Animal Kingdom Class 11 Biology: Basis of Classification, Non-chordates and Chordates

What Animal Kingdom is about

Weightage: This chapter is part of Unit I, Diversity of Living Organisms, which carries 15 of the 70 theory marks in the school annual exam together with The Living World, Biological Classification and Plant Kingdom.Source: CBSE Biology (044) syllabus 2026-27, Class XI course structure, Unit I Diversity of Living Organisms

Key concepts

Basis of classification: organisation, symmetry and germ layers

NCERT section 4.1 Basis of Classification (4.1.1 Levels of Organisation, 4.1.2 Symmetry, 4.1.3 Diploblastic and Triploblastic Organisation)

Levels of organisation:

• Cellular level: cells are loosely aggregated, with some division of labour (sponges).
• Tissue level: cells performing the same function form tissues (coelenterates).
• Organ level: tissues form organs, each for a specific function (platyhelminthes).
• Organ-system level: organs form systems (annelids, arthropods, molluscs, echinoderms, chordates).

Digestive system: incomplete (a single opening serving as both mouth and anus, e.g. Platyhelminthes) or complete (separate mouth and anus).
Circulatory system: open (blood pumped out of the heart bathes cells and tissues directly) or closed (blood circulates in vessels of varying diameter: arteries, veins, capillaries).

Symmetry:

• Asymmetrical: no plane divides the body into equal halves (most sponges).
• Radial: any plane through the central axis divides the body into identical halves (coelenterates, ctenophores, adult echinoderms).
• Bilateral: only one plane gives identical left and right halves (annelids, arthropods and others).

Germ layers:

• Diploblastic: cells in two embryonic layers, outer ectoderm and inner endoderm, with an undifferentiated mesoglea between them (coelenterates).
• Triploblastic: a third layer, mesoderm, between ectoderm and endoderm (platyhelminthes to chordates).

Worked example

Distinguish between diploblastic and triploblastic animals and between radial and bilateral symmetry, with one example of each. (3 marks)

Try it first, then show the solutionSolution

1. Diploblastic: two germ layers (ectoderm, endoderm) with mesoglea between, e.g. Hydra/coelenterates. Triploblastic: three layers including mesoderm, e.g. earthworm. (1½)
2. Radial: any plane through the central axis divides the body into identical halves, e.g. jellyfish or adult starfish. Bilateral: only one plane gives identical halves, e.g. cockroach or frog. (1½)

Answer: Diploblastic (coelenterates) vs triploblastic (annelids onward); radial (cnidarians, adult echinoderms) vs bilateral (annelids, arthropods, chordates).

Basis of classification: coelom, segmentation and notochord

NCERT section 4.1.4 Coelom; 4.1.5 Segmentation; 4.1.6 Notochord

Coelom is a body cavity lined by mesoderm, between the body wall and the gut wall.

• Coelomates: have a true coelom (annelids, molluscs, arthropods, echinoderms, hemichordates, chordates).
• Pseudocoelomates: a body cavity that is not lined by mesoderm; the mesoderm is present as scattered pouches between ectoderm and endoderm (aschelminthes).
• Acoelomates: no body cavity (platyhelminthes).

Segmentation (metamerism): in some animals the body is divided externally and internally into segments with a serial repetition of at least some organs, e.g. earthworm. This is metameric segmentation.

Notochord: a rod of mesodermal origin that develops along the back (dorsal side) of some animals during embryonic life. Animals that have it are chordates; those without are non-chordates (Porifera to Echinodermata).

Worked example

Classify (a) Ascaris (b) Taenia (c) earthworm according to body cavity, giving the reason in each case. (3 marks)

Try it first, then show the solutionSolution

1. (a) Ascaris: pseudocoelomate; its body cavity is not lined by mesoderm (mesoderm present as scattered pouches). (1)
2. (b) Taenia: acoelomate; it has no body cavity. (1)
3. (c) Earthworm: coelomate; its body cavity is lined by mesoderm. (1)

Answer: Ascaris pseudocoelomate, Taenia acoelomate, earthworm coelomate.

