Set-II: Past Entrance Papers

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(d) Hydra which belongs to the phylum coelenterata has nerve cells but no brain. Its nervous system consists of nerve cells and their processes. Sensory cells are also present. Sponges do not have nerve cells, they lack nervous system. Earthworm (annelida) has nervous system consisting of a circumenteric nerve ring and a solid, double, midventral nerve cord with ganglia. Cockroach (arthropoda) has the nervous system as that of earthworm.

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(a) Chordates are the animals that have notochord, a skeletal rod present at some stage in the life cycle. In lower vertebrates, notochord persists throughout life while in higher vertebrates it is replaced by vertebral column in adults. Nonchordates never develop notochord, not even in embryonic stage.

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(a) The function of the contractile vacuole is osmoregulatory. Water in freshwater protozoa enters the organism by endosmosis and during feeding. If the organism does not possess a mechanism to get rid of this excess water, it will swell to the point of rupture and dissolution. The mechanism which is assumed to affect water regulation is the contractile vacuole. The vacuole periodically increases in volume (diastole) to get filled with water and contracts (systole) to discharge its water content to the surrounding environment.

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(d) Snakes are limbless reptiles with an elongated cylindrical body, covered with overlapping scales differentiated into shields and plates, and have post-anal tail which is long.

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(c) In Hydra indigestible residues are egested through the mouth, for there is no anus. Egestion occurs by a sudden squirt due to muscular contraction of the body, so that the debris is thrown at a distance. Hydra has neither blood and blood vessels, nor organs of excretion. Due to the thinness of the body wall and the circulation of water in gastrovascular cavity, most cells of the body remain freely exposed to the surrounding water. Therefore, excretion of waste nitrogenous matter (chiefly ammonia) occurs directly by diffusion through cell membranes in the outside world.

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(b) Hydra, has tissue level of organization. Its body is multicellular and the cells occur in 2 distinct layers or tissues of specialized cells. Sponges have cellular level of organization. Liver fluke and Ascaris have organ-system level of organization.

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(a) Sexual dimorphism is the difference in the form of individuals of different sexes but of same species. Sexes in Ascaris are separate and sexual dimorphism is well defined. Males are smaller than females. They possess a recurved tail with pre and post anal papillae, a cloaca, and a pair of spicules or penial setae. In Anopheles, the ends of maxillary palps in males are club-shaped while in females they are not.

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(a) Main component of bone is collagen which is a complex combination of amino acids. When frog’s bone is treated with \(\mathrm{HCl}\), these compounds are broken down and the bone becomes flexible.

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(a) Diaphragm is a membrane that separates the thoracic cavity from the abdominal cavity. It is present only in mammals. All other chordates do not have diaphragm as their body cavity is not divided into thoracic and abdominal cavities. Chordates are coelomate animals having a true coelom, entercoelic and shizocoelic in origin. Pharyngeal gill slits are present at some stage, and may or may not be functional. The nerve cord is dorsal and tubular.

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(a) Mammals are viviparous i.e., they give birth to young ones. Protherians (e.g., Platypus) are primitive mammals and lay eggs, so they are oviparous.

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(b) The waste material of aquatic reptiles chiefly consists of urea, so they are ureotelic. Land forms are uricotelic i.e., their water material consists of uric acid.

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(a) Poikilothermic animals are those whose body temperature varies with the temperature of the environment. All animals except birds and mammals are poikilothermic. Although unable to maintain a constant body temperature, they can respond to compensate for very low or very high temperatures. For example, the tissue composition (especially cell osmotic pressure) can change to regulate the blood flow to peripheral tissues (and thus increase heat loss or heat absorption), and the animals can actively seek sun or shade.

Homoiothermic animals are those whose body temperature remains constant irrespective of the variations in the temperature of the environment.

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(b) The body of a sponge is a collection of a few different types of cells loosely arranged in a gelatinous matrix called a ‘mesohyl’, mesoglea, or mesenchyme. This mesohyl is the connective tissue of a sponge body and it is supported by the skeletal elements. The skeletal elements of sponges are variable and important in taxonomy. Throughout this body run canals through which water flows, there is considerable variation in the complexity of these canals. The canals have openings to the outside which are called pores, where the water enters the sponge system these pores are usually small and are called ‘ostia’, and where the water leaves the sponge system the pores are larger, often singular, and are called as ‘oscula’ (singular osculum).

