Unit–I Diversity of Living Organisms 27 Periods
Chapter – 1 : The Living World
What is living ? Biodiversity; Need for classification; three domains of life : taxonomy and systematics; concept of species and taxonomical hierarchy; binomial nomenclature; tools for study of taxonomy-museum, zoological parks, herbaria, botanical gardens.
Chapter – 2 : Biological Classification
Two kingdom classification, Five kingdom classification; Salient features and classification of Monera,Protista and Fungi into major groups; Lichens,Viruses and Viroids.
Chapter – 3 : Plant Kingdom
Salient features and classification of plants into major groups – Algae, Bryophyta, Pteriodophyta, Gymnospermae and Angiospermae (three to five salient and distinguishing features and at least two examples of each category); Angiosperms –classification upto class, characteristic features and examples.
Chapter – 4 : Animal Kingdom
Salient features and classification of animals non-chordates up to phyla level and chordates up to class level (three to five salient features and at least two examples of each category). **(No live animals or specimen should be displayed.)
Unit–II Structural Organisation in Animals and Plants 27 Periods
Chapter – 5 : Morphology of Flowering Plants
Morphology and modifications : Internal morphology of different plants : root, stem, leaf, Inflorescence, flower, fruit and seed. (to be dealt with relevant experiments of the Practical Syllabus).
Chapter – 6 : Anatomy of Flowering Plants
Anatomy and functions of different tissues.
Chapter – 7 : Structural Organisation in Animals
Animal tissues (epithelial, connective, muscular and nervous tissue), Brief account of morphology, anatomy and functions of different systems (digestive, circulatory, respiratory, nervous and reproductive) of an insect (cockroach).
Unit–III Cell : Structure and Function 26 Periods
Chapter – 8 : Cell-The Unit of Life
Cell theory and cell as the basic unit of life : Structure of prokaryotic and eukaryotic cells; Plant cell and animal cell; cell envelope; cell membrane, cell wall; cell organelles–structure and function; endomembrane system, endoplasmic reticulum, Golgi bodies, lysosomes, vacoules ; mitochondria, ribosomes, plastids, microbodies; cytoskeleton, cilia, flagella, centrioles (ultrastructure and function); nucleus.
Chapter – 9 : Biomolecules
Chemical constituents of living cells : Biomolecules, structure and function of proteins, carbohydrates, lipids, nucleic acids, enzymes– types, properties, enzymes action.
Chapter – 10 : Cell Cycle and Cell Division
Cell cycle, mitosis, meiosis and their significance.
Unit–IV Plant Physiology 40 Periods
Chapter – 11 : Transport in Plants
Movement of water, gases and nutrients; cell to cell transport, Diffusion, facilitated diffusion, active transport; plant-water relations, imbibition, water potential, osmosis, plasmolysis; long distance transport of water–absorption, apoplast, symplast, transpiration pull, root pressure and guttation; opening and closing of stomata and transpiration; Uptake and translocation of mineral nutrients – transport of food, phloem transport, mass-flow hypothesis.
Chapter – 12 : Mineral Nutrition
Essential minerals, macro-and micronutrients and their role; deficiency symptoms; mineral toxicity; elementary idea of hydroponics as a method to study mineral nutrition; nitrogen metabolism, nitrogen cycle, biological nitrogen fixation.
Chapter – 13 : Photosynthesis in Higher Plants
Photosynthesis as a mean of autotrophic nutrition; site of photosynthesis, pigments involved in photosynthesis (elementary idea); photochemical and biosynthetic phases of photosynthesis, cyclic and non-cyclic photophosphorylation; chemiosmotic hypothesis; photorespiration; C3 and C4 pathways; factors affecting photosynthesis.
Chapter – 14 : Respiration in Plants
Exchange of gases; cellular respiration–glycolysis, fermentation (anaerobic), TCA cycle and electron transport system (aerobic); energy relations–number of ATP molecules generated; amphibolic pathways; respiratory quotient.
