Microbes In Human Welfare | Useful Microbes

Table of Contents

Useful Microbes – Microbes In Human Welfare

• • Antibiotics and Vaccination
  • Chemicals, Enzymes and other Bioactive Molecules
  • Milk to Curd
  • Microbes and Fermentation
  • Fermented Beverages
  • Microbes in sewage treatment
  • Microbes in production of biogas
  • Microbes as biocontrol agents
    • Biological control of pests and diseases
  • Microbes as biofertilisers
• Preservatives
• Summary

Useful Microbes – Microbes In Human Welfare: Microbes in the production of Antibiotics, Vaccines, Curd, Fermented beverages, Biogas, Biofertilisers etc.

Useful Microbes – Microbes In Human Welfare

• Microorganisms include bacteria, fungi, protozoa, some algae, viruses, viroids and also prions. Microorganisms may be single-celled like bacteria, some algae and protozoa, or multicellular, such as algae and fungi.
• Some microorganisms are harmful [pathogens] as they cause various diseases in humans. A list of common diseases caused by microorganisms are given in the previous post [Diseases Caused by Microorganisms].
• Some other microorganisms are beneficial and contribute to human welfare. This post is about such useful microorganisms [useful microbes].

Antibiotics and Vaccination

• Whenever you fall ill the doctor may give you some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms.
• These medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called ANTIBIOTICS.
• These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.
• In 1929, Alexander Fleming was working on a culture of disease-causing bacteria [Staphylococci]. Suddenly he found the spores of a little green mould [Penicillium notatum] in one of his culture plates. He observed that the presence of mould prevented the growth of bacteria. In fact, it also killed many of these bacteria. From this the mould penicillin was prepared.
• Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough, diphtheria and leprosy, which used to kill millions all over the globe. Today, we cannot imagine a world without antibiotics.
• Antibiotics taken unnecessarily may kill the beneficial bacteria in the body.
• Antibiotics, however, are not effective against cold and flu as these are caused by viruses.
• When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes. This is how a vaccine works.
• Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination. Edward Jennerdiscovered the vaccine for smallpox in 1798.

Chemicals, Enzymes and other Bioactive Molecules

• Microbes are also used for commercial and industrial production of certain chemicals like organic acids, alcohols and enzymes. Examples of acid producers are

1. Aspergillus niger (a fungus) of citric acid
2. Acetobacter aceti (a bacterium) of acetic acid
3. Clostridium butylicum (a bacterium) of butyric acid
4. Lactobacillus (a bacterium) of lactic acid.

• Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.
• Lipases are used in detergent formulations and are helpful in removing oily stains from the laundry.
• You must have noticed that bottled fruit juices bought from the market are clearer as compared to those made at home. This is because the bottled juices are clarified by the use of pectinases and proteases.
• Streptokinase produced by the bacterium Streptococcus and modified by genetic engineering is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infraction leading to heart attack.
• Another bioactive molecule, cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Tnchoderma polysporum.
• Statins produced by the yeast Monascus purpureus have been commercialized as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

Milk to Curd

• Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd.
• During growth, the LAB produce acids that coagulate and partially digest the milk proteins.

• A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing VITAMIN B12 [helps in the synthesis of DNA and RBC (red blood cells). Vitamin B12 deficiency causes Anemia, severe damage to nervous system etc.].
• In our stomach too, the LAB play very beneficial role in checking disease-causing microbes.

Microbes and Fermentation

• Sugar is converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation. Louis Pasteur discovered fermentation in 1857.
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• The dough, which is used for making foods such as dosa and idli is fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas which is released by the microbes.
• Similarly the dough, which is used for making bread, is fermented using baker’s yeast (Saccharomyces cerevisiae).
• A number of traditional drinks and foods are also made by fermentation by the microbes. ‘Toddy’, a traditional drink of some parts of southern India is made by fermenting sap from palms.
• Microbes are also used to ferment fish, soyabean and bamboo- shoots to make foods.
• Cheese, is one of the oldest food items in which microbes were used. The large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii.

