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Animal Kingdom – CBSE NCERT Study Resources

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11th

11th - Biology

Animal Kingdom

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Overview of the Chapter

The chapter "Animal Kingdom" in the CBSE Grade 11 Biology curriculum introduces students to the diverse classification of animals based on their body organization, symmetry, germ layers, coelom, and other fundamental characteristics. It covers the major phyla of the animal kingdom, their distinguishing features, and examples of organisms belonging to each group.

The Animal Kingdom is classified into various phyla based on criteria such as body symmetry, presence or absence of coelom, and segmentation.

Basis of Classification

Animals are classified based on several fundamental features:

  • Levels of Organization: Cellular, tissue, organ, and organ system levels.
  • Symmetry: Asymmetrical, radial, or bilateral symmetry.
  • Germ Layers: Diploblastic (two layers) or triploblastic (three layers).
  • Coelom: Acoelomate, pseudocoelomate, or coelomate.
  • Segmentation: Presence or absence of metameric segmentation.
  • Notochord: Presence or absence of a notochord (Chordates vs. Non-chordates).

Major Phyla of the Animal Kingdom

1. Phylum Porifera

These are the simplest multicellular animals, commonly known as sponges. They are mostly marine, asymmetrical, and have a cellular level of organization.

Poriferans are pore-bearing organisms with a canal system for water circulation.

2. Phylum Coelenterata (Cnidaria)

Coelenterates are aquatic, mostly marine, diploblastic, and radially symmetrical. They possess cnidoblasts for defense and prey capture.

  • Examples: Hydra, Jellyfish, Sea anemone.

3. Phylum Platyhelminthes

Flatworms are bilaterally symmetrical, triploblastic, and acoelomate. Many are parasitic.

  • Examples: Planaria, Liver fluke, Tapeworm.

4. Phylum Nematoda

Roundworms are bilaterally symmetrical, triploblastic, and pseudocoelomate. They have a complete digestive system.

  • Examples: Ascaris, Wuchereria.

5. Phylum Annelida

Annelids are segmented worms with bilateral symmetry, triploblastic organization, and a true coelom.

  • Examples: Earthworm, Leech.

6. Phylum Arthropoda

Arthropods are the largest phylum, characterized by jointed appendages and an exoskeleton of chitin.

  • Examples: Cockroach, Spider, Prawn.

7. Phylum Mollusca

Molluscs are soft-bodied animals, often with a calcareous shell. They have a muscular foot for locomotion.

  • Examples: Snail, Octopus, Pila.

8. Phylum Echinodermata

Echinoderms are marine animals with radial symmetry in adults and a water vascular system.

  • Examples: Starfish, Sea urchin.

9. Phylum Chordata

Chordates are characterized by the presence of a notochord, dorsal nerve cord, and pharyngeal gill slits at some stage of life.

Chordates are divided into three subphyla: Urochordata, Cephalochordata, and Vertebrata.

Vertebrata

Vertebrates possess a vertebral column and are further classified into:

  • Class Cyclostomata: Jawless vertebrates (e.g., Lamprey).
  • Class Chondrichthyes: Cartilaginous fishes (e.g., Shark).
  • Class Osteichthyes: Bony fishes (e.g., Rohu).
  • Class Amphibia: Dual-life animals (e.g., Frog).
  • Class Reptilia: Creeping vertebrates (e.g., Lizard).
  • Class Aves: Birds (e.g., Pigeon).
  • Class Mammalia: Milk-producing animals (e.g., Human).

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
Define notochord.
Answer:

Definition: A flexible rod-like structure present in chordates during embryonic development.

Question 2:
Name the phylum with radial symmetry.
Answer:

Phylum Cnidaria and Echinodermata.

Question 3:
What is the function of cnidocytes?
Answer:

Used for prey capture and defense in Cnidaria.

Question 4:
Give an example of a pseudocoelomate animal.
Answer:

Ascaris (roundworm).

Question 5:
Which class do frogs belong to?
Answer:

Class Amphibia.

Question 6:
What is the respiratory organ in arthropods?
Answer:

Gills, tracheae, or book lungs.

Question 7:
Name the excretory organ in platyhelminthes.
Answer:

Flame cells.

Question 8:
Identify the phylum with tube feet.
Answer:

Phylum Echinodermata.

Question 9:
What type of symmetry do molluscs exhibit?
Answer:

Bilateral symmetry.

Question 10:
Name the largest phylum in the animal kingdom.
Answer:

Phylum Arthropoda.

Question 11:
Give an example of a segmented worm.
Answer:

Earthworm (Phylum Annelida).

Question 12:
What is the body cavity of nematodes called?
Answer:

Pseudocoelom.

Question 13:
Which animal has a water vascular system?
Answer:

Starfish (Phylum Echinodermata).

Question 14:
Name the phylum with choanocytes.
Answer:

Phylum Porifera.

Question 15:
Name the phylum to which Hydra belongs.
Answer:

Hydra belongs to the phylum Cnidaria (Coelenterata). It exhibits radial symmetry and has specialized stinging cells called cnidocytes.

Question 16:
What is the characteristic feature of organisms in the phylum Platyhelminthes?
Answer:

Organisms in the phylum Platyhelminthes are flatworms with a dorsoventrally flattened body. They are acoelomate (lack a body cavity) and exhibit bilateral symmetry.

Question 17:
Give an example of an animal that belongs to the phylum Annelida.
Answer:

Earthworm (Pheretima posthuma) is an example of an animal belonging to the phylum Annelida. Annelids are segmented worms with a true coelom.

Question 18:
What type of circulatory system is found in Arthropoda?
Answer:

Organisms in the phylum Arthropoda (e.g., cockroach, prawn) have an open circulatory system, where blood (hemolymph) is not confined to blood vessels.