Porifera, Coelenterata (Cnidaria) and Ctenophora

NCERT section 4.2.1 Porifera; 4.2.2 Coelenterata (Cnidaria); 4.2.3 Ctenophora

Porifera (sponges): mostly marine, mostly asymmetrical, primitive multicellular animals with cellular level of organisation. They have a water canal system: water enters through tiny pores (ostia) into a central cavity, the spongocoel, and leaves through the osculum. This helps in food gathering, respiratory exchange and removal of waste. Choanocytes (collar cells) line the spongocoel and canals. Digestion is intracellular. The skeleton is made of spicules or spongin fibres. Sexes are not separate (hermaphrodite); asexual reproduction by fragmentation, sexual by gametes; fertilisation internal, development indirect (larval stage). Examples: *Sycon* (*Scypha*), freshwater sponge (*Spongilla*), bath sponge (*Euspongia*).

Coelenterata (Cnidaria): aquatic, mostly marine, sessile or free-swimming, radially symmetrical. Named after cnidoblasts (cnidocytes), stinging cells with nematocysts on tentacles and body, used for anchorage, defence and capture of prey. Tissue level, diploblastic. A central gastro-vascular cavity with a single opening, the mouth, on the hypostome. Digestion extracellular and intracellular. Some (corals) have a calcium carbonate skeleton. Two body forms: polyp (sessile, cylindrical, e.g. *Hydra*, *Adamsia*) and medusa (umbrella-shaped, free-swimming, e.g. *Aurelia*, jellyfish). Forms with both show alternation of generation (metagenesis): polyps produce medusae asexually and medusae produce polyps sexually (*Obelia*). Examples: Portuguese man-of-war (*Physalia*), sea anemone (*Adamsia*), sea-pen (*Pennatula*), sea-fan (*Gorgonia*), brain coral (*Meandrina*).

Ctenophora (sea walnuts, comb jellies): exclusively marine, radially symmetrical, diploblastic, tissue level. The body bears eight external rows of ciliated comb plates used for locomotion. Digestion extracellular and intracellular. Bioluminescence (emitting light) is well marked. Sexes are not separate; reproduction is only sexual, with external fertilisation and indirect development. Examples: *Pleurobrachia*, *Ctenoplana*.

Worked example

Trace the path of water through a sponge and give two functions of this canal system. (2 marks)

Try it first, then show the solutionSolution

1. Water enters through ostia into the spongocoel and leaves through the osculum. (1)
2. Functions (any two): food gathering, respiratory exchange, removal of wastes. (1)

Answer: Ostia → spongocoel → osculum; food gathering, gas exchange, waste removal.

Platyhelminthes, Aschelminthes and Annelida

NCERT section 4.2.4 Platyhelminthes; 4.2.5 Aschelminthes; 4.2.6 Annelida

Platyhelminthes (flatworms): dorso-ventrally flattened, mostly endoparasites in animals including humans. Bilateral, triploblastic, acoelomate, organ level. Hooks and suckers in parasitic forms; some absorb nutrients directly through the body surface. Specialised flame cells help in osmoregulation and excretion. Sexes not separate; internal fertilisation; development through many larval stages. Some (*Planaria*) have high regeneration capacity. Examples: tapeworm (*Taenia*), liver fluke (*Fasciola*).

Aschelminthes (roundworms): body circular in cross-section. Free-living, aquatic and terrestrial, or parasites in plants and animals. Organ-system level, bilateral, triploblastic, pseudocoelomate. Alimentary canal complete with a well-developed muscular pharynx. An excretory tube removes body wastes through the excretory pore. Sexes separate (dioecious); females are longer than males. Internal fertilisation; development direct or indirect. Examples: roundworm (*Ascaris*), filaria worm (*Wuchereria*), hookworm (*Ancylostoma*).

