Blood: plasma and formed element

 Blood 

Blood performs several vital functions of the blood; hence it has been frequently referred to as the seat of the soul. It distributes nutrients, oxygen, detoxicating compounds, and maintains a uniforms body temperature. It is a carrier of hormones which control and integrate the activities of the various organs. It conveys antibodies and cells that protect the body from invading pathogens and also transport drugs administered to the body so that they may produce their therapeutic effects on specific sites of ailment. 

The blood also collects the waste material generated by the body's metabolic activities. The blood can carry out its functions efficiently only if it is kept circulating in the body. This is affected by the heart which acts as a pump, and an intricate system of distributing pipes the blood vessels, viz, arteries, veins and capillaries. The heart and the blood vessels together form the cardio-vascular system.

Blood as a fluid Tissue: -

In human beings there is about 90 ml of blood per kilogram of body weight. However, this volume depends on the age and health of the Individual. Blood has a specific gravity of 1.05 to 1.06, and a pH of 7.4. It is made up of a fluid matrix called Plasma, and several types of cells termed formed elements. These two components separate when blood is centrifuged. The plasma forms 54% of the blood volume and the cells 45%. The latter is reffered to as the hematocrit or packed cell volume(PCV). The plasma contains many inorganic and organic substances. The formed elements consist of red blood cells(RBC) or erythrocytes, white blood cells(WBC) or leucocytes, and platelets or thrombocytes.

PLASMA

Blood plasma is the straw colored fluid obtained when all formed element are removed from blood. The ratio of plasma to formed elements is held relatively constant by the homeostatic controls of the body. The plasma contains inorganic salts with a dominance of chloride (Cl), sodium (Na+), and calcium (Ca++) ions, and lesser quantities of potassium(K+) and magnesium (Mg++) ions. Smaller concentrations of bicarbonate, sulphate, and phosphate, and traces of iron, copper, and iodine are also present.

The Plasma also contain glucose which is used as a principal energy source in cellular metabolism. A variety of other substances, such as amino acid, vitamins, lipids (neutral fats and cholesterol), hormones, urea, uric acid, and other metabolite waste produces are also present in the plasma. In addition, it contains dissolved oxygen, carbon dioxide, and nitrogen. Plasma also reflects certain abnormal conditions occurring in cells and tissue of the body. For example, within few hours following a heart attack, there is a noticeable increase in the level of the enzymes transaminase and lactic dehydrogenase in the plasma arising from the affected heart muscles. This has proved to be of significant value to a clinician is the diagnosis of heart attacks.

The plasma of a man contains about 70g proteins/L. Some of these proteins possess enzymic activity (e.g., phosphatases), While other function shows no activity at all. The function of the plasma proteins can be summarized as follow: -

1. Lipoproteins carry lipids and also transport lipid soluble vitamins and steroids hormones.
2. They are amphoteric compound because they act both as acids and bases. At the pH of human blood (pH- 7.4) proteins behave as acids and combines with cations such as Na+ and form a buffer, they are however, weak buffers.
3. Being macromolecules plasma proteins create a colloidal osmotic pressure in the blood which is higher than the colloidal osmotic pressure in the blood which is higher than the colloidal osmotic pressure in the interstitial fluid. This favors the passage of interstitial fluid into the plasma Finally (4) plasma, proteins, prothrombin and fibrinogen participate in blood clotting. 

FORMED ELEMENT 

The formed elements consist of the erythrocytes, leucocytes, and the thrombocytes.

ERYTHROCYTES: -

The red blood cells or erythrocytes are small (diameter: -7.5 in man and 9.0 in elephant) biconcave dices. Mammalian erythrocyte, except for the camel does mot possess a nucleus. In contrast, other vertebrates possess a nucleus. The erythrocytes are immobile and move with the flow of blood stream. The average concentration of erythrocytes is approximately 5000000/mm3 of blood in the adult human female. The erythrocytes are reddish in colour due to the presence of a respiratory pigment hemoglobin. Each erythrocyte contains an estimated 200 to 300 million molecules of hemoglobin. The latter serves to transport oxygen and, do some extent carbon dioxide, to and form the lungs. Hemoglobin is easily removed when the cell is broken (or lysed) by exposure to a hypotonic medium, or water. the resulting structure of the erythrocyte is called a "ghost" which consists of a network of protein and lipids.

The average life span of an erythrocyte in man is about 120days the old erythrocytes are continuously breaking down and new once are formed. The erythrocytes are destroyed by the phagocytic macrophages found in the reticulo-endothelial system (in bone marrow, spleen, liver, etc.). The porphyrin section of the hemoglobin is catabolized and formed bile pigment (bilirubin and biliverdin). However, most of the iron is retained in the bone marrow to be again incorporated into new erythrocytes.

LEUCOCYTES: -

The leucocytes are nucleated cells and are somewhat larger than the erythrocytes the white blood cells are also less abundant than the red blood cells. There are 5000 to 9000 leucocytes/mm3 of blood. An increase in the number of leucocytes above 10000/mm3 of blood is known as leukocytosis is caused by violent exercise, infection, hemorrhage, and a high protein diet. Leucopenia results from malnutrition, deficiency of vitamin B12, folic acid, and pyridoxine. 

The leucocytes are classified into granulocytes and agranulocytes depending on the presence or absence of granules in the cytoplasm.

Granulocytes are divided into three basic types, viz., neutrophils, eosinophils, and basophils. This classification of the granulocytes is based on the nuclear structure and affinity of the cytoplasmic granules to dyes (acid or base). In the neutrophils the cytoplasm is filled with fine uniformly distributed granules which do not show any affinity to either acid or basic dyes, and hence the name neutrophil. The nucleus is polymorphic divided unequally in 3-5 lobes and separated by deep indentations or by narrow strands of chromatin, therefore neutrophils are also referred to as polymorphocytes. These form 65-75% of the total leucocytes. The size of each neutrophil range from 10-12u. The eosinophils are loaded with granules which are relatively bigger in size than in the neutrophils. The granules show affinity to the acid dyes such as eosin the latter imparts them an intense red colour, and hence the name eosinophils. These are also referred to as acidophils. The nucleus is bilobed and the two lobes are connected by a thin stand of chromatin. The eosinophils form 2-4% of the total number of leucocytes. In the basophil, the cytoplasm takes an intense blue colored with basic dyes. The nucleus in the basophil is irregularly polymorphic. The basophils have the least representation in the total leucocyte count the normal percentage is only 0.15.

Agranulocytes are of two types, viz, lymphocytes and monocytes. The structure of the nucleus of agranulocytes is not polymorphic and is therefore, different form that of the granulocytes. Lymphocytes fall into two categories- small and large lymphocytes. The nucleus of the small lymphocyte is larger and it almost occupied the entire cell leaving only a peripheral cytoplasm, whereas the largest lymphocytes have relatively more cytoplasm. The lymphocytes form the second largest group of leucocytes; the small lymphocytes constitute about 25% and largest lymphocytes about 3% of the total leucocytes. The size of the small lymphocyte is about 7u, Whereas it is 10-12u in the large lymphocytes.