Question 19:
Name the respiratory organ in Mollusca.
Answer:

In Mollusca (e.g., snails, octopus), respiration occurs through gills (ctenidia) in aquatic forms and lungs in terrestrial forms.

Question 20:
Which phylum includes animals with a notochord at some stage of their life?
Answer:

The phylum Chordata includes animals that possess a notochord at least during their embryonic development. Examples include humans, birds, and fish.

Question 21:
What is the excretory organ in Aschelminthes?
Answer:

In Aschelminthes (roundworms), excretion is carried out by renette glands or specialized excretory canals.

Question 22:
Differentiate between diploblastic and triploblastic animals.
Answer:
  • Diploblastic animals (e.g., Cnidaria) have two germ layers: ectoderm and endoderm.
  • Triploblastic animals (e.g., Annelida) have three germ layers: ectoderm, mesoderm, and endoderm.
Question 23:
Name the locomotory organ in Echinodermata.
Answer:

In Echinodermata (e.g., starfish), locomotion is carried out by tube feet, which are part of the water vascular system.

Question 24:
What is the symmetry of animals in the phylum Ctenophora?
Answer:

Animals in the phylum Ctenophora (comb jellies) exhibit biradial symmetry, a combination of radial and bilateral symmetry.

Question 25:
Give an example of a pseudocoelomate animal.
Answer:

Ascaris (roundworm) is an example of a pseudocoelomate animal, where the body cavity is not lined by mesoderm.

Question 26:
Which class of Chordata includes animals with feathers?
Answer:

The class Aves (birds) in the phylum Chordata includes animals with feathers, which aid in flight and insulation.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Name the phylum to which Hydra belongs and mention one distinguishing feature.
Answer:

Hydra belongs to the phylum Cnidaria.
One distinguishing feature is the presence of cnidocytes (stinging cells) used for defense and capturing prey.

Question 2:
Differentiate between diploblastic and triploblastic animals with an example of each.
Answer:

  • Diploblastic animals have two germ layers (ectoderm and endoderm), e.g., Cnidarians like Jellyfish.
  • Triploblastic animals have three germ layers (ectoderm, mesoderm, and endoderm), e.g., Annelids like Earthworm.

Question 3:
What is the significance of notochord in chordates?
Answer:

The notochord is a flexible rod-like structure that provides mechanical support and serves as a precursor to the vertebral column in higher chordates. It also aids in embryonic development.

Question 4:
Give two examples of asymmetrical animals and name their phylum.
Answer:

  • Sponges (Phylum: Porifera)
  • Amoeba (Phylum: Protozoa)

Question 5:
Why are Platyhelminthes called flatworms?
Answer:

Platyhelminthes are called flatworms because their bodies are dorsoventrally flattened, which helps in diffusion of gases and nutrients due to the lack of a circulatory system.

Question 6:
Name the respiratory organ in Mollusca and Arthropoda.
Answer:

  • Mollusca: Gills (ctenidia)
  • Arthropoda: Tracheae or book lungs

Question 7:
What is the function of radula in mollusks?
Answer:

The radula is a rasping, tongue-like organ used for scraping or cutting food before ingestion, found in most mollusks except bivalves.

Question 8:
How does metamerism benefit annelids?
Answer:

Metamerism (segmentation) allows efficient locomotion and specialization of body regions, enhancing survival in diverse environments.

Question 9:
Identify the phylum with tube feet and state their function.
Answer:

Phylum Echinodermata has tube feet.
They function in locomotion, respiration, and food capture through a water vascular system.

Question 10:
Why are Amphibia considered dual-life animals?
Answer:

Amphibia live both in water (larval stage with gills) and on land (adult stage with lungs), hence called dual-life animals.

Question 11:
List two unique features of Aves.
Answer:

  • Feathers for flight and insulation.
  • Hollow bones (pneumatic) to reduce weight for flying.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Differentiate between diploblastic and triploblastic organization in animals with examples.
Answer:

Animals with diploblastic organization have two primary germ layers: ectoderm and endoderm (e.g., Hydra, Jellyfish).
Animals with triploblastic organization have three germ layers: ectoderm, mesoderm, and endoderm (e.g., Earthworm, Humans).
The mesoderm allows for complex organ development in triploblastic animals.

Question 2:
Explain the significance of notochord in chordates with an example.
Answer:

The notochord is a flexible rod-like structure that provides skeletal support in chordates during embryonic development.
In some chordates like Amphioxus, it persists throughout life, while in vertebrates, it is replaced by a vertebral column.
It also plays a role in signaling during embryonic development, influencing the formation of the nervous system.

Question 3:
Compare open and closed circulatory systems with examples.
Answer:

Open circulatory system: Blood is not confined to vessels and flows freely in body cavities (e.g., Arthropods like insects).
Closed circulatory system: Blood flows within vessels, ensuring efficient transport (e.g., Annelids like earthworms, vertebrates).
Closed systems allow for higher metabolic rates due to better oxygen and nutrient delivery.

Question 4:
Describe the unique features of Porifera with an example.
Answer:

Porifera (sponges) are:

  • Simplest multicellular animals with a porous body.
  • Lack true tissues and organs.
  • Have a canal system for water flow and filter feeding.
Example: Sycon.
Their body is supported by spicules or spongin fibers.

Question 5:
How does metamerism benefit annelids? Provide an example.
Answer:

Metamerism (segmentation) in annelids like Earthworm allows:

  • Specialization of body regions for different functions.
  • Improved locomotion due to independent muscle movement in segments.
  • Redundancy; damage to one segment doesn’t affect the whole organism.
This enhances survival and adaptability.