Annelida: aquatic (marine and freshwater) or terrestrial, free-living or sometimes parasitic. Organ-system level, bilateral, triploblastic, metamerically segmented and coelomate. The body surface is distinctly marked into segments (metameres), hence the name (Latin *annulus*: little ring). Longitudinal and circular muscles help locomotion. Aquatic annelids like *Nereis* have lateral appendages, parapodia, for swimming. Closed circulatory system. Nephridia for osmoregulation and excretion. A double ventral nerve cord with paired ganglia connected by lateral nerves. *Nereis* is dioecious; earthworms and leeches are monoecious. Examples: *Nereis*, earthworm (*Pheretima*), blood-sucking leech (*Hirudinaria*).

Worked example

Name the excretory structure of (a) flatworms (b) annelids. Give one feature of each phylum's body cavity and one example. (3 marks)

Try it first, then show the solutionSolution

1. (a) Flame cells; acoelomate; e.g. Taenia. (1½)
2. (b) Nephridia; coelomate (true coelom), metamerically segmented; e.g. Pheretima. (1½)

Answer: Flame cells (acoelomate, Taenia); nephridia (coelomate, Pheretima).

Arthropoda and Mollusca

NCERT section 4.2.7 Arthropoda; 4.2.8 Mollusca

Arthropoda: the largest phylum of Animalia, including insects; over two-thirds of all named species on earth are arthropods. Organ-system level, bilateral, triploblastic, segmented, coelomate. The body is covered by a chitinous exoskeleton and divided into head, thorax and abdomen. Jointed appendages (*arthros*: joint; *poda*: appendages). Respiration by gills, book gills, book lungs or tracheal system. Open circulatory system. Sense organs: antennae, eyes (compound or simple), statocysts (balance). Excretion by Malpighian tubules. Mostly dioecious; fertilisation usually internal; mostly oviparous; development direct or indirect. Examples: economically important insects honey bee (*Apis*), silkworm (*Bombyx*), lac insect (*Laccifer*); mosquito vectors *Anopheles*, *Culex* and *Aedes*; gregarious pest locust (*Locusta*); living fossil king crab (*Limulus*).

Mollusca: the second largest phylum; terrestrial or aquatic. Organ-system level, bilateral, triploblastic, coelomate. Body covered by a calcareous shell, unsegmented, with a distinct head, muscular foot and visceral hump. The visceral hump is covered by a soft, spongy skin fold called the mantle; the gap between the two is the mantle cavity, in which feather-like gills do respiratory and excretory work. The anterior head has sensory tentacles. The mouth has a file-like rasping organ for feeding, the radula. Usually dioecious and oviparous, with indirect development. Examples: apple snail (*Pila*), pearl oyster (*Pinctada*), cuttlefish (*Sepia*), squid (*Loligo*), devil fish (*Octopus*), sea hare (*Aplysia*), tusk shell (*Dentalium*), chiton (*Chaetopleura*).

Worked example

Give two features each that distinguish arthropods from molluscs, and one economically important example of each phylum. (3 marks)

Try it first, then show the solutionSolution

1. Arthropods: chitinous exoskeleton, jointed appendages, segmented body (head, thorax, abdomen). (1)
2. Molluscs: calcareous shell, unsegmented body with head, muscular foot and visceral hump; radula for feeding; mantle. (1)
3. Examples: Bombyx (silk) or Apis (honey); Pinctada (pearl oyster). (1)

Answer: Exoskeleton and jointed legs vs shell, foot and radula; Bombyx/Apis and Pinctada.

Echinodermata, Hemichordata and the chordate features

NCERT section 4.2.9 Echinodermata; 4.2.10 Hemichordata; 4.2.11 Chordata (Table 4.1)

Echinodermata: spiny-bodied animals with an endoskeleton of calcareous ossicles (hence 'echinoderm': spiny skin). All are marine, organ-system level, triploblastic, coelomate. Adults are radially symmetrical but larvae are bilaterally symmetrical. Digestive system complete, with the mouth opening on the underside (ventral) and the anus on the upper side (dorsal). Their most distinctive feature is the water vascular system, used for moving about, catching and carrying food, and breathing. No excretory system. Sexes separate; external fertilisation; indirect development with a free-swimming larva. Examples: starfish (*Asterias*), sea urchin (*Echinus*), sea lily (*Antedon*), sea cucumber (*Cucumaria*), brittle star (*Ophiura*).