In monocytes the cytoplasm is more abundant in relation to the nucleus; the nucleus is ovoid, kidney shaped or with  many indentations. Moreover, characteristically, the nucleus is always placed eccentrically in the cells. The monocytes form 5-7% of total leucocytes. There size range from 10-15u. 

The average life span of leucocytes is two days. All leucocytes defend the body against invasion by microorganism which are engulfed and digested by the leucocytes by a process known as phagocytosis. Additionally, the lymphocytes form antibodies against proteinaceous matter gaining entry into the body. The relative ratio of the leucocytes changes during many diseases. This phenomenon is of great use to pathologists in diagnosis of diseases. For example, the concentration of eosinophils increases significantly during infection by worms, and in allergic conditions such as asthma and hay fever. 

Leukemia is very serious disorder of the body. This is a form of blood cancer and is characterized by an uncontrolled increase in the number of leucocytes (up to 1000000/mm3 of blood), with the appearance of immature forms in the blood stream. Leukemia is accompanied by anemia and is eventually fatal because the bone marrow cells that normally produce erythrocytes are displaced by leukemia cells. 

Thrombocytes or platelets: - In addition to the erythrocytes and the leucocytes, thrombocytes or platelets are another group of a formed the leucocytes, thrombocytes or platelets are another group of formed elements observed in the blood. These are small fragments (2-5u) of cells which lake nuclei, and function in blood clotting. They are oval in shape and have the capability of amoeboid movements. There are 250000 platelets/mm3  of blood. The life span of the thrombocytes is also very short perhaps only a few days in duration.

population| types| function| definition| structure| curve| commensalism| mutualism| Amensalism|

Population

It can be defined as the total number of individuals of a species in a specific geographical area, which can interbreed under natural conditions to produce fertile offspring and function as a unit of biotic community. 

Population Ecology 

It is an important area of ecology as it links ecology to the population genetics and evolution.

Population Attributes 

These are certain characteristics of a population. Some of them are as follows:

Population Size or Density 

It is the number of individuals of a species per unit area or volume at a given time.

Population Density: -

Death Rate or Mortality 

• It is expressed as the number of deaths per 1000 individuals of a population per year, e.g. if 4 individuals in a population of 40 fruit flies died during a specified time interval (say a week). 
• Death rate= 4/40 = 0.1 (individual per fruit fly per week)

Sex Ratio 

• It is expressed as the number of females and males per 1000 individuals of a population in a given time, e.g., 60% females and 40% males in population. 

Age Pyramid 

1. When the age distribution (per cent individuals of a given age or age group) is plotted for the population in which. pre-reproductive age is at base, reproductive is in middle and post-reproductive is at top, we get a pyramid called age pyramid.
2. The shape of the pyramids reflects the growth status of the population that whether it is expanding (triangular-shaped), stable (bell-shaped) or declining (Urn-shaped).

   

   Fig: - Representation of age pyramids for human population
   
   
   

Population Growth: -

• The size of a population for any species is   not a static parameter. 
• It keeps changing with time, depending on various factors including food availability, predation, pressure and adverse weather conditions.
• The density of a population in a given habitat during a given period fluctuates due to changes in four basic processes:

(a) Natality is the number of births during a given period in the population that are added to the initial density.

(b) Mortality is the number of deaths in the population during a given period.

(c) Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration. 

(d) Emigration is the number of individuals of the population who left the habitat and  moved elsewhere during a given time Period. 

Figure: -Factors influencing population density

Note: - Natality and immigration contribute to an increase in population density and mortality and emigration contributes to a decrease.

• Population density can be given by the following equation 

          N1+1 = N1 + [(B + I) - (D + E)] this is density at time t + 1.

Where, N = population density, t = Time,

       B = Birth rate,I = Immigration, D = Death rate, E = Emmigration, N1 = Population in beginning.

The equation demonstrates that the population density will increase, if the number of births plus the number of immigrants (B + I) is more than the number of deaths plus the number of emigrants (D + E), otherwise it will decrease. 

• Although total number is the most appropriate measure of population density. In some cases, it is difficult to determine. So, in these cases, the per cent cover or biomass is a more appropriate measure of the population size, e.g. 200 Parthenium plants and a single huge banyan tree. In this case, the banyan tree produces much more biomass. 
• Total number is not an appropriate measure in case of huge population size. In such case, relative densities are used. For example, the number of fishes caught per trap is a good measure of its total population density in the lake. It is an indirect method to estimate population size.
• In some cases, population size is estimated indirectly. Without actually counting or seeing them, e.g. the tiger census is based on pug marks and faecal pellets.
• Growth curves of population are of the following types: -

(a) Exponential growth (A-curve) occurs normally when resources, i.e., food and space are unlimited. 

• Equation for exponential growth can be represented as follows: -

dN/dt = (b-d) N

let (b-d) = r, then 

dN/dt = rN

Where,

N = Population size,

Nt = Population density after time t

N.= Population density at time zero, 

r = Intrinsic rate of natural increase

e = Base of natural logarithms (2.71828), 

b = Birth rate and 

d = Death rate

Fig: - Population growth curve, A- when responses are limiting the growth, plot is exponential,
B- when responses are limiting the growth, plot is logistic, K- is carrying capacity.

• r is an important parameter assessing impacts of any biotic or abiotic factor on population growth.
• In exponential growth, when N in relation to time (t) is plotted on graph, the curve becomes J-shaped as shown in graph. 

(b) Logistic growth (B-curve) occurs when resources become limited at certain point of time, so no population can grow exponentially. 

• Due to competition between individuals for limited resources, the fittest individual will survive and reproduce. 
• In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. This is called carrying capacity (K) of a habitat.
• A population growing in a habitat with limited resources shows initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote, when the population density reaches the carrying capacity. 
• The logistic growth shows sigmoid curve and this is also called Verhulst-Pearl logistic growth. 
• The logistic growth model is considered more realistic since, resources for groWth of most animal populations are finite and become limited sooner or later.

Life History Variation 

(i) Darwinian fitness (high r value) states that the Populations evolve to maximize their reproductive fitness in the habitat in which they live. 

(ii) Under a particular set of selection pressures, organisn1s evolve towards the most efficient reproductive strategy.

(iii) The rate of breeding varies from species to species, e.g. Pacific salmon fish and bamboo breed only once in their lifetime, while most birds and mammals breed many times in their life.

(iv) Some organisms produce a large number of small-sized offspring (oysters, pelagic fishes), while birds and mammals produce a small number of large-sized offspring.

(v) Ecologists suggest that life history traits of organisms have evolved in relation to the constraints imposed by the abiotic and biotic components of the habitat in which they live.