Question 6:
Explain the term bilateral symmetry and its evolutionary advantage with an example.
Answer:

Bilateral symmetry means the body can be divided into two identical halves along one plane (e.g., Humans, Butterflies).
Advantages:

  • Streamlined body for directional movement.
  • Better cephalization (concentration of sense organs at the front).
  • Efficient predator-prey interactions.
This symmetry is common in actively moving animals.

Question 7:
Differentiate between diploblastic and triploblastic animals with examples.
Answer:

Diploblastic animals have two primary germ layers: ectoderm and endoderm. They lack a mesoderm. Examples include Hydra and Jellyfish (Cnidarians).

Triploblastic animals have three germ layers: ectoderm, mesoderm, and endoderm. The mesoderm allows for complex organ development. Examples include Earthworms (Annelida) and Humans (Chordata).

Question 8:
Explain the significance of notochord in chordates.
Answer:

The notochord is a flexible rod-like structure present during embryonic development in all chordates. Its key roles are:

  • Provides structural support and serves as a precursor to the vertebral column in vertebrates.
  • Acts as an axis for muscle attachment, enabling efficient movement.
  • In some primitive chordates (e.g., Amphioxus), it persists throughout life.
Question 9:
Describe the key features of Porifera with an example.
Answer:

Porifera (sponges) are primitive, sessile aquatic animals with:

  • Cellular level organization (no true tissues/organs).
  • Body perforated by ostia (pores) and a central spongocoel.
  • Choanocytes (collar cells) for filter-feeding.
  • Example: Sycon (marine sponge).

They reproduce both sexually and asexually (budding).

Question 10:
What are pseudocoelomates? Give two examples.
Answer:

Pseudocoelomates are animals with a false body cavity (pseudocoelom) derived from the blastocoel, not lined by mesoderm. Examples:

  • Roundworms (Aschelminthes, e.g., Ascaris).
  • Rotifers (microscopic aquatic animals).

Their pseudocoelom acts as a hydrostatic skeleton and aids in nutrient distribution.

Question 11:
How do annelids differ from arthropods in terms of body segmentation?
Answer:

Annelids (e.g., earthworms) show true metamerism: segments are identical externally and internally, with septa separating them. Each segment has repeating organs (e.g., nephridia).

Arthropods (e.g., insects) exhibit tagmatization: segments fuse into specialized body regions (head, thorax, abdomen). Appendages are jointed and modified for functions like feeding or locomotion.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Compare diploblastic and triploblastic organization in animals with examples. Highlight the evolutionary significance.
Answer:
Theoretical Framework

Diploblastic animals have two germ layers (ectoderm and endoderm), while triploblastic animals have three (ectoderm, mesoderm, and endoderm). Our textbook shows Hydra (diploblastic) and Earthworm (triploblastic) as examples.

Evidence Analysis
  • Diploblastic: Simpler body plan (e.g., Hydra)
  • Triploblastic: Complex organs (e.g., Earthworm with muscular system)
Critical Evaluation

Triploblasty enabled organ specialization, driving evolutionary complexity. Diploblasts are limited to radial symmetry.

Future Implications

Studying these patterns helps trace evolutionary relationships, like the divergence of Cnidaria from Bilateria.

Question 2:
Analyze how open and closed circulatory systems differ in efficiency, citing two examples.
Answer:
Theoretical Framework

Open systems (e.g., cockroach) have hemolymph in sinuses, while closed systems (e.g., earthworm) confine blood in vessels.

Evidence Analysis
  • Open: Slower transport (limited to arthropods/mollusks)
  • Closed: Faster O2 delivery (vertebrates/annelids)
Critical Evaluation

Closed systems support higher metabolic rates, as seen in active predators like Homo sapiens.

Future Implications

Research on circulatory efficiency aids bioengineering of artificial vascular networks.

Question 3:
Explain metamerism in annelids with its advantages. Contrast it with non-metameric animals.
Answer:
Theoretical Framework

Metamerism is body segmentation (e.g., earthworm), absent in non-metameric animals like Hydra.

Evidence Analysis
  • Advantages: Redundancy (damaged segments don’t kill organism)
  • Specialization: Segments adapt for locomotion/excretion
Critical Evaluation

Metamerism enabled evolutionary innovations like arthropod appendages. Non-segmented animals lack this flexibility.

Future Implications

Studying segmentation aids regenerative medicine (e.g., stem cell therapies).

Question 4:
Evaluate the role of notochord in chordate evolution. How does it differ in vertebrates vs. protochordates?
Answer:
Theoretical Framework

The notochord is a rod-like structure in chordates (e.g., Amphioxus vs. Homo sapiens).

Evidence Analysis
  • Protochordates: Notochord persists (support)
  • Vertebrates: Replaced by vertebrae (advanced mobility)
Critical Evaluation

Notochord was pivotal for spinal column evolution, enabling vertebrate dominance.

Future Implications

Research on notochord genes may treat spinal disorders like scoliosis.

Question 5:
Justify why annelids and arthropods were once grouped together. What evidence led to their reclassification?
Answer:
Theoretical Framework

Both show metamerism, but molecular evidence reclassified them into separate phyla.

Evidence Analysis
  • Similarity: Segmented bodies (e.g., earthworm vs. cockroach)
  • Difference: Arthropods have chitinous exoskeleton/jointed legs
Critical Evaluation

DNA sequencing revealed arthropods are closer to nematodes (Ecdysozoa).

Future Implications

Such revisions highlight the need for integrative taxonomy combining morphology and genetics.

Question 6:
Compare diploblastic and triploblastic organization in animals with examples. Highlight the evolutionary significance of triploblasty.
Answer:
Theoretical Framework

We studied that diploblastic animals (e.g., Hydra, jellyfish) have two germ layers (ectoderm and endoderm), while triploblastic animals (e.g., earthworms, humans) have three (ectoderm, mesoderm, endoderm).