Fermented Beverages

• Microbes especially yeasts have been used from time immemorial for the production of beverages like wine, beer, whisky, brandy or rum.
• For this purpose the same yeast Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, to produce ethanol.
• Depending on the type of the raw material used for fermentation and the type of processing (with or without distillation) different types of alcoholic drinks are obtained.
• Wine and beer are produced without distillation whereas whisky, brandy and rum are produced by distillation of the fermented broth.

Microbes in sewage treatment

• Sewage contains large amounts of organic matter and microbes. Many of which are pathogenic.
• Treatment of waste water is done by the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.
• The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures).
• While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (biochemical oxygen demand) of the effluent.
• BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.
• The sewage water is treated till the BOD is reduced. BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, more is its polluting potential.
• Once the BOD of sewage or waste water is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge.
• A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum or starter.
• The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge.
• During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as source of energy as it is inflammable.
• The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.

Microbes in production of biogas

• Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel.
• Certain bacteria, which grow anaerobicallyon cellulosic material, produce large amount of methane [greenhouse gas] along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment.
• These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Thus, the excreta (dung) of cattle, commonly called gobar, is rich in these bacteria. Dung can be used for generation of biogas, commonly called gobar gas. [Humans cannot digest cellulose. Hence their faecal waste cannot produce methane].

Microbes as biocontrol agents

• Biocontrol refers to the use of biological methods for controlling plant diseases and pests. Biological agents are a better alternative to weedicides and pesticides.

Biological control of pests and diseases

• In agriculture, there is a method of controlling pests that relies on natural predation rather than introduced chemicals.
• A key belief of the organic farmer is that biodiversity furthers health. The more variety a landscape has, the more sustainable it is. The organic farmer, therefore, works to create a system where the insects that are sometimes called pests are not eradicated, but instead are kept at manageable levels by a complex system of checks and balances within a living and vibrant ecosystem.
• Contrary to the ‘conventional’ farming practices which often use chemical methods to kill both useful and harmful life forms indiscriminately, this is a holistic approach that seeks to develop an understanding of the webs of interaction between the myriad of organisms that constitute the field fauna and flora.
• The organic farmer holds the view that the eradication of the creatures that are often described as pests is not only possible, but also undesirable, for without them the beneficial predatory and parasitic insects which depend upon them as food or hosts would not be able to survive. Thus, the use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides.
• An important part of the biological farming approach is to become familiar with the various life forms that inhabit the field, predators as well as pests, and also their life cycles, patterns of feeding and the habitats that they prefer. This will help develop appropriate means of biocontrol.
• The very familiar beetle with red and black markings – the Ladybird, and Dragonfliesare useful to get rid of aphids and mosquitoes, respectively.
• An example of microbial biocontrol agents that can be Introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt).
• These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leave other insects unharmed.
• Because of the development of methods of genetic engineering in the last decade or so, the scientists have introduced thuringiensistoxin genes into plants. Such plants are resistant to attack by insect pests. Bt-cotton is one such example, which is being cultivated in some states of our country.
• A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma. Trichoderma species are free-living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens.
• Baculoviruses are pathogens that attack insects and other arthropods. They have been shown to have no negative impacts on plants, mammals, birds, fish or even on non-target insects.

Microbes as biofertilisers

• Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungiand cyanobacteria.
• You may be knowing about the nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient.
• Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
• Fungi are also known to form symbiotic associations with plants (mycorrhiza). Many members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant.
• Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.
• Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatona, etc.
• In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility.

Preservatives

• Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.
• Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
• Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
• Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.
• Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 700 C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.

