Exercises
What are the difficulties that you would face in classification of animals, if common fundamental features are not taken into account?
Answer
Without common fundamental features, animal classification would face several difficulties:
(i) Animals would be classified based on superficial features like colour, size, or habitat, which would put unrelated animals together and separate related ones.
(ii) There would be no universal, consistent basis for classification, leading to different classifications by different scientists and confusion in communication.
(iii) It would be impossible to understand evolutionary relationships – we would not know which organisms share common ancestors.
(iv) Identification of organisms would become unreliable, and the classification would not reflect true biological diversity.
Using fundamental features like body symmetry, coelom type, segmentation, notochord, and level of organisation creates a natural, phylogenetic classification.
If you are given a specimen, what are the steps that you would follow to classify it?
Answer
Steps to classify a given specimen:
(i) Observe the level of body organisation – cellular, tissue, organ, or organ-system level.
(ii) Note the body symmetry – asymmetrical, radially symmetrical, or bilaterally symmetrical.
(iii) Check for the presence or absence of coelom (body cavity) and its type – acoelomate, pseudocoelomate, or coelomate.
(iv) Check for segmentation of the body.
(v) Look for the presence or absence of a notochord – if present, the animal belongs to Phylum Chordata.
(vi) Observe the nature of the digestive system (complete/incomplete), reproduction (sexual/asexual), and presence of special structures (setae, wings, fins, etc.).
(vii) Use a taxonomic key to narrow down to the correct phylum, class, order, family, genus, and species.
How useful is the study of the nature of body cavity and coelom in the classification of animals?
Answer
The nature of body cavity (coelom) is one of the most important criteria in animal classification:
(i) Acoelomates: No coelom at all; space between body wall and gut is filled with mesodermally derived cells (mesenchyme). Example: Platyhelminthes.
(ii) Pseudocoelomates: Body cavity is present but not lined entirely by mesoderm; derived from blastocoel. Example: Aschelminthes (nematodes).
(iii) Coelomates (Eucoelomates): True coelom – body cavity is entirely lined by mesoderm (peritoneum). Example: Annelida, Arthropoda, Mollusca, Echinodermata, Chordata.
The coelom allows organ development, provides hydraulic support (in some animals), and is important for locomotion and reproduction. The nature of coelom reflects the evolutionary grade of an animal.
Distinguish between intracellular and extracellular digestion?
Answer
Intracellular digestion: Digestion occurs inside the cells, within food vacuoles by lysosomal enzymes. The food is engulfed by phagocytosis and digested within the cell. This is seen in lower invertebrates like sponges (Porifera) and Amoeba.
Extracellular digestion: Digestion occurs outside the cells, inside a digestive cavity (gut). Digestive enzymes are secreted into the gut lumen and food is digested before absorption. This is seen in most animals, including annelids, arthropods, and vertebrates. It is more efficient, allowing digestion of large food particles.
What is the difference between direct and indirect development?
Answer
Direct development: The young ones that hatch from the egg (or are born) closely resemble the adult in form and structure, and gradually grow into adults without a larval stage. No metamorphosis occurs. Example: Reptiles, birds, mammals, earthworms.
Indirect development: The egg hatches into a larva which is morphologically and often ecologically very different from the adult. The larva undergoes metamorphosis to transform into the adult form. Example: Frogs (tadpole
⇒ frog), insects (caterpillar
⇒ butterfly), many marine invertebrates.
What are the peculiar features that you find in parasitic platyhelminthes?
Answer
Parasitic platyhelminthes (flatworms) show the following adaptations for parasitism:
(i) The body is flattened dorsoventrally, which is suited to living inside host organs.
(ii) They have hooks and suckers for attachment to host tissues (e.g., tapeworms have a scolex with hooks and suckers).
(iii) The body surface is covered by a tegument – a syncytial outer covering that is resistant to host digestive enzymes.
(iv) Digestive system is either absent (tapeworms – absorb pre-digested nutrients through the body surface) or poorly developed.
(v) They have a complex life cycle involving one or more intermediate hosts.
(vi) Reproductive capacity is very high to compensate for losses during transmission between hosts. Examples: Taenia (tapeworm), Fasciola (liver fluke), Schistosoma.
What are the reasons that you can think of for the arthropods to constitute the largest group of the animal kingdom?
