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P S Verma & V K Aggarwal (biology) Solutions for Class 9 Science Chapter 4 - Diversity In Living Organisms

P S Verma & V K Aggarwal (biology) Solutions for Class 9 Science Chapter 4 Diversity In Living Organisms are provided here with simple step-by-step explanations. These solutions for Diversity In Living Organisms are extremely popular among class 9 students for Science Diversity In Living Organisms Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the P S Verma & V K Aggarwal (biology) Book of class 9 Science Chapter 4 are provided here for you for free. You will also love the ad-free experience on Meritnation’s P S Verma & V K Aggarwal (biology) Solutions. All P S Verma & V K Aggarwal (biology) Solutions for class 9 Science are prepared by experts and are 100% accurate.

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Answer:

Types of species diversity are listed below:

(i) Point diversity
(ii) Alpha diversity or local diversity
(iii) Gamma diversity
(iv) Epsilon diversity or regional diversity

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A single tree may be considered a unit of alpha diversity (as it belongs to a particular habitat); its leaf may be considered as an area of point diversity (as many leaves together inhabit a tree); a group of trees present together as an area of gamma diversity (consisting of large number of trees) and the forest within which the trees are located as an area of epsilon diversity (as the forest represents a group of gamma diversity areas of trees).

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Classification is needed because there are large number of living organisms on earth. To study the diversity among such a large group separately at an individual level is almost impossible. Hence, to make the studies more systematic, it is important to classify various kinds of organisms in an ordered manner. The similarities and the differences help us understand the inter-relationships among different groups of animals and understand evolutionary processes and the geographical distribution of plants and animals. Thus, classification also forms a base for other biological sciences, such as evolutionary biology and biogeography.

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The classification of organisms is based on their body design in relation to their form and function. For instance, some characteristics have more wide-ranging changes in the body design of different organisms than other characteristics. Another factor that influences classification is the evolution of characteristics with time. The characteristics that came into existence earlier are usually considered to be more fundamental than the ones that came later.

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The complexity of a cell structure and its number serves a very important role in classification. The organisms are divided into eukaryotes (possess membrane-bound cell organelles) and prokaryotes (lack membrane-bound cell organelles) on the basis of their cell structure.

According to Whittaker's five-kingdom classification, eukaryotic organisms are classified into unicellular (one cell) and multicellular (more than one cell) depending upon the number of cells they possess.

The prokaryotes are grouped into the kingdom Monera, whereas the unicellular eukaryotes are grouped into the kingdom Protista. The multi-nucleate and/or multi-cellular eukaryotes are divided into kingdoms Fungi, Plantae and Animalia.

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The seven categories of hierarchical classification include the following:

(i) Species
(ii) Genus
(iii) Family
(iv) Order
(v) Class
(vi) Phylum/Division and 
(vii) Kingdom

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Plants Animals
Plants are generally immobile. Animals are generally mobile.
Plants are autotrophic.   Animals are heterotrophic.
Plant cells possess cell wall. Animal cells lack cell wall.
Plants have indefinite growth due to the presence of growing points. Growth in animals is definite and they stop growing after reaching maturity.
Body forms of plants are irregular due to the presence of branches. Animals generally possess a definite shape, size and symmetry, with the exception of some lower forms.

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Disadvantages of the two-kingdom classification are:

(i) Unicellular organisms do not fit in either of the kingdoms. This system does not provide a separate distinction for such organisms.
(ii) It grouped the photosynthetic organisms (plants) and the non-photosynthetic organisms (fungi) in the same kingdom, Plantae.

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Five kingdom classification

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The main characteristics of kingdom Protista are:

(i) It includes unicellular eukaryotic organisms such as unicellular algae, protozoans and unicellular fungi.
(ii) Some of them possess hair-like cilia (e.g. Paramecium) or whip-like flagellum (e.g. Euglena).

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Lichens are an example of symbiotic relationship between fungi and algae i.e. they co-exist for mutual benefit. The algal partner (usually blue-green algae or cyanobacteria) is known as phycobiont and it provides food for its fungal partner. The fungal partner is known as mycobiont and it absorbs water and minerals and supplies it to the phycobiont. Lichens can tolerate prolonged drought and drastic temperatures and therefore thrive in hostile habitats like rocks, barks of trees and the ground. Lichens are sensitive to air pollution. They are classified into three types -  Crustose lichens (Rhizocarbon), Foliose lichens (Parmelia) and Fruticose lichens (Usnea).