Hemichordata: earlier a sub-phylum of Chordata, now a separate phylum under non-chordates. A small group of worm-like marine animals with organ-system level, bilateral symmetry, triploblastic and coelomate. The cylindrical body has an anterior proboscis, a collar and a long trunk. Open circulatory system; respiration by gills; excretion by the proboscis gland. Sexes separate; external fertilisation; indirect development. They have a rudimentary structure in the collar region called the stomochord, similar to a notochord. Examples: *Balanoglossus*, *Saccoglossus*.

Phylum Chordata is characterised by three fundamental features:
1. A notochord (at least at some stage).
2. A dorsal, hollow, single nerve cord.
3. Paired pharyngeal gill slits.
They are bilaterally symmetrical, triploblastic, coelomate, organ-system level, with a post-anal tail and a closed circulatory system.

Chordates vs non-chordates: notochord present vs absent; central nervous system dorsal, hollow and single vs ventral, solid and double; pharynx perforated by gill slits vs no gill slits; heart ventral vs dorsal (if present); post-anal tail present vs absent.

Worked example

Give three differences between chordates and non-chordates. Why is Balanoglossus no longer placed in Chordata? (3 marks)

Try it first, then show the solutionSolution

1. Notochord present in chordates, absent in non-chordates; CNS dorsal, hollow and single vs ventral, solid and double. (1)
2. Pharyngeal gill slits present vs absent (also heart ventral vs dorsal; post-anal tail present vs absent). (1)
3. Balanoglossus has only a stomochord, a rudimentary structure in the collar, not a true notochord, so hemichordates are now a separate non-chordate phylum. (1)

Answer: Notochord, dorsal hollow nerve cord, gill slits; Balanoglossus has only a stomochord.

Protochordates, Cyclostomata and fishes

NCERT section 4.2.11 Chordata (subphyla); 4.2.11.1 Cyclostomata; 4.2.11.2 Chondrichthyes; 4.2.11.3 Osteichthyes

Chordata has three subphyla: Urochordata (Tunicata), Cephalochordata and Vertebrata. The first two are called protochordates and are exclusively marine.

• Urochordata: notochord present only in the larval tail. Examples: *Ascidia*, *Salpa*, *Doliolum*.
• Cephalochordata: notochord extends from head to tail and persists throughout life. Example: *Branchiostoma* (*Amphioxus*, lancelet).

Vertebrata: notochord present in the embryo, replaced by a cartilaginous or bony vertebral column in the adult. So all vertebrates are chordates but all chordates are not vertebrates. Their muscular heart lies ventrally and has two to four chambers; kidneys handle excretion and water balance; and they bear paired fins or limbs. Vertebrata is divided into Agnatha (no jaws: Cyclostomata) and Gnathostomata (jawed: superclasses Pisces and Tetrapoda).

Cyclostomata: ectoparasites on some fishes. Elongated body with 6-15 pairs of gill slits. Sucking, circular mouth without jaws. Body without scales and paired fins. Cranium and vertebral column cartilaginous. Closed circulation. Marine but migrate to fresh water for spawning, die a few days after spawning, and larvae return to the ocean after metamorphosis. Examples: lamprey (*Petromyzon*), hagfish (*Myxine*).

