Animal Kingdom Class 11 Biology NCERT Solutions

Step-by-step solution

1. 1The point of the question is that classification must rest on fundamental features, so the answer lists what goes wrong when it does not. There are three main difficulties, and they are all about resemblance.
2. 2The first difficulty is that superficial resemblance would group together animals that are fundamentally different, and separate animals that are fundamentally alike. An animal would be judged only by what can be seen from outside, so a whale would be classed with fishes because both live in water and have a streamlined body and fins, and a bat would be classed with birds because both fly, while a crocodile would be placed with fishes because both are ectothermic and lay eggs on land. All three pairings are wrong, because in each case the visible characters are convergent adaptations and not evidence of common ancestry.
3. 3The second difficulty is that the internal and fundamental characters would be ignored. Structural features such as the level of organisation, the presence and type of a coelom, the nature of the digestive tract, the type of symmetry, and the presence of a notochord are far more reliable than external appearance, and these are exactly the characters that decide the place of an animal in the scheme. A classification based on appearance alone would leave out the whole internal organisation, which is the part that actually records the evolutionary history.
4. 4The third difficulty is that the arrangement would be artificial and would not indicate natural relationships, so it could not show evolution. A classification is useful only when it reflects phylogeny, that is, when the groups it creates correspond to lines of descent. Without fundamental features, unrelated animals would be brought together and the resulting groups would be collections of superficial look-alikes with no common ancestry, so the classification would carry no evolutionary information and could not be used to explain anything.
5. 5So the conclusion to give is that classification must be based on fundamental features such as the level of organisation, the coelom and the notochord, and only then can it reflect natural affinities and show the evolutionary relationships among living organisms.

Step-by-step solution

1. 1The steps are a fixed routine, and they are best given in the order in which they are actually performed, since that is how the marks are allocated.
2. 2Step one is to establish the level of organisation, since this is the broadest and most fundamental character. The specimen is examined to see whether it is at the cellular level, as in sponges, at the tissue level, as in cnidarians, or has organ and organ-system levels. Everything else depends on this answer.
3. 3Step two is to determine the symmetry. The specimen is examined to see whether it is asymmetric, as in Porifera, radial, as in Cnidaria and Echinodermata, or bilateral, which covers all the remaining phyla.
4. 4Step three is to establish the diploblasty or triploblasty, that is, whether the body has two germ layers, ectoderm and endoderm, or three, ectoderm, mesoderm and endoderm. This separates the two diploblastic groups, Porifera and Cnidaria, from all the triploblastic groups.
5. 5Step four is to examine the coelom, and this is the step that carries the most weight. The specimen is checked for the presence, the position and the nature of a true coelom. Acoelomate, with no coelom, gives Porifera, Platyhelminthes and Aschelminthes; pseudocoelomate, with a coelom that is not fully lined by mesoderm, gives Aschelminthes; and coelomate, with a true coelom fully lined by mesoderm, gives Annelida, Arthropoda, Mollusca, Echinodermata and Chordata. Within the coelomates the next characters used are the nature of the digestive tract, the type of the body cavity contents, the presence of a notochord, and the number and arrangement of the heart chambers.
6. 6Step five, once the phylum has been reached, is to fix the animal within it by using the remaining characters of that phylum, such as the type of the digestive system, the presence of a well developed nervous system, the nature of the reproductive system, and the specific internal organs, and the standard practice is to write the systematic name of the specimen with its genus and species and to place it in the scheme.