Evidence Analysis
  • Mesoderm enables complex organ systems (e.g., circulatory, muscular).
  • Triploblasty allows bilateral symmetry and cephalization.
Critical Evaluation

Our textbook shows triploblasty as a key adaptation for larger body size and mobility. Diploblasts are limited to simpler forms.

Future Implications

Understanding germ layers aids in evolutionary biology and regenerative medicine research.

Question 7:
Analyze how open and closed circulatory systems differ in efficiency. Support your answer with examples from Arthropoda and Annelida.
Answer:
Theoretical Framework

Open systems (e.g., cockroaches) lack vessels, while closed systems (e.g., earthworms) use blood vessels for precise transport.

Evidence Analysis
  • Closed systems deliver oxygen faster (annelids show higher metabolic rates).
  • Open systems are energy-efficient for small arthropods.
Critical Evaluation

Our textbook highlights that closed systems support active lifestyles, as seen in predatory annelids versus sedentary arthropods.

Future Implications

Studying these systems helps design bio-inspired fluid transport technologies.

Question 8:
Explain the metameric segmentation in Annelida with two examples. Discuss its functional advantages.
Answer:
Theoretical Framework

Metamerism is body segmentation into repeating units (e.g., earthworm, leech). Each segment contains muscles, nerves, and nephridia.

Evidence Analysis
  • Enables localized movement (earthworm burrowing).
  • Redundancy: Damage to one segment doesn’t paralyze the whole organism.
Critical Evaluation

Our textbook shows this as an evolutionary precursor to specialized segmentation in vertebrates.

Future Implications

Robotics researchers mimic metamerism for flexible, resilient designs.

Question 9:
Contrast protostomes and deuterostomes in terms of cleavage, coelom formation, and fate of blastopore. Provide one example each.
Answer:
Theoretical Framework

Protostomes (e.g., snails) show spiral cleavage, schizocoely, and blastopore→mouth. Deuterostomes (e.g., starfish) have radial cleavage, enterocoely, and blastopore→anus.

Evidence Analysis
  • Deuterostome development allows more complex body plans.
  • Protostomes dominate invertebrate diversity.
Critical Evaluation

Our textbook links deuterostome patterns to vertebrate evolution, including humans.

Future Implications

Embryonic studies aid in understanding congenital disorders.

Question 10:
Evaluate the ecological role of cnidocytes in Cnidaria. How do they support both predation and defense?
Answer:
Theoretical Framework

Cnidocytes are stinging cells in jellyfish and corals containing nematocysts. We studied they inject toxins via harpoon-like structures.

Evidence Analysis
  • Predation: Immobilizes prey (e.g., fish larvae).
  • Defense: Deters predators (e.g., turtles avoid tentacles).
Critical Evaluation

Our textbook shows cnidocytes as a key adaptation for sessile and slow-moving species survival.

Future Implications

Research on cnidocyte toxins inspires new biomedical compounds for pain relief.

Question 11:
Compare the digestive systems of annelids and arthropods, highlighting their adaptations for different diets. (5 marks)
Answer:

The digestive systems of annelids and arthropods exhibit distinct adaptations based on their dietary habits.

Annelids (e.g., earthworms):
1. They have a complete digestive tract with specialized regions like the pharynx, esophagus, crop, gizzard, and intestine.
2. The gizzard helps grind soil and organic matter, while the intestine absorbs nutrients.
3. They are detritivores, feeding on decaying organic material, and their digestive system is adapted for efficient breakdown of cellulose.

Arthropods (e.g., grasshoppers):
1. Their digestive system includes a foregut (mouth, esophagus, crop), midgut (stomach with digestive glands), and hindgut (intestine, rectum).
2. Mandibles or chelicerae help in mechanical breakdown, while digestive enzymes in the midgut aid chemical digestion.
3. Arthropods show diverse diets (herbivores, carnivores, omnivores), and their digestive system varies accordingly (e.g., filter-feeding in crustaceans).

Key difference: Annelids rely on extracellular digestion in a straight tube-like gut, while arthropods often have ceca or gastric pouches for enhanced digestion.

Question 12:
Explain the respiratory systems of molluscs and echinoderms, emphasizing their habitat-based adaptations. (5 marks)
Answer:

The respiratory systems of molluscs and echinoderms are adapted to their respective habitats.

Molluscs:
1. Aquatic molluscs (e.g., Pila) use gills (ctenidia) for respiration, which are feathery structures with a large surface area for oxygen exchange.
2. Terrestrial molluscs (e.g., snails) have a pulmonary sac (modified mantle cavity) that functions like a lung.
3. Gills are often associated with filter-feeding in bivalves, showing dual functionality.

Echinoderms:
1. They rely on tube feet and dermal branchiae (skin gills) for respiration.
2. The water vascular system aids in oxygen transport through diffusion across thin-walled tube feet.
3. Their slow movement and marine habitat reduce the need for complex respiratory structures.

Adaptation insight: Molluscs show habitat-specific respiratory organs (gills/lungs), while echinoderms use simple diffusion due to their aquatic lifestyle and low metabolic demands.

Question 13:
Compare and contrast the features of annelids and arthropods under the following headings: (a) Body symmetry, (b) Circulatory system, (c) Segmentation, (d) Excretory organs. Provide examples for each group.
Answer:

Annelids and arthropods are both bilaterally symmetrical and segmented, but they differ in several key features:

  • (a) Body Symmetry: Both exhibit bilateral symmetry, meaning their bodies can be divided into two identical halves along a single plane.
  • (b) Circulatory System: Annelids have a closed circulatory system (e.g., earthworm), where blood flows in vessels. Arthropods possess an open circulatory system (e.g., cockroach), where blood (hemolymph) flows freely in body cavities.
  • (c) Segmentation: Both show metameric segmentation, but in annelids, segments are externally and internally similar (homonomous). In arthropods, segments often fuse to form specialized body parts (heteronomous).
  • (d) Excretory Organs: Annelids use nephridia for excretion, while arthropods use Malpighian tubules (insects) or green glands (crustaceans).