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Characters of division Thallophyta (Algae):

(i) They do not have a differentiated plant body, which is in the form of an undivided thallus.
(ii) Their reproductive organs are single-celled, and there is no embryo formation after fertilisation.
(iii) They have  cellulose in their cell walls.
(iv) They lack a vascular system.

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Algae Fungi
They contain photosynthetic pigments. They lack photosynthetic pigments.
They are autotrophic. They are heterotrophic.
Cell wall is made up of cellulose. Cell wall is made up of chitin.
They store food in the form of starch. They store food in the form of glycogen and oil.

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Characteristics of algae:

(i) The plant body is in the form of undivided thallus and is not differentiated into stems, roots and leaves.
(ii) They are autotrophic and mostly aquatic.
(iii) Their cell walls are made of cellulose.
(iv) They contain starch as a stored food material.

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Dicots Monocots
Embryo in the seeds bears two cotyledons. Embryo in the seeds bears one cotyledon.
Leaves of dicots have reticulate venation. Leaves of monocots have parallel venation.
Vascular bundles of the stem are open and arranged in a ring. Vascular bundles of the stem are closed and scattered in the ground tissue.
They have a tap root system. They have an adventitious root system.

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Bryophytes Pteridophytes
They have a gametophytic plant body. They have a sporophytic plant body.
Real stems and leaves are absent and thallose or fallose comprises the plant body. Real stems and leaves are present.
Plant body is fixed by rhizoids. Plant body is fixed by roots.
Sporophyte is parasitic over the gametophytic plant body throughout its life. The gametophyte is small and independent.
They are non-vascular in nature. They are vascular in nature.

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Characteristics of Bryophyta:

(i) They are multi-cellular green land plants.
(ii) Their plant body is a flat, green thallus in liverworts and a leafy, erect structure in mosses. They lack real roots, stems, leaves and flowers.
(iii) They lack a true vascular system.
(iv) Gametophyte is attached to substratum via hair-like outgrowths called rhizoids.
Examples: Riccia and Marchantia.

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Characteristics of Pteridophyta:

(i) Their plant body consists of roots, stems and leaves.
(ii) They have a well-developed vascular system for conduction of water and other substances.
(iii) These plants lack flowers and hence, do not produce seeds.
(iv) Sex organs are multicellular and enclosed by sterile cells.
Examples: Pteris and Dryopteria

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Characteristics of gymnosperms:

(i) The seeds of these plants are naked and are not enclosed in fruits.
(ii) They are usually perennial, evergreen and woody.
(iii) Sporophylls are aggregated to form cones with separate male and female cones.
(iv) Xylem lacks vessels and phloem lacks companion cells.
Examples: Cycas, Pinus and Cedrus

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Characteristics of angiosperms:

(i) The seeds produced by these plants are enclosed within the fruit.
(ii) They are also called flowering plants because they produce flowers and their reproductive organs are aggregated within the flower.
(iii) Plant embryos in seeds have a structure called cotyledons (seed leaves).
(iv) Endosperm has triploid cells and supplies nutrients to the developing embryo in the seed.
Examples: Pea (Pisum sativum), maize (Zea mays) and wheat (Triticum aestivum)

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Nonchordata Chordata
They lack notochord. Notochord is present in them at some of their developmental stages.
Heart, if present, is dorsal in position. Heart is always present and is ventral in position.
Their circulatory system is of open or closed type. Their circulatory system is of closed type.
Pharyngeal gill slits are absent. Pharyngeal gill slits are present.
Their central nervous system is solid and ventral. Their central nervous system is hollow and dorsal.

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Porifera  Cnidaria (Coelenterata)
They have a cellular level of organisation. They have a tissue level of organisation.
Muscle and nerve cells are absent. Muscle and nerve cells are present.
Their bodies have several inhalant pores called ostia and a single exhalant pore called osculum. Their bodies have a single opening.
Appendages are absent in these animals. Appendages are present in these animals in the form of tentacles.
Digestion is intracellular. Digestion is both intracellular and extracellular.

