animal kingdom class 11 the difficulties that you would face in classification of animals, if

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2.If you are given a specimen, what are the steps that you would follow to classify it?
soln. Various steps considered to classify a specimen are:
(i)Mode of nutrition – It can be autotrophic, holozoic, saprophytic or parasitic.
(ii)Complexity of body structure – Whether the specimen is unicellular or multicellular.
(iii)Presence or absence of membrane bound organelles.
(iv)Body symmetry, i.e., the plane by which organism can be divided into two equal halves.
(v)Presence or absence of coelom, it can be acoelomates, pseudocoelomates, eucoelo- mates.
(vi)Phylogenetic relationship.

3.How useful is the study of the nature of body cavity and coelom in the classification of animals?
soln. Organisms can be classified according to presence or absence of the coelom. The body cavity, which is lined by mesoderm is called coelom. Animals possessing coelom are called coelomates, e.g., annelids, molluscs, arthropods, echinoderms, hemichordates and chordates. In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates, e.g., aschelminthes. In pseudocoelomates, body cavity is derived from blastocoel of the embryo. The animals in which the body cavity is absent are called acoelomates, e.g., platyhelminthes.

6.What are the peculiar features that you find in parasitic platyhelminthes?
soln.Following are the peculiar features of parasitic platyhelminthes:



(i) The thick tegument (body covering) resistant to the host’s digestive enzymes and anti-toxins.
(ii)Adhesive organs like suckers in flukes and the hooks and suckers in tapeworms for a firm grip on or in the host’s body.
(iii)Loss of locomotory organs.
(iv)Digestive organs are absent in tapeworms because digested and semidigested food of the host is directly absorbed’ through the body surface.
(v) Reproductive system is best developed in parasitic flatworms.
(vi)Parasitic flatworms, such as liver fluke and tapeworms perform anaerobic respiration.
(vii)They possess a considerable osmotic adaptability, as they can successfully live in different media.

7.What are the reasons that you can think of for the arthropods to constitute the largest group of the animal kingdom?
soln. Arthropods are most successful animals and constitute the largest group of the animal kingdom. They have conquered land, sea and air and make up over three fourth of currently known living and fossil organisms. They range in distribution from deep sea to mountain peaks. Thick, tough, non-living chitinous cuticle forms the exoskeleton which protects the organism from predators, help to withstand temperature upto 100°C or more and prevents water loss. They have ability to reproduce very fast and less time is needed for young ones to hatch from their eggs. Due to metamorphosis, there is less competition among larval and adult forms for food. Cockroaches can even survive nuclear radiations and poisoned earth. All these factors made arthropods the largest phylum among animals.
8.Water vascular system is the characteristic of which group among the following ?
(a) Porifera
(b) Ctenophora
(c) Echinodermata
(d) Chordata
soln. (c) Echinodermata

9.”All vertebrates are chordates but all chordates are not vertebrates”. Justify the statement.
soln. Chordates are the animals that possess notochord (a stiff, supporting rod like structure present on the dorsal side) at some stage of their lives. Phylum Chordata is divided into three Subphyla: Urochordata or tunicata, Cephalochordata and Vertebrata. Subphyla Urochordata and Cephalochordata are often referred to as protochordates and are exclusively marine. In urochordata, notochord is present only in tail of larva and disappears in adults, while in cephalochordata, it extends from head to tail region and persists throughout the life.
The members of Subphylum Vertebrata a possess notochord during the embryonic period and is replaced by a cartilaginous or bony vertebral column in the adult. Thus all vertebrates are chordates but all chordates are not vertebrates.

10.How important is the presence of air bladder in
Pisces?
soln. Bony fishes have a sac-like outgrowth, the swim bladder also called air bladder, that arises as an outgrowth from the dorsal wall of oesophagus. It is hydrostatic in function. It regulates buoyancy and helps them to swim up and down, thus preventing them from sinking. In some species air bladder also helps in respiration. It also serves as resonating chamber to produce or receive sound.