Step-by-step solution

1. 1The study is very useful, and the reason to give is that the coelom is a fundamental internal character with a clear evolutionary meaning, so it divides the animal kingdom into large natural groups.
2. 2What has to be defined first is the coelom itself, since the question uses the word. The coelom is the body cavity between the body wall and the gut, and it is present only in animals from Annelida onwards. The condition for a true coelom is that the cavity must be completely lined by mesoderm, which is a mesodermal lining, and it is this complete lining that makes the cavity a coelom.
3. 3On that definition the animal kingdom falls into three great groups, and this is the usefulness. First the acoelomate animals, which have no body cavity at all between the body wall and the gut, so the gut is directly attached to the body wall. The examples are Porifera, Platyhelminthes and Aschelminthes, and in the flatworms the space is entirely filled with a mesodermal parenchyma.
4. 4Second the pseudocoelomate animals, in which there is a body cavity, but it is not fully lined by mesoderm; it is lined only on the outer side, the gut being suspended by mesenteries. The examples are Aschelminthes and the rotifers, and they are the first animals in which a body cavity appears, though it is an incomplete one.
5. 5Third the coelomate animals, which have a true coelom lined by mesoderm on all sides, and this is the group that includes Annelida, Arthropoda, Mollusca, Echinodermata and Chordata. Within the coelomates a further division is made, since in the protostomes such as Annelida, Arthropoda and Mollusca the blastopore becomes the mouth and the coelom arises by splitting of the mesoderm, which is schizocoely, while in the deuterostomes such as Echinodermata and Chordata the blastopore becomes the anus and the coelom arises by outpocketing of the archenteron, which is enterocoely.
6. 6The usefulness is therefore that the coelom character is a fundamental one, and because it reflects the mode of embryonic development it also gives the evolutionary history. It divides the kingdom into three large groups, and it separates the protostomes from the deuterostomes, and that is why it is one of the most important single characters in the classification of animals.

Step-by-step solution

1. 1The distinction is the site of digestion, and the two processes also represent the two levels of organisation, since intracellular digestion is a tissue-level character and extracellular digestion is an organ-level one.
2. 2In intracellular digestion the food material is engulfed directly into the cells of the organism and the digestion takes place inside the cell, in a food vacuole. No digestive tract is involved, and the process is characteristic of the sponges, and also occurs in the coelenterates and the protozoans, where the gastrodermal cells engulf the food. It is a slower process, since it can take place over a long time inside the cell, and it is the primitive condition.
3. 3In extracellular digestion the food material is engulfed into a cavity or a tract formed outside the cells, and the secretion of enzymes into that cavity digests the food. The undigested food is then eliminated, and the process is organ-level and characteristic of all the higher animals from Cnidaria onwards, where the gastrovascular cavity of a coelenterate and the alimentary canal of a higher animal both serve as the site.
4. 4The two should be compared on a consistent set of headings. The site is inside the cell in one and outside the cell in a cavity or tract in the other. The necessity of a digestive tract is absent in one and present in the other. The level of organisation is tissue level in one and organ or organ-system level in the other. The efficiency is lower in one, because the cell must handle the whole food particle, and higher in the other, because a tract can process a continuous stream. The examples are sponges and protozoans for intracellular, and coelenterates and all higher animals for extracellular.
5. 5The important scientific point to add is that the two are not alternatives that replace each other but successive stages, and that in higher animals both still occur, since extracellular digestion reduces the food particles and the soluble end products are then taken into the cells and completed intracellularly.

Step-by-step solution

1. 1The difference is the presence or absence of a free-living larval stage between the zygote and the adult, and the two terms also describe how different the young and the adult look.
2. 2In direct development there is no larval stage, and the young individual is a miniature of the adult. The zygote undergoes cleavage and differentiation without any intervening free-living larva, so the hatchling or the newly born animal resembles the parent in form and structure and grows into it. The larvae are absent, the young are very much like the adults, and this is seen in the cephalopods such as Sepia and in the amniotes, that is the reptiles, birds and mammals. In the human case the embryo grows inside the body of the mother, so the young one is born fully formed.
3. 3In indirect development there is a larval stage, and the larva is a free-living, feeding, growing, aquatic form that is quite unlike the adult, so a distinct metamorphosis is needed to reach the adult. The larval form is usually the one that feeds and grows and the adult the one that reproduces, and this division of labour is what makes the scheme indirect. The larva has a different body form, different food and often a different habitat from the adult, and the examples are the frog, where the tadpole is the larva and the frog the adult, the sea urchin, where the Bipinnaria and the Pluteus are the larval forms, the tunicate in which a tadpole-like larva swims freely before it loses its tail and settles as a sessile adult, and the silkworm in which the larva is a worm and the adult a moth.
4. 4So on the headings to use: the presence of a larva, absent in direct and present in indirect; the resemblance of the young to the adult, close in direct and marked in indirect; the occurrence of metamorphosis, absent in direct and required in indirect; the place of growth and the food, and the examples given above. The advantage of the indirect route is that the larva and the adult exploit different foods and different habitats, so the two do not compete, which is a further point worth adding.