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Polyp Medusa
It is the non-motile form of cnidarians. It is the free-swimming or motile form of cnidarians.
It has a cylindrical body. It has an umbrella-like body.
It reproduces asexually. It reproduces by sexual reproduction.
Examples: sea pen, red coral Examples: Jellyfish, Rhizostoma

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General characteristics of Porifera:

(i) These are the simplest multicellular, diploblastic animals.
(ii) They are asymmetrical or radially symmetrical.
(iii) Their cells are loosely held together in a gelatinous matrix, mesoglea and do not form tissues.
(iv) Skeleton is made up of minute calcareous or silicious spicules or spongin fibre (collagen) or both.
Examples: Sycon and Spongilla.

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General characteristics of cnidarians (coelentrates):

(i) These are aquatic animals and mostly marine, but some are fresh water animals as well.
(ii) These are multicellular, diploblastic animals with tissue level of organisation.
(iii) There body is radially symmetrical.
(iv) They lack respiratory, circulatory and excretory organs.
Examples: Hydra and Tubipora (organ pipe coral)



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Question 1:

  

Answer:

Hierarchical system of classification was proposed by Linnaeus. In this classification, he arranged organisms into an ascending series of increasing inclusiveness forms. The taxonomic groups are arranged in a definite order, from higher to lower categories. Each category is called a taxon.

The taxa used in classifying organisms are:

(i) Species- It is the lowest category that includes individuals with similar morphological characteristics, which are able to breed among themselves and reproduce. For example, horse (Equus cabalus) and ass (Equus acinus) belong to the same genera Equus but are different species.

(ii) Genus- It includes related species which have less characteristics in common. Members of a genus have identical reproductive organs. For example, a banyan and a fig tree differ from each other in vegetative structures but resemble each other in reproductive organs, and thus they belong to the same genus Ficus.

(iii) Family- Group of related genera are included in a family. More similar genera are placed together in a single family. For example, a cat and a lion belong to the same family Felidae. They both possess similar structures and retractable claws.

(iv) Order- Families resembling one another in few characteristics are assembled in an order. For example, a tiger and a wolf share characteristics such as jaws with powerful incisors, large, sharp canines and carnivores. Thus they both belong to the same order Carnivora.

(v) Class- It includes organisms of related order. For example, chordates such as rats, dogs, bats, monkeys and camels belong to class Mammalia as they have similar characteristics such as hairy exoskeleton, mammary glands and external ears.

(vi) Phylum (in animals)/division (in plants)- Different classes having few common characteristics are placed in a single phylum. For example, all animals which have a notochord in the embryo belong to phylum chordata.

(vii) Kingdom- Organisms that share a set of distinguishing common characteristics are placed in the same kingdom.

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Importance of classification

Classification is the method of organising or arranging organisms into separate groups on the basis of similarities and differences. It is a very important branch of science that deals with systematic arrangement of living organisms for further studies.

Classification of organisms is important because of the following reasons:

(i) It helps in studying wide variety of living organisms.
(ii) It provides a clear picture of all life forms before us.
(iii) It helps in understanding the inter-relationship among different groups of organisms.
(iv) It provides a base for the development of other biological sciences.

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Hierarchy of categories refers to an arrangement of different taxonomic groups in a definite order from higher to lower categories. A category is called a taxon.The main aim of hierarchical taxonomy is to assign an organism an appropriate place within the systematic framework of classification.The categories or taxa in the hierarchy are placed in ascending order. As we move upwards from species to kingdom, the level of similarities between the organisms decreases. 

The taxa or categories used in classifying plants and animals are:


(i) Species- It is the lowest category that includes individuals with similar morphological characters and reproduces to form offsprings.
(ii) Genus- It includes related species which have less characteristics in common.
(iii) Family- Group of related genera are included in a family. More similar genus groups are placed together in a single family.
(iv) Order- Families resembling one another in few characteristics are assembled in an order.
(v) Class- It includes organisms of related order.
(vi) Phylum (in animals)/division (in plants)- Different classes having few common characteristics are placed in a single phylum.
(vii) Kingdom- Organisms that share a set of distinguishing common characteristics are placed in the same kingdom.

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Kingdom Monera: This kingdom includes prokaryotic and unicellular organisms. It includes bacteria, blue-green algae or cyanobacteria, and mycoplasma. This kingom is classified into the following sub-kingdoms:

1. Archaebacteria:
These are autotrophs, which obtain energy from the oxidation of chemical energy sources for their metabolic activities such as reduced gases like ammonia, methane or hydrogen sulphide. They produce their own amino acids and proteins.