Summary

• Microbes are a very important component of life on earth. Not all microbes are pathogenic. Many microbes are very useful to human beings.
• We use microbes and microbially derived products almost every day.
• Bacteria called lactic acid bacteria (LAB) grow in milk to convert it into curd.
• The dough, which is used to make bread, is fermented by yeast called Saccharomyces cerevisiae.
• Certain dishes such as idli and dosa, are made from dough fermented by microbes.
• Bacteria and fungi are used to impart particular texture, taste and flavor to cheese.
• Microbes are used to produce industrial products like lactic acid, acetic acid and alcohol, which are used in a variety of processes in the industry.
• Antibiotics like penicillins produced by useful microbes are used to kill disease-causing harmful microbes.
• Antibiotics have played a major role in controlling infectious diseases like diphtheria, whooping cough and pneumonia.
• For more than a hundred years, microbes are being used to treat sewage (waste water) by the process of activated sludge formation and this helps in recycling of water in nature.
• Methanogens produce methane (biogas) while degrading plant waste.
• Biogas produced by microbes is used as a source of energy in rural areas.
• Microbes can also be used to kill harmful pests, a process called as biocontrol.
• The biocontrol measures help us to avoid heavy use of toxic pesticides for controlling pests

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BASIS OF CLASSIFICATION –

Levels of Organisation

1. Cellular level – cells are arranged as loose cell aggregates. Some division of labour (activities) occur among the cells. e.g., Sponges.
2. Tissue level – the cells performing the same function are arranged into tissues. e.g., coelenterates.
3. Organ level – tissues are grouped together to form organs, each specialized for a particular function. e.g., Platyhelminthes, ascheminthes.
4. Organ system level – organs are associated to form functional systems, each system concerned with a specific physiological function. e.g., Annelids, Arthropods, Molluscs, Echinoderms and Chordates.

Symmetry

1. Asymmetrical – any plane that passes through the centre does not divide body into equal halves. e.g., Sponges.
2. Radial symmetry – When any plane passing through the central axis of the body divides the organism into two identical halves. e.g., Coelenterates, ctenophores and echinoderms (adults only).
3. bilateral symmetry – the body can be divided into identical left and right halves in only one plane. e.g., Annelids, Arthropods, Molluscs, Echinoderms (larvae) and Chordates.

 germ layers

1. Diploblastic – Animals in which the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm. An undifferentiated layer, mesoglea, is present in between the ectoderm and the endoderm. e.g., Sponges, coelenterates.
2. Triploblastic – Animals in which the cells are arranged in three embryonic layers, an external ectoderm, an internal endoderm and middle mesoderm. e.g., Platyhelminthes, ascheminthes, Annelids, Arthropods, Molluscs, Echinoderms and Chordates.

 Coelom

The body cavity, which is lined by mesoderm on both sides is called coelom.

1. Acoelomates – animals in which the body cavity is absent. e.g., Sponges, coelenterates, platyhelminthes.
2. Pseudocoelomates – 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, g., aschelminthes
3. Coelomates – Animals possessing coelom are called coelomates, g., annelids, molluscs, arthropods, echinoderms, hemichordates and chordates.

 Segmentation

In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs. The body shows this pattern called metameric segmentation and the phenomenon is known as metamerism. e.g., in earthworm.

Notochord

Notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals.

1. Chordates – Animals with notochord in any stage of life. e.g., Fishes, Amphibians, Reptiles, Birds, Mammals etc.
2. Nonchordates – Those animals which do not form this structure are called non-chordates, e.g., Porifera to echinoderms.

 Digestive system

1. Incomplete digestive system – digestive system has only a single opening to the outside of the body that serves as both mouth and anus. e.g., Coelenterates, Platyhelminthes
2. Complete digestive system – digestive system has two openings, mouth and anus. e.g., aschelminthes to chordates.

Circulatory system

1. open type – Blood is pumped out of the heart and the cells and tissues are directly bathed in it or
2. closed type in which the blood is circulated through a series of vessels of varying diameters (arteries, veins and capillaries).

CLASSIFICATION OF ANIMALS

Phylum – Porifera (Sponges)

• Habitat – Aquatic – generally marine, some are fresh water.
• Symmetry – mostly asymmetric.
• Organization level – multicellular with cellular level of organisation.

• Canal system – Sponges have a water transport or canal system. Water enters through minute pores (ostia) in the body wall into a central cavity, spongocoel, from where it goes out through the osculum.

This pathway of water transport is helpful in food gathering, respiratory exchange and removal of waste.

• Special cells – Choanocytes or collar cells line the spongocoel and the canals. These cells are flagellated.
• Digestion – Intracellular.
• Skeleton – Made up of spicules or sponging fibres.
• Reproduction –    Bisexual or hermaphrodite animals.