Step-by-step solution

1. 1The question is about the adaptations of a parasitic group, so the answer is a list of modifications, and it should be organised under the four headings the NCERT table uses: the body covering, the locomotory structures, the digestive and absorbing structures, and the reproductive structures.
2. 2The general setting: the platyhelminthes are the flatworms, and a large number of them are parasites living inside the body of another animal, the host, on which they feed and which they harm. So these are the adaptations for an endoparasitic life.
3. 3The body covering: the body is covered by a thick cuticle, which is an epidermal layer, and this is a resistant covering that protects the parasite from the enzymes of the host and from its immune system, since a parasite living inside a host has to survive in an environment that contains digestive juices and antibodies. The body is also dorsoventrally flattened, which helps it to move within the host's gut, and it is unsegmented, which is unlike the segmented body of the annelids.
4. 4The locomotory structures: locomotion is reduced or absent, since the flukes living in the gut of the host do not need locomotory organs, and the free-living turbellarians move by cilia on the ventral epidermis. Where movement is needed the fluke shows muscular movements, and it is worth noting that the absence of locomotory structures in the adults contrasts with the presence of cilia in the larvae of some, which need to reach the host.
5. 5The digestive and absorbing structures: digestion is both extracellular and intracellular, there is no anus, so the undigested food is thrown out through the mouth, and the gut is incomplete. The branched gut is designed for absorption rather than for storage, since a parasite has to draw ready nourishment from the host. Where the parasite is in a part of the body where the host food is already digested, the digestive system is altogether absent, as in the tapeworm Taenia, which absorbs the already digested food of the host through the body surface and has no gut at all. This is the important extreme case.
6. 6The reproductive structures: these are the most peculiar features, and they are what makes the tapeworm remarkable. The reproductive system is highly developed and the body of the tapeworm is divided into segments called proglottids, each of which is a self-contained reproductive unit carrying both male and female organs, that is the animal is bisexual or hermaphrodite. The proglottids are self-fertilising, and the mature proglottids detach and pass out with the faeces of the host. Each proglottid contains numerous eggs, and this enormous output compensates for the fact that the parasite has a low rate of sexual reproduction and a high rate of loss, since it leaves the host frequently. The eggs are protected by an operculum and by hooks in the case of some species, which help them survive outside the body and reach the next host. The life cycle also needs an intermediate host, since the larva develops in an intermediate host before reaching the human definitive host, and the cysticerus larva of Taenia is the example.
7. 7One more feature to add: the young hooks of Taenia attach to the wall of the intestine by a structure called the scolex, which has hooks and suckers, so the tapeworm resists being dislodged, and this is the holdfast organ.