They are divided into three groups:
(a) Methanogens- They produce methane by their metabolic activities. They cannot survive in the presence of oxygen.
(b) Thermoacidophiles- These archaea favour extremely hot and acidic environments. They use hydrogen sulphide as their energy source.
(c) Halophiles- They inhabit extremely salty and alkaline environments.

2. Eubacteria:
These are prokaryotic unicellular organisms which are enclosed in a porous, rigid cell wall. The plasma membrane surrounds a non-compartmentalised cytoplasm. The eubacteria lack membrane-bound cell organelles such as nucleus, mitochondria, Golgi apparatus etc. They possess a single, circular DNA which is coiled into one region of the cell, referred to as the nucleoid. They are divided into different categories on the basis of their body shape. These are:

(a) Bacilli (rod-shaped)
(b) Cocci (spherical)
(c) Spirilla (corkscrew)
(d) Vibrio (comma-shaped)

Electron transport and photosynthesis take place on the plasma membrane, which sometimes folds into the interior of the cell. The cell wall of eubacteria consists of a unique material called peptidoglycam which is composed of chains of sugars cross-linked by peptides. The eubacteria can be differentiated into two distinct types based on their cell wall composition - gram-positive bacteria and gram-negative bacteria. Many bacteria are also motile by means of appendages called flagella. Another set of appendages called pili help in sexual reproduction and attachment to the substrate.

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Characteristics of Kingdom Protista:

(i) They include unicellular, eukaryotic organisms.
(ii) They may be free-living or parasitic or symbiotic in nature. Some also exist in colonies.
(iii) They may be autotrophic (e.g. algae and diatoms) or heterotrophic (protozoans).
(iv) They may be uninucleate, binucleate or multinucleate.
(v) Some of these organisms use appendages such as hair-like cilia or whip-like flagellum.
(vi) They reproduce asexually by binary fission or multiple fission and sexually by conjugation.

The Kingdom Protista is further classified into Phylum Protozoa:

(a) This phylum contains unicellular, mostly aquatic organisms.
(b) The body is either naked or covered by pellicle or hard shells. The body shape may also be varied.
(c) The cytoplasm is differentiated into an outer ectoplasm and an inner endoplasm.
(d) Locomotion is through finger-like pseudopodia, flagella or cilia.
(e) The protozoa undergo asexual reproduction by binary fission or multiple fission and sexual reproduction is by conjugation.

Phylum Protozoa is further divided into five classes:

Class 1- Mastigophora
Example : Euglena

Class 2- Sarcodina
Example : Amoeba

Class 3- Sporozoa
Example : Plasmodium

Class 4- Ciliata
Example : Paramecium

Class 5-Suctoria
Example : Ephelota

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Kingdom Fungi - 

Fungi include heterotrophic, eukaryotic and non-photosynthetic organisms.

(a) Some fungi are known parasites, such as Puccinia, Albugo and Ustilago, and derive nutrition from hosts.
(b) Some fungi such as Mucor, Rhizopus, Penicillium and Agaricus are decomposers, saprophytes or saprobionts.

Fungi maybe unicellular (yeast) or filamentous. The body of a filamentous fungus is called a mycelium and it is composed of several thread-like structures called appendages. Cell wall of fungi is composed of chitin and cellulose. Chitin is a tough complex of sugar.They store food in the form of glycogen. Fungi also exist in symbiotic association with algae, known as lichens. 
Certain fungi form a symbiotic association with an algal partner. This symbiotic association of fungi and algae is called a lichen. The algal component of the lichen is known as phycobiont and the fungal component of the lichen is known as mycobiont.

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General characteristics of old division spermatophyta:

(i) It includes higher plants that bear flowers and seeds.
(ii) The plants in this division have a sporophytic plant body with differentiated root, stem and leaves. The gametophytes are nutrition dependent on the sporophytes.
(iii) They have a well developed vascular system.
(iv) Plants have conspicuous, multicellular sex organs. Fertilisation does not require an external water source.
(v) Division spermatophyta was divided into following two subdivisions, depending upon whether the ovule was covered or naked and the presence of fruits. 
(a) Sub-division Gymnospermae
(b) Sub-division Angiospermae
Examples: Cycas, Pisum sativum, etc.

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Pteridophytes include those plants that lack flowers and do not produce seeds. Their body is well differentiated into roots, stems and leaves. They have a well-developed vascular system with multicellular sex organs.

Examples of Pteridophytes- Selaginella, Dryopteris, Pteris, etc.