Population Interactions

Population interactions explain that in nature, animals, plants and microbes cannot live in an isolation but interact in various ways to form a biological community.

(i) Interspecific interactions arise from the interaction of populations of two different species. 

(ii) This interaction may be 

(a) Beneficial/positive (+) 

(b) Detrimental/harmful (-) 

(c) Neutral (neither harm nor benefit) to one of the species or both (O) 

Population Interactions

Some of the population interactions are as follows: -

Predation: -

It is an interspecific interaction, where an animal called predator kills and consumes the other weaker animal called prey. This is a biological control method.

(i) It is the nature's way of transferring energy to higher trophic levels, which is fixed by plants, e.g. tiger eating a deer, sparrow eating seeds, etc. 

(ii) Important roles of predators are: - 

• They keep prey population under control. 
• They help in maintaining species diversity in a community by reducing the intensity of competition among prey species. For example, in American Pacific coast, the star fish Pisaster is an important predator. When all the fishes were removed from an area more than 10 species of invertebrates became extinct within a year due to in Ter specific competition.
• In the absence of predators, prey species could achieve very high population densities and cause instability. So, besides acting as 'conduits' for energy transfer across trophic levels, predators play very important role to provide population stability.

(iii)When certain exotic species are introduced into a geographical area, they become invasive and start spreading fast because the invaded land does not have natural predators, e.g. prickly pear cactus introduced in Australia (1920s) caused havoc by spreading rapidly over a large area. It was controlled only after a cactus feeding predator (a moth) was brought from its natural habitat. 

(iv) If a predator is too efficient and over exploits its prey, then the prey might become extinct. Following it, the predator will also become extinct because of the lack of food.

(v) Prey species have evolved various defense mechanisms to lesser the impact of predation. Some of them are: -

• Some species of insects and frogs are cryptically colored (camouflaged) to avoid being detected easily by the predator. Some are poisonous and therefore, avoided by the predator.
• Phytophagous insects like Monarch butterfly is highly distasteful to its. predators (birds) because of a special chemical present in its body. The . butterfly acquires this chemical dunng its caterpillar stage by f ceding on a poisonous plant (weed). 
• Some plants have thorns or spines fo r defence mechanism, e.g. Acacia, cactus. 
• Some plants produce highly poisonous chemicals like cardiac glycosides, nicotine, caffeine, quinine, strychnine, opium, etc. These are actually defence mechanisms against grazers and browsers. e.g. Calotropis. These chemicals make the herbivore sick when th ey are eaten, inhibit digestion, disrupt reproduction or even kill them.

Competition: -

It is a type of interaction, where both the species suffer. It occurs when species (closely related or even unrelated), compete for the same resources that are limited, e.g. in some shallow South American lakes visiting flamingoes and resident fishes compete for their common food, i.e. Zooplanktons. In other words, it can be defined as a process in which the fitness of one species (measured in terms of its 'r' the intrinsic rate of increase) is lower in the presence of another species. 

(i) It may be 

• Intraspecific (within same species). 
• Interspecific (between different species).

(ii) In interference/interspecific competition the feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of other species, although the resources (food and space) are plenty. 

(iii) Competitive release is a phenomenon. in which a species whose distribution is restricted to a small geographical area because of the presence of competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally · removed. 

(iv) Connels' elegant field experiments showed that on the rocky seacoasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area and excludes the smaller barnacle Chatha malus from that zone. 

(v) Gause's competitive exclusion principle states that two closely related species competing for the Sarne resources cannot coexist indefinitely and the competitively inferior one will be eliminated eventually (true if resources are limiting), e.g. when goats were introduced in Galapagos Islands, the Abingdon tortoise became extinct within a decade due to greater browsing efficiency of the goats.

(vi) Resource partitioning states that if two species compete for the same resource, they could avoid competition by choosing, for instance, different lines for feeding or different foraging patterns. In this relation, McArthur showed that five closely related species of warblers living on the same tree were able to avoid competition and coexist due to behavioral differences in their foraging activities.

Parasitism: -

It is the mode of interaction between two species in which one species (parasite)depends on the other species (host) for food and shelter and in this process the parasite damages the host. Hence, one organism is benefitted (parasite), while the other is being harmed (host).

(i) Adaptions of a parasite are: -

• Parasite is host specific in a way that both and parasite tend to coevolve. 
• Loss of unnecessary sense organs.
• The presence of adhesive organs or suckers.
• Loss of digestive system 
• High reproductive capacity.

(ii)  The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host, e.g.

• Human liver fluke (a trematode parasite) depends on two intermediate hosts ( a snail and a fish) to complete its life cycle.
• Malarial parasite (Plasmodium) needs a vector (mosquito) to spread disease to other hosts. 

(iii) Majority of parasites harm the host. They reduce the survival, growth and reproduction ability of the host and reduce its population density, by making it physically weak. They render the host more vulnerable to predation.

(iv) Parasites can be of the following two types 

• Ectoparasites live on the external surface of the host organism for food and shelter. Examples are the lice on humans, ticks on dogs, copepods, Cuscula, etc.
• Endoparasite's live inside the hosts body at different sites like liver, kidney, lungs, etc., for food and shelter, e.g., tapeworm, liver fluke, Plasmodium, etc. The life cycles of endoparasites are more complex because of their extreme specialization.

(v)female mosquito is not considered as parasite because it does not complete its life cycle in human body for reproduction.

(vi) Brood parasitism is a phenomenon in which one organism (parasite) lays its eggs in the nest of another organism, e.g., eggs of cuckoo (Koel) and the crow resemble in the size and colour. To reduce the chances of the crow (host) detecting the foreign eggs (cuckoo's) and ejecting them out from the nest, cuckoo lays its egg in crow's nest and let the host incubate them. 

Commensalism: -

It is the interaction between two species, where one species is benefitted and the other is neither harmed nor benefitted.

Some examples of commensalism are: -

• An orchid growing as an epiphyte on a mango tree. Orchid gets shelter and support from mango tree, while the mango tree is neither benefitted nor harmed. 
• Barnacles growing on the back of whale. Barnacles are benefitted to move to different locations for food as well as shelter, while the whales are neither benefitted nor harmed. 
• Egrets always forage close to where the cattle are grazing. Because, the cattle move, they stir up the bushes and insects are flushed out from the vegetation to be catched by cattle egrets.
• Sea anemone has stinging tentacles and the clown fish lives among them. The fish gets protection from predators, which stay away from the stinging tentacles.
• The anemone does not appear to derive any benefit by hosting the clown fish. 

Mutualism: -

It is an interaction that confers benefits to both the interacting species. 