Chapter – 15 : Plant–Growth and Development
Seed germination; phases of plant growth and plant growth rate; conditions of growth; differentiation, dedifferentiation and redifferentiation;’ sequence of developmental processes in a plant cell; growth regulators–auxin, gibberellin, cytokinin, ethylene, ABA; seed dormancy; vernalisation; photoperiodism.
Unit–V Human Physiology 40 Periods
Chapter – 16 : Digestion and Absorption
Alimentary canal and digestive glands, role of digestive enzymes and gastrointestinal hormones; Peristalsis, digestion, absorption and assimilation of proteins, carbohydrates and fats; calorific values of proteins, carbohydrates and fats; egestion; nutritional and digestive disorders–PEM, indigestion, constipation, vomiting, jaundice, diarrhoea.
Chapter – 17 : Breathing and Exchange of Gases
Respiratory organs in animals (recall only); Respiratory system in human; mechanism of breathing and its regulation in humans–exchange of gases, transport of gases and regulation of respiration, respiratory volume; disorders related to respiration–asthma, emphysema, occupational respiratory disorders.
Chapter – 18 : Body Fluids and Circulation
Composition of blood, blood groups, coagulation of blood; composition of lymph and its function; human circulatory system–structure of human heart and blood vessels; cardiac cycle, cardiac output, ECG; double circulation; regulation of cardiac activity; disorders of circulatory system–hypertension, coronary artery disease, angina pectoris, heart failure.
Chapter – 19 : Excretory Products and Their Elimination
Modes of excretion–ammonotelism, ureotelism, uricotelism; human excretory system–structure and function; urine formation, osmoregulation of kidney function–renin–angiotensin, atrial natriuretic factor (ANF), ADH and diabetes insipidus; role of other organs in excretion;’ disorders– uraemia, renal failure, calculi, nephritis; dialysis, artificial kidney and kidney transplant.
Chapter – 20 : Locomotion and Movement
Types of movement–Ciliary, flagellar, muscular; skeletal muscle–contractile proteins and muscle contraction; skeletal system and its functions; joints; disorders of muscular and skeletal system–myasthenia gravis, tetany, muscular dystrophy, arthritis, osteoporosis, gout.
Chapter – 21 : Neural Control and Coordination
Neuron and nerves; Nervous system in humans–central nervous system; peripheral nervous system and visceral nervous system; generation and conduction of nerve impulse; reflex action; sensory perception sense organs; elementary structure and functions of eye, ear, nose and tongue.
Chapter – 22 : Chemical Coordination and Integration
Endocrine glands and hormones; human endocrine system–hypothalamus, pituitary, pineal, thyroid, parathyroid, adrenal, pancreas, gonads; mechanism of hormone action (elementary idea); role of hormones as messengers and regulators, hypo–and hyperactivity and related disorders; dwarfism, acromegaly, cretinism, goiter, exophthalmic goitre, diabetes, Addison’s disease.
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A. List of Experiments 60 Periods
1. Study and description of three locally available common flowering plants, one from each of the families Solanaceae, Fabaceae and Liliaceae including dissection and display of floral whorls, anther and ovary to show number of chambers (floral formulae and floral diagrams). Types of root
(Tap and adventitious); stem (herbaceous and woody); leaf (arrangement, shape,venation, simple and compound).
2. Preparation and study of T.S. of dicot and monocot roots and stems (primary).
3. Study of osmosis by potato osmometer.
4. Study of plasmolysis in epidermal peels (e.g. Rhoeo leaves).
5. Study of distribution of stomata in the upper and lower surface of leaves.
6. Comparative study of the rates of transpiration in the upper and lower surface of leaves.
7. Test for the presence of sugar, starch, proteins and fats. Detection in suitable plant and animal materials.
8. Separation of plant pigments through paper chromatography.
9. Study of the rate of respiration in flower buds/leaf tissue and germinating seed
10. Test for presence of urea in urine.
11. Test for presence of sugar in urine.
12. Test for presence of albumin in urine.
13. Test for presence of bile salts in urine.
B. Study/observation of the following (spotting)
1. Study of the parts of a compound microscope.
2. Study of the specimens/slides/models and identification with reasons– Bacteria, Oscillatoria, Spirogyra, Rhizopus, mushroom, yeast, liverwort, moss, fern, pine, one monocotyledonous plant, one dicotyledonous plant and one lichen.