Comparison between bryophytes and pteridophytes:

Bryophytes Pteridophyte
They have a gametophytic plant body. They have a sporophytic plant body.
Sporophyte is parasitic over the gametophytic plant body throughout its life. The gametophyte is small and independent.
Real stems and leaves are absent and the plant body is either thallose or folliose. Real stems and leaves are present.
Plant body is fixed by rhizoids. Plant body is fixed by roots.
They are non-vascular in nature. They are vascular in nature.

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General characteristics of Platyhelminthes:

(i) Their body is bilaterally symmetrical and dorsoventrally flattened.
(ii) They are acoelomate and triploblastic animals i.e. their tissues differentiate from three embryonic germ layers.
(iii) Circulatory and respiratory systems and skeleton are absent.

(iv) Their excretory system consists of blind tubules called protonephridia. Blind end of a tubule bears a tuft of cilia or a flagellum called the flame cell.
(v) They are hermaphrodites i.e. both male and female reproductive organs occur in the same individual.
Examples: Liver fluke (Fasciola) and blood fluke (Schistosoma)

General characters of Nematoda:

(i) They are bilaterally symmetrical, triploblastic, pseuodocoelomate and unsegmented animals.
(ii) They have a cylindrical or flattened, worm-like body. Their body is covered with a tough, resistant cuticle.
(iii) Sexes are separate.
(iv) Alimentary canal straight and complete with mouth and anus.
(v) Parasitic nematodes are pathogenic and are responsible for diseases such as elephantiasis (Wuchereria bancrofti),  ascariasis (Ascaris) and enterobiasis (Enterobius).

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General characteristics of phylum Annelida:

(i) They are triploblastic, bilaterally symmetrical, soft, elongated and dorsoventrally flattened.
(ii) Their body is metamerically segmented externally by transverse grooves and internally by septa.
(iii) Their body is covered by thin cuticles and exoskeleton is absent.
(iv) They are true coelomates with closed blood vascular system. There is extensive organ differentiation.

(v) They have a tube-like alimentary canal, which is complete and extends straight from mouth to anus.
(vi) Reproduction is sexual. Sexes may be separate or united (hermaphrodite).
(vii) Segmented nephridia are present for excretion which removes wastes from coelom and blood stream directly to the exterior.
(viii) They are usually found in aquatic, marine or fresh-water habitats. Some are terrestrial and inhabit moist soil and some are free living forms.

Phylum Annelida is divided into three classes:
Class 1- Polychaeta
Example : Nereis.

Class 2- Oligochaeta
Example : Pheretima.

Class 3- Hirudinea
Example : Hirudinaria

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General characteristics of phylum Mollusca:

(a) They have a soft, bilaterally symmetrical body with little segmentation and without appendages.
(b) Body is divisible into an anterior head, a ventral foot and a dorsal visceral mass. The entire body is covered by a fold of thin skin called mantle, which secretes a hard calcareous shell of one or more pieces.
(c) Respiration occurs via gills, mantle or a "lung" of the mantle.
(d) Sexes are usually separate.
(e) They have an open circulatory system (except in cephalopods). The body cavity is haemocoel and the true coelom is reduced and restricted to the pericardial cavity and the lumen of the gonads and nephridia.
(f) Some species have sensory organs of touch, smell, taste and vision.
(g) They excrete via metanephridia or kidneys.
(h) The molluscs are aquatic, mostly marine with a few freshwater and terrestrial forms.

Examples:
(i) Class Gastropoda: Pila (apple snail)
(ii) Class Pelecypoda: Teredo (ship worm)
(iii) Class Cephalopoda: Octopus

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Answer:

General characteristics of phylum Arthropoda: 

(a) They are triploblastic, bilaterally symmetrical and metamerically segmented animals.
(b) Body segments are grouped into two regions - cephalothorax and abdomen or three regions - head, thorax and abdomen. 
(c)Body cavity is haemocoel and the coelom is reduced to the spaces of the genital and excretory organs.
(d) They have a complete alimentary canal, with mouth and anus lying opposite each other.
(e) Sexes are separate. Sexual dimorphism is well marked in several forms. Fertilisation is usually internal, oviparous or ovoviviparous and often with metamorphosis.
(f) They have gills, trachea or book-lungs for respiration.
(g) They lack true nephridia and excretion occurs via coelomoducts, malpighian tubules or green or coxal glands.
(h) Circulatory system is open with dorsal heart, arteries and haemocoel but without capillaries and veins.
(i) Their exoskeleton comprises cuticle containing protein, lipid, chitin. Often, calcium carbonate is secreted by underlying epidermis and shed at intervals.

