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Classification of phylum echinodermata.
1. Class Asteroidea : Body flat star-like, arms not sharply marked off from central disc, arms bear ambulacral grooves. Example : Asterias.
2. Class Ophiuroidea : Body flat star like, arms sharply marked off from central disc,. no ambulacral grooves. Example : Ophiothrix.
3. Class Echinoidea : Body globular or disc-like with ambulacral, no arms and ambulacral grooves. Examples : Echinus, Echinarachinus.
4. Class Holothuroidea : Body cylindrical with ambulacral areas no arms, or ambulacral grooves, no spines. Example : Cucumaria.
5. Class Crinoidea : Body fixed by cirri, arms branched with ciliated ambulacral grooves, no spines and madreporite. Example : Antedon.

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Classes of phylum arthropoda.
Class 1. Crustacea ; Predominantly aquatic, two body divisions (cephalothorax and abdomen), two pairs of antennae, each segment with a pair of biramous appendages, gills for respiration, green glands for excretion. Examples : Daphnia, Palaemon.
Class 2. Chilopoda : Body with two regions (head and trunk), one pair of antennae, each segment with one pair of legs, first pair of modified into poison claws, respiration by tracheae, excretion by malpighian tubules, terrestrial. Example : Scolopendra.

Class 3. Diplopoda : Body with three regions (head, thorax and abdomen), a single pair of antennae, legs one pair per thoracie segment and two pairs per abdominal segment, tracheae for respiration malpighian tubules for excretion, terrestrial. Example; Julus.
Class 4. Insecta : Body with three regions (head, thorax and abdomen), one pair of antennae, thorax with 3 pairs of legs and usually two or one pair of wings, tracheae for respiration, malpighian tubules for excretion, aquatic or terrestrial or parasitic. examples : Lepisma, Poecilocerus, Schistocerca.
Class 5.  Arachnida ; Body with two regions (cephalothorax and abdomen) or without regions, no antennae, mouth parts comprise chelicerae and pedipalpi, four parts of walking legs, respiration by tracheae orbook lungs or both, excretion by malpighian tubules or coxal glands or both, free-living or parasitic. examples: Palamnaeus

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Structure of  Chlamydomonas

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Examples of slime moulds :
1. Physasrum               2. Dictyostelium

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Characters of class Euglenophtya.
1. Flexible pellicle present.
2. Presence of chlorophyll 'a' and chlorophyll 'b' in the chloroplasts.
3. Locomotion with the help of flagellum.
Example : Euglena.
Characters of class Mastigophora.
1. Locomotion with the help of flagella.
2. Presence of tough pellicle as the   outermost protective covering.
3. Asexual reproduction by binary fission.
Example : Trypanosoma, Leishmania.
Characters of class Chrysophyta.
1. Coloured protists with chlorophyll 'a' and 'c' but chlorophyll 'b' absent.
2. Presence of silica or calcium in the cell wall.
3. Presence of two unequal sized flagella.
Example : Trieratium, Trinacria.

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Planktons. The planktons consisting of floating organisms which are regulated by direction of flow of water on the water surface are called planktons. They include plants and animals thus respectively called phyto and zooplanktons.
2. Nektons. This group of aquatic organisms include swimmers at any depth of water. They have well developed swimming organs.
3. Benthos. Organisms found along the bottom of the sea, river, pond or lake.

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Inter-relationship between various species.
Interactions among the species of a community are based on modes of obtaining food, shelter, and habits.
Interactions between two species may be positive, such as scavenging, commensalism, protocooperation, mutualism and plant animal interdepedence, or negative such as amensalism, competiton, parasitism and predation.
1. Symbiosis is an association of two species for obtaining food by one or both the partners.
2. Scavenging is a direct food relationship in which an animal feeds on a dead animal or an animal killed by another animal. Example : Feeding by vultures on carcases.
3. Commensalism is the relationship of two species of which the smaller one is benefited  and the larger one is unaffected. Example : suckerfish and shark.
4. Protocooperation is an association of two species both of which are benefited but cannot be equally well without association. Example : bird and crocodile.
5. Mutualism is an association of two species both of which are benefited but cannot live separately. Example : Termites and flagellates.
6. Amensalism is an interaction in which one species is harmed and the other remains unaffected. Example : Killing of bacteria by penicillin released by a mould Penicillium notatum.
7. Parasitism is an association of two species in which the smaller species is benefited and the larger one is harmed. Example : Tapeworm in human intestine.
8. Predation is a direct food relationship in which one organism captures and eats up another. Example ; Frog catches an insect. Predation may be used for biological control of pests.
9. Competition is an interaction between organisms for the life requirements  (nutrition, shelter, sunlight etc. ). It is of two types : intraspecific and interspecific. Efforts of a tiger and a leopard for a prey is an interspecific competition.
10. Mimicry is the resemblance of organisms with other organisms or with non-living objects in the form, colour and behaviour to escape predator's eye. Example : Resemblance of stick-insect with dry twig.