Answer
Arthropods are the most successful and largest group of animals due to:
(i) Exoskeleton: A hard chitinous exoskeleton provides protection, prevents desiccation, and allows life on land.
(ii) Jointed appendages: Versatile jointed limbs allow diverse locomotion (walking, swimming, flying), food capture, and other functions.
(iii) Small size: Reduces resource requirements, allowing many individuals to survive in small habitats.
(iv) Flight in insects: Enables colonisation of new habitats, escape from predators, and finding food over large areas.
(v) High reproductive rate: Short life cycles and large numbers of offspring allow rapid population growth.
(vi) Ability to moult (ecdysis): Periodic shedding and renewal of exoskeleton allows growth.
(vii) Diverse adaptations: Arthropods have adapted to virtually every habitat – land, freshwater, marine, aerial, and parasitic.
Water vascular system is the characteristic of which group of the following: (a) Porifera (b) Ctenophora (c) Echinodermata (d) Chordata
Answer
(c) Echinodermata. The water vascular system (also called the ambulacral system) is the defining feature of echinoderms. It consists of a network of fluid-filled canals used for locomotion (tube feet), feeding, respiration, and excretion. Examples of echinoderms include starfish (Asterias), sea urchin, and sea cucumber.
"All vertebrates are chordates but all chordates are not vertebrates". Justify the statement.
Answer
Phylum Chordata is defined by three fundamental features: (i) a notochord, (ii) a dorsal hollow nerve cord, and (iii) pharyngeal gill slits, present at least during some stage of development. The phylum is divided into:
(i) Urochordata (e.g., Ascidia) – notochord only in larva, not in adult; no vertebral column.
(ii) Cephalochordata (e.g., Amphioxus) – notochord throughout life; no vertebral column.
(iii) Vertebrata – notochord replaced by a vertebral column (backbone) in the adult.
Thus, Urochordates and Cephalochordates are chordates but do NOT have a vertebral column – they are not vertebrates. All vertebrates, however, possess the three chordate features and are therefore chordates. Hence, all vertebrates are chordates but all chordates are not vertebrates.
How important is the presence of air bladder in Pisces?
Answer
The air bladder (swim bladder) in bony fishes (Osteichthyes) is extremely important:
(i) It is a gas-filled sac that regulates buoyancy – by adjusting the amount of gas in the swim bladder, the fish can maintain its position at any desired depth in water without expending energy on constant swimming.
(ii) In some fishes it may assist in respiration (serving as a primitive lung).
(iii) In certain fishes it may be involved in sound production and detection.
Cartilaginous fishes (Chondrichthyes) lack the air bladder and must keep swimming to avoid sinking.
What are the modifications that are observed in birds that help them fly?
Answer
Birds show numerous adaptations for flight:
(i) Streamlined body shape: Reduces air resistance.
(ii) Forelimbs modified into wings: Covered with feathers for generating lift and thrust.
(iii) Feathers: Provide insulation and are aerodynamically efficient.
(iv) Hollow (pneumatic) bones: Reduce body weight without compromising structural strength.
(v) Well-developed flight muscles (pectorals): Attached to the large keel of the sternum for powerful wing beats.
(vi) Warm-blooded (homeothermic): Maintain constant high metabolic rate for sustained flight.
(vii) Efficient respiratory system: Air sacs supplementing lungs provide continuous unidirectional airflow for high oxygen supply during flight.
(viii) Absence of urinary bladder and teeth: Reduces weight.
Could the number of eggs or young ones produced by an oviparous and viviparous mother be equal? Why?
Answer
No, they generally cannot be equal. An oviparous mother (lays eggs) produces a much larger number of eggs than the young ones produced by a viviparous mother (gives birth to live young).
In oviparous animals, eggs are exposed to environmental hazards (predation, temperature extremes, desiccation), so large numbers are produced to ensure at least some survive. In viviparous animals, the embryo is protected and nourished inside the mother's body, so far fewer young ones are needed – the survival rate is much higher. Producing many offspring (oviparous) is an r-strategy, while producing fewer but better-cared-for young (viviparous) is a K-strategy.