Some examples of mutualism are: -

• Lichens represent an intimate mutualistic relationship between a fungus and photosynthesizing algae or cyanobacteria. Here, the fungus helps in the absorption of nutrients and provides protection, while algae prepare the food.
• Mycorrhizae are close mutual association between fungi and the roots of higher plants. Fungi help the plant in absorption of nutrients, while the plant provides food for the fungus.
• Plants and animals also show mutual relationship. Plants need help from animals for pollination and dispersal of seeds. In return, plants provide nectar, pollens and fruits to the pollinators, e.g. the female wasp uses the fig fruit not only as an oviposition (egg-laying) site but uses the developing seeds within the fruit for nourishing its larvae. The wasp pollinates the fig's inflorescence, while searching for suitable egg-laying sites. In return, fig provides the wasp some seeds as food for the developing wasp larvae. 
• Not all orchids offer rewards, e.g. Mediterranean orchid Ophrys employs 'sexual deceit' to get pollinated by a species of bee. One petal of its flower bears an uncanny resemblance to the female of the bee in size, colour and markings. The male bee is attracted to what it perceives as a female and pseudo copulates with the flower.
• During that process, pollen is dusted from the flower. When the same bee pseudo copulates with another flower. It transfers pollen to it and hence, pollinates the flower. This case indicates the process of coevolution. If the female bee's colour pattern changes even slightly during evolution, pollination success will be reduced unless the orchid flower coevolve to maintain the resemblance of its petal to female bee.

Amensalism: -

It is an interaction between different species, in which one species is harmed and the other is neither benefitted nor harmed, e.g. Penicillium, a Mould secretes penicillin, which kills bacteria but the Mould itself remains unaffected.

greenhouse effect| Causes, effect, Control, case study| example|

Greenhouse Effect 

It is a naturally occurring phenomenon that is responsible for heating of earth's surface and atmosphere due to the presence of certain gases in the atmosphere. 

1. In the absence of greenhouse effect, the average temperature of earth would have been chilly -l8°C rather than the present average of l5°C.
2. Clouds and gases reflect about one-fourth of the incoming solar radiation and absorb some of it. But, almost half of incoming solar radiation falls on earth's surface heating it, while a small proportion is reflected back.
3. Earth's surface re-emits heat in the form of infrared radiation, but part of this does not escape into space and atmospheric gases (e.g., carbon dioxide, methane, etc.) absorb a major fraction of it.
4. These gases radiate heat energy and a major part of which again comes to earth's surface, thus heating it up once again. This cycle is repeated again and again. 
5. The above-mentioned gases-carbon dioxide and thane are commonly known as greenhouse gases because they are responsible for the greenhouse effect. 

Global Warming 

It is the gradual and continuous increase in average temperature of surface of the earth a result of increase in concentration of greenhouse gases. 

Cause of Global Warming 

High levels of greenhouse gases (CO 2, CFCs, CH4, etc.) in the atmosphere. All these gases allow the heat waves to reach earth but prevent their escape and the earth become warm. 

Effects of Global Warming 

These are as follows: -

• Earth's temperature has increased by 0.6°C in last three decades. This ca uses change in precipitation patterns.
• The rise in temperature leads to harmful effects in environment leading to odd climatic changes, e.g., El Nino effect.
• The high temperature will result in melting of polar ice caps, which will lead to rise in sea level and many coastal areas will be submerged.
• The high level of temperature leads to increased weed growth, eruption of diseases and pests. Thus, the crop productivity will decrease. 

  

  Fig: - Relative contribution of various greenhouse gases to total global warming

  
  

Control of Global Warming: -

It can be done by: - 

1. Cutting down the use of fossil fuels. 
2. Improving efficiency of energy usage. 
3. Reducing deforestation. 
4. Planting trees, slowing down the growth of human population. 
5. Taking international initiatives to reduce the emission of greenhouse gases into the atmosphere. 

Ozone Depletion in the Stratosphere: -

• Ozone can be: - Bad ozone It is formed in troposphere and is harmful to plants and animals. 
• Good ozone It is present in stratosphere and acts as a shield, absorbing harmful UV radiation from the sun.
• The thickness of the ozone is measured in Dobson Units (DU). 
• Ozone gas is continuously formed by the action of UV-rays on molecular oxygen. 

• There should be a balance between production and degradation of ozone in the stratosphere. 
• This balance gets disrupted due to enhancement of ozone degradation by Chlorofluorocarbons (CFCs). CFCs are used as refrigerants.
• Ozone degradation When CFCs are discharged into lower part of the atmosphere, they move upward and reach the stratosphere. 
• In stratosphere, UV-rays act on them releasing chlorine (Cl) atoms.
• Cl degrades ozone releasing molecular oxygen with these atoms acting merely as catalysts.
• Cl atoms are not consumed in the reaction. 
• Hence, whatever CFCs are added to the stratosphere, they have permanent and continuous effect on ozone levels. 
• The ozone depletion is particularly marked over the Antarctic region. This led to the formation of a large area of thinned ozone layer, called as ozone hole. 

 Ozone Depletion by CFCs 

Harmful Effects of Ozone Depletion 

These are as follows: -

• UV-B damages DNA, causing mutation. 
• Ageing of skin, damage to skin cells and various types of skin cancer. 
• High dose of UV-B causes inflammation of cornea. This is called snow-blindness, cataract, etc. Such exposure may permanently damage the cornea. 

Control of Ozone Depletion 

Some measures for controlling ozone layer depletion are as follows: - 

• An international treaty, known as the Montreal Protocol, was signed at Montreal (Canada) in 1987 (effective in 1989) to control the emission of ozone depleting substances. 
• More protocols have been laid down for controlling emission of CFCs and other ozone depleting chemicals, separately for developed and developing countries. 

Degradation by Improper Resource Utilization and Maintenance 

It includes: -

1. The degradation of natural resources can occur not just by the action of pollutants, but also by improper resource utilization practices.
2. Results of improper resource utilization are: -

(a)Soil Erosion and Desertification 

• The formation of fertile topsoil takes centuries. 
• Due to human activities like overcultivation, unrestricted grazing, deforestation and poor irrigation practices, fertile topsoil is removed, resulting into arid patches of land.
• These barren patches when left for long time, form deserts. 
• Desertification is a major problem now a days due to increased urbanization.

(b)Water Logging and Soil Salinity

•  Irrigation without proper drainage of water leads to water logging in the soil.
• This leads to more salt deposition on the land surface or collection at the roots of the plants. 
• This salt content inhibits the growth of crops and damages agriculture. 
• Green revolution. has increased water logging and soil salinity. 

 Deforestation: -

It is the conversion of forested areas to non-forested areas: - 

1. Almost 40% forests have been lost in the tropics, compared to only I% in the temperate region. 
2. In India, in the beginning of the 20th century, forests covered about 30% of the land, whereas by the end of the century, it is reduced to 19.4%.
3. The National Forest Policy (1988) has recommended 33% forest cover for the plains and 67% for the hills. 