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(d) Forelimbs are absent in birds as they are modified into wings for flight. They are attached high on the back, to the anterior or thoracic region of the trunk, and are very powerful when compared with the size and strength of the bird. Each wing is elongated, flattened, and distally pointed with its longitudinal axis at right angles to that of the trunk. Hindlimb is made of three parts – thigh, shank, and foot. Pectoral girdle on each side consists of three bones – a large coracoid, scapula, and clavicle. The pelvic girdle consists of the ilium, ischium, and pubis.

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(c) Aves are the animals that fly so their body weight should be less and for this, their bones are hollow and connected by air passages. Reptilia, land vertebrates, and mammals do not have hollow bones.

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(c) Obelia belongs to the Phylum Coelenterata. In Obelia, the life cycle includes two clearly defined phases: a fixed polypoid phase (hydroid colony) and a pelagic medusoid phase. Hydroid colony has no gonads and reproduces by asexual budding to give rise to medusae. On the other hand, medusae reproduce exclusively by sexual method (ova and sperms) to give rise to new hydroid colonies. This fact apparently seems to have given rise to the idea of alternation of generations, also called metagenesis.

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(a) Dentary is a membrane bone, present in the lower jaw of the vertebrates, that supports the teeth. In mammals, the dentary is the sole bone of the lower jaw. The dentary bone is a relatively short comma-shaped bone.

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(c) Silver fish, scorpion, crab, and honey bee all have compound eyes. These are present on each lateral side of the head and are convex. This eye consists of numerous visual units, the ommatidia. Each ommatidium consists of an outer cuticle covering a lens, beneath which are 6-8 retinal cells surrounding a light-sensitive rhabdom. Adjacent ommatidia are separated by pigment cells. 

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(b) The embryonated egg of Ascaris represents an egg with a juvenile. In the case of Ascaris, the eggs containing the second stage of juvenile are called embryonated egg. These are infective to human host. In suitable conditions of temperature and moisture these eggs can survive for 5 to 6 years in the soil.

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(b) Sponges may have calcareous or siliceous spicules. All sponges are not marine, some are freshwater living also. Sponges may be asymmetrical or bilaterally symmetrical, besides being radially symmetrical. So, these characters are exception. The character without exception is the regenerative power of sponges.

All sponges have a good power of regeneration. They can regrow any part of the body lost or cut off. Small fragments can grow into a complete sponge.

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(c) Coelom is a fluid-filled cavity that forms the main body cavity of vertebrate and most invertebrate animals. It is found between mesoderm and body wall (endoderm).

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(c) Pneumatic bone is present in pigeon to keep the bones lightweight because the pigeon has to fly. Pneumatic bone has a hollow cavity, which makes it light.

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(b) Analogous organs are organs of very disparate organisms and are superficially similar but have evolved from vastly different origins. They have the same function but different structure. The nephridia in earthworm are analogous to flame cells of Planaria since both of them have excretory functions. Nematoblasts of Hydra are organs of locomotion, food capture, and anchorage. Gills and trachea are organs of respiration in prawn and insects respectively.

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(d) The body wall of sponges encloses a large cavity, the spongocoel and in most cases also contains in its thickness numerous small cavities, the canals. Either the spongocoel or certain canals are lined by choanocytes with flagella. The ceaseless beating of flagella maintains a steady current of water through the canals in the sponge body. The current of water enters through small pores, the dermal ostia, perforating the porocytes and, after passing through various canals, enters the spongocoel, and finally leaves through a larger aperture, the osculum, or apertures, the oscula.

All the cavities in a sponge body are intercommunicating and are collectively referred to as the canal system. The current of water that flows through the canal system brings in food and oxygen and carries away carbon dioxide and nitrogenous waste materials. Thus, the canal system helps the sponge in nutrition, respiration, and excretion.

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(a) Euglena possesses the characteristics of both plant and animal. It has chlorophyll, thus it is autotrophic like plants. In contrast to this, it has flagellated locomotion-like animals.

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(d) Metamerism means that the body is externally and internally divided into repetitive segments. Animals included in the phylum Annelida, Arthropoda, and Chordata show true metamerism. Cestoda is a class of Platyhelminthes. Acanthocephala is a phylum of parasitic worms and does not show metamerism.

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(a) The function of the contractile vacuole is osmoregulatory. Water in freshwater protozoa enters the organism by endosmosis and during feeding. If the organism does not possess a mechanism to get rid of this excess water, it will swell to the point of rupture and dissolution. The mechanism which is assumed to affect water regulation is the contractile vacuole. The vacuole periodically increases in volume (diastole) to get filled with water and contracts (systole) to discharge its water content to the surrounding environment.