Chondrichthyes (cartilaginous fishes): marine, streamlined, cartilaginous endoskeleton. Mouth ventral. Notochord persistent throughout life. Gill slits separate, without operculum. Skin tough with minute placoid scales; teeth are modified placoid scales, backwardly directed. Jaws very powerful; predaceous. No air bladder, so they must swim constantly to avoid sinking. Heart two-chambered (one auricle, one ventricle). Some have electric organs (*Torpedo*) or a poison sting (*Trygon*). Cold-blooded (poikilothermous). Sexes separate; males have claspers on pelvic fins; internal fertilisation; many viviparous. Examples: dogfish (*Scoliodon*), sawfish (*Pristis*), great white shark (*Carcharodon*), sting ray (*Trygon*).

Osteichthyes (bony fishes): marine and freshwater, bony endoskeleton, streamlined body. Mouth mostly terminal. Four pairs of gills covered by an operculum. Skin with cycloid or ctenoid scales. Air bladder regulates buoyancy. Heart two-chambered; cold-blooded. Sexes separate; usually external fertilisation; mostly oviparous, direct development. Examples: marine flying fish (*Exocoetus*), sea horse (*Hippocampus*); freshwater rohu (*Labeo*), katla (*Catla*), magur (*Clarias*); aquarium fighting fish (*Betta*), angel fish (*Pterophyllum*).

Worked example

Give four differences between cartilaginous and bony fishes, with one example each. (3 marks)

Try it first, then show the solutionSolution

1. Endoskeleton: cartilaginous vs bony; mouth ventral vs mostly terminal. (1)
2. Gills: separate gill slits without operculum vs four pairs of gills covered by operculum; scales: placoid vs cycloid/ctenoid. (1)
3. Air bladder absent (must swim continuously) vs present; examples: Scoliodon vs Labeo. (1)

Answer: Cartilage, ventral mouth, no operculum, placoid scales, no air bladder (Scoliodon) vs bone, terminal mouth, operculum, cycloid/ctenoid scales, air bladder (Labeo).

Tetrapods: Amphibia, Reptilia, Aves and Mammalia

NCERT section 4.2.11.4 Amphibia; 4.2.11.5 Reptilia; 4.2.11.6 Aves; 4.2.11.7 Mammalia

Amphibia: live in aquatic and terrestrial habitats; most have two pairs of limbs. Head and trunk distinct; a tail in some. Moist skin without scales. The eyes have lids and a tympanum serves as the ear. The gut, urinary duct and reproductive ducts all open into one shared chamber, the cloaca. Respiration by gills, lungs and skin. Heart three-chambered (two auricles, one ventricle). Cold-blooded. Sexes separate; external fertilisation; oviparous; development direct or indirect. Examples: toad (*Bufo*), frog (*Rana*), tree frog (*Hyla*), salamander (*Salamandra*), limbless amphibian (*Ichthyophis*).

Reptilia: name refers to their creeping or crawling mode of locomotion (Latin *repere*: to creep). Mostly terrestrial; body covered by dry, cornified skin with epidermal scales or scutes. No external ear opening; tympanum represents the ear. Limbs two pairs when present. Heart usually three-chambered, but four-chambered in crocodiles. Cold-blooded. Snakes and lizards shed their scales as skin cast. Sexes separate; internal fertilisation; oviparous; direct development. Examples: turtle (*Chelone*), tortoise (*Testudo*), tree lizard (*Chameleon*), garden lizard (*Calotes*), crocodile (*Crocodilus*), *Alligator*, wall lizard (*Hemidactylus*); poisonous snakes cobra (*Naja*), krait (*Bangarus*), viper (*Vipera*).

Aves (birds): feathers, and most can fly (except flightless birds like the ostrich). They have a beak. Forelimbs are modified into wings; hind limbs have scales and are modified for walking, swimming or clasping tree branches. Their skin is dry and has no glands apart from the oil gland near the tail base. Endoskeleton fully ossified; long bones are hollow with air cavities (pneumatic). The digestive tract has extra chambers: crop and gizzard. Heart four-chambered. Warm-blooded (homoiothermous). Respiration by lungs, with air sacs connected to the lungs supplementing respiration. Sexes separate; internal fertilisation; oviparous; direct development. Examples: crow (*Corvus*), pigeon (*Columba*), parrot (*Psittacula*), ostrich (*Struthio*), peacock (*Pavo*), penguin (*Aptenodytes*), vulture (*Neophron*).