Examples: Annelids include earthworms and leeches, while arthropods include insects (butterfly), arachnids (spider), and crustaceans (prawn).

Question 14:
Explain the unique characteristics of chordates with reference to the presence of a notochord, dorsal nerve cord, and pharyngeal gill slits. How do these features vary in different subphyla of chordates?
Answer:

Chordates are characterized by three key features at some stage of their life cycle:

  • Notochord: A flexible rod-like structure providing support. In vertebrates, it is replaced by a vertebral column, but remains in urochordates (e.g., tunicates) and cephalochordates (e.g., Amphioxus).
  • Dorsal Nerve Cord: A hollow nerve cord located dorsally, developing into the brain and spinal cord in vertebrates.
  • Pharyngeal Gill Slits: Openings in the pharynx for filter-feeding or respiration. In aquatic chordates (e.g., fish), they persist as gills, while in terrestrial vertebrates, they modify into structures like the Eustachian tube.

Variations in Subphyla:
Urochordates (Tunicates): Notochord and nerve cord present only in larval stage.
Cephalochordates (Amphioxus): All features persist throughout life.
Vertebrates: Notochord replaced by vertebrae, nerve cord becomes the central nervous system, and gill slits are modified or absent in adults.

Question 15:
Compare the features of Annelida and Arthropoda based on their body symmetry, coelom, segmentation, and circulatory system. Provide examples for each phylum.
Answer:

Comparison between Annelida and Arthropoda:

  • Body Symmetry: Both Annelida (e.g., earthworm) and Arthropoda (e.g., cockroach) exhibit bilateral symmetry.
  • Coelom: Annelida have a true coelom (schizocoelom), while Arthropoda possess a haemocoel (reduced coelom).
  • Segmentation: Both show metameric segmentation, but in Arthropoda, segments fuse to form specialized body parts (e.g., head, thorax, abdomen).
  • Circulatory System: Annelida have a closed circulatory system (e.g., blood flows in vessels), whereas Arthropoda have an open circulatory system (e.g., blood flows freely in spaces).

Examples: Annelida – Earthworm, leech; Arthropoda – Cockroach, prawn.

Value-added info: Arthropoda is the largest phylum, with adaptations like exoskeleton and jointed appendages for survival.

Question 16:
Compare the digestive systems of herbivores and carnivores, highlighting the structural and functional adaptations that suit their respective diets. (5 marks)
Answer:

The digestive systems of herbivores and carnivores exhibit distinct adaptations to their diets:

  • Herbivores:
    1. Longer alimentary canal to allow prolonged fermentation of cellulose by symbiotic bacteria.
    2. Specialized stomach chambers (e.g., rumen in ruminants) for microbial digestion.
    3. Well-developed cecum in non-ruminants (e.g., rabbits) for cellulose breakdown.
    4. Broad, flat teeth for grinding tough plant material.
  • Carnivores:
    1. Shorter digestive tract as meat is easier to digest.
    2. Sharp, pointed teeth (canines and incisors) for tearing flesh.
    3. Strong jaw muscles to hold and kill prey.
    4. Reduced cecum due to minimal cellulose digestion.

These adaptations ensure efficient nutrient extraction from their respective food sources, reflecting evolutionary specialization.

Question 17:
Compare the features of annelids and arthropods under the following headings: (a) Body symmetry, (b) Circulatory system, (c) Segmentation, (d) Exoskeleton. (5 marks)
Answer:

Comparison between Annelids and Arthropods:


(a) Body Symmetry:
Both annelids and arthropods exhibit bilateral symmetry, meaning their bodies can be divided into two identical halves along a single plane.


(b) Circulatory System:
Annelids have a closed circulatory system, where blood flows through vessels. Example: Earthworm.
Arthropods have an open circulatory system, where blood (hemolymph) flows freely in body cavities. Example: Cockroach.


(c) Segmentation:
Annelids show true metameric segmentation, where each segment is similar and contains repeating organs.
Arthropods also have segmented bodies, but their segments are often specialized (e.g., head, thorax, abdomen) with fused segments.


(d) Exoskeleton:
Annelids lack an exoskeleton; their body is covered by a thin cuticle.
Arthropods possess a hard chitinous exoskeleton, which provides protection and support but requires molting for growth.


Additional Note: While both groups are protostomes, arthropods have jointed appendages, a feature absent in annelids.

Question 18:
Compare the digestive systems of annelids and arthropods, highlighting their structural and functional differences. Support your answer with examples.
Answer:

The digestive systems of annelids and arthropods exhibit distinct structural and functional adaptations based on their habitats and feeding habits.

Annelids (e.g., Earthworm):
1. Alimentary canal is straight and complete, running from mouth to anus.
2. Divided into specialized regions: pharynx (for ingestion), esophagus, crop (storage), gizzard (grinding), and intestine (absorption).
3. Digestion is primarily extracellular, aided by enzymes secreted by the gut wall.
4. Earthworms are detritivores, feeding on decaying organic matter.

Arthropods (e.g., Grasshopper):
1. Alimentary canal is also complete but may have regional modifications like gastric caeca for enzyme secretion.
2. Divided into foregut (mechanical breakdown), midgut (chemical digestion), and hindgut (water absorption).
3. Digestion involves both extracellular and intracellular processes, with enzymes secreted by digestive glands.
4. Grasshoppers are herbivores, feeding on plant material, and have mandibles for chewing.

Key Differences:
1. Specialization: Annelids lack appendages for feeding, while arthropods have mouthparts adapted to their diet (e.g., mandibles, proboscis).
2. Digestive glands: Arthropods often have additional glands like salivary glands, absent in annelids.
3. Mechanical breakdown: Arthropods rely more on external structures (e.g., mandibles), whereas annelids use internal structures like the gizzard.