Sponges reproduce asexually (fragmentation) and sexually.

• Fertilisation – Internal
• Development – Indirect having a larval stage which is morphologically distinct from the adult.
• Examples: Sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia (Bath sponge).

Phylum – Coelenterata (Cnidaria)

• Habitat – Aquatic, mostly marine, sessile or free-swimming,
• Symmetry – Radially symmetrical.

• Special cells – cnidoblasts or cnidocytes (which contain the stinging capsules or nematocytes) present on the tentacles and the body.

Cnidoblasts are used for anchorage, defense and for the capture of prey.

• Level of organization – tissue level of organisation and diploblastic.
• Body Cavity – Absent, central gastro-vascular cavity present with a single opening, hypostome.
• Digestion – both extracellular and intracellular.
• Skeleton – Some of the cnidarians – corals have a skeleton composed of calcium carbonate.
• Basic body forms – Cnidarians exhibit two basic body forms called polyp and medusa.

Polyp – It is a sessile and cylindrical form like Hydra, Adamsia, etc.

Medusa – it is umbrella-shaped and free-swimming like Aurelia or jelly fish.

• Alternation of generation (Metagenesis) – some cniderians exist in both polyp and medusa forms and exhibit alternation of generation (Metagenesis), i.e., polyps produce medusae asexually and medusae form the polyps sexually (e.g., Obelia).

• Examples: Hydra, Aurelia (Jelly fish), Obelia (Sea Fur), Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan) and Meandrina (Brain coral).

Phylum – Ctenophora (Sea walnuts or Comb jellies)

• Habitat – Exclusively marine.
• Symmetry – radially symmetrical.
• Level of organization – tissue level of organization and diploblastic.
• Special organ – eight external rows of ciliated comb plates, which help in locomotion.
• Digestion – both extracellular and intracellular.
• Special property – Bioluminescence (the property of a living organism to emit light).
• Reproduction – Bisexual animals (Hermaphrodites).

                              Only sexual reproduction.

• Fertilisation – external.
• Development – indirect development.
• Examples: Pleurobrachia and Ctenoplana.

Phylum – Platyhelminthes

• Body shape – They have dorso-ventrally flattened body, hence are called flatworms.
• Habitat – Mostly endoparasites found in animals.
• Symmetry – bilaterally symmetrical.
• Body organization – organ level of organisation and triploblastic.
• Body cavity – Absent, acoelomates.
• Special structures – Hooks and suckers are present in the parasitic forms for support and absorption. Some of them absorb nutrients from the host directly through their body surface.
• Excretory cells – flame cells help in osmoregulation and excretion.
• Reproduction – Bisexual animals (Hermaphrodites).
• Fertilisation – Internal.
• Development – Indirect through many larval stages.
• Some members like Planaria possess high regeneration capacity.
• Examples: Taenia (Tapeworm), Fasciola (Liver fluke), Planaria.

 Phylum – Aschelminthes

• Body shape – Circular in cross-section, hence, the name roundworms.
• Habitat – They may be free living, aquatic and terrestrial or parasitic in plants and animals.
• Level of organization – organ-system level of body organization and triploblastic.
• Symmetry – bilaterally symmetrical.
• Body Cavity – Pseudocoelomate animals.
• Digestive system – Alimentary canal is complete with a well developed muscular pharynx.
• Excretion – An excretory tube removes body wastes from the body cavity through the excretory pore.
• Reproduction – unisexual or dioecious. Also show sexual dimorphism (females are longer than males)
• Fertilisation – internal.
• Development – direct (the young ones resemble the adult) or indirect (larvae is present).
• Examples: Ascaris (Round Worm), Wuchereria (Filaria worm), Ancylostoma (Hookworm).