Mammalia: found in polar ice caps, deserts, mountains, forests, grasslands and dark caves; some can fly or live in water. The most unique features are mammary glands (milk-producing glands to nourish the young) and hair on the skin. Two pairs of limbs adapted for walking, running, climbing, burrowing, swimming or flying. Skin has hair. External ears (pinnae) present. Different types of teeth in the jaw. Heart four-chambered; warm-blooded; respiration by lungs. Sexes separate; internal fertilisation; with a few exceptions viviparous, with direct development. Examples: oviparous platypus (*Ornithorhynchus*); viviparous kangaroo (*Macropus*), flying fox (*Pteropus*), camel (*Camelus*), monkey (*Macaca*), rat (*Rattus*), dog (*Canis*), cat (*Felis*), elephant (*Elephas*), horse (*Equus*), common dolphin (*Delphinus*), blue whale (*Balaenoptera*), tiger (*Panthera tigris*), lion (*Panthera leo*).

Worked example

A frog, a lizard and a pigeon are kept in a cool room. Which of them keeps a steady body temperature, and why? Give one feature of the skin of each that helps you classify it. (2 marks)

Try it first, then show the solutionSolution

1. Only the pigeon: birds are warm-blooded (homoiothermous) with a four-chambered heart; the frog (amphibian) and lizard (reptile) are cold-blooded, so their body temperature falls with the room. (1)
2. Skin: frog moist and without scales; lizard dry and cornified with epidermal scales; pigeon covered with feathers, with no glands except the oil gland near the tail. (1)

Answer: The pigeon (warm-blooded); frog skin moist and scaleless, lizard skin dry with scales, pigeon skin with feathers and only an oil gland.

Animal Kingdom in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Basis of Classification of Animals
• Chordate Classes: Fishes to Mammals

Animal Kingdom: key facts

Levels of organisation

$\text{cellular}\to \text{tissue}\to \text{organ}\to \text{organ-system}$

Porifera; Cnidaria and Ctenophora; Platyhelminthes; Aschelminthes onwards.

Body cavity

$\text{acoelomate (Platyhelminthes)};\text{pseudocoelomate (Aschelminthes)};\text{coelomate (Annelida onwards)}$

True coelom is lined by mesoderm.

Chordate hallmarks

$\text{notochord}+\text{dorsal hollow nerve cord}+\text{pharyngeal gill slits}$

Plus post-anal tail, ventral heart.

Heart chambers

$\text{fishes 2};\text{amphibians 3};\text{reptiles 3 (crocodile 4)};\text{birds 4};\text{mammals 4}$

Birds and mammals are warm-blooded.

Chordate subdivisions

$\text{Urochordata},\text{Cephalochordata},\text{Vertebrata (Agnatha}+\text{Gnathostomata)}$

Protochordates are the first two.

Animal Kingdom: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Animal Kingdom

The question patterns to expect, and the method that works for each.

Tricks to remember Animal Kingdom

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Please Come Children, Play And Act Around My Exciting Home

  Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata.

  Use it when: Order of non-chordate phyla.

• Excretion ladder

  Flame cells (flatworms), excretory pore/tube (roundworms), nephridia (annelids), Malpighian tubules (insects), proboscis gland (hemichordates), none in echinoderms.

  Use it when: Excretory structure questions.

• CCO-ARAM

  Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, Mammalia: the seven vertebrate classes in order.

  Use it when: Listing classes.

• 2-3-3-4-4 hearts

  Fish 2, frog 3, lizard 3 (crocodile 4), bird 4, mammal 4.

  Use it when: Heart chamber questions.

• Uro-tail, Cephalo-whole

  Urochordates: notochord only in the larval tail; cephalochordates: from head to tail, for life.

  Use it when: Protochordate comparison.