Reasons of Deforestation 

These include: - 

(i)Urbanization 

(ii) Cattle ranching 

(iii) Forest fires 

(iv) Demand of wood and other forest products

(v) Slash and burn agricultural or Jhum cultivation: -In this, Farmers cut down the trees and burn the plant remains. They ash is used as used for farming or cattle grazing. After cultivation, the area is left for several years to allow its recovery. In earlier time, enough times gap was given so that the land recovered from the effect of cultivation, this recovery phase is not available leading to deforestation.

Effects of Deforestation 

Various effect of deforestation are as follows: -

1. Increased levels of CO2concentration in the atmosphere.
2. Loss of biodiversity due to habitat destruction.
3. Disturbs hydrologic cycle.
4. Leads to soil erosion.
5. Desertification also occurs in extreme cases.

Conservation of Forests

Reforestation is the process of restoring a forest that once existed but was removed at some point of time in the past. Reforestation may occur naturally in a deforested area, or it can be speed up by planting trees.

Case Study: -People's Participation in Conservation of Forests

Case studies related to conservation of forests are as follows: -

• In 1731, a Bishnoi woman Amrita Devi (Jodhpur) showed, exemplary courage by hugging a tree and prevented it from cutting. Her three daughters and hundreds of other Bishnoi's followed her and lost their lives while saving the trees.
• The Government of India has recently instituted the Amrita Devi Bishnoi Protection Award for individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife. 
• Chipko movement in Garhwal Himalayas started in 1974. Local women showed enormous courage in protecting trees from. the axe of contractors by hugging them. 
• The Government of India in 1980s has introduced the concept of Joint Forest Management (JFM), after realizing the value of participation of local communities in forest conservation. In return for their services to the forest, the communities get benefit of various forest products, thus sustainable development of forest can occur.

pollution| types| harmful effect| control methods| causes of pollution| case study| Eutrophication|

 Pollution  

It is an undesirable change in the physical, chemical and biological characteristics of air, water, land and soil.

(i) Pollutants are agents that cause undesirable change in the environment. 

(ii) The Government of India has passed the Environment Protection Act, 1986 to protect and improve the quality of our environment (air, water and soil).

Air Pollution

It is the presence of toxic chemicals or compounds (including those of biological origin) in the air, at levels that pose a health risk. Air pollutants cause injury to all living organisms. They deleteriously affect respiratory system of humans and animals.

Causes of Air Pollution 

• Smokestacks from thermal power plants, forest fires, volcanic eruptions, etc. 
• Garbage decomposition also releases unwanted gases in the air. 
• Excessive use of fossil fuels by automobiles and industries release particulate and air pollutants. 
• Use of leaded petrol.

Types of Air Pollutant 

Air pollutants can be divided into following types: -

1. Suspended Particulates Matter (SMP): -Metallic particles, dust Particles, soot, aerosol and smoke 
2. Gaseous Pollutants: - Carbon monoxide, nitrogen dioxide, hydrogen sulphide and Sulphur dioxide.

Harmful Effects of Air Pollution on Health

These effects depend on the concentration of pollutants, duration of exposure and the organism. 

1. Carbon monoxide (CO) causes giddiness, headache, cardiovascular malfunction, asphyxia, etc. 
2. Hydrogen supplied (H2S) causes nausea, eye and throat irritation. 
3. Sulphur dioxide (S02) causes respiratory tract diseases like asthma, bronchitis, cancer, emphysema, etc. 
4. Fine particulates released by industries cause breathing and respiratory problems, inflammation and damage to the lungs. 
5. In plants reduced growth and yield and premature death occurs.

Control Methods of Air Pollution 

Air pollutants must be separated/filtered out from the exhaust before releasing into the ionosphere. For this several methods are used for controlling air pollution in India. These include: -

(i)Electrostatic Precipitator (ESP) is an electrical device to re1nove particulate matter present in the exhaust of thermal power plant.  About 99% of particulate matter can be removed by ESP.

• It has electrode wires and a stage of collecting plates. 
• Electrode wires are provided with an electric current of several thousand volts, which produces a corona that releases electrons.
• These electrons get attach to the dust particles and give them negative charge within a small fraction of a second.
• Collecting plates are grounded which attract the charged dust particles. 
• The velocity of air between the plates must be low enough to allow the dust to fall. 

Figure 16.1 Electrostatic precipitotor 

(ii) Scrubber is used to remove harmful gases like Sulphur dioxide from industrial exhaust. 

Figure 16.2 Scrubber

• The exhaust is passed through a spray of water or lime. 
• Water dissolves the gases and lime reacts with sulphur dioxide to form a precipitate of calcium sulphate and sulphide.
• Drawbacks Recently, the dangers of particulate matter (very small particles that cannot be removed by these precipitators) has been found. 
• According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) if inhaled can cause breathing and respiratory problems, irritation, damage to lungs and premature deaths.

(iii)Catalytic convertors are fitted into automobiles for reducing emission of poisonous gases like NO2 and CO.

• They are made up expensive metals like platinum, palladium and rhodium as catalysts.
• When exhaust passes through the catalytic convertor, nitric oxide splits into nitrogen and oxygen, carbon monoxide is oxidized into carbon dioxide and unburnt hydrocarbons get burnt completely into CO2 and H20.
• However, only unleaded petrol should be used in motor vehicles fitted with catalytic convertor as leaded petrol inactivates the catalyst.

A case Study- Control of Air Pollution in Delhi: -

• Delhi leads the country in high level of air pollution due to large numbers of vehicles. In 1990s, Delhi ranked fourth among the 41 most ITI polluted cities of the world.
• As per directives of Supreme Court, all buses of Delhi were converted to run on Compressed Natural Gas (CNG) by the end of 2002. 
•  Benefits of CNG over diesel/petrol, burns most efficiently and leaves no unburnt remains. 
• Cheaper than diesel/petrol. Cannot be siphoned off by thieves and adulterated like petrol or diesel. 

Learn about Diversity in living World

• The problem with switching over to CNG is the difficulty of laying down pipelines to deliver CNG through distribution points and ensuring uninterrupted supply.
• 0ther ways to reduce vehicular pollution Phasing out of old vehicles. Use of unleaded petrol.
• Use of low-Sulphur petrol and diesel. Application of stringent pollution level norms for vehicles.
• Use of catalytic convertors in vehicles.

Auto Fuel Policy of Government of India 

• Euro II norm s stipulate that Sulphur be controlled at 350 parts per million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42% of the concerned fuel.
• According to it, all automobiles have to meet the Euro III emission specification in eleven Indian cities by 1 April 2005.
• The same eleven cities have to meet the Euro IV norms by I April 2010. 
• The rest of the country will have Euro III emission norm compliant automobiles and fuels by 2010. 
• By all these efforts, a substantial fall in CO2 and S02 level has been found in Delhi between 1997 and 2005.