Phylum – Annelida

• Their body surface is distinctly marked out into segments or metameres (Latin, annulus : little ring) and, hence, the phylum name Annelida.
• Habitat – aquatic (marine and fresh water) or terrestrial; free-living, and sometimes parasitic.
• Level of organization – organ-system level and triploblastic animals.
• Symmetry – bilateral symmetry.
• Body cavity – present and coelomates.
• Locomotory organ – Body wall which has longitudinal and circular muscles. Aquatic annelids like Nereis possess lateral appendages, parapodia (for swimming).
• Circulatory system – closed circulatory system.
• Excretory organ – Nephridia which help in osmoregulation and excretion.
• Nervous system – consists of paired ganglia connected by lateral nerves to a double ventral nerve cord.
• Reproduction – some are unisexual or dioecious (Nereis) and some are bisexual or monoecious (earthworms and leeches). Reproduces sexually.
• Examples: Nereis, Pheretima (Earthworm) and Hirudinaria (Blood sucking leech).

Phylum – Arthropoda

• This is the largest phylum of Animalia which includes insects.
• Level of organization – organ-system level of organisation.
• Symmetry, body cavity – bilaterally symmetrical, triploblastic, segmented and coelomate animals.
• Skeleton – exoskeleton made up of chitin.
• Body division – The body consists of head, thorax and abdomen.
• Locomotion – by jointed appendages (arthros-joint, poda-appendages), hence name arthropoda.
• Respiration – by gills, book gills, book lungs or tracheal system.
• Circulatory system – open type.
• Sensory organs – antennae, eyes (compound and simple), statocysts or balance organs are present.
• Excretion – through malpighian tubules.
• Reproduction – mostly dioecious animals.
• Fertilisation – usually internal. They are mostly oviparous.
• Development – direct or indirect.
• Examples:

Economically important insects    –    Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect)

Vectors                                     –    Anopheles, Culex and Aedes (Mosquitoes)

Gregarious pest                          –    Locusta (Locust)

Living fossil                              –    Limulus (King crab).

Phylum – Mollusca

• This is the second largest animal phylum.
• Habitat – terrestrial or aquatic (marine or fresh water).
• Symmetry, coelom – bilaterally symmetrical, triploblastic and coelomate animals.
• Body division – Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump.
• Special structure – A soft and spongy layer of skin forms a mantle over the visceral hump.
• Respiration and excretion – The space between the hump and the mantle is called the mantle cavity in which feather like gills are present. They have respiratory and excretory functions.
• Sense organs – The anterior head region has sensory tentacles.
• Feeding organ – The mouth contains a file-like rasping organ for feeding, called radula.
• Reproduction and development – usually dioecious and oviparous with indirect development.
• Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Seahare), Dentalium (Tusk shell) and Chaetopleura (Chiton).

Phylum – Echinodermata

• These animals have an endoskeleton of calcareous ossicles and, hence, the name Echinodermata (Spiny bodied).
• Habitat – All are marine.
• Symmetry – The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.
• Digestive system – complete with mouth on the lower (ventral) side and anus on the upper (dorsal) side.
• Water vascular system – distinctive feature. Helps in locomotion, capture and transport of food and respiration.
• Excretory system – absent.
• Reproduction – Dioecious animals ,  Reproduction is sexual.
• Fertilisation – usually external.
• Development – indirect with free-swimming larva.
• Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber) and Ophiura (Brittle star).

Phylum – Hemichordata

• Earlier considered as a sub-phylum under phylum Chordata, but now it is placed as a separate phylum under non-chordata.
• Habitat – consists of a small group of worm-like marine animals.
• Level of organization, symmetry, body cavity –organ-system level of organization, bilaterally symmetrical, triploblastic and coelomate animals.
• Body shape and division – The body is cylindrical and is composed of an anterior proboscis, a collar and a long trunk.
• Circulatory system – Open type.
• Respiration – through gills.
• Excretory organ – proboscis gland.
• Reproduction, fertilisation, development –Diocious animals, external Fertilisation, indirect Development.
• Examples: Balanoglossus and Saccoglossus.

 

Phylum – Chordata

• Characteristic features –

a notochord,

a dorsal hollow nerve cord

paired pharyngeal gill slits

post anal tail

closed circulatory system

• Symmetry, body cavity, level of organization –These are bilaterally symmetrical, triploblastic, coelomate with organ-system level of organisation.
• Phylum Chordata is divided into three subphyla : Urochordata or Tunicata, Cephalochordata and Vertebrata.
• Subphyla Urochordata and Cephalochordata are often referred to as protochordates.