Examples:
(i) Class Crustacea: Palaemon
(ii) Class Myriapoda: Scolopendra
(iii) Class Insecta: Lepisma
(iv) Class Arachnida: Sarcoptes

 

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Kingdom Animalia has been classified into 11 major phylums. These are:

1. Phylum Porifera:  
These are the simplest, multicellular, diploblastic, asymmetrical or radially symmetrical animals. Example: Sycon.

2. Phylum Cnidaria or Coelenterata:
These are diploblastic, radially symmetrical organisms with tissue level of organisation. Example: Hydra.

3. Phylum Ctenophora: 
They are bilaterally symmetrical, triploblastic animals with eight longitudinal rows of ciliary comb-plates for locomotion.
Example: Pleurobrachia.

4. Phylum Platyhelminthes:
They are bilaterally symmetrical, triploblastic, acoelomate and hermaphrodite animals.
Example: Taenia solium.

5. Phylum Nematoda:
They are bilaterally symmetrical, triploblastic, pseudocoelomate and unsegmented animals.
Example: Ascaris.

6. Phylum Annelida:
They are bilaterally symmetrical, triploblastic, true coelomate animals.
Example: Hirudinaria.

7. Phylum Arthropoda:
They are triploblastic, bilaterally symmetrical, haemocoelomate animals with metamerically segmented body.
Example: Palaemon.

8. Phylum Mollusca:
They are bilaterally symmetrical, haemocoelomate animals with little segmentation.
Example: Chiton.

9. Phylum Echinodermata
They are triploblastic, coelomate, radially symmetrical animals with spiny hard calcareous endoskeleton.
Example: Antedon.

10. Phylum Hemichordata
They are bilaterally symmetrical animals with unsegmented body and have gill slits for respiration.
Example: Balanoglossus.

11. Phylum Chordata:
They possess dorsal, hollow, tubular nerve cord with a presence of notochord and paired gill-slits in the pharynx.
Example: Herdmania.

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Characteristics of mammals:

(i) Mammals are warm-blooded vertebrates. Their body is divisible into head, trunk, neck and tail. Movable eyelids are present.
(ii) Females have mammary glands that secrete milk for the nourishment of the young.
(iii) A muscular diaphragm separates thoracic and abdominal cavities.
(iv) Respiration is through lungs only and the heart is four-chambered. Mammals possess non-nucleated biconcave red blood corpuscles.
(v)Fertilisation is internal, and mammals are known to be viviparous.
(vi)Two pairs of pentadactyl limbs are present. Teeth are thecodont and heterodont. Fleshy external ear (pinnae) is present.

(vii) Hair and subcutaneous fat forms an insulating layer. Cutaneous glands such as sweat glands, scent glands and sebaceous glands are present.
Example: Macropus and Rattus.


Characteristics of  birds:
(i) Warm-blooded, tetrapodous vertebrates.
(ii) Forelimbs are modified into wings for flight, whereas the hind limbs bear four clawed digits and are adapted for walking, perching or swimming.
(iii) Their bones are light and spongy due to presence of air cavities.
(iv) They excrete semi-solid urine with uric acid. They do not possess a bladder.
(v) Horny scales are present on the feet but most of the body is covered by feathers.
(vi) Birds undergo internal fertilisation and are oviparous.
(vii) Their narrow jaws form a horny beak which is modified for different purposes. Teeth are absent.
(viii) They breathe through lungs and have a four-chambered heart.

Examples: Gallus and Columba.

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Pisces is a super class of subphylum Gnathostomata, which consists of following two classes:

Class 1: Chondrichthyes
(a) Marine fishes with entirely cartilaginous endoskeleton.
(b) 
They have a streamlined body that is either compressed laterally or flattened dorsoventrally.
(c) 
Mouth is ventral in position.
(d) 
Skin is tough and covered with minute placoid scales.
(e) Respiration occurs via gills.
Examples: Scoliodon and Torpedo

Class 2: Osteichthyes:
(a) Marine and fresh-water fish with partial or full bony endoskeleton.
(b) T
heir size varies from 10 mm to 4 metres.
(c) They have a spindle-shaped body.
(d) 
Four pairs of gills are present for respiration.
(e) 
They excrete ammonia (ammonotelic animals).
Examples: Labeo and Protopterus.