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(b) Oestrous cycle comprises cyclic changes in the female reproductive system of non-primate mammals like cows, dogs, etc. The oestrous cycle consists of a short period of oestrous or ‘heat’ (e.g., 18 hours in cow) followed by the rest of the period of anoestrous or ‘passive’. During oestrous, the female receives the male for copulation. During anoestrus, the female becomes passive and does not receive the male. Although the breakdown of tissues takes place in the female reproductive tract at the end of an oestrous cycle, yet there is no menstruation.

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(d) The sub-phylum vertebrata or craniata have a well-developed central nervous system that is differentiated into the brain and spinal cord. The brain is protected by a brain box called cranium, so they are also called as craniata.

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(d) The cells characteristic of the coelenterates include stinging cells (cnidocytes or cnidoblasts or nematoblasts) for offence and defence. The stinging cells, when discharged, give out from a sac, the cnide or cnidocyst or nematocyst, a long thread-tube that may coil around the prey, or attach to it, or inject a toxin, called hypnotoxin, into it to paralyse it.

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(a) Birds and lizards are uricotelic. Uricotelic animals are those that excrete nitrogenous waste in the form of uric acid. It is being insoluble in water, and does not require water for its elimination. Frogs and cartilaginous fish are ureotelic, that is they excrete nitrogenous waste in the form of urea. The main excretory matter of insects is uric acid and of bony fish is ammonia (ammoniotelic). Molluscs may be ammoniotelic or uricotelic. Mammals are ureotelic (excretory matter is urea).

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(d) Air passes from the external nares into the nasal cavity where the dust particles are trapped. From the nasal cavity, the air moves into the pharynx which is a short, vertical tube. It further leads into two tubes, the trachea and oesophagus. Larynx is the upper part of trachea. Besides forming a part of the respiratory tract, it also serves as the voice box. Trachea is a thin-walled tube that extends downward through the neck. It divides into two primary bronchi which on entering the lungs divide into fine branches called bronchioles which enter the alveoli. The exchange of gases occurs in alveoli.

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(a) In the open circulatory system, the blood is not confined to the blood vessels, but it flows in the open spaces. Prawn, Chelifer and cockroach have an open circulatory system. Frog’s tadpole has a closed circulatory system, that is the blood flows in the blood vessels.

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(a) Hydra possesses a very primitive type of nervous system. It includes bipolar and multipolar nerve cells or neurones lying immediately above the muscle processes and forming an irregular and discontinuous nerve net or nerve plexus. Neighbouring nerve cells are not fused together, but their processes or neurites form synaptic junctions. Such a nerve net is called a synaptic nerve net. Nerve cells are numerous around mouth and on pedal disc but show no groupings in the form of a nerve controlling centre like brain or nerve ring. A difference from higher animals is that the nerve net of Hydra is unpolarized so that impulses can pass in all directions (diffuse transmission). In brief, the nerve net shows diffuse unpolarized transmission, the autonomy of parts, and paucity of reflexes.

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(b) Budding is an asexual mode of reproduction in Hydra and sponges. Bud is formed as an outgrowth on the body surface, then detached to form a new animal.

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(d) In butterfly, the larval stage is known as catterpillar, in frog is known as tadpole and in mosquito is known as wriggler.

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(d) Gorilla, chimpanzee, monkeys, and humans belong to the same order i.e., primates. They have well-developed brain, and flat nails on fingers and toes. The first digit is usually opposable, an adaptation for grasping. Eyes are typically large and turned forward.

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(b) Whale, bat, and rat are mammals. Diaphragm is present in mammals. The diaphragm separates the thoracic cavity (with lung and heart) from the abdominal cavity (with the digestive system and urogenital system). In its relaxed state, the diaphragm is shaped like a dome. It is controlled by the phrenic nerve.

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(a) The common Indian bull frog Rana tigrina lives in or near-permanent freshwater lakes, ponds, and streams. It is in the water most of the time. It lives near water mainly for two reasons : (i) To keep skin moist to carry on cutaneous respiration, and (ii) To immediately jump or slip into the water to escape from enemies.

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(d) Cockroaches are found in places where there is warmth, dampness, and plenty of organic food to devour. Indoors, they are a common pest in kitchens, latrines, hotels, restaurants, godowns, storerooms, board ships, etc.

Cockroaches are nocturnal creatures. During the daytime, they remain inactive and hiding. During the night, they show much activity and run here and there in search of food. Being omnivorous and scavengerous in diet, they devour any animal or vegetable substance and even non-living materials like leather, paper, cloth, etc., causing great loss.