Step-by-step solution

1. 1The answer is a list of reasons, and they fall into two kinds: the structural adaptations of the arthropod body plan, and the consequences of those adaptations for their success as animals. Give both, in that order.
2. 2The first reason is the exoskeleton. The body is covered by a hard, jointed, chitinous cuticle, and because it does not grow continuously it is moulted periodically by a process called ecdysis. Its value is that it is a protective armour, it prevents loss of water, and it supplies the muscle attachment points, but the price is that the animal must moult to grow, and the soft new cuticle leaves it vulnerable while it does so.
3. 3The second reason is segmentation and the appendages. The body is metamerically segmented, and the segments are grouped into a cephalothorax and an abdomen in many groups, and the appendages are jointed and specialised for different functions. Specialisation of the appendages is the crucial point, because one animal can then use the same body plan for walking, swimming, feeding, sensing and biting, and the jointed limb with its movable segments also gives a large range of movement, so arthropods are very versatile.
4. 4The third reason is the body cavity and the respiratory system. The coelom is reduced, since the haemocoel is the main body cavity and it contains the haemolymph, so the haemolymph carries out transport, and the respiratory organs are gills in the aquatic forms and tracheae, book lungs or book gills in the terrestrial forms, so the group has solved the problem of breathing both in water and on land.
5. 5The fourth is the sense organs and the nervous system. The antennae and the compound eyes are well developed, and the compound eye gives mosaic vision, so the arthropods detect and respond to changes very quickly, and they also have a well developed statocyst or balancing organ in some, and a high degree of sensory acuity is a real advantage in a competitive group.
6. 6The fifth is the reproductive and developmental strategy. The sexes are separate with dimorphism, and there is internal fertilisation, and many undergo metamorphosis, so the larva and the adult live in different habitats and eat different food and do not compete, which lets a single species exploit two niches at once. Fecundity is very high, with large numbers of small eggs and a short life cycle, and the offspring disperse widely, and the presence of a protective larval or pupal stage raises the survival of the individual.
7. 7Finally, the diversity of feeding habits and habitats is itself a reason, since arthropods include herbivores, carnivores, scavengers, parasites and omnivores, in aquatic and in terrestrial habitats, from the deep sea to the mountains, and this very adaptability, more than any single structural character, is what has made the phylum the largest.

Step-by-step solution

1. 1The answer is (c) Echinodermata, and it is a unique feature of the group, so the explanation is what the system is and what it does.
2. 2The water vascular system is a network of fluid-filled canals in the body of an echinoderm, and it is used chiefly in locomotion, in the movement of the tube feet, and it also helps in food transport, in excretion and in respiration by diffusion, since it is connected to the dermal branchiae and the tube feet act as gills.
3. 3Its structure is distinctive. The madreporite, or the stone canal, is the madreporite, and the water enters through a sieve-like calcareous plate called the madreporite, passes into the stone canal, then into the ring canal around the mouth, and from the ring canal into the radial canals running into each arm, and from the radial canals into the tube feet, so it is a hydraulically operated system.
4. 4The system is absent from the larva and appears only in the adult, since the larva of an echinoderm is a free-swimming larva with a bilaterally symmetrical body, the Bipinnaria or the Pluteus, and it is in the adult that the water vascular system and the radial symmetry develop. This is a good point to add, because it is examined.
5. 5So for the other options, the reason they are wrong is short: the water vascular system is not present in sponges, which have a canal system for water and food, nor in ctenophores, which have tentacles, nor in chordates, which have a water vascular system nowhere in the group.

Step-by-step solution

1. 1The statement is a statement of one-way inclusion, and the way to justify it is to show the two inclusions separately. Vertbrates are a subphylum within Chordata, and the whole subphylum is a part of the phylum, which is why every vertebrate is a chordate.
2. 2The first inclusion holds because Vertebrata is a subphylum of the phylum Chordata, so a vertebrate possesses all the four chordate characters. These are a notochord, a dorsal hollow nerve cord, paired pharyngeal gill slits, and a post-anal tail, and a vertebrate has at least some of these at some stage of its development, even when they are later modified or lost.
3. 3The reverse does not hold because Chordata contains four subphyla, and only one of them is Vertebrata. The other three are Cephalochordata, Urochordata and Hemichordata, and none of these is a vertebrate, so a chordate need not be a vertebrate.
4. 4The reason is that in these three subphyla notochord remains a prominent, separate and lifelong structure, whereas in the vertebrates it is replaced by the vertebral column. The members of the other subphyla are consequently called the invertebrate chordates, and it is this group of invertebrate chordates that makes the second half of the statement true.
5. 5So the justification closes as follows: every vertebrate is a chordate because Vertebrata is a subphylum within Chordata and possesses the notochord, the dorsal hollow nerve cord, the pharyngeal gill slits and the post-anal tail; but a chordate need not be a vertebrate, because the phylum also includes the invertebrate chordates, namely the cephalochordates such as Branchiostoma, the urochordates such as Ascidia, and the hemichordates such as Balanoglossus, in which the notochord is never replaced by a backbone.

