CBSE Class 11 Biology Animal Kingdom Assignments

Chapter-4

ANIMAL KINGDOM

POINTS TO REMEMBER

Circulatory System: Open type - Blood pumped out through heart. Cells and tissues are directly bathed in it.
Closed type: Blood is circulated through vessels.
Symmetry:
- Asymmetrical: Cannot be divided into equal halves through median plane. e.g., Sponges.
- Radial symmetry: Any plane passing through central axis can divide organism into equal halves. e.g., Hydra.
- Bilateral symmetry: Only one plane can divide the organism into equal halves. e.g., Annelids and Arthropods.

CLASSIFICATION ON BASIS OF GERMINAL LAYERS:
- Diploblastic: Cells arranged in two embryonic layers i.e., external ectoderm and internal endoderm. (Mesoglea may be present in between ectoderm and endoderm) e.g., Coelenterates (Cnidarians).
- Triploblastic: Three layers present in developing embryo i.e., ectoderm, mesoderm and endoderm e.g., Chordates.

Coelom (Body cavity which is lined by mesoderm):
- Coelomates: Have coelom e.g., Annelids, Chordates etc.
- Pseudocoelomates: No true coelom as mesoderm is present in scattered pouches between ectoderm and endoderm. e.g., Aschelminthes.
- Acoelomates: Body cavity is absent. e.g., Platyhelminthes.

Metamerism: If body is externally and internally divided into segments with serial repetition of atleast some organs then phenomenon is called metamerism. e.g., Earthworm.

Notochord: Rod-like structure formed during embryonic development on the dorsal side. It is mesodermally derived. e.g., Chordates.

PHYLUM PORIFERA:
- Also called sponges.
- Have cellular level of organisation.
- Food gathering, respiratory exchange and removal of wastes occurs through water canal system. Digestion intracellular.
- Ostia (minute pores on body), spongocoel (body cavity) and osculum help in water transport. They are lined by choanocytes (collar cells).
- Body wall has spicules and spongin fibres.
- Animals are hermaphrodite. Fertilisation internal. Development is indirect (i.e., has a larval stage distinct from adult stage) e.g., Sycon, Euspongia.

PHYLUM COELENTERATA:
- Also called Cnidarians.
- Are usually marine and radially symmetrical.
- Have tissue level of organisation.
- Are diploblastic.
- Food gathering, anchorage and defense occurs through cnidoblasts present on tentacles.
- Digestion extracellular and intracellular.
- Have gastro-vascular cavity and an opening, hypostome.
- Body wall composed of calcium carbonate.
- Exhibit two body forms: polyp and medusa e.g., Hydra, Aurelia.
- Alternation of generation between body forms called Metagenesis occurs in Obelia where Medusa  sexually 
\(\longrightarrow\)
 assexually  Polyp.
- e.g., Physalia, Adamsia.

PHYLUM CTENOPHORA:
- Also called as sea walnuts or comb jellies.
- Are exclusively marine, radially symmetrical.
- Have tissue level organisation, are diploblastic.
- Digestion both extra and intracellular.
- Body has eight external rows of ciliated comb plates for locomotion.
- Show Bioluminescence (living organism emit light).
- Only sexual reproduction occurs. External fertilisation. Indirect development. e.g., Ctenoplana.

PHYLUM PLATYHELMINTHES:
- Also called as 'flat worms'.
- Have dorsoventrally flattened body. Are endoparasites in animals.
- Are bilaterally symmetrical, triploblastic, acoelomate.
- Absorb nutrients through body surface.
- Parasite forms have hooks and suckers.
- 'Flame cells' help in osmoregulation and excretion.
- Fertilisation internal. Many larval stages. Planaria has high regeneration capacity.
- e.g., Taenia, Fasciola.

PHYLUM ASCHELMINTHES:
- Also called 'round worms'.
- May be free living, parasitic, aquatic or terrestrial.
- Are bilaterally symmetrical, triploblastic, pseudocoelomate.
- Alimentary canal complete (has muscular pharynx), wastes removed through excretory pore.
- Sexes separate. Shows dimorphism.
- Females longer than males.
- Fertilisation internal. Development direct or indirect.
- e.g., Ascaris, Wuchereria.

PHYLUM ANNELIDA:
- Are aquatic or terrestrial, free-living or parasitic.
- Are bilaterally symmetrical, triploblastic, organ-system level of organisation and metamerically segmented body.
- Have longitudinal and circular muscles for locomotion.
- Nereis (dioecious and aquatic annelid) has lateral appendages called parapodia for swimming.
- Have nephridia for osmoregulation and excretion.
- e.g., Earthworm (Pheretima) and Leech (Hirudinaria) which are hermaphrodites (i.e., monoecious).