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Bilateral Symmetry Radial Symmetry
Limbs and organs are paired. Limbs and organs occur all around the central axis.
Cephalization is present. Cephalization is absent.
Body can be divided into two equal halves (mirror images) by mid-sagittal plane. Body can be divided into two equal halves by any vertical plane passing through the central axis.
Examples: Earthworms, humans etc. Examples: Starfish , Hydra etc.

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Characteristics of Ctenophora:

(i) They have a transparent body with biradial symmetry and are triploblastic.
(ii) They bear two tentacles and eight longitudinal rows of ciliary comb-plates for locomotion.
(iii) They are marine, solitary or free-swimming.
(iv) They lack nematocysts but adhesive cells (colloblasts) are present.
Examples: Pleurobrachia (comb jelly) and Ctenoplana

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Answer:

Main characteristics of Platyhelminthes:

(i) Their body is bilaterally symmetrical.
(ii) They are triploblastic animals i.e. their tissues differentiate from three embryonic germ layers.
(iii) Excretory system consists of blind tubules called protonephridia, which bear a tuft of cilia at the end called a flame cell.
(iv) They are hermaphrodites i.e. both male and female reproductive organs occur in the same individual.
Examples: Liver fluke (Fasciola) and blood fluke (Schistosoma)

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Main characteristics of Nematoda:

(i) They are bilaterally symmetrical, triploblastic, pseudocoelomate and unsegmented animals.
(ii) They have a cylindrical or flattened, worm-like body.
(iii) Sexes are separate.
(iv) Body is covered with a tough, resistant cuticle.
Examples: Ascaris (round worm) and Wuchereria bancrofti (filarial worm)

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Main characteristics of Annelida:

(i) They are triploblastic, bilaterally symmetrical, coelomate, soft and elongated animals.
(ii) Their body is metamerically segmented externally by transverse grooves and internally by septa.
(iii) They have a tube-like alimentary canal, which is complete and extends straight from mouth to anus.
(iv) Reproduction is sexual. Sexes may be separate or united (hermaphrodite).
Examples: Sea mouse, leech, earthworm etc.

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Hermaphrodites are those organisms in which the sexes are not separate i.e. both male and female reproductive organs occur in the same individual.

Examples: Animals of phylum Platyhelminthes, such as liver fluke and blood fluke, are hermaphrodites.

Certain forms of phylum Annelida, such as earthworm and Eutypheus, are also hermaphrodites.

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Triploblastic animals are those which have three germ layers in the embryo. The outer layer is called ectoderm, the inner layer is called endoderm and the middle layer is called mesoderm. 

Examples: Animals of phylum Ctenophora, such as comb jelly and Venus's girdle.
                Animals of phylum Platyhelmithes, such as Planaria and blood fluke.

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Coelomate animals refer to those animals that possess a true body cavity or coelom. The coelom originates from mesoderm and is lined by epithelial cells of mesodermal origin.

Examples: Animals of phylum Annelida, such as earthworm and leech
                Animals of phylum Mollusca, such as octopus and pearl oyster

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General characteristics of phylum Arthropoda: 

(i) They are triploblastic, bilaterally symmetrical and metamerically segmented animals with haemocoel body cavity.
(ii) The body segments are grouped into  cephalothorax and abdomen or into head, thorax and abdomen.
(iii) They have a complex muscular system with exoskeleton for attachment, striated muscles for rapid actions and smooth muscles for visceral organs.
(iv) Sexes are usually separate and sexual dimorphism is marked in several forms.
Examples: Prawn (Palaemon) and centipede (Scolopendra)

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General characteristics of phylum Mollusca:

(i) They have a soft, bilaterally symmetrical body with little segmentation and without appendages. Body cavity is haemocoel.
(ii) Body is divisible into an anterior head, a ventral foot and a dorsal visceral mass. The entire body is covered by a thin fold of skin called mantle, which secretes a hard calcerous shell of one or more pieces.
(iii) Respiration occurs via gills, mantle or a "lung" of the mantle.
(iv) Sexes are usually separate.
Examples: Chiton and Pila

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General characteristics of phylum Echinodermata:

(i) Their body is triploblastic, coelomate, unsegmented and radially symmetrical.
(ii) Digestive system is usually complete. Excretory organs are absent and anus is absent in class Ophiuroidea.
(iii) Body wall is covered with spiny hard calcareous plates that form a rigid or flexible endoskeleton.
(iv) Body cavity is organised into water vascular system, which moves respiratory and locomotary organs.
Examples: Antedon and sea urchin (Echinus)
 

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(a) Prawn: Palaemon
(b) House fly: Musca
(c) Star fish: Asterias
(d) Squid: Teuthida
(e) Apple snail: Pila
(f) Fresh water mussel: Unio

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Ambulacral system is present in phylum echinodermata. 