3. Study of virtual specimens/slides/models and identification with reasons– Amoeba, Hydra, liver-fluke, Ascaris, leech, earthworm, prawn, slik-worm, honeybee, snail, starfish, shark, rohu, frog, lizard, pigeon and rabbit.
4. Study of tissues and diversity in shapes and sizes of plant and animal cells (palisade cells, guard cells, parenchyma, collenchyma, sclerenchyma, xylem, phloem, squamous epithelium, muscle fibers and mammalian blood smear) through temporary/permanent slides.
5. Study of mitosis in onion root tip cells and animals cells (grasshopper) from permanent slides.
6. Study of different modifications in roots, stems and leaves.
7. Study and identification of different types of inflorescence (cymose and racemose).
8. Study of imbibition in seeds/raisins.
9. Observation and a comments on the experimental set up for showing :
(a) Anaerobic respiration
(b) Phototropism
(c) Effect of apical bud removal
(d) Suction due to transpiration
10. Study of human skeleton and different types of joints with the help of virtual images/models only.
11. Study of external morphology of cockroach through virtual images/models. Practical Examination for Visually Impaired Students
Note : Same Evaluation scheme and general guidelines for visually impaired students as given for Class XII may be followed. Items for Identification/Familiarity with the apparatus/equipments/ animal and plant material/chemicals etc. for assessment in practicals
(All experiments)
1. Plants of—
- Solanaceae–Brinjal, Petunia, any other
- Fabaceae–Rice, Wheat, any other
- Liliaceae–Any of the Lilies
2. A compound microscope, seeds of monocot and dicot–maize and gram or any other Model of Human skeleton to show–
- Ball and socket joints of girdles and limbs
- Rib cage
3. Test tube, honey comb, Mollusc shell, Models of Pigeon and Star fish, mushroom, petridish, succulents such as Aloe vera/kalenchoe, raisins, beaker, potatoes, scalpel, chromatography paper, chromatography chamber, alcohol, specimen/model of cockroach.
List of Practicals
1. Study three locally available common flowering plants of the families – Solanaceae, fabaceae, Liliaceae
2. Identify the types of :
- roots as Tap and Adventitious
- stems as Herbaceous or Woody
- leaves as Compound or Simple
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CBSE Class 11 Biology Revision Test Paper - 2020
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Chemical Control and Coordination Notes Class 11 Chapter 22
The Living World Notes Chapter 1 Biology CBSE Class 11
Breathing and Exchange of Gases Notes Class 11 Chapter 17
Chapter 18 Body fluids and Circulation Notes Class 11
Chapter 2 Biological Classification Notes CBSE Class 11
Chapter 4 Animal Kingdom Notes Class 11 Biology
Chapter 9 Biomolecules Notes Class 11 Biology
Chapter 11 Transport in Plants Notes Biology Class 11
1-The Living World
Biology is the science, which deals with the study of living organisms and their life processes. The term ‘Biology’ was first introduced by GR Treviranus and Jean Baptiste de Lamarck (1802).
What is Living?
Living organisms show certain key characteristics which distinguish them from non-living things. These are
● Growth is shown by living organisms by an increase in mass and an increase in the number of individuals. A multicellular organism grows by cell division.
● Reproduction is the process of producing offspring possessing features similar to those of their parents. It takes place by sexual or asexual mode.
● Metabolism comprises of both constructive reactions (anabolism) and destructive reactions (catabolism), continuously occurring in the body.
● Cellular organisation The cells are the building blocks of all living organisms may it be plants, animals or humans. Thus, organisms can be unicellular or multicellular.
● Consciousness is the ability of living organisms to sense their surroundings or environment and respond to these environmental stimuli, which could be physical, chemical and biological.