PHYLUM ARTHROPODA:
- Largest phylum of Animalia.
- Are bilaterally symmetrical, triploblastic and organ system level of organisation, coelomate.
- Body divisible into head, thorax, abdomen and has a chitinous exoskeleton. Jointed appendages are present.
- Respiration by gills, book gills, lungs or tracheal system. Excretion through malpighian tubules.
- Sensory organs: Antennae, eyes; Organs of balance: Statocysts.
- Fertilisation internal. Development is indirect or direct. Are mostly oviparous.
- e.g., Apis, Bombyx, Anopheles, Locusta, Limulus.

PHYLUM MOLLUSCA:
- Second largest phylum of Animalia.
- Are bilaterally symmetrical, triploblastic and organ system level of organisation, coelomate.
- Body divisible into head, muscular foot and visceral hump and is covered by calcareous shell and is unsegmented.
- Mantle: Soft and spongy layer of skin; Mantle cavity: Space between visceral hump and mantle.
- Respiration and excretion by feather like gills in mantle cavity.
- Head has sensory tentacles. Radula-file like rasping organ for feeding.
- Are oviparous, dioecious, have indirect development.
- e.g., Pila, Pinctada, Octopus.

PHYLUM ECHINODERMATA:
- Are spiny bodied organisms.
- Are exclusively marine, radially symmetrical in adult but bilaterally symmetrical in larval stage. Organ system level of organisation.
- Digestive system complete. Mouth ventral, Anus on dorsal side.
- Food gathering, respiration, locomotion carried out by water vascular system.
- Excretory system is absent.
- Fertilisation external. Development indirect (free swimming larva)
- e.g., Asterias, Cucumaria.

PHYLUM HEMICHORDATA:
- Has small worm-like organisms.
- Was earlier placed as sub-phylum of Phylum Chordata.
- Bilaterally symmetrical, triploblastic and coelomate.
- Body cylindrical, has proboscis, collar and trunk.
- Respiration by gills, excretion by proboscis gland.
- Sexes separate, external fertilisation, indirect development.
- e.g., Balanoglossus

PHYLUM CHORDATA:
- Presence of Notochord
- Have dorsal hollow nerve chord.
- Have paired pharyngeal gill slits.
- Heart is ventral.
- Post anal tail present.
(i) SUB-PHYLA UROCHORDATA: Notochord present only in larval tail. e.g., Ascidia, Sepia.
(ii) SUB-PHYLA CEPHALOCHORDATA: Notochord extends from head to tail. e.g., Amphioxus.
(iii) SUB-PHYLA VERTEBRATA:
- Have notochord only during embryonic period.
- Notochord gets replaced by bony or cartilaginous vertebral column.
- Have ventral muscular heart, paired appendages and kidneys for excretion and osmoregulation.

SUB-PHYLUM VERTEBRATA
(a) AGNASHA (Lack Jaw) : Class : Cyclostomata
- Have sucking and circular mouth without jaws.
- Live as ectoparasites on some fishes.
- No scales, no paired fins.
- Cranium and vertebral column is cartilaginous.
- Migrate to fresh water for spawning and die after spawning.
- Larva returns to ocean after metamorphosis.
- e.g., Petromyzon.

(b) GNATHOSTOMATA (Bear Jaws)
SUPER-CLASS : PISCES
1. Class : Chondrichthyes
- Have cartilaginous endoskeleton.
- Mouth ventral.
- Gill slits without operculum
- Skin has placoid scales.
- Usually oviparous, fertilisation internal.
- No air bladder, so swim constantly to avoid sinking.
- Teeth are backwardly directed, modified placoid scales.
- Notochord is persistent throughout life. Males have claspers on pelvic fins.
- e.g., Torpedo, Trygon, Scoliodon.
2. Class : Osteichthyes
- Have bony endoskeleton.
- Mouth is usually terminal.
- Four pairs of gill slits covered by operculum.
- Skin has cycloid/ctenoid scales.
- Usually viviparous, fertilisation external.
- Have air bladder which regulates buoyancy.
- e.g., Hippocampus, Labeo, Catla, Betta.