The ambulacra are present on the oral surface of the body and help the echinoderms in locomotion and gathering food.

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Certain adaptation characteristics in fish, due to which they are aquatic, include:
(i) Presence of gills for respiration
(ii) Fins for locomotion (swimming) and balance with a streamlined or spindle-shaped body
(iii) Cold-blooded (ecothermic)

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Characteristics of chondrichthyes:

(i) They are marine fish with completely cartilaginous endoskeleton and a two-chambered heart.
(ii) They have a streamlined body which is either compressed laterally or flattened dorsoventrally. They have paired or median fins for locomotion and the tail or caudal fin is heteroceral.
(iii) Mouth is ventral in position and respiration occurs via gills.
(iv) Skin is tough and covered with minute placoid scales.
Examples: Scoliodon and Torpedo.

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Characteristics of Osteichthyes:

(i) Marine and fresh-water fish with partial or full bony endoskeleton.
(ii) They have a spindle-shaped body and the skin is either naked or covered with cycloid or ctenoid scales.
(iii) Four pairs of gills are present for respiration. The gills are covered by operculum and are filamentous.
(iv) Cloaca is absent and anal and urogenital apertures are distinct. They excrete ammonia (ammonotelic animals).
Examples: Labeo and Protopterus.

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(a) 

Cartilaginous fish Bony fish
They have a cartilaginous endoskeleton. They have a bony endoskeleton.
They contain 5-7 pairs of gill slits and operculum is absent in them. They contain 5-7 pairs of gill slits which are covered with an operculum.

(b) 
Amphibia Reptilia
They have a glandular, smooth and moist skin. They have a non-glandular, dry and keratinised skin.
Fertilisation is external. Fertilisation is internal.

(c) 
Aves Mammals
The body is covered with feathers and scales. They lack feathers and scales; however, they have hair on their body.
They have a toothless beak and hollow and pneumatic bones. They do not have beaks; teeth are present and the bones do not possess air cavities.

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Characteristics of mammals:

(i) Their body is divisible into head, trunk, neck and tail. Cutaneous glands such as sweat glands, scent glands and sebaceous glands are present.
(ii) Females have mammary glands which secrete milk for the nourishment of the young.
(iii) A muscular diaphragm separates thoracic and abdominal cavities and respiration takes place through lungs only.
(iv) Two pairs of pentadactyl limbs are present. Teeth are thecodont and heterodont.
Example: Macropus and Rattus, Macaca.

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Adaptations in birds for flight:

(i) Possess a spindly or boat-shaped body covered mostly by feathers.
(ii) Forelimbs are modified into wings for flight.
(iii) Bones are light and spongy due to presence of air cavities.

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Main characteristics of chordates:

(i) They have a dorsal, hollow, tubular nerve cord.
(ii) Notochord is present that is ventral to the nerve cord.
(iii) They possess paired gill-slits in the pharynx.
(iv) They have a ventral heart with dorsal and ventral blood vessels and closed blood vascular system.
Examples: Salpa and Herdmania.

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Protochordates belong to phylum Chordata. They are further subdivided into two subphylums:

(i) Urochordata
They are bag-like, sessile, soft-bodied, non-metameric animals. In these organisms, the notochord is present only in the tail of free-living tadpole-like larva. The dorsal tubular nerve chord also degenerates in the form of small ganglion in the adult. The only chordate character present in the adult form are the numerous gill slits. Urochordates are hermaphrodites. Example: Herdmania.

(ii) Cephalochordata
They are fish-like, metamerically segmented, headless and coelomate animals. In these organisms, notochord and nerve cord extend throughout the length of the body. The notochord, nerve chord and pharyngeal gill slits are retained throughout life. Sexes are separate in Cephalochordates. Example: Amphioxus.

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Example of Urochordata: Herdmania and Salpa.
Example of Cephalochordata: Amphioxus or Branchiostoma.

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Notochord is ventral and its cells are filled with semi-fluid, whereas nerve cord is dorsal and hollow.



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