SolveItClass 11 · NCERT

NCERT Solutions · Class 11 Biology Animal Kingdom

15 questions · 15 still being checked

Exercises 4.11–4.15 (part 2 of 2)

  1. Exercise 4.11

    What are the modifications that are observed in birds that help them fly?

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    Birds are modified throughout the body for flight:
    The forelimbs are modified into wings, which provide the surface that lifts and drives the bird.
    The body bears feathers, which give the flight surface and streamline the body; most birds can fly, except flightless ones such as the ostrich.
    The endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities — pneumatic bones — so the skeleton is strong but light.
    Air sacs connected to the lungs supplement respiration, meeting the high oxygen demand of flight.
    The heart is completely four-chambered and birds are warm-blooded (homoiothermous), maintaining a constant body temperature and so a steady, high rate of metabolism.
    Jaws are drawn out into a light beak and the digestive tract has additional chambers, the crop and gizzard, so food is stored and ground in the body instead of by heavy teeth.
    The skin is dry and without glands except the oil gland at the base of the tail, whose secretion is used to dress the feathers.
    The hind limbs, freed from carrying the body in the air, generally bear scales and are modified for walking, swimming or clasping tree branches.

  2. Exercise 4.12

    Could the number of eggs or young ones produced by an oviparous and viviparous mother be equal? Why?

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    No — for the same number of offspring to survive, an oviparous mother must produce far more eggs than a viviparous mother produces young.
    Oviparous animals lay eggs which then develop outside the mother's body: reptiles, birds, most bony fishes, amphibians, and among mammals Ornithorhynchus (platypus).
    Those eggs are left exposed to the outside environment and to predators, and in fishes and amphibians fertilisation itself is external, so a large share of eggs is never fertilised or never hatches — losses are made good only by laying in very large numbers.
    Viviparous animals give birth to young ones: most mammals, and many Chondrichthyes, which have internal fertilisation and are viviparous.
    Here the embryo develops inside the mother's body, protected and nourished, so almost all of the young survive; a few are enough, and the mother could not carry many in any case.
    So the numbers differ because the chance of survival differs — high protection means few offspring, no protection means many.

  3. Exercise 4.13

    Segmentation in the body is first observed in which of the following:
    (a)
    Platyhelminthes
    (b)
    Aschelminthes
    (c)
    Annelida
    (d)
    Arthropoda

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    (c) Annelida.
    In annelids the body is externally and internally divided into segments, or metameres, with a serial repetition of at least some organs — this is metameric segmentation, the phenomenon called metamerism, seen in the earthworm.
    The body surface is distinctly marked out into these rings, which is what gives the phylum its name (Latin, annulus — little ring).
    Platyhelminthes and Aschelminthes are unsegmented, so segmentation cannot begin with them.
    Arthropods are also segmented, but they come after Annelida in the classification, so Annelida is where segmentation is first observed.

  4. Exercise 4.14

    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

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    The pairs are:
    (a) Operculum – (viii) Osteichthyes — bony fishes have four pairs of gills covered by an operculum (gill cover) on each side; in Chondrichthyes the gill slits are separate and without an operculum.
    (b) Parapodia – (v) Annelida — aquatic annelids such as Nereis possess lateral appendages, parapodia, which help in swimming.
    (c) Scales – (iv) Reptilia — the reptilian body is covered by dry and cornified skin with epidermal scales or scutes; snakes and lizards shed them as a skin cast.
    (d) Comb plates – (i) Ctenophora — the body bears eight external rows of ciliated comb plates, which help in locomotion.
    (e) Radula – (ii) Mollusca — the mouth contains a file-like rasping organ for feeding, called the radula.
    (f) Hairs – (vii) Mammalia — the skin of mammals is unique in possessing hair.
    (g) Choanocytes – (iii) Porifera — choanocytes or collar cells line the spongocoel and the canals of sponges.
    (h) Gill slits – (vi) Cyclostomata and Chondrichthyes — cyclostomes have an elongated body bearing $\displaystyle 6$–$\displaystyle 15$ pairs of gill slits for respiration, and in Chondrichthyes the gill slits are separate and without an operculum.

  5. Exercise 4.15

    Prepare a list of some animals that are found parasitic on human beings.

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    Animals named in this chapter that are parasitic on human beings:
    Platyhelminthes (flatworms) — mostly endoparasites found in animals including human beings, with hooks and suckers for attachment:
    Taenia — tapeworm.
    Fasciola — liver fluke.
    Aschelminthes (roundworms) — parasitic in plants and animals, with a complete alimentary canal and separate sexes:
    Ascaris — roundworm.
    Wuchereria — filaria worm.
    Ancylostoma — hookworm.
    Annelida —
    Hirudinaria — the blood-sucking leech, an ectoparasite.
    Arthropoda — blood-feeding vectors that live on human blood:
    Anopheles, Culex and Aedes — mosquitoes.
    All of these are endoparasites except the leech and the mosquitoes, which attack from outside the body.