SUB-PHYLUM VERTEBRATA : GNATHOSTOMATA
SUPER CLASS : TETRAPODA
1. Class : Amphibia
- Can live in aquatic as well as terrestrial habitats.
- Body divisible into head and trunk.
- Skin moist. No scales.
- Tympanum represents ear.
- Cloaca is the common chamber where alimentary, urinary and reproductive tracts open.
- Respiration by gills, lungs or skin.
- Heart is 3-chambered.
- Oviparous. Indirect development.
- e.g., Bufo, Rana, Hyla.
2. Class : Reptilia
- Creep or crawl to locomote.
- Body has dry and cornified skin and epidermal scales or scutes.
- Tympanum represents ear.
- Limbs when present are two pairs.
- Snakes and lizards shed scales as skin cast.
- Heart 3-chambered but 4-chambered in crocodiles.
- Oviparous. Direct development.
- e.g., Testudo, Naja, Vipera, Calotes.
3. Class : Aves
- Presence of feathers and beak.
- Forelimbs are modified into wings.
- Hind limbs have scales.
- No glands on skin except oil gland at base of tail.
- Endoskeleton bony with air cavities (pneumatic) and hollow bones to assist in flight.
- Air sacs are connected to lungs to supplement respiration.
- Oviparous. Direct development.
- e.g., Columba, Struthio.
4. Class : Mammalia
- Have mammary glands to nourish young ones.
- Have two pairs of limbs.
- Skin has hairs.
- External ears or pinna present.
- Different types of teeth in jaw.
- Viviparous. Direct development.
- e.g., Rattus, Canis Elephas, Equus. Oviparous mammal is Ornithorhynchus.

QUESTIONS

Very Short Answer Questions (1 mark each)

Question 1. What is mesogloea ? Where is it found ?
Answer: Mesogloea is an undifferentiated jelly-like layer present between the outer ectoderm and the inner endoderm. It is found in phylum Coelenterata (Cnidaria).
In simple words: It is a jelly layer between two body layers found in jellyfish and Hydra.

Exam Tip: Remember that mesogloea is non-cellular and characteristic of diploblastic animals like coelenterates.

Question 2. When is the development of an organism called as Indirect ?
Answer: The development of an organism is called indirect when there is a larval stage that is morphologically distinct from the adult stage during its life cycle.
In simple words: Development is indirect if the young one (larva) looks completely different from the adult.

Exam Tip: Highlight the presence of a distinct larval stage to score full marks.

Question 3. Why are corals important ?
Answer: Corals are important because they have a skeleton composed of calcium carbonate which gets deposited over millions of years and can lead to the formation of extensive land forms such as coral reefs and islands (e.g., Lakshadweep).
In simple words: Corals build hard calcium shells that form coral reefs and islands over time.

Exam Tip: Mention calcium carbonate skeleton and island formation (like Lakshadweep) as key points.

Question 4. What is the difference between class Amphibia and class Reptilia in respect of their skin ?
Answer: Class Amphibia has moist skin without scales, whereas Class Reptilia has dry, cornified skin with epidermal scales or scutes.
In simple words: Amphibians have moist, scaleless skin, while reptiles have dry skin covered in scales.

Exam Tip: Always contrast 'moist and scaleless' with 'dry and cornified with scales'.

Question 5. Which phylum consists of organisms with cellular level of organisation ?
Answer: Phylum Porifera consists of organisms with a cellular level of organisation.
In simple words: Sponges (Porifera) have cells working independently without forming true tissues.

Exam Tip: Associate Porifera strictly with cellular organization, the simplest grade among multicellular animals.

Question 6. Name the arthropod which is a (i) Living fossil, (ii) Gregarious pest.
Answer: (i) Living fossil: Limulus (King crab)
(ii) Gregarious pest: Locusta (Locust)
In simple words: Limulus is an ancient living fossil, and Locusta is a destructive swarming pest.

Exam Tip: Memorize these exact examples as they are frequently asked in competitive exams.

Question 7. Which organ helps in excretion in (i) Arthropods, (ii) Hemichordates ?
Answer: (i) Arthropods: Malpighian tubules (or green glands/coxal glands)
(ii) Hemichordates: Proboscis gland
In simple words: Arthropods use malpighian tubules and hemichordates use a proboscis gland to remove wastes.

Question 8. Distinguish between poikilothermous and homoiothermous organisms.
Answer: Poikilothermous (cold-blooded) organisms lack the ability to regulate their body temperature, meaning their body temperature changes with ambient environmental temperature. Homoiothermous (warm-blooded) organisms can regulate and maintain a constant body temperature regardless of external temperature fluctuations.
In simple words: Cold-blooded animals change body temperature with the weather, while warm-blooded animals keep their body temperature steady.

Exam Tip: Use the terms 'cold-blooded' and 'warm-blooded' alongside their scientific equivalents for clarity.

Question 9. Define metagenesis with a suitable example.
Answer: Metagenesis is the phenomenon of alternation of generation in which a diploid asexual phase alternates with a diploid sexual phase. For example, in Obelia, polyps produce medusae asexually and medusae produce polyps sexually.
In simple words: Metagenesis is when an animal alternates between two forms during its life cycle, like asexual polyps and sexual medusae in Obelia.