Animal Kingdom: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Animal Kingdom

The slips examiners see most often, and what to write instead.

• ✗Mistake: Calling echinoderms bilateral

  Larval and adult symmetry are confused.

  ✓Do this: Adults are radially symmetrical; larvae are bilaterally symmetrical.

  Usually costs: 1 mark.

• ✗Mistake: Writing that all chordates have a vertebral column

  Chordate and vertebrate are used as synonyms.

  ✓Do this: Protochordates have a notochord but no vertebral column; only vertebrates replace it with a backbone.

  Usually costs: 1 mark.

• ✗Mistake: Saying sharks have an operculum

  Bony fish features are generalised.

  ✓Do this: Cartilaginous fishes have separate gill slits without an operculum.

  Usually costs: ½-1 mark.

• ✗Mistake: Giving a three-chambered heart to all reptiles

  The exception is forgotten.

  ✓Do this: Crocodiles have a four-chambered heart.

  Usually costs: ½ mark.

• ✗Mistake: Mixing up Ctenophora and Coelenterata

  Both are radial and diploblastic.

  ✓Do this: Ctenophores have eight rows of comb plates and no cnidoblasts; coelenterates have cnidoblasts.

  Usually costs: 1 mark.

• ✗Mistake: Wrong example for a phylum

  Common names mislead (starfish is not a fish; silverfish is an insect).

  ✓Do this: Learn genus names with phyla: Asterias is an echinoderm.

  Usually costs: 1 mark.

NCERT exercise guide: Animal Kingdom

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Practice questions on Animal Kingdom

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Flame cells are the excretory structures of:
   (a) Annelida (b) Platyhelminthes (c) Aschelminthes (d) Arthropoda

   Hint

   Flatworms.

   Answer

   (b) Platyhelminthes

2. Q2 · 1 mark · MCQExam level

   Which of these is a cartilaginous fish?
   (a) Labeo (b) Catla (c) Scoliodon (d) Hippocampus

   Hint

   Dogfish.

   Answer

   (c) Scoliodon

3. Q3 · 2 marks · Very short answerExam level

   Name the phylum and give the common name: (a) Pheretima (b) Pila (c) Ancylostoma (d) Pleurobrachia. (2 marks)

   Hint

   NCERT examples.

   Answer

   (a) Annelida, earthworm (b) Mollusca, apple snail (c) Aschelminthes, hookworm (d) Ctenophora, comb jelly (½ each).

4. Q4 · 2 marks · Very short answerHarder exam level

   What is metameric segmentation? Give one example. (2 marks)

   Hint

   Serial repetition.

   Answer

   Division of the body externally and internally into segments with serial repetition of at least some organs (1); e.g. earthworm (Pheretima) (1).

5. Q5 · 2 marks · Very short answerHarder exam level

   Give two differences between Urochordata and Cephalochordata with an example each. (2 marks)

   Hint

   Where and how long the notochord lasts.

   Answer

   Urochordata: notochord only in larval tail (Ascidia) (1); Cephalochordata: notochord from head to tail throughout life (Branchiostoma) (1).

6. Q6 · 3 marks · Short answerHarder exam level

   Suppose a student says a jellyfish and a starfish are both fish. Correct him, naming their phyla and one distinguishing feature each. (3 marks)

   Hint

   Common names mislead.

   Answer

   Neither is a fish (fishes are vertebrates) (1). Jellyfish: Coelenterata, with cnidoblasts and medusa form (1). Starfish: Echinodermata, with water vascular system and spiny calcareous endoskeleton (1).

7. Q7 · 2 marks · Very short answerHarder exam level

   Name the respiratory organs of (a) prawn (b) cockroach (c) Pila (d) frog. (2 marks)

   Hint

   Gills, trachea, gills, lungs-skin.

   Answer

   (a) Gills (b) tracheal system (c) gills in the mantle cavity (d) lungs and skin (gills in tadpole) (½ each).