Diversity in the Living World
● Biodiversity refers to the number and types of organisms present on earth. Our earth possesses a wide range of living organisms. A number of plants and animals have been identified and described. However, a large number of organisms are still unknown to us.
● A rich diversity among organisms or biodiversity in terms of size, colour, habitat, physiological and morphological features can be observed on earth. Therefore, it is necessary to standardise the methods to identify and classify them on the basis of their defining characteristics.
● Certain rules and principles have been formulated for the identification, nomenclature and classification of organisms, which facilitate the study of vast diversity of organisms present on earth.
● Identification involves the process of finding the correct name and place of an organism. The morphological and anatomical characters are examined for proper identification.
● Nomenclature involves standardising appropriate naming of living organisms, so that they can be recognised and differentiated from others easily across the world.
● To ease the process of studying different organisms, a scientific name is assigned to each organism.
The principles of naming have been established by International Code for Botanical Nomenclature (ICBN) and International Code for Zoological Nomenclature (ICZN) for plants and animals, respectively.
● Organisms are identified on the basis of their resemblance and distinct differences from others. They are assigned a correct scientific/biological name.
● Binomial System of Nomenclature was developed by Carolus Linnaeus in 1751 and was published in his book Species Plantarum (1753). As per this system, a biological name comprises of two words namely, generic name and the specific epithet.
● Nomenclature of organisms follows certain universal rules, which are as follows
■ Biological names are generally in Latin and are written in Italics. These are latinised or derived from Latin irrespective of their origin.
■ Both the words in a biological name, when handwritten are separately underlined or printed in Italics to indicate their Latin origin.
■ The first letter of the generic name is written in capital letter while that of specific epithet is written in small letter, e.g. Mangifera indica.
■ Name of the author appears after the specific epithet at the end of the biological name and is written in an abbreviated form, e.g. Mangifera indica Linn, where Linn is for Linnaeus.
● Classification is the process by which organisms are grouped into convenient categories based on some easily observable characters. The scientific term used for different categories is taxa.
● Taxonomy is the branch of science which deals with different aspects of identification, nomenclature and classification of organisms. Linnaeus is known as the Father of Taxonomy.
● Systematics is the study of systematic arrangement of organisms and the evolutionary relationships amongst them.
Biological classification refers to the scientific procedure in which living organisms are classified and arranged into groups and sub-groups in a hierarchial manner on the basis of their similarities and dissimilarities.
● Aristotle was the earliest to attempt a scientific basis for classification. Later Linnaeus (1758) gave the two kingdom system of classification with Plantae and Animalia kingdoms.
● This system though used till very recently, but was unable to distinguish between the eukaryotes and prokaryotes, unicellular and multicellular organisms and photosynthetic (plants) and non-photosynthetic organisms (fungi).
● In 1969, RH Whittaker proposed a five kingdom system of classification. He divided all living organisms into Monera, Protista, Fungi, Plantae and Animalia
Earlier classification systems considered bacteria, BGA (Blue-Green Algae), fungi, mosses, ferns, gymnosperms and angiosperms as plants due to the presence of cell wall in them. This classification system placed prokaryotic bacteria and BGA with other eukaryotic groups.
● It also grouped unicellular and multicellular, organisms together, e.g. Chlamydomonas and Spirogyra (in algae).
● This system did not consider the differences in mode of nutrition and cell wall composition, so grouped fungi (heterotroph, chitinous cell wall) with plants (autotroph, cellulosic cell wall).
● Five kingdom classification considered such characteristics and segregated prokaryotic organism under Monera, unicellular eukaryotes in Protista (this united Chlamydomonas and Chlorella with Paramecium and Amoeba earlier placed in plants and animals, respectively).
Kingdom – Monera Eubacteria
● Bacteria are the sole members of this kingdom.
● Bacteria are the most abundant microorganisms occurring in air, water, soil as well as in extreme habitats like deserts, snow, hot springs, etc.
● Bacteria have been grouped under four categories based on their shape.