Step-by-step solution

1. 1The air bladder is a gas-filled organ in most bony fishes, and the question asks how important it is, so the answer should say what it does and then judge its importance, including the important fact that the organ is not essential in all cases.
2. 2Its first function is to help the fish to change its depth, that is to move up and down in the water column, and it does so by adjusting the volume of gas inside it, since increasing the volume reduces the density and the fish rises, while reducing the volume increases the density and the fish sinks, so the fish is neutrally buoyant at any chosen depth without swimming.
3. 3Its second function is to keep the fish buoyant, so that the fish does not have to spend continuous energy in swimming merely to stay up, and this conserves energy, which matters because the fish would otherwise lose most of its energy to overcome gravity.
4. 4Its third function is respiratory in some fishes. The wall of the air bladder is vascular, and in fishes such as gar, which is a bowfin, and in some others, the bladder is used for respiration, so that the fish can gulp air, and it is worth noting that in the Polypterus, or bichir, the air bladder is used as a lung. It also functions as a resonating chamber that helps a fish such as the Sciaenid, or the croaker, and the clupeid, or the herring, to produce sounds.
5. 5The important qualification is about the organ's status. The air bladder is found in most bony fishes, that is the Teleostei, and it is not present in the cartilaginous fishes, and the Sharks, the Rays and the Skates, so it cannot be essential to the group as a whole. Moreover, in some of the fishes that do possess it, such as the mackerel, the air bladder is small and the fish has to keep swimming to stay afloat, so in these the organ is greatly reduced and almost non-functional, which shows that it is an adaptation and not a fundamental requirement.
6. 6So the judgement to give is that the air bladder is very important to the bony fishes, since it controls depth, maintains buoyancy and saves energy, and in a few it also respires and resonates, but it is not indispensable, as it is absent in the chondrichthyes and reduced or functionless in some teleosts, and it is a modification of the lungs of the ancestral bony fishes.

Step-by-step solution

1. 1The question is a collection of adaptations, so give them as a list under the headings of the shape of the body, the covering, the skeleton, the respiratory and digestive systems, and the reproductive system. The NCERT table of the pigeon is the model.
2. 2The shape of the body: the body is compact and streamlined, spindle-shaped and tapering at both ends, and this reduces the resistance offered to the air, and the neck is short and the head small.
3. 3The covering: the body is covered by dry, cornified, keratinised scales or feathers. Feathers are unique to birds and are made of keratin, and their three functions are to form the aerodynamic surface, to insulate against cold, and to help in courtship display. The important structural point is that the flight feathers are borne on the wings and the tail, and the tail forms the rudder.
4. 4The skeleton: the bones are pneumatic, that is hollow and filled with air, so the skeleton is light, and some of the bones are fused, which makes the body rigid and does not add weight. The bones lack a marrow cavity in part, the sternum is broad and carries a keel or carina to give the large flight muscles a surface to attach to, and the jaws are reduced and replaced by a light horny beak, and there is no teeth. The forelimbs are modified into wings, and the hind limbs are modified for perching and walking, and the neck vertebrae are highly modified and mobile, which is why a bird can turn its head so far round.
5. 5The respiratory system: the lungs are small and compact and are connected to nine air sacs, eight of which are paired. The sacs act as bellows that keep air flowing through the lungs during both inspiration and expiration, so the lungs receive a continuous supply of fresh air, and there is therefore no mixing of fresh and used air, the air flowing unidirectionally through the lung, and the oxygen supply is very efficient. Birds thus have the most efficient respiratory system among the vertebrates. The lungs are attached to the body wall and are not inflated in the way a mammal's are.
6. 6The digestive and excretory systems: birds have a beak and no teeth, so digestion is helped by the crop, which stores and softens the food, and by the gizzard, which grinds it, and since flight needs a light body there is no urinary bladder, the excretory waste being semisolid and passed as uric acid, which conserves water and weight. The body is light, which is why the bird has a small, compact body.
7. 7The reproductive system: the female lays one egg at a time and lays many eggs over the season, and the egg is hard-shelled with a calcareous shell and a large yolk, so it contains all the food the embryo needs, and the male has a copulatory organ. Fertilisation is internal, so the sperm reaches the ovum, and the development of the young is a direct development with no larval stage.
8. 8Finally, the general point that ties the list together: the adaptations of a bird all serve the same purpose, to reduce weight and increase the surface available to the air and the efficiency of the flight muscles, and every one of them can be read as either a reduction in mass or an increase in power.