These differences reflect their evolutionary adaptations to diverse ecological niches.

Question 19:
Compare the features of annelids and arthropods under the following headings: (a) Body symmetry, (b) Circulatory system, (c) Excretory organs, (d) Segmentation, and (e) Examples. (5 marks)
Answer:

Comparison between Annelids and Arthropods:

  • (a) Body Symmetry: Annelids exhibit bilateral symmetry, meaning their body can be divided into two identical halves along a single plane. Arthropods also show bilateral symmetry.

  • (b) Circulatory System: Annelids have a closed circulatory system, where blood flows through vessels. Arthropods, on the other hand, possess an open circulatory system, where blood (hemolymph) flows freely in body cavities.

  • (c) Excretory Organs: Annelids use nephridia for excretion, which filter waste from the body fluids. Arthropods excrete waste through Malpighian tubules (in insects) or green glands (in crustaceans).

  • (d) Segmentation: Both groups show metameric segmentation, but in annelids, segments are similar (homonomous), while in arthropods, segments are often specialized (heteronomous).

  • (e) Examples: Annelids include earthworms (Pheretima) and leeches (Hirudinaria). Arthropods include insects (e.g., cockroach), arachnids (e.g., spider), and crustaceans (e.g., prawn).

Value-added note: While both belong to the Bilateria group, arthropods are more diverse due to adaptations like exoskeletons and jointed appendages, enabling survival in varied habitats.

Question 20:
Compare the features of annelids and arthropods based on their body symmetry, coelom, and circulatory system. Provide examples for each phylum.
Answer:

Annelids and arthropods are both bilaterally symmetrical, triploblastic organisms, but they exhibit distinct differences in their body structure and physiological systems.

Body Symmetry: Both annelids and arthropods display bilateral symmetry, meaning their bodies can be divided into two identical halves along a single plane.

Coelom:
1. Annelids have a true coelom (schizocoelom) that is fluid-filled and acts as a hydrostatic skeleton.
2. Arthropods have a reduced coelom called a haemocoel, where blood directly bathes the organs.

Circulatory System:
1. Annelids possess a closed circulatory system, where blood flows through vessels (e.g., earthworm).
2. Arthropods have an open circulatory system, where blood (haemolymph) is not confined to vessels (e.g., cockroach).

Examples:
1. Annelids: Earthworm (Pheretima), Leech (Hirudinaria).
2. Arthropods: Cockroach (Periplaneta), Butterfly (Danaus).

Additional Note: Arthropods have jointed appendages and an exoskeleton made of chitin, while annelids have segmented bodies with setae for locomotion.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
In our study of poriferans, we observed their unique canal system. Analyze how this system aids in their survival, comparing it to the gastrovascular cavity of cnidarians.
Answer:
Case Deconstruction

Poriferans use a canal system for filter-feeding, where water enters through ostia and exits via osculum. Cnidarians rely on a gastrovascular cavity for digestion and circulation.

Theoretical Application
  • Poriferans: No true tissues; water flow delivers nutrients.
  • Cnidarians: Single opening for ingestion/egestion.
Critical Evaluation

The canal system maximizes surface area for feeding, while the gastrovascular cavity combines digestion and distribution, showing evolutionary divergence.

Question 2:
During a lab dissection, we compared open and closed circulatory systems in arthropods and annelids. Justify which system is more efficient for active locomotion.
Answer:
Case Deconstruction

Arthropods (e.g., cockroach) have an open system where hemolymph bathes organs directly. Annelids (e.g., earthworm) use a closed system with blood vessels.

Theoretical Application
  • Closed systems allow faster nutrient/O2 delivery.
  • Annelids show higher metabolic rates due to efficient circulation.
Critical Evaluation

The closed system supports sustained activity, as seen in earthworm burrowing, while arthropods rely on tracheal systems for O2.

Question 3:
Our textbook mentions metamerism in earthworms and pseudometamerism in tapeworms. Differentiate these with evidence from their body plans.
Answer:
Case Deconstruction

Metamerism in earthworms involves true segments with repeated organs (e.g., nephridia). Tapeworms show pseudometamerism (proglottids) without organ repetition.

Theoretical Application
  • Earthworms: Segments aid locomotion via septa.
  • Tapeworms: Proglottids are reproductive units.
Critical Evaluation

True metamerism enhances mobility, while pseudometamerism is adaptive for parasitic reproduction, as seen in Taenia.

Question 4:
A researcher claims chondrichthyes are more advanced than osteichthyes due to their cartilaginous skeleton. Critically evaluate this using two functional adaptations.
Answer:
Case Deconstruction

Sharks (chondrichthyes) have buoyant livers, while bony fish (osteichthyes) use swim bladders. Both exhibit lateral line systems.

Theoretical Application
  • Cartilage reduces weight but limits size.
  • Bony fish dominate diverse habitats due to ossified skeletons.
Critical Evaluation

While cartilage aids speed (e.g., great white shark), bony fish demonstrate broader ecological success, disproving the claim.

Question 5:
In a lab, two specimens were observed: Ascaris (roundworm) and Pheretima (earthworm). Compare their body symmetry, coelom type, and digestive system with justifications.
Answer:
Case Deconstruction
  • Ascaris shows bilateral symmetry, while Pheretima also exhibits bilateral symmetry.
  • Ascaris has a pseudocoelom, whereas Pheretima has a true coelom.
Theoretical Application

Our textbook shows that pseudocoelomates like Ascaris lack mesodermal lining, while true coelomates like Pheretima have a complete digestive system with specialized regions.

Critical Evaluation

The differences highlight evolutionary adaptations: Pheretima's true coelom supports complex organ systems, unlike Ascaris.