Note: - 

• The entire nation is next targeted to be covered under BS IV (Bharat norms under European Regulation) by 1 April 2017.
• The BS IV norms were introduced in 13 cities.
• apart from the NCR from April 2010 onwards. 
• BS IV norms stipulates the permissible limit of Sulphur to be only 50 ppm compared with 350 ppm under BS 111. Also, the limit of hydrocarbons, N02 and particulate matter emissions have been lowered further.

Noise Pollution: -

It is undesirable high level of sound. In India, the Air (Prevention and Control of Pollution) Act came into force in 1881 but was amended in l 987 to include noise as an air pollutant.

Noise Measurement 

Sound is expressed in decibels (dB). A sound of over 115 dB is very harmful for ears. Prolonged exposure to noise level above 80 dB leads to permanent hearing loss. 

Causes: -

(i) Use of loudspeakers and music systems. 

(ii) Jet planes and rockets during take-off (150 dB). 

(iii) Industrial, factory noises, etc. 

Harmful Effects: -

These include sleeplessness, stress, increased heartbeat, breathing problems, damage to ear drums and impaired hearing ability.

Control Methods: -

Noise pollution can be controlled by adopting following measures: -

(i) By using sound absorbent materials during constructions or by muffing noise in industrial units.

(ii) Delimitation of horn free zones around hospitals and schools.

(iii) Strict laws for permissible sound levels of crackers and loudspeakers sound be followed.

(iv)Loudspeakers should be played up to a fixed time only.

Water Pollution

It is any undesirable change in the physical, chemical or biological properties of water that may affect the human beings and aquatic species. The Government of India has passed the Water (Prevention and Control of Pollution) Act. 1974 to safeguard our water resources.

Sources of Water Pollution 

(i) Domestic sewage includes everything that comes from residential area to common public sewage. A mere 0.1% impurities make domestic sewage unfit for human use.

• It mainly contains biodegradable organic wastes, which are readily decomposed with the help of decomposers.
• Other components of domestic sewage are suspended solids, e.g. sand, slot and clay. 
• Colloidal materials, e.g., faecal matter. bacteria, cloth and paper fibers.
• Dissolved materials, e.g., nutrients (nittrate, ammonia, phosphate, sodium and calcium)
• During sewage treatment, it is easy to remove solid, but very difficult to remove dissolved salts such as nitrates, phosphates and toxic metal ions from wastewater.

Learn about Evolution 

(ii) Industrial wastes arc released by petroleum, paper manufacturing, metal extraction and processing units. It contains heavy metals like mercury and many organic compounds.

(iii) Heated (Thermal) wastewater flowing out of electricity genera ting units, e.g., thermal power plants. 

Harmful Effects of Water Pollution 

(i) Death of biodiversity Thermal wastewater, eliminates or reduces the number of organisms sensitive to high temperature and may enhance the growth of' plants and fish in extremely cold area s, but only after causing damage to the indigenous flora and fauna.

(ii) Biological magnification can be defined as an increase in concentration of toxicant is at successive trophic levels in aquatic food chain. Mercury and DDT arc well-known cause of biological magnification

• Toxic material cannot be metabolized or excreted. Therefore, they get accumulated in an organism and pass on to higher trophic levels.
• DDT accumulates in birds and disturbs calcium metabolism, which results in thinning of eggshell and their premature breaking. this results in decline of bird population.

(iii) Eutrophication can be defined as the natural ageing of a lake by nutrient enrichment of its water. 

Process of Eutrophication 

• Water in young lake is cold and clear to support little life. 
• Gradually with time, it gets enriched with nutrients such as nitrogen and phosphorus by streams draining in it.
• Due to this, aqua tic life (plants and animals) flourish in lake.
• Organic deposit at the bottom of the lake and with time, water becomes warmer. This warm water support even more growth of plants. Eventually, floating plants develop in the lake, finally converting it into land. Natural 
• Eutrophication generally takes 1000 of years or more. Bur, human activities have accelerated this natural process and as a result many lakes are already extinct. It is caused due to dumping of nutrient rich and thermal waste into lakes. This is known as Accelerated or cultural eutrophication.

(iv) Biochemical Oxygen Demand (BOD) is the amount of oxygen required for microbial breakdown of biodegradable organic matter. It is higher in polluted water and lesser in clean water. 

(v) Algal bloom is excessive growth of planktonic (free-floating) algae in aquatic bodies.

• In domestic sewage, nutrients like nitrogen and phosphorus Favours the growth of algal bloom. 
• It causes fish mortality and deterioration of water quality. Example, Excessive growth of water hyacinth (Eichhornia crassipes). It is the most problematic aquatic weed, also called Terror of Bengal. 
• It grows abundantly in eutrophic water bodies and imbalances water ecosystem. 

A Case Study- Integrated Wastewater Managemet: -

(i) Wastewater including sewage can be treated in an integrated manner by utilizing a mix of artificial and natural processes. 

• One such example is town of Arcata situated along. Northern coast of California. An integrated wastewater treatment process was developed with the treatment process was developed with the help of biologists from Humboldt State University in this town. The cleaning occurs in two steps: -
• (a) The heavy conventional sedimentation, filtration and chlorine treatment is carried out the treated water still contains loss of heavy metals and other toxic pollution.
• (b) In second step, algae, fungi and through which this water flows. These life forms neutralize, absorbed and assimilate the pollutants and purify the water naturally, the marshes also constitute a sanctuary, with a high level of biodiversity.
• A citizen's group called Friends of the Arcata Marsh (FOAM) are responsible for the upkeep and safeguarding of this project.

(ii) Ecosan' toilets have been developed in areas of Kerala and Sri Lanka for ecological sanitation. The advantages of ecological sanitation are:

• A practical, hygienic and efficient method of disposal. 
• Cost effective approach. 
• Human excreta can be recycled into natural fertiliser to red uce need of chemical fertiliser.

Solid Wastes 

Solid wastes refer to everything that goes out in trash. The various types are: -

• Municipal solid wastes contain wastes from homes, offices, schools, hospitals, etc, that are collected and disposed by the municipality, which generally consists of paper, leather, textile, rubber and glass, metals and plastic, elc
• Industrial wastes contain wastes like scraps, fly ash, etc. generated by industries. 
• Hospital wastes contain disinfectants and other harmful chemicals generated by hospitals. 
• Electronic wastes (e-wests) are the damaged electronic goods and irreparable computers. 
• All wastes can be categorized into Three types:

1. Biodegradable
2. Recyclable 
3. Non-biodegradable

Methods of Solid Waste Disposal 

There are various methods of solid waste disposal. Some of them are: - 

• Open burning involves burning of municipal waste in open dumps, but the unburnt piled waste serves as breeding ground for rats and flies.
• Sanitary landfills are areas where wastes are dumped in a depression or trench a ft er compaction and covered with dirt. The problem is seepage of chemicals from these landfills can pollute underground water resources. 
• Rag-pickers and kabadiwalas collect and separate out wastes int o reusable or recyclable categories.
• Natural breakdown involves dumping biodegradable materials into deep pits for natural degradation.
• Incineration is a method of hospital waste disposal. It involves burning of waste materials to ash.

e-Wastes 

• e-wastes are buried in landfills or incinerated.
• About half of thee-wastes generated in the developed world are exported to developing countries, mainly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during recycling process.
• Developed countries have specifically built facilities for recycling of e-wastes. 
• Recycling is the only solution available for treating e-waste, but caution should be taken to carry out this process in environment friendly ways. 