Exam Tip: Mention both the alternating body forms (polyp and medusa) and the mode of reproduction for each.

Question 10. List the characteristic features of class Mammalia.
Answer: The characteristic features of class Mammalia include: (1) Presence of mammary glands to nourish young ones, (2) Skin covered with hairs, (3) External ears or pinnae present, (4) Presence of different types of teeth in the jaws, and (5) Viviparity (mostly giving birth to live young ones, except oviparous monotremes like Ornithorhynchus).
In simple words: Mammals have hair, mammary glands to feed milk, external ears, and different kinds of teeth.

Exam Tip: Mammary glands and hair are diagnostic features unique to mammals.

Short Answer Questions-I (3 marks each)

Question 11. What is the difference between organisms on the basis of the coelom ? Give examples for each.
Answer: Based on the presence or absence of a body cavity (coelom) lined by mesoderm, animals are classified into three groups: (1) Coelomates: Organisms possessing a true coelom lined by mesoderm on all sides (e.g., Annelids, Arthropods, Chordates). (2) Pseudocoelomates: Organisms in which the body cavity is not lined by mesoderm, instead, mesoderm is present as scattered pouches between ectoderm and endoderm (e.g., Aschelminthes). (3) Acoelomates: Organisms in which the body cavity is completely absent (e.g., Platyhelminthes).
In simple words: Animals are divided into true coelomates (with cavity), pseudocoelomates (false cavity), and acoelomates (no cavity).

Exam Tip: Draw a quick mental sketch of the embryonic germ layers for coelomates, pseudocoelomates, and acoelomates to ensure accurate definitions.

Question 12. Compare the water transport (vascular) system of poriferans and the echinoderms.
Answer: In poriferans (sponges), the water transport (canal) system involves water entering through minute pores (ostia) into the central spongocoel and going out through the osculum, driven by choanocytes; it helps in food gathering, respiratory exchange, and waste removal. In echinoderms, the water vascular system consists of a network of water-filled canals that operate tube feet; it primarily assists in locomotion, capture and transport of food, and respiration.
In simple words: Sponges use a canal system for filtering water through pores, while echinoderms use a water vascular system to operate tube feet for movement.

Question 13. What are the features of class Aves which help them in flying ?
Answer: The flight adaptations of class Aves include: (1) Forelimbs are modified into wings for flight, (2) Endoskeleton is fully ossified (bony) with air cavities (pneumatic bones) making the body lightweight, (3) Presence of feathers and a streamlined body to reduce air resistance, (4) Air sacs connected to lungs supplement respiration and provide extra buoyancy, and (5) Metabolic rate and body temperature regulation support high energy demands.
In simple words: Birds fly easily because they have wings, lightweight hollow bones, feathers, and powerful lung air sacs.

Question 14. Distinguish between the chordates and non-chordates.
Answer:
- Chordates: (1) Notochord present at some stage of life cycle, (2) Central nervous system is dorsal, hollow, and single, (3) Pharynx pierced by gill slits, (4) Heart is ventral, and (5) A post-anal tail is present.
- Non-Chordates: (1) Notochord is entirely absent, (2) Central nervous system is ventral, solid, and double, (3) Gill slits are absent, (4) Heart is dorsal (if present), and (5) Post-anal tail is absent.
In simple words: Chordates have a backbone/notochord, dorsal nerve cord, and gill slits, while non-chordates lack all these features.

Exam Tip: Present the differences in a comparative point-by-point format for maximum scoring.

Question 15. Differentiate between class Chondrichthyes and class Osteichthyes.
Answer:
- Class Chondrichthyes: (1) Endoskeleton is cartilaginous, (2) Mouth is ventrally located, (3) Gill slits are separate and without an operculum, (4) Skin possesses placoid scales, (5) Air bladder is absent, so they must swim constantly to avoid sinking, (6) Fertilization is internal.
- Class Osteichthyes: (1) Endoskeleton is bony, (2) Mouth is usually terminal, (3) Four pairs of gill slits are covered by an operculum, (4) Skin possesses cycloid or ctenoid scales, (5) Air bladder is present to regulate buoyancy, (6) Fertilization is usually external.
In simple words: Chondrichthyes have cartilage skeletons and ventral mouths (like sharks), while Osteichthyes have bone skeletons, operculum-covered gills, and swim bladders (like bony fishes).

Exam Tip: Focus on skeleton type (cartilage vs bone), operculum presence, and air bladder presence as key diagnostic contrasts.