Segmentation in the body is first observed in which of the following: (a) Platyhelminthes (b) Aschelminthes (c) Annelida (d) Arthropoda
Answer
(c) Annelida. True metamerism (segmentation of the body into repeating units – metameres or somites – each containing organs from all three germ layers) first appears in Annelida. Examples: earthworm (Pheretima), leech. Arthropoda also show segmentation but they are derived from annelid-like ancestors.
Q14. Match the following
(a) Operculum – (b) Parapodia – (c) Scales – (d) Comb plates – (e) Radula – (f) Hairs – (g) Choanocytes – (h) Gill slits
(i) Ctenophora – (ii) Mollusca – (iii) Porifera – (iv) Reptilia – (v) Annelida – (vi) Cyclostomata and Chondrichthyes – (vii) Mammalia – (viii) Osteichthyes
Ans.
(a) Operculum – (viii) Osteichthyes (bony fishes have a bony operculum covering the gills)
(b) Parapodia – (v) Annelida (locomotory appendages in polychaetes)
(c) Scales – (iv) Reptilia
(d) Comb plates – (i) Ctenophora
(e) Radula – (ii) Mollusca (a file-like rasping organ for feeding)
(f) Hairs – (vii) Mammalia
(g) Choanocytes – (iii) Porifera (collar cells that create water current)
(h) Gill slits – (vi) Cyclostomata and Chondrichthyes
Prepare a list of some animals that are found parasitic on human beings.
Answer
Animals parasitic on humans:
(i) Taenia solium (pork tapeworm) – Platyhelminthes; lives in the small intestine.
(ii) Ascaris lumbricoides (roundworm) – Aschelminthes; intestinal parasite.
(iii) Wuchereria bancrofti (filarial worm) – Aschelminthes; causes filariasis (elephantiasis).
(iv) Ancylostoma duodenale (hookworm) – Aschelminthes; intestinal parasite.
(v) Entamoeba histolytica – Protozoa; causes amoebic dysentery.
(vi) Plasmodium vivax – Protozoa; causes malaria.
(vii) Pediculus humanus (head louse) – Arthropoda; ectoparasite.
(viii) Sarcoptes scabiei (itch mite) – Arthropoda; causes scabies.
Important Extra Questions
What is the difference between diploblastic and triploblastic animals?
Answer
Diploblastic animals have two embryonic germ layers – ectoderm (outer) and endoderm (inner) – with an undifferentiated layer (mesoglea) in between. Example: Coelenterata (Cnidaria). Triploblastic animals have three germ layers – ectoderm, mesoderm, and endoderm. The mesoderm gives rise to muscles, connective tissue, and other structures. All animals above coelenterates are triploblastic.
What are the distinguishing features of the phylum Chordata?
Answer
Phylum Chordata is characterised by three features present at some stage of life: (i) a notochord (flexible rod providing support), (ii) a dorsal hollow nerve cord (develops into brain and spinal cord in vertebrates), and (iii) paired pharyngeal gill slits (for filter feeding or respiration). A post-anal tail is also typically present.
What are the unique features of class Mammalia?
Answer
Unique features of Mammalia: (i) Presence of mammary glands (milk-producing) for nourishing young ones. (ii) Body is covered with hair. (iii) They are homeothermic (warm-blooded). (iv) They have a diaphragm for breathing. (v) The heart has four chambers. (vi) Most are viviparous (except monotremes like platypus). (vii) They have teeth set in sockets (thecodont) and most show heterodonty (different types of teeth).
What are open and closed circulatory systems? Give examples.
Answer
In an open circulatory system, blood flows through open spaces (sinuses/haemocoel) and is not always confined to vessels; blood (haemolymph) bathes tissues directly. Example: Arthropoda, Mollusca (except cephalopods). In a closed circulatory system, blood is always enclosed within blood vessels and does not directly contact body cells. This allows higher blood pressure and more efficient transport. Example: Annelida, Cephalopoda, all Vertebrates.
Distinguish between Amphibia and Reptilia.
Answer
Amphibia: Cold-blooded; moist, glandular skin without scales; three-chambered heart; require water for reproduction (lay eggs in water; larvae are aquatic tadpoles); undergo metamorphosis. Example: Frog, toad, salamander. Reptilia: Cold-blooded; dry, scaly skin (epidermal scales); three-chambered heart (except crocodiles with 4 chambers); produce amniotic eggs with leathery shells on land (no aquatic larval stage). Example: Lizard, snake, crocodile.