat) glands.
3. Teeth — milk teeth + permanent teeth.
4. Ear — pinna present; middle ear bones: malleus, incus, stapes.
5. Thermoregulation — endothermic, homeothermic.
6. Heart — four-chambered, left aortic arch.
7. Diaphragm — separates thoracic & abdominal cavities.
8. Larynx — voice apparatus with vocal cords + epiglottis.
9. Fertilization — internal.

Classification — three groups

i. Monotremes — egg-laying (oviparous) e.g. Duckbill platypus, echidna (spiny anteater).

ii. Marsupials — pouch (marsupium); immature young complete development in pouch e.g. opossum, kangaroo, Tasmanian wolf.

iii. Placental mammals — most advanced; placenta nourishes foetus & removes waste; viviparous e.g. dolphin, rat, monkey, bat, elephant, human.

CLASSIFICATION OF VIRUSES
Q22. Why are viruses not part of any domain/kingdom?

Acellularity: Viruses are acellular (not made of cells); lack characteristics of the three domains; not classified in any domain/kingdom.

Structure: Nucleic acid (DNA or RNA) surrounded by a protein coat.

Reproduction: No independent metabolism; depend on host cell (plants, animals, bacteria) to replicate and synthesize proteins.

Classification: Based on genetic material, replication strategy, morphology, and hosts infected — per International Committee on Taxonomy of Viruses (ICTV) guidelines.

Q23. Write a note on classification of viruses on the basis of host range, morphology and genetic material.

1. Host Range

Animal viruses (Influenza, Rabies), Plant viruses (Tobacco mosaic virus, Potato virus X), Bacteriophages (T4 phage, Lambda phage), Archaea viruses (Sulfolobus spindle-shaped virus).

2. Morphology

Helical (Tobacco mosaic virus, Rabies virus); Icosahedral (Adenoviruses, Herpesviruses); Complex (Bacteriophages); Enveloped (Influenza virus, HIV); Non-enveloped/Naked (Poliovirus, Adenovirus).

3. Genetic Material

DNA viruses — dsDNA (Adenoviruses, Herpes viruses), ssDNA (Parvoviruses); RNA viruses — ssRNA (Coronaviruses, Influenza), dsRNA (Rotaviruses).

4. Replication Strategy

Positive-sense RNA viruses (Poliovirus, Hepatitis C virus); Negative-sense RNA viruses (Rabies virus, Ebola virus); Reverse transcribing viruses — RNA genome e.g. HIV (AIDS), DNA genome e.g. Hepatitis B virus.

★Q24. Describe the concept of an ecosystem and niche.

Ecosystem: A dynamic, interactive system of living organisms and their physical environment — includes biotic and abiotic factors.

i. Biotic Components: All living organisms supported by the biosphere (extends ~8–10 km into atmosphere and ocean depths).

ii. Abiotic Components: Atmosphere (air), hydrosphere (water), lithosphere (earth/soil).

Niche: The role or function of a species within an ecosystem — its habitat, interactions (predation, competition, symbiosis), and role in energy flow. Includes physical factors necessary for survival (temperature range, humidity, pH).

Q25. Define Biodiversity. Explain the different levels at which biodiversity can be assessed.

Biodiversity refers to the variety of life forms present in different ecosystems — species, genes, and ecosystems.

i. Species Level: Identifying/counting species — number, abundance, distribution; helps identify threatened/endangered species for conservation.

ii. Genetic Level: Variety of genetic information within a species; crucial for adaptability and survival; helps conserve species with low genetic variety (higher extinction risk).

iii. Ecosystem Level: Range of habitats (forests, wetlands, grasslands, deserts); helps protect and restore degraded ecosystems.

Q26. What is random sampling? Discuss its importance in ecological studies.

Sampling investigates abundance/distribution of species in a given time and area — random or systematic. In random sampling, location is selected by chance.

Importance: 1. Minimizes bias 2. Provides reliable estimates 3. Facilitates comparisons 4. Enhances representativeness 5. Supports conservation efforts.

Q27. Describe the various methods to assess biodiversity and discuss their importance.

Methods to Assess Distribution

1. Quadrat Sampling — dividing area into a grid, sampling randomly selected squares; useful for plant populations/sessile organisms.

2. Transect Sampling — line/strip across study area, recording species at intervals; effective for studying distribution across environmental gradients (e.g. coastal high-to-low tide line).

3. Aerial Surveys — aircraft/drones observe organism distribution over large areas.

Methods to Assess Abundance

Point counts, Mark-recapture, Quadrat counts, Capture-recapture methods, Remote sensing (satellite/drone imagery).

SPECIES AND SPECIATION
Q28. Define species and speciation. Explain the concept of species according to the biological species concept. Discuss the mechanisms of speciation.

Species: A group of individuals that can interbreed and produce fertile offspring under natural conditions, sharing common characteristics and genetic makeup that distinguish them from other species. Identification by physical traits alone can be problematic due to cryptic species (similar-looking but genetically distinct).

German-American biologist Ernst Mayr emphasized reproductive isolation as the key criterion — species are groups of interbreeding natural populations; members of different species do not typically mate or produce viable, fertile offspring.

Speciation: The evolutionary process by which new species arise from a common ancestor, through accumulation of genetic changes leading to reproductive isolation.

Mechanisms of Speciation

1. Allopatric Speciation — geographic separation into isolated groups; different environments → independent evolution → reproductive isolation even if barrier removed. Example: Darwin's finches, Galápagos Islands.

2. Peripatric Speciation — small isolated population at edge of larger population; rapid evolutionary change → divergence. Example: island species from a small founding population.

3. Parapatric Speciation — adjacent populations, different environments along a gradient; limited gene flow → reproductive isolation. Example: grass species Anthoxanthum odoratum, adapted to varying soil conditions across a gradient.

4. Sympatric Speciation — new species arise within same geographic area, no physical barriers; via polyploidy or niche differentiation. Example: certain plants undergoing polyploidy → immediate reproductive isolation.