Bacteria show a wide range of mode of nutrition. They may be autotrophic (synthesise their own food from inorganic substrates), chemotrophic (photosynthetic autotrophic), saprophytic or heterotrophic (depend on other organisms for food).
Archaebacteria
● Archaebacteria live in extreme environmental conditions. These include
■ Halophiles Bacteria residing in salty areas, e.g. Halococcus.
■ Thermoacidophiles Bacteria residing in hot springs, e.g. Thermoproteus.
■ Methanogens Bacteria which survive in marshy areas (these are present in gut of many ruminant animals like cows and buffaloes), e.g. Methanococcus.
● Archaebacteria differ from other bacteria in having different cell wall structure. Their cell wall is made up of murein and contains high amount of unsaturated fatty acids, which is responsible for ensuring their survival in extreme conditions.
Eubacteria
Another class–Eubacteria is also known as ‘true bacteria’.
● These have rigid cell wall made up of peptidoglycan.
● They could be photosynthetic autotrophs, chemosynthetic autotrophs and heterotrophic bacteria.
● Photosynthetic autotrophs include blue-green algae, which have chlorophyll-a similar to green plants. They are also known as cyanobacteria.
● These could be unicellular, colonial or filamentous, freshwater/marine or terrestrial algae.
● Some bacteria can fix atmospheric nitrogen in specialised cells known as heterocyst, e.g. in Nostoc and Anabaena.
● Some bacteria utilise inorganic substances like nitrate, nitrite, ammonia, etc., for oxidation and release of energy for ATP production. These are known as chemosynthetic autotrophic bacteria.
● Heterotrophic bacteria (most abundant in nature) are dependent on other organisms for nutrition. These include N2-fixing bacteria, pathogens, etc.
● These reproduce asexually by binary fission. ● During unfavourable conditions, these form spores.
● These also show conjugation, a type of sexual reproduction in which DNA is transferred from one bacteria to another through a conjugal tube.
● Pleomorphic bacteria, which lack cell wall is known as mycoplasma. They are pathogenic and the smallest microorganism known.
Class 11 Biology Question Paper ( Session Ending Exam 2014 )
Chemical Coordination and Integration Class 11 Notes and Q&A
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Body Fluids And Circulation Class 11 Notes & Questions
Breathing and Exchange of Gases Class 11 Notes & Questions
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Respiration in Plants Class 11 Notes & Question and Answers
Photosynthesis in Higher Plants Class 11 Notes & Questions
Mineral Nutrition Class 11 Notes & Question Answers
Class 11 Biology Notes of Transport in Plants with Q&A
Cell Cycle and Cell Division Class 11 Notes & Questions
Biomolecules Class 11 Biology Notes with Question Answers
Cell The Unit of Life Class 11 Notes & Question Answers
Structural Organisation in Animals Class 11 Notes with Q&A
Class 11 Biology Notes of Morphology of Flowering Plants with Q&A
Class 11 Biology Notes Anatomy of Flowering Plants with Q&A
CBSE Class 11 Biology Notes of Animal Kingdom with Q&A
Plant Kingdom Class 11 Biology Notes & Question Answers
Class 11 Biology Notes Biological Classification with Q&A
The Living World Class 11 Biology Notes & Question Answers
Half Yearly Sample Papers for Class 11 Biology - 1
Half Yearly Sample Papers for Class 11 Biology - 2
Half Yearly Sample Papers for Class 11 Biology - 3
Half Yearly Sample Papers for Class 11 Biology - 4
Class 11 Biology Sample Question Paper of VBPS
Class 11 Biology Question Paper Annual Exam Apeejay
Biology Question Paper of Class 11 Apeejay School - 2018
Biology Question Paper of Class 11 Apeejay School - 2017
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Plant Growth and Development Important Questions Class 11
Plant kingdom includes all multicellular, eukaryotic, photosynthesising organisms, grouped as algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
● Plants were classified on the basis of different characters.