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Causes of water pollution.
1. Domestic effluents.
2. Sewage.
3. Industrial effluents
4. Agricultural effluents
5. Oil pollution.
Main effects of water pollution :
1. Compounds of mercury, arsenic and lead present in polluted water are poisonous.
2. Some compounds affect water treatment plants.
3. Organic sulpher compounds interfere with nitrificaton.
4. Inorganic nitrates and phosphates stimulate excessive plant growth in lakes and reservation.
5. Some residues left behind such as organo-chlorides as a result of  use of certain pesticides re highly persistent and pass through food chains.The pesticides result in the destruction of aquatic life.
6. Change in colour is very common effect. It is produced by the dyes, inorganic substances like chromium and iron compounds present in the discharges.
7. Soaps, detergents and alkalies form foam.
8. Fluoride contents of water causes fluorosis.
9. Eutropication in the lakes becomes a natural process.
10. Unpleasant odour is resulted due to presence of free chlorine, phenol, hydrogen sulphide, ammonia, algae and micro-organisms.
Control  of water pollution ;
Although water pollution can not be altogether prevented, measures can be taken to reduce it. These include the following :
1. Sewage disposal. The sewage should be disposed off into the agricultural fields instead of rivers or sea.
2. Treatment of sewage. It is one of the most important means to recover usuable water from the sewage by removing the pollutants. It requires three steps :-
(a) In the first step, the larger and suspended particles  are removed by simple physical methods such as   sedimentation and filtration.
(b) In the second step (secondary treatment) aeration is supplied to promote the bacterial decomposition of the organic matter followed by chlorination to kill the germs.
(c) finally in the third step, the salts like nitrates and phosphates are removed by precipitation technique which is expensive and difficult.
3. The water pollution through industrial effluents can be controlled by suitably treating it to remove the pollutants. The process requires different steps depending upon the nature of pollution. For example, acids and alkalies can be neutralized, the colloidal materials can be coagulated while the metallic salts can be precipitated.
4. Recycling of water.

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Consumer community of a pond ecosystem :
Consumers. (i) Primary consumers e.g. zooplanktons, microscopic  protozoans, (Paramecium, Amoeba, Euglena) insects, rotifers, crustaceans (Daphnia and Cyclops), mollusc and others.
(ii) Secondary consumers :  e.g. Unio, Pila, fishes, frogs and insects.
(iii) Top consumers (Tertiary consumers) e.g. large fishes, king fishers, crane, water snakes.

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Food web, in nature the food chains are not strictly linear, but are interrelated and interconnected with one another. Generally, the various food chains in a community are so inter linked as to form a sort of web. With the result, one animal may be a link in more than one food chain. A net work of food chains in a community are reffered to as food web. A food web may have all or some of the three types of food chains i.e, Detritus, predator and parasitic. The food webs become more complicated because of variability of taste and preference, availability and compulsion and several other factors at each level. For example, tigers normally do not eat fish or crab, but they are forced to feed on them in the Sundarbans.

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Co-operative relationships among organisms.
All species show various cooperative and competitive interactions among their members.
Cooperative interactions include :
1. Mating, a universal interaction among unisexual animals.
2. Parental care, shown by many animals for eggs and offspring.
3. Family formation, exhibited by monogamous (swans, wolves) and polygamous (seals, walruses, deer) animals.
4. Aggregations, some fish live in shoals, birds in flocks and mammals in herds for easy defence, food hunting, mate finding, learning and specialisation.
5. Dominance, subordination established by mock or real fight or specific displays.
6. Territoriality shown by many birds and mammals for breeding to ensure food for young ones, territorial boundaries are often marked and defended.
7. Altruism, in which a superior individual is defended by others at the risk of their life.
8. Societies, formed by bees, ants, wasps , and termites for division of labour.
9. Communication, among members by chemcial, tactile, visual or auditory signals. The chemicals used for communication are called pheromones.