8. Q8 · 3 marks · Short answerHarder exam level

   Explain why birds are warm-blooded and how their skeleton helps flight. (3 marks)

   Hint

   Four-chambered heart and pneumatic bones.

   Answer

   A four-chambered heart keeps oxygenated and deoxygenated blood separate, supporting high metabolism that maintains constant body temperature (homoiothermy) (1½). Long bones are hollow with air cavities (pneumatic), reducing weight for flight (1½).

9. Q9 · 2 marks · Very short answerHarder exam level

   Distinguish between open and closed circulatory systems with an example of each phylum. (2 marks)

   Hint

   Vessels or sinuses.

   Answer

   Open: blood pumped out of the heart bathes tissues directly in spaces, e.g. Arthropoda (1). Closed: blood flows in vessels (arteries, veins, capillaries), e.g. Annelida or Chordata (1).

10. Q10 · 3 marks · Short answerHOTS / competency

    Suppose a newly found animal has a notochord only in its larval tail, a sac-like adult attached to rocks and gill slits in the pharynx. (a) Place it in phylum and subphylum. (b) Is it a vertebrate? Why? (3 marks)

    Hint

    Tunicates.

    Answer

    (a) Chordata, subphylum Urochordata (like Ascidia) (1½). (b) No; it has no vertebral column, and its notochord does not persist or get replaced by a backbone (1½).

11. Q11 · 5 marks · Long answerHOTS / competency

    (a) Explain how the presence or absence of a coelom has been used to group animals. (b) Why is the coelom considered an evolutionary advance? (c) Give one example each of an acoelomate, a pseudocoelomate and two different coelomate phyla. (5 marks)

    Hint

    Space for organs.

    Answer

    (a) Animals with a mesoderm-lined cavity are coelomates; with a cavity not lined by mesoderm are pseudocoelomates; with no cavity are acoelomates (2). (b) A coelom gives space for organs to grow and move independently of the body wall, cushions organs and allows a separate circulatory and excretory system (1). (c) Acoelomate: Taenia; pseudocoelomate: Ascaris; coelomates: Pheretima (Annelida) and Rana (Chordata) (2).

12. Q12 · 1 mark · Assertion-reasonHOTS / competency

    Assertion (A): Echinoderms are placed among the advanced invertebrates although adults are radially symmetrical.
    Reason (R): Their larvae are bilaterally symmetrical, and they are triploblastic and coelomate.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Radial symmetry is secondary.

    Answer

    (a)

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What are choanocytes?Show answer

   Collar cells lining the spongocoel and canals of sponges.

2. 2.What is metagenesis?Show answer

   Alternation of polyp and medusa forms in coelenterates such as Obelia.

3. 3.Which animals show bioluminescence among phyla studied?Show answer

   Ctenophores (comb jellies).

4. 4.Name the largest animal phylum.Show answer

   Arthropoda.

5. 5.What is the radula?Show answer

   A file-like rasping organ in the mouth of molluscs.

6. 6.What is the water vascular system?Show answer

   A system of water-filled canals in echinoderms used for locomotion, food capture and transport, and respiration.

7. 7.Name the living fossil arthropod.Show answer

   Limulus (king crab).

8. 8.Which fishes have claspers?Show answer

   Males of cartilaginous fishes (on pelvic fins).

9. 9.What are pneumatic bones?Show answer

   Hollow long bones with air cavities, found in birds.

10. 10.Name an oviparous mammal.Show answer

    Ornithorhynchus (platypus).

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you name the level of organisation and symmetry of each phylum?
• ☐Can you explain acoelomate, pseudocoelomate and coelomate with examples?
• ☐Can you trace water flow in a sponge?
• ☐Can you name the excretory organ of each non-chordate phylum?
• ☐Can you list five differences between chordates and non-chordates?
• ☐Can you compare cartilaginous and bony fishes?
• ☐Can you give the heart chambers and body-temperature type of each vertebrate class?
• ☐Can you name three NCERT examples for each phylum and class?

Animal Kingdom: frequently asked questions