● The various systems used in classification of plants are
(i) Artificial system of classification It was given by Linnaeus and is based on morphological characters
(ii) Natural system of classification It was developed by Bentham and Hooker and based on natural affinities among the organisms. It was based on both external and internal features like anatomy, structure and embryology. It is the most common system of classification followed.
(iii) Phylogenetic system of classification It was given by Engler and Prantl and is based on evolutionary relationships of an organism. It is also known as Hutchinson’s system.
● Classification done on the basis of chemical constituents of plant is known as chemotaxonomy.
● Numerical taxonomy includes classification on the basis of observed characters.
● Cytotaxonomy is based on cytological information like chromosome number, structure, behaviour and types of chromosomes.
Algae
These are chlorophyll bearing, simple, thalloid, autotrophic and mostly aquatic organisms (both freshwater and marine water).
● These include unicellular forms like Chlamydomonas, colonial forms like Volvox, filamentous like Ulothrix and Spirogyra.
● Algae reproduce vegetatively by fragmentation and asexually by zoospores, aplanospores, akinetes, etc.
● Sexual reproduction in algae occurs through fusion of two gametes. These gametes could be
■ Isogamous Both gametes are similar in size and non-motile, e.g. Spirogyra.
■ Anisogamous Both gametes dissimilar in size, e.g. Chlamydomonas.
■ Oogamous Fusion between one large female gamete and a smaller motile male gamete, e.g.
Volvox and Fucus.
● Algae play an important role in carbon dioxide
fixation on earth through photosynthesis thereby increasing the level of O2 in the environment. They are chief primary producers.
● About 70 species of marine algae like Porphyra, Laminaria and Sargassum are used as food.
● Algae are used commercially for various products like
■ Algin from brown algae.
■ Carrageenan from red algae.
■ Agar from Gelidium and Gracilaria.
● Spirulina and Chlorella are used by space travellers as food supplements.
Classification of Algae
The algae are divided into three main classes which are as follows
Class–Chlorophyceae (Green Algae)
● Members of Chlorophyceae are unicellular, colonial or filamentous.
● They are green due to the presence of chlorophyll-a and b pigments localised in definite chloroplast.
● Shape of the chloroplast varies like discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped.
● Algae store food in the form of starch in specialised structures called pyrenoids located in chloroplast. Food may be stored in the form of oil droplets in some algae.
● Inner layer of cell wall is made up of cellulose, while outer layer is made up of pectose.
Vegetative reproduction occurs through fragmentation. Asexual reproduction is done by zoospores by zoosporangia.
● Sexual reproduction occurs through different modes like isogamous, anisogamous or oogamous, e.g. Volvox, Ulothrix, Spirogyra, Chlamydomonas and Chara.
Class–Phaeophyceae (Brown Algae)
● Members of Phaeophyceae are brown in colour due to the presence of fucoxanthin pigment.
● They range from simple branched, filamentous forms to profusely branched forms like kelps, which reach up to a height of 100 metres.
● They have gelatinous coating outside the cellulosic cell wall called algin.
● Cell contains chloroplast (plastid), centrally located vacuole and nucleus.
● Plant body is differentiated into holdfast (substratum), stripe (stalk) and frond (photosynthetic organ).
● Asexual reproduction occurs through biflagellate zoospores (having unequal laterally attached flagella).
● Sexual reproduction may be oogamous, isogamous or anisogamous. Union of gametes takes place in water within oogonium in case of oogamous species, e.g. Sargassum, Fucus, Ectocarpus, Dictyota and Laminaria.
Class–Rhodophyceae (Red Algae)
● Members of Rhodophyceae are red due to the
presence of pigment r-phycoerythrin. These are usually marine, occur close to the surface of water as well as in deep oceans.
● They reproduce vegetatively through fragmentation.
● They reproduce sexually and asexually through non-motile spores/gametes. Sexual reproduction is oogamous.
Animals are multicellular, heterotrophic, eukaryotes who exhibit different patterns of organisation of several types of cells.