Subphylum – Urochordata

• Exclusively marine.
• notochord is present only in larval tail,
• Examples: Ascidia, Salpa ,Doliolum.

Subphylum – Cephalochordata

• Notochord extends from head to tail region and is persistent throughout their life.
• Example: Branchiostoma (Amphioxus or Lancelet).

Subphylum – Vertebrata

• Possess notochord during the embryonic period.
• The notochord is replaced by a cartilaginous or bony vertebral column in the adult.
• Thus all vertebrates are chordates but all chordates are not vertebrates.
• Vertebrates have a ventral muscular heart with two, three or four chambers, kidneys for excretion and osmoregulation and paired appendages which may be fins or limbs.

TABLE: Comparison of Chordates and Non- chordates
Chordates	Non-chordates
Notochord present	Notochord absent
Central nervous system is dorsal	Central nervous system is ventral, solid, hollow and single. and double
Pharynx perforated by gill slits	Gill slits are absent
Heart is ventral	Heart is dorsal (if present).
A post-anal part (tail) is present.	Post-anal tail is absent.

  Classification of Vertebrata –

Class – Cyclostomata

• Habitat – ectoparasites on some fishes. Body shape – elongated body
• Respiration – 6-15 pairs of gill slits.
• Mouth – Cyclostomes have a sucking and circular mouth without jaws.
• Scales and paired fins are absent.
• Cranium and vertebral column are cartilaginous.
• Circulation is of closed type.
• Marine but migrate to fresh water for spawning. After spawning, within a few days, they die. Their larvae, after metamorphosis, return to the ocean.
• Examples: Petromyzon (Lamprey) and Myxine (Hagfish).

Class – Chondricthyes

• marine animals.
• Their body is streamlined and they have cartilaginous endoskeleton.
• Mouth is located ventrally.
• Notochord is persistent throughout life.
• Gill slits are separate and without operculum (gill cover).
• The skin is tough, containing minute placoid scales.
• Teeth are modified placoid scales which are backwardly directed.
• Their jaws are very powerful. These animals are predaceous.
• Due to the absence of air bladder, they have to swim constantly to avoid sinking.
• Heart is two-chambered (one auricle and one ventricle).
• Some of them have electric organs (e.g., Torpedo) and some possess poison sting (e.g., Trygon).
• They are cold-blooded (poikilothermous) animals, i.e., they lack the capacity to regulate their body temperature.
• Sexes are separate. In males pelvic fins bear claspers. They have internal fertilisation and many of them are viviparous.
• Examples: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray), Torpedo (electric ray).

Class – Osteichtyes

• Both marine and fresh water fishes
• Their body is streamlined and they have bony endoskeleton skeleton.
• Mouth is mostly terminal.
• They have four pairs of gills which are covered by an operculum on each side.
• Skin is covered with cycloid/ctenoid scales.
• Air bladder is present which regulates buoyancy.
• Heart is two chambered (one auricle and one ventricle).
• They are cold-blooded animals.
• Sexes are separate. Fertilisation is usually external. They are mostly oviparous and development is direct.
• Examples:

Marine              –    Exocoetus (Flying fish), Hippocampus (Sea horse);

Freshwater         –    Labeo (Rohu), Catla (Katla), Clarias (Magur);

Aquarium          –    Betta (Fighting fish), Pterophyllum (Angel fish).

Class – Amphibia

• amphibians can live in aquatic as well as terrestrial habitats.
• Most of them have two pairs of limbs.
• Body is divisible into head and trunk. Tail may be present in some.
• The amphibian skin is moist (without scales).
• The eyes have eyelids.
• A tympanum represents the ear.
• Alimentary canal, urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior.
• Respiration is by gills, lungs and through skin.
• The heart is three chambered (two auricles and one ventricle).
• These are cold-blooded animals.
• Sexes are separate. Fertilisation is external. They are oviparous and development is direct or indirect.
• Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Ichthyophis (Limbless amphibia).