Question 6:
A student noted that Platyhelminthes (tapeworm) and Annelida (leech) differ in segmentation and excretory organs. Explain these differences with examples.
Answer:
Case Deconstruction
  • Platyhelminthes are unsegmented, while Annelida show metameric segmentation.
  • Tapeworms use flame cells for excretion, whereas leeches have nephridia.
Theoretical Application

We studied that segmentation in Annelida aids locomotion, and nephridia are more efficient than flame cells for waste removal.

Critical Evaluation

These adaptations reflect habitat needs: leeches thrive in aquatic environments, while tapeworms are parasitic.

Question 7:
Analyze how respiratory pigments in Arthropoda (cockroach) and Mollusca (octopus) adapt to their habitats. Support with current data.
Answer:
Case Deconstruction
  • Cockroaches use hemocyanin in hemolymph, while octopuses rely on hemocyanin in blood.
  • Both pigments bind oxygen but differ in efficiency.
Theoretical Application

Recent studies show octopus hemocyanin adapts to deep-sea pressure, unlike cockroach pigments suited for terrestrial life.

Critical Evaluation

This highlights how respiratory systems evolve to meet environmental oxygen demands.

Question 8:
Contrast reproductive strategies of Osteichthyes (bony fish) and Amphibia (frog) with evidence-based arguments.
Answer:
Case Deconstruction
  • Bony fish exhibit external fertilization, while frogs show external fertilization with amplexus.
  • Fish lay numerous eggs, whereas frogs lay fewer eggs with jelly coating.
Theoretical Application

Our textbook shows frog adaptations reduce predation, unlike fish relying on quantity for survival.

Critical Evaluation

These strategies reflect trade-offs between energy investment and offspring survival rates.

Question 9:
In our study of poriferans, we observed their unique canal system. Compare the asconoid, syconoid, and leuconoid types with examples.
Answer:
Case Deconstruction

Poriferans have three canal systems: asconoid (simplest, e.g., Leucosolenia), syconoid (folded walls, e.g., Sycon), and leuconoid (complex, e.g., Spongilla).


Theoretical Application
  • Asconoid: Single-layered, direct water flow.
  • Syconoid: Radial canals increase surface area.
  • Leuconoid: Chambers boost filtering efficiency.

Critical Evaluation

Leuconoid’s complexity aligns with higher metabolic demands, while asconoid suits smaller species. Our textbook shows these adaptations optimize nutrient uptake in varying habitats.

Question 10:
Analyze how metamerism in annelids (e.g., earthworm) differs from pseudometamerism in tapeworms.
Answer:
Case Deconstruction

Metamerism in annelids (e.g., Pheretima) involves true segmentation of organs, while pseudometamerism in tapeworms (e.g., Taenia) is superficial repetition of body units.


Theoretical Application
  • Annelid segments: Independent muscles, nerves, and nephridia.
  • Tapeworm proglottids: Identical reproductive units without organ systems.

Critical Evaluation

True metamerism enhances locomotion and redundancy, whereas pseudometamerism aids parasitic reproduction. Our studies confirm annelid segmentation is evolutionarily advanced.

Question 11:
Contrast open and closed circulatory systems using arthropods and cephalopods as examples.
Answer:
Case Deconstruction

Open systems (e.g., cockroach) lack vessels, bathing organs in hemolymph, while closed systems (e.g., octopus) confine blood to vessels for efficient transport.


Theoretical Application
  • Arthropods: Low-pressure flow, slower nutrient delivery.
  • Cephalopods: High-pressure flow supports active predation.

Critical Evaluation

Closed systems correlate with higher metabolic rates, as seen in cephalopods. Our textbook highlights this as an adaptation for larger body sizes.

Question 12:
Explain how poikilothermy in frogs and homeothermy in birds influence their habitat choices.
Answer:
Case Deconstruction

Poikilothermic frogs (e.g., Rana) rely on external heat, limiting them to warm climates, while homeothermic birds (e.g., pigeon) regulate temperature internally, enabling global distribution.


Theoretical Application
  • Frogs: Hibernate in cold; thrive near water.
  • Birds: Migrate or fluff feathers to retain heat.

Critical Evaluation

Homeothermy’s energy cost is offset by survival in diverse niches. We studied how this explains birds’ dominance over amphibians in colder regions.

Question 13:

During a field trip, students observed an aquatic animal with a streamlined body, lateral line system, and gills for respiration. However, it lacked paired fins and jaws. The teacher asked them to identify the phylum and class of the organism and justify their answer with two features.

Answer:

The observed organism belongs to the Phylum Chordata and Class Cyclostomata.

Justification:

  • The presence of a streamlined body and lateral line system confirms it is an aquatic chordate.
  • The absence of paired fins and jaws is a characteristic feature of Cyclostomata (e.g., lampreys and hagfish).

Additionally, Cyclostomata are ectoparasites or scavengers with a circular mouth, which aligns with the observed features.

Question 14:

A student examined two organisms: Organism A had a segmented body, jointed appendages, and an exoskeleton, while Organism B had a soft body, a muscular foot, and a mantle. Compare their phyla based on any four distinguishing features.

Answer:

Comparison:

  • Organism A belongs to Phylum Arthropoda due to features like segmented body, jointed appendages, chitinous exoskeleton, and open circulatory system.
  • Organism B belongs to Phylum Mollusca as it shows soft body, muscular foot for locomotion, mantle secreting the shell, and radula (in some) for feeding.

Arthropods are mostly terrestrial/aquatic with high diversity, while molluscs are predominantly aquatic with a calcareous shell in many species.

Question 15:

In a biodiversity survey, a student observed an aquatic animal with the following features: radial symmetry, cnidocytes, and a gastrovascular cavity. The animal also exhibits two body forms—polyp and medusa.