A Case Study - Remedy for Plastic Waste 

• A plastic sack manufacturer, Ahmad Khan from Bengaluru realized that plastic waste was a real problem. 
• His company developed a fine powder, called polyblend of recycled modified plastic. 
• This mixture is mixed with the bitumen and used to lay roads. 

Learn about Biodiversity

• It enhanced the bitumen's water repellant properties and helped to increase road life by a factor of three.
• Using this technique, by the year 2002, more than 40 kms of road in Bengaluru has already been laid.

Soil Pollution 

It is any undesirable change in soil profile affecting its productivity. Green revolution led to manifold increase in crop production by the use of inorganic fertilizers and pesticides. Pesticides, herbicides, fungicides, etc., are being increasingly used afterwards which resulted in soil pollution.

Causes of Soil Pollution 

(i) Chemical seepage from industries. 

(ii) Excessive use of inorganic fertilizers, pesticides, etc. 

Harmful Effects of Soil Pollution 

(i) Non-target organisms are killed in the soil, due to pesticides. 

(ii) Soil becomes unfertile. 

(iii) Pesticides can result in biomagnification, as well as eutrophication.

Control Methods 

(i) Strict ways should be adopted by the industries and other sources for waste disposal. 

(ii) Use of organic farming It is a cyclic, zero-waste method, where waste products from one process are cycled in as nutrients for other processes, allowing maximum utilization of resources and increasing the efficiency of production.

A Case Study- Organic Farming 

• Ramesh Chandra Dagar, a farmer in Sonipat (Haryana) included beekeeping, dairy management, water harvesting, composting and agriculture in a chain of processes.
• This chain supports each other and allow an extremely economical and sustainable venture.
• Chemical fertilizers are not required as cattle excreta is used as manure. 
• Crop waste is used for making compost, which is u sed as natural fertilizer or to generate natural gas, which is u sed for satisfying energy needs of farm.
• To spread information and help the practice of integrated organic farming. Dagar has created the Haryana Kisan Welfare club, with current membership of 5000 farmers.

Radioactive Wastes 

The waste produced from nuclear fission of heavy atoms such as uranium, thorium, etc., for the production of power is radioactive waste. Radiation that is given off by nuclear waste is extremely damaging to biological organisms. 

• Nuclear energy was initially considered as a non-polluting way for generating electricity initially.
• Later, two serious inherent problems were realized. The first is accidental leakages as occurred in the Three Mile Island and Chernobyl, which proved that radioactive wastes are most potent pollutants. The second is safe disposal of radioactive wastes. 

Harmful Effects 

(i) Radiations cause mutation at a very high rate. 

(ii) At high doses, nuclear radiations are lethal. 

(iii) At low doses, these cause disorders and diseases like cancer. 

Disposal method of Radioactive wastes 

It involves pretreatment and storage in shielded containers and then burying at about 500 m deep below the earth's surface. However, this method of disposal is getting opposition from public. 

Phylum Echinodermata, Characteristics, Function, Classification,

 Phylum Echinodermata 

Phylum Echinodermata (Gr., echinus=spiny + derma = skin, ata = characterized by) includes exclusively marine invertebrates displaying pentamerous radial symmetry and an endoskeleton of calcareous plates and spines. Jacob Klein gave the name Echinodermata. This phylum is a collection of about 7,000 living species and constitute some of the most beautiful members of sea fauna, such as starfishes or sea stars, sea urchins, sea cucumber, sea lillies and sand dollars etc. The name ‘starfish’ is, however, misleading as these animals are not true fishes. A more suitable name suggested for them is ‘sea star’. Common genera of sea stars are Asterias, Pentaceros, Astropecten, Solaster, Heliaster, Luidia, Asterina etc. Genus Asterias includes about 150 species of which most common is A. Rubens. 

The echinoderms are important both biologically and geologically. Biologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Echinoderms generally have remarkable powers of regeneration of tissue, organs, limbs, and of asexual reproduction, and in some cases, complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment.

Echinoderms possess a simple digestive system which varies according to diet. In many species, the large cardiac stomach can be everted and digest food outside the body. Gonads are present in each arm. In echinoderms such as sea stars, every arm bear two rows of tube feet on the oral side which help in attachment to the substratum. Echinoderms are efficient scavengers of decaying matter on the seafloor. They prey upon a variety of small organisms, thereby helping to regulate their numbers. In addition, echinoderms produce vast numbers of larvae that provide food for other, planktonic organisms. 

General characters: -

1. Echinoderms are exclusively marine, free living and mostly bottom dwellers. 
2. Organ system grade of body organization. 
3. Body triploblastic, coelomate and symmetrical. 
4. Body unsegmented with globular, star-like, spherical, discoidal or elongated with radiating arms. 
5. Head absent. Body generally pentameric. 
6. Body surface with five radial areas, the ambulacra, with tube feet and five inter-radial areas, the inter-ambulacra. 
7. Endoskeleton is made up of spines and calcareous spicules. 
8. Coelom is a large cavity lined by ciliated peristomium, coelomic fluid with coelomaocytes. 
9. Water vascular system or ambulacral system present, usually with a madreporite. 
10. Nervous system without brain but with a circum-oral ring and radial nerves. 
11. Sense organs are poorly developed. 
12. Alimentary canal straight or coiled. 
13. Respiratory organs include dermal branchia, tube feet, respiratory tree and bursae. 
14. Circulatory or haemal or blood lacunar system is typically present. 
15. Excretory organs absent.
16. Reproduction is usually sexual, but few reproduce asexually or by regeneration. 
17. Sexes are separate; fertilization is external, development indirect through free-swimming larval forms. 

A few other Echinoderms: -

• Echinus: -

Echinus is commonly called sea-urchin. It is a species of marine invertebrate in the echinidae family. It is a deep-sea animal found from intertidal zone to a depth of 5000 meters. In the North Sea, the species is common in all areas with hard substrates. It is found off the coasts of Portugal, Spain, France, Belgium, the Netherlands, Denmark, Norway, Sweden, the United Kingdom and Ireland. Sea urchins feed mainly on algae but can also feed on sea cucumbers and a wide range of invertebrates, such as mussels, polychaetas, sponges, brittle stars, and crinoids. 