Step-by-step solution

1. 1The answer is no, and the whole reasoning turns on where the young develop and how much each mother has to invest in each one.
2. 2In an oviparous mother the young develop outside her body, in eggs that are laid and hatched in the external environment, and that is why the eggs are large, because each egg has to carry enough yolk to supply the embryo until it hatches, and because the egg has to survive on its own without the mother. So a very large number of eggs can be produced, since the investment per egg is a stored food supply and nothing more, and the total burden on the mother is the mass of the eggs.
3. 3In a viviparous mother the young develop inside her body, attached to her and nourished directly from her tissues through a placenta or an equivalent arrangement, and so the mother must supply the whole of the nutrition, and she must carry the young to term, so each young represents a far greater investment of her own tissue and energy, and the physiological and metabolic cost of pregnancy is high.
4. 4The consequence follows directly: because each young one costs a viviparous mother much more, she can produce far fewer of them, whereas an oviparous mother can lay a very large number of relatively cheap eggs. So the number of eggs and the number of young produced by the two are not equal, and the oviparous strategy is the high-number, low-investment one while the viviparous strategy is the low-number, high-investment one, in which each offspring has a much better chance of surviving.
5. 5It is worth adding that the two terms are not opposites in a strict sense, since viviparity can mean either internal development with nourishment from the yolk, as in the sharks and in some fishes and reptiles, or internal development with direct nourishment from the mother, as in the mammals, and only the second carries the full cost of the mother and so gives the cleanest contrast with the oviparous condition.

Step-by-step solution

1. 1The answer is (c) Annelida, and the reason is that true metameric segmentation first appears in this phylum, and every other group listed has an unsegmented body.
2. 2Segmentation here means true metamerism, that is the division of the body into a linear series of similar segments, or metameres, so that each segment repeats the same structure and the same organs, and such repetition is a sign of a higher degree of organisation and of metameric segmentation.
3. 3Platyhelminthes, option (a), is unsegmented and the body is undivided from head to tail, so the appearance of repeated structures in it, such as the repeated reproductive units of a tapeworm, is not true segmentation but is repeated organ duplication in an unsegmented body, and the septa between the proglottids are incomplete. Aschelminthes, option (b), is also unsegmented and is a roundworm, so neither of these shows metamerism.
4. 4Annelida, option (c), is the first phylum in which the body is divided externally and internally into a series of ring-like segments separated by septa, and the segments are genuinely repeated, each with its own pair of nephridia, and the repetition of the body wall, the blood vessels, the nerves and the excretory organs in every segment is the criterion for true metamerism. The familiar earthworm, Nereis and leech are the examples, and the leech shows external segmentation only, with the internal septa absent.
5. 5Arthropoda, option (d), is also segmented, and it is heavily so, but the segmentation is a secondary feature that arose in that group and is not the first occurrence, so the correct answer to a question asking where segmentation is first observed is Annelida and not Arthropoda.