Class – Reptilia

• Locomotion is creeping or crawling.
• mostly terrestrial animals.
• body is covered by dry and cornified skin, epidermal scales or scutes
• They do not have external ear openings. Tympanum represents ear.
• Limbs, when present, are two pairs.
• Heart is usually three-chambered, but four-chambered in crocodiles.
• Reptiles are poikilotherms.
• Snakes and lizards shed their scales as skin cast.
• Sexes are separate. Fertilisation is internal. They are oviparous and development is direct.
• Examples: Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator). Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra), Bangarus (Krait), Vipera (Viper).

Class – Aves

• The characteristic features are the presence of feathers and most of them can fly except flightless birds (e.g., Ostrich).
• They possess beak.
• The forelimbs are modified into wings.
• The hind limbs generally have scales and are modified for walking, swimming or clasping the tree branches.
• Skin is dry without glands except the oil gland at the base of the tail.
• Endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities (pneumatic).
• The digestive tract of birds has additional chambers, the crop and gizzard.
• Heart is completely four chambered.
• They are warm-blooded (homoiothermous) animals, i.e., they are able to maintain a constant body temperature.
• Respiration is by lungs. Air sacs connected to lungs supplement respiration.
• Sexes are separate. Fertilisation is internal. They are oviparous and development is direct.
• Examples : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).

Class – Mammalia

• They are found in a variety of habitats – polarice caps, deserts, mountains, forests, grasslands and dark caves.
• Some of them have adapted to fly or live in water.
• The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which the young ones are nourished.
• They have two pairs of limbs, adapted for walking, running, climbing, burrowing, swimming or flying.
• The skin of mammals is unique in possessing hair.
• External ears or pinnae are present.
• Different types of teeth are present in the jaw.
• Heart is four chambered.
• They are homoiothermous.
• Respiration is by lungs.
• Sexes are separate and fertilisation is internal.
• They are viviparous with few exceptions and development is direct.
• Examples:

Oviparous – Ornithorhynchus (Platypus);

Viviparous – Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Macaca (Monkey), Rattus (Rat), Canis (Dog), Felis (Cat), Elephas (Elephant), Equus (Horse), Delphinus (Common dolphin), Balaenoptera (Blue whale), Panthera tigris (Tiger), Panthera leo (Lion).

Table : Salient features of different phyla of Animal kingdom
Phylum	Level of Organi­sation	Symme­try	Coelom	Segmen­tation	Digestive System	Circulatory System	Respiratory System	Distinctive Features
Porifera	Cellular	Many	Absent	Absent	Absent	Absent	Absent	Body with pores and Canals In walls.
Coelenterata (Cnidaria)	Tissue	Radial	Absent	Absent	Incomplete	Absent	Absent	Cnidoblasts present
Ctenophora	Tissue	Radial	Absent	Absent	Incomplete	Absent	Absent	Comb plates for locomotion.
Platyhelminthes	Organ & Organ-system	Bilateral	Absent	Absent	Incomplete	Absent	Absent	Flat body, suckers.
Aschelminthes	Organ- system	Bilateral	Pseudo coelomate	Absent	Complete	Absent	Absent	Often worm shaped, elongated.
Annelida	Organ- system	Bilateral	Coelomate	Present	Complete	Present	Present	Body segment ation like rings.
Arthropoda	Organ- system	Bilateral	Coelomate	Present	Complete	Present	Present	Exoskeleton of cu­ticle, jointed ap­pendages.
Mollusca	Organ- system	Bilateral	Coelomate	Absent	Complete	Present	Present	External skeleton shell usually present.
Echinodermata	Organ- system	Radial	Coelomate	Absent	Complete	Present	Present	Water vascular system, radial symmetry.
Heml-chordata	Organ- system	Bilateral	Coelornate	Absent	Complete	Present	Present	Worm-like with proboscis, collar and trunk.
Chordata	Organ- system	Bilateral	Coelomate	Present	Complete	Present	Present	Notochord, dorsal hollow nerve cord, gill slits with limbs or fins.