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(b) All the mammals are viviparous except monotremes. The platypus are monotreme, found only in Australia, and is one of the five mammal species of that lay eggs instead of giving birth to live young. The other egg-laying mammals are four species of echidna. Cow, whale, and rat do not lay eggs.

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(b) Homoeostasis is the regulation by an organism of the chemical composition of its body fluids and other aspects of its internal environment so that physiological processes can proceed at optimum rates. It involves monitoring changes in the external and internal environment by means of receptors and adjusting the composition of the body fluids accordingly; excretion and osmoregulation are important in this process. Examples of homeostatic regulation are the maintenance of the acid-base balance and body temperature.

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(b) Radial symmetry is the arrangement of parts in an organ or organism such that cutting through the centre of the structure in any direction produces two halves that are mirror images of each other. All animals belonging to the cnidaria (e.g., jellyfish) and echinodermata (e.g., starfish) are radially symmetrical.

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(c) Musca is the zoological name of the house fly which is regarded as mechanical carrier of many diseases. It is very active and keeps on visiting on dirty things and eatables as well.

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(a) Flame cells are scattered throughout parenchyma from which they remove metabolic wastes. A flame cell is of irregular shape, with granular cytoplasm and a nucleus. Bundle of cilia, or flame, arises from basal granules near nucleus. Cilia are enclosed into a funnel-shaped lumen formed by the terminal blind end of a capillary. Protonephridia are found in flatworms, Malpighian tubules in insects, and green glands in crustaceans.

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(a) In insects Malpighian tubules are attached to the alimentary canal at the extreme anterior end of the hindgut. These are fine, long, unbranched, yellowish, and blind tubules lying freely in the haemolymph. These are between 60 to 150 in number and are arranged in 6-8 bundles. These excrete out nitrogenous wastes from the body in the form of uric acid.

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(c) The diagnostic characters of chordates are notochord, dorsal hollow nerve cord, pharyngeal slits, and post anal tail. The tail is the part of the body behind the cloacal or anal opening. It contains skeletal elements, muscles, blood vessels, and nerves but no viscera. It provides much of propulsive force in aquatic species. The tail is reduced or absent in the adults of some chordates.

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(b) Jelly fish belongs to the Class Scyphozoa of the Phylum Cnidaria. Its genus is Aurelia.Aurelia is found in the coastal waters of the tropical and temperate seas. Aurelia may float passively or swim actively, singly, or in shoals. It is carnivorous and unisexual. It has a soft, gelatinous, saucer-like body. Its margin bears numerous short tentacles and 8 sense organs, called rhopalia, in notches of the margin. Each sense organ is enclosed by a pair of leaf-like lappets. At the centre of the lower (subumbrellar) surface is the squarish mouth surrounded by 4 long oral arms.

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(d) Gambusia is a species of freshwater fish. It is remarkably hardy, surviving in waters of very low oxygen saturations, high salinities, and high temperatures. For these reasons, this species may now be the most widespread freshwater fish in the world, having being introduced as a biocontrol in certain countries to control mosquitoes. It feeds on larval and pupal stages of mosquitoes.

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(d) Order Cetacea includes whales, dolphins, and porpoises. These are the most highly modified mammals. They have a fish-like body with smooth, hairless skin devoid of sweat and oil glands, far posterior nares, small eyes, minute ear openings without pinnae, paddle-like forelimbs, no hindlimbs, abdominal testes, and flattened tail ending in two horizontal flaps or flukes.

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(b) Bird vertebrae are heterocoelous i.e., the centra of vertebrae have saddle-shaped ends. Acoelous refers to vertebrae that are flat on both ends (mammals). Amphicoelous means both ends of the centrum are concave (fish). Procoelous means concave in front and convex in back (anurans and reptiles).

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(a) Hindlimbs are variously modified for various functions like perching, grasping, etc. In the kingfisher, they are modified for wading. The legs and toes are exceptionally long and slender and serve to walk over aquatic vegetation or marshes.

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(c) Pigeons are noted for their unique ability to produce “pigeon’s milk”, a soft, cheesy, and nourishing secretion, especially during the breeding season. It is formed by the degeneration of the epithelial cells lining the crop. It is regurgitated into the mouth of the young birds until they are old enough to manage a grain diet like their parents. The pigeon’s milk includes water, fat, protein (casein), and lactose. The milk is produced by both sexes and contains 35 percent of fat.