Step-by-step solution

1. 1The eight matches are (a) to (vi), (b) to (v), (c) to (iv), (d) to (i), (e) to (ii), (f) to (vii), (g) to (iii) and (h) to (viii), and each is decided by naming the phylum of the structure.
2. 2(a) Operculum — (vi) Cyclostomata and Chondrichthyes, because the operculum is the hard cover over the gill chamber of the cartilaginous fishes, the sharks and rays, and the horned jawless fishes.
3. 3(b) Parapodia — (v) Annelida, because these are the paired lateral paddle-like appendages of the marine annelids, the Nereis, that act as locomotory organs.
4. 4(c) Scales — (iv) Reptilia, because the body of a reptile is covered by dry, cornified scales or scutes.
5. 5(d) Comb plates — (i) Ctenophora, because these are the ciliary plates that give the ctenophores, the comb jellies, their name and their iridescent shimmer.
6. 6(e) Radula — (ii) Mollusca, because the radula is the rasping tongue of the molluscs, used for feeding and for drilling, as in the Limax.
7. 7(f) Hairs — (vii) Mammalia, because the skin of mammals is unique in bearing hairs, which are epidermal in origin and serve for insulation, sensation and display.
8. 8(g) Choanocytes — (iii) Porifera, because these are the collar cells of the sponges, each with a single flagellum, and they are the characteristic cell of the phylum.
9. 9(h) Gill slits — (viii) Osteichthyes, because the pharyngeal gill slits are the chordate character seen in the bony fishes; the two other options, Cyclostomata and Chondrichthyes, are already matched to the operculum.

Step-by-step solution

1. 1Group them by the organ or system they inhabit, since that is the clearest presentation for a list question, and name the group in the same order. Also give the disease in brackets, because a named example is more useful than a bare name in the examination.
2. 2The alimentary canal and the liver: the roundworms Ascaris lumbricoides, the threadworm Enterobius vermicularis and the whipworm Trichuris trichiura, which live in the intestine and cause ascariasis, enterobiasis and trichuriasis respectively, and the tapeworm Taenia solium, which causes taeniasis and, in its larval cysticercus stage, causes cysticercosis, and the liver fluke Fasciola hepatica, which causes fascioliasis, and Echinococcus granulosus, the tapeworm of the dog, whose larva forms a hydatid cyst.
3. 3The blood and the lymphatic system: Plasmodium vivax, P. malariae, P. ovale and P. falciparum, the malarial parasites of the genus Plasmodium, which cause malaria, and Wuchereria bancrofti, the filarial worm, which causes the blockage of the lymph vessels in filariasis or elephantiasis, and Trypanosoma gambiense and T. rhodesiense, which cause African sleeping sickness, and Leishmania donovani, the sandfly parasite causing kala-azar. The genus Plasmodium alone settles the question, so it is the safest single example to name if only one is remembered.
4. 4The respiratory and the mouth region: the lung fluke Paragonimus westermani, which causes paragonimiasis, and the tongue worm Linguatula serrata, and this last one is the parasite NCERT uses to illustrate a female whose length is far greater than that of the male, so it is worth naming.
5. 5The skin and the subcutaneous tissue: the itch mite Sarcoptes scabiei, which causes scabies or itch, and the larva of the rat mite, and the guinea worm Dracunculus medinensis, which lives in the subcutaneous tissue.
6. 6Finally the general note: many of these are not specific to human beings, since the human being shares most of them with other animals, so the introduction of many is the eye of the larva of a mosquito, of a rat, of a pig and of a dog, and the life cycle of the malarial parasite, of the filarial worm and of the guinea worm each requires an intermediate host. The list may end there.