(a) Identify the phylum to which this animal belongs.
(b) Explain how the presence of cnidocytes aids in its survival.
(c) Differentiate between polyp and medusa forms with one example each.

Answer:

(a) The animal belongs to the phylum Cnidaria (or Coelenterata).

(b) Cnidocytes are specialized cells containing stinging structures called nematocysts. They help in:

  • Capturing prey by injecting toxins.
  • Defense against predators.

(c) Differences between polyp and medusa:

  • Polyp: Sessile, cylindrical form (e.g., Hydra).
  • Medusa: Free-swimming, umbrella-shaped form (e.g., Aurelia jellyfish).

Question 16:

A farmer found a segmented organism in his field with metamerism, closed circulatory system, and excretory structures called nephridia.

(a) Name the phylum and class of this organism.
(b) How does a closed circulatory system benefit this organism?
(c) Briefly describe the role of nephridia.

Answer:

(a) The organism belongs to phylum Annelida, class Oligochaeta (e.g., earthworm).

(b) A closed circulatory system ensures:

  • Efficient oxygen and nutrient transport.
  • Faster circulation due to blood confined in vessels.

(c) Nephridia are excretory organs that:

  • Remove nitrogenous wastes (e.g., urea).
  • Maintain osmotic balance by filtering coelomic fluid.

Question 17:

During a field trip, students observed an aquatic animal with a streamlined body, lateral line system, and gill slits. It also had a cartilaginous skeleton. Based on these features, identify the phylum and class of the organism. Justify your answer with two characteristic features of the identified group.

Answer:

The observed organism belongs to the phylum Chordata and class Chondrichthyes.


Justification:

  • The presence of gill slits and a cartilaginous skeleton confirms it as a member of Chondrichthyes.
  • The streamlined body and lateral line system are adaptations for aquatic life, common in cartilaginous fishes like sharks and rays.

Additional features of Chondrichthyes include placoid scales and a heterocercal tail, which aid in swimming efficiency.

Question 18:

A student found an organism with a segmented body, jointed appendages, and an exoskeleton made of chitin. It also undergoes molting during growth. Identify the phylum of this organism and explain two key features that support your answer. How does molting benefit this organism?

Answer:

The organism belongs to the phylum Arthropoda.


Key features:

  • Jointed appendages and a chitinous exoskeleton are definitive traits of arthropods.
  • The segmented body aligns with the metameric segmentation seen in this phylum.

Molting benefit: The rigid exoskeleton limits growth, so molting (ecdysis) allows the organism to shed its old exoskeleton and form a larger one, facilitating growth and development.

Question 19:

During a field trip, students observed an aquatic animal with a streamlined body, gill slits, and a cartilaginous skeleton. The animal was also found to be cold-blooded. Based on these observations, answer the following:

  • Identify the phylum and class to which this animal belongs.
  • Provide two distinguishing features of this class.
  • Explain how the streamlined body aids in its survival.
Answer:

The observed animal belongs to the phylum Chordata and the class Chondrichthyes.

  • Distinguishing features of Chondrichthyes:
    1. They possess a cartilaginous skeleton instead of a bony one.
    2. They have placoid scales covering their skin, which reduce drag in water.

Streamlined body adaptation: The streamlined body reduces water resistance, enabling swift movement for hunting prey and escaping predators. This is crucial for survival in aquatic habitats.

Question 20:

A student examined two organisms: one with a segmented body, jointed appendages, and an exoskeleton, and another with a soft, unsegmented body and a mantle. Answer the following:

  • Classify these organisms into their respective phyla.
  • Compare their circulatory systems.
  • Explain one adaptive advantage of the exoskeleton in the first organism.
Answer:

The first organism belongs to the phylum Arthropoda, and the second belongs to the phylum Mollusca.

  • Comparison of circulatory systems:
    1. Arthropoda: They have an open circulatory system, where blood (hemolymph) is not confined to vessels.
    2. Mollusca: Most have an open circulatory system, except cephalopods (e.g., squids), which have a closed circulatory system.

Adaptive advantage of exoskeleton: The exoskeleton provides structural support, protection from predators, and prevents water loss, which is vital for terrestrial arthropods.

Question 21:
A marine biologist discovered a new organism with the following characteristics: radial symmetry, presence of cnidocytes, and a gastrovascular cavity. Identify the phylum of this organism and explain any two key features of this phylum with examples.
Answer:

The organism belongs to the phylum Cnidaria due to its radial symmetry, presence of cnidocytes (stinging cells), and a gastrovascular cavity.

Two key features of Cnidaria are:

  • Radial Symmetry: The body is arranged symmetrically around a central axis, allowing them to detect and respond to stimuli from all directions. Example: Hydra and Aurelia (jellyfish).
  • Polymorphism: Many cnidarians exhibit two body forms—polyp (sessile, cylindrical) and medusa (free-swimming, umbrella-shaped). Example: Obelia shows both forms in its life cycle.

Additionally, cnidarians have a simple nervous system called a nerve net and reproduce both sexually and asexually.

Question 22:
A student observed an animal with a segmented body, jointed appendages, and an exoskeleton made of chitin. Identify the phylum and class of this animal. Differentiate between the two major classes under this phylum based on their respiratory structures.
Answer:

The animal belongs to the phylum Arthropoda and likely the class Insecta or Crustacea based on the given features.

The two major classes under Arthropoda and their respiratory structures are:

  • Insecta: Respiration occurs through a network of tracheae (air tubes) that open externally via spiracles. Example: Grasshopper.
  • Crustacea: Respiration occurs through gills or branchiae, which are specialized for aquatic life. Example: Prawn.

Other differences include:
Insects have three pairs of legs and typically wings, while crustaceans have two pairs of antennae and biramous appendages.

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