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(c) Typhlops is a genus of blind snakes (nonpoisonous snake) found in Europe, Africa, Asia, and Central and South America. Sea snake is a poisonous snake while grass snake is a non-poisonous snake. Glass snake is a lizard.

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(c) Necturus is a mud puppy belonging to the Order Urodela of Class Amphibia. Hell bender is a large salamander. Amphiuma is a Congo Eel and Ichthyophis is a blind worm.

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(c) Tortoise belongs to the Class Reptilia. Its body is protected by a shell consisting of a dorsal carapace and ventral plastron.

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(c) More than \(70 \%\) of all the species recorded are animals. Among animals, insects are the most species rich taxonomic group, making more than \(70 \%\) of the total. It means out of every 10 animals on this planet, 7 are insects.

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(d) Coelom is a fluid-filled space between the body wall and alimentary canal which is lined by the parietal peritoneum (mesoderm) on the outer side and visceral peritoneum (mesoderm) on the inner side.

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(c) Toads possess a pair of large parotid glands behind the tympana. They produce a milky poisonous fluid. Statocysts are the organs of equilibrium and sensory perception located at the base of antennae. Flame cells in liver fluke are the excretory organs.

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(d) Duck-billed platypus is an egg-laying mammal.

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(b) Dorsal hollow nervous system is one of the important feature of vertebrates.

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(d) Mucus helps frog in forming moist skin as it is necessary for cutaneous respiration during hibernation of the frog.

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(d) Frog is an amphibian and its skin is well adapted or in other words, acts as a secondary respiratory organ when it is in water.

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(d) Cockroach belongs to the phylum Arthropoda. It has 10 pairs of Spiracles ( 2 pairs on the thorax and 8 pairs on the abdomen).

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(c) Human possesses enucleated RBCs in a mature state. But frog blood has both white and red blood cells which are nucleated. Frog cells do not lack platelets.

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(c) Cockroach & snail have an open type of circulatory system. A closed type of blood circulatory system occurs in cuttlefish.

Closed circulatory systems (evolved in echinoderms and vertebrates) have the blood closed at all times within vessels of different size and wall thickness. In this type of system, blood is pumped by a heart through vessels and does not normally fill body cavities. Blood flow is not sluggish.

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(d) All chordate possess :
– Notochord at some stage of life
– Dorsal tubular nervous system
– Pharyngeal gill slits at same stage of the life cycle.

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(b) Sponges show cell aggregate body organization. Cell tissue organization appear in coelenterates. Platyhelminthes show tissue organ organizations.

Hydra is a genus of small, fresh-water organisms of the phylum Cnidaria and class Hydrozoa. They are native to the temperate and tropical regions. Biologists are especially interested in Hydra because of their regenerative ability – they do not appear to die of old age, or indeed to age at all.

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(a) Metamorphosis refers to the transformation of a larva into adult. An animal that perform metamorphosis is said to have indirect development. Metamorphosis includes, in insects, the transformation of a maggot into an adult fly and a caterpillar into a butterfly, and, in amphibians, the changing of a tadpole into a frog. In earthworms, development is direct which means no larval stages are there and hence no metamorphosis.

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(a) Organisms passively floating on the surface of the water are planktons. Floating animals are called zooplanktons and plants are phytoplanktons.

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(b) Presence of nematocysts or stinging cells are the characteristic feature of the phylum Coelenterata. It serves the function of offence and defence by producing toxins to kill the prey & enemy.

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(b) Sponges are marine with the exception of the family spongilidae, the members of which occur in freshwater e.g. Spongilla. Their endoskeleton is made of either spicules or spongin fibres or both. Sponges reproduce asexually by fragmentation or by budding or through gemmules and reduction bodies. Sponges also exhibit sexual reproduction.

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(a) The body cavity (coelom) of earthworm is filled with an alkaline, colourless or milky coelomic fluid containing water salts some proteins, and four types of coelomic corpuscles i.e. phagocytes, mucocytes, circular nucleated cells, and chloragogen cells. During burrowing the coelomic fluid becomes turgid and acts as hydraulic skeleton.

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(a)
Classification of housefly
A. Family – Muscidae
B. Order-Diptera
C. Class – Insecta
D. Phylum-Arthropoda
Short Trick The question can be easily solved via elimination technique as (D) phylum is given with (2) Arthropoda combination in only option (a). This easily eliminates other options as the correct answer. Thus, saves your time too.

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(b) Since, terrestrial animals do not have automatic access to either fresh or salt water, they must regulate water content in other ways, balancing off gains and losses.

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(b)

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(b)