Classification of Animals
Broadly kingdom–Animalia is classified as follows
I. Non-chordates
The non-chordates include the following phyla
1. Phylum–Porifera
● It includes sponges, which are usually marine
and mostly asymmetrical animals with canal system as most important feature.
● Central cavity present in sponges is known as spongocoel, it is lined by collar cells or choanocytes and it opens to outside by osculum.
● Water enters the spongocoel through minute pores called ostia and moves out through osculum.
● The body is supported by spicules or spongin and protein fibres, which form skeletal system.
● They are hermaphrodites, i.e. both male and female gametes are produced within same individual. Fertilisation is internal and development is indirect.
● Sponges reproduce asexually by fragmentation and sexually by gamete formation. Larval forms are morphologically distinct form adults, e.g. Sycon, Spongilla and Euspongia.
2. Phylum–Cnidaria (Coelenterata)
● It consists of aquatic, mostly marine, sessile, radially symmetrical animals having tissue level organisation.
● Tentacles are either present over the mouth or around their body edges. Cells called cnidoblasts or cnidocytes are present on the tentacles and the body. These cells are used for anchorage, defense and capture of prey.
● A central gastrovascular cavity (coelenteron) with a single opening, mouth on hypostome is present.
● Some cnidarians, e.g. corals, have skeleton composed of CaCO3.
● They show polymorphism with two basic body plans, i.e. polyps are fixed, sessile, cylindrical, e.g. Hydra, Adamsia, etc., and medusae are umbrella- shaped and free-swimming, e.g. Aurelia.
● The cnidarians exist in both forms and exhibit alternation of generation (metagenesis), i.e. polyps produce medusae asexually and medusae produce polyps sexually (e.g. Obelia).
3. Phylum–Ctenophora (Comb jellies or Sea walnuts)
● These are exclusively marine, diploblastic, radially symmetrical, acoelomate organisms with tissue level of organisation.
● Body is soft, transparent and gelatinous with well-marked bioluminescence (the property of a living organism to emit light).
● Eight external rows or ciliated comb plates help in locomotion.
● Digestion is both extracellular and intracellular.
● These are sexually reproducing, monoecious organisms with external fertilisation and indirect development, e.g. Ctenophora and Pleurobrachia.
4. Phylum–Platyhelminthes (Flatworms)
● These are dorsoventrally flattened, bilaterally symmetrical, triploblastic and acoelomate animals. They are mostly endoparasites and show organ level of organisation. Hooks and suckers are present in parasitic forms.
● They have specialised cells for excretion and osmoregulation called flame cells.
● They possess a high regeneration capacity. Fertilisation is internal and development is through many larval stages, e.g. Planaria, Taenia (tapeworm) and Fasciola (liver fluke).
5. Phylum–Aschelminthes (Roundworms)
● They are bilaterally symmetrical, triploblastic and pseudocoelomate animals with the body being circular in cross-section.
● They are free-living, aquatic, terrestrial or parasitic forms.
● They are dioecious (separate sexes) and show internal fertilisation with indirect/direct development. Females are often longer than males.
● Alimentary canal is complete with a well-developed muscular pharynx.
● Excretion is through excretory pore. Fertilisation is internal and development may be direct or indirect, e.g. Ascaris (roundworm), Wuchereria (filaria worm) and Ancylostoma (hookworm).
6. Phylum–Annelida (Segmented worms)
● They are triploblastic show organ level of body organisation and are bilaterally symmetrical.
● They show metameric segmentation, i.e. body surface is distinctly marked out into segments or metameres.
● Locomotion is aided by longitudinal and circular muscles. In Nereis, swimming is achieved by lateral appendages called parapodia.
● Respiration is through skin or gills, circulatory system is closed and digestive system is complete.
● Excretion and osmoregulation is through nephridia. Both dioecious, e.g. Nereis and monoecious forms, e.g. Pheretima (earthworm) and Hirudinaria (leech) occur. Neural system consists of paired ganglia connected by lateral nerves to a double ventral nerve cord.
● They reproduce sexually.
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