It has a globe-shaped body enclosed within a shell or corona and having very long movable spines. The surface of corona is divided into five ambulacral regions alternating with five interambulacral regions. In each ambulacral region, there are two rows of tube feet. Mouth is present on oral surface and is surrounded by peristome. The chewing apparatus or Aristotle’s lantern projects from the mouth. Anus is surrounded by a periproct and is present in the center of the aboral surface. Water vascular system is well developed. Development is indirect and involves free swimming echinopluteus larva. Removal of the sea urchins results in the overgrowth of seaweeds and the devastation of the coral reef habitat. When present in large numbers, sea urchins can devastate seagrass beds in the tropics, adversely affecting the organisms dwelling within. 

Fig: - Echinus

• Ophioderma: -

Ophioderma is also known as brittle star. It occurs from the lower shore to depths of around 150m, living on hard substrates. The common brittle star is extremely variable in coloration, ranging from violet, purple or red to yellowish or pale grey, often spotted with red. The arms are usually white or grey with pink bands. Body is made up of a roughly pentagonal central disc and five freely movable arms arising from the base of the disc. Arms are covered with calcareous plates and on either side by spines. Each arm has two grooves called bursal slits. Brittle star moves by means of its tube feet. Development is indirect through free-swimming ophiopluteus larva. The common brittle star is a scavenger, feeding on dead organisms.

• Holothuria: -

Holothuria is a genus of marine animals of the family Holothuriidae. It is commonly known as sea-cucumber and is found in nearly every marine environment but is most diverse on tropical shallow-water coral reefs. They creep slowly while engulfing micro-organisms alongwith mud. The Holothuria, or sea cucumbers, are an abundant and diverse group of worm-like and usually soft-bodied echinoderms. Their habitat ranges from the intertidal, where they may be exposed briefly at low tide, to the floor of the deepest oceanic trenches. 

The body is elongated, sausage-shaped, covered with leathery skin and having well-developed respiratory tree. The mouth and anus are at the opposite ends. Body bears numerous podia or feet, locomotory on the ventral surface and papilliate on the dorsal surface. Mouth is anteriorly placed, surrounded by 1-30 peltate tentacles. Sexes are separate. Reproduction is sexual. Development is indirect. It includes two larval stages-auricularia and doliolaria respectively. Several species can swim and there are even forms that live their entire lives as plankton, floating with the ocean currents. Sea cucumbers have great economic importance. Some species produce toxins (antimicrobial, anti-inflammatory agents and anticoagulants) that are of interest to pharmaceutical firms. They also form an important part of gourmet food industry in the orient. 

• Pentaceros: -

 Pentaceros is known as sea pentagon. Central disc is large and the five arms are short and tapering. Aboral surface is convex and bears rows of definitely arranged spines. Oral surface is concave, having a central mouth, communicating with five ambulacral groves, each bearing two double rows of tube feet. Pedicellariae are small and valvate type. Pentaceros is very harmful to pearl industry as it feeds on pearly oysters.

• Astropecten: -

 Astropecten is a common starfish, inhabiting the sandy bottom of seas. Body consists of a large central disc with 5 tapering arms and each having 2 rows of conspicuous marginal plates bearing along spines. Oral surface has a centrally positioned mouth which comes out only occasionally and communicates with 5 ambulacral grooves. Water-vascular system includes two to four polian vesicles in each interradius and the stone canal is structurally complicated. There occurs no brachiolaria larva. 

• Antedon: -

Antedon is commonly known as feather star. It occurs in sea waters of the Atlantic, Western Africa, the Mediterranean and West of Tropical America. It feeds on plankton and debris and has great power of regeneration and autotomy. Body consists of a central disc and a series of ten radiating arms. The upward directed oral surface bears mouth and a projecting papilla which bears the anus while downward directed aboral surface bears several long appendages called cirri for anchoring or crawling on the substratum. Tube feet or podia without suckers present along the edges of ambulacral grooves. Sexes are separate. Reproduction is sexual. Development includes a free swimming doliolaria larva. 

Important point: -

• Phylum Echinodermata (Gr., echinos=spiny+derma=skin, ata=characterized by) includes exclusively marine invertebrates displaying pentamerous radial symmetry and an endoskeleton of calcareous plates and spines. Jacob Klein gave the name Echinodermata.
• Echinoderms are exclusively marine, free living and mostly bottom dwellers. Organ system grade of body organization.
• Asterias are free-living marine animals that can be found at all water depths as well as crawling over rocks and shells.
• Asterias feed mainly upon molluscs, especially bivalves and snails. In addition, they act as scavengers on any dead animals.
• Most Asterias possess a pentamerous radial symmetry, secondarily derived from a larval bilateral symmetry. The body is flattened and flexible, with a pigmented and ciliated epidermis. Average size of Asterias ranges from 10 to 25 cm in diameter.
• The aboral and abactinal surfaces are beset with numerous short but stout spines arranged in irregular rows parallel to the long axis of the arms.
• The mouth is situated in the center of the oral surface in the form of a five-rayed aperture. 
• Pedicellariae of sea stars are minute, whitish jaw-like structures, found on both the body surfaces, in association with spines. The pedicellariae help in the capture and removal of debris and minute organisms, such as larvae, which may settle on the body surface and interfere with respiration by covering the dermal branchiae and tube feet. In some starfishes, the pedicellariae may help in capturing of small prey.
• Sea star possesses a complete digestive tract situated in the central disc. Between the mouth and anus, it can be differentiated into esophagus, stomach and intestine.
• Asterias is carnivorous, feeding on any slow-moving animal but mainly upon molluscs such as oysters, clams, mussels, snails, etc. The fish crabs and barnacles also make its food.
• Locomotion is performed with the help of water-vascular system which sets up a hydraulic pressure.
• Asterias or starfish is unisexual, but there is no sexual dimorphism. The reproductive organs of primitive type and lack copulatory organs, accessory glands and receptacles or reservoirs for storing sperms and ova.
• There are five pairs of testes or ovaries with one pair at the base of each arm lying freely between pyloric caeca and ampullae of the tube feet.
• Fertilization is external. The eggs and sperms are shed in seawater. The female lays about 200 million eggs in a season.
• The development of starfish includes the following larval stages- Dipleurula larva or early bipinnaria, Bipinnaria larva and Brachiolaria larva.

 💦Self-Assessment question (Terminal Question): -

💥Long Answer type questions: - 

1. Describe the classification of phylum Echinodermata. 
2. Give an account of larval forms found in Sea star. 
3. Discuss the digestive system of starfish.
4. Explain the reproduction of star fish.

💥Short Answer type Question :-

1. Write about the external morphology of star fish?

2. Draw a well labeled diagram of starfish?

3. Discuss brachiolaria larva?

4. Comments on bipinnaria larva?

5. Write short notes on Echinus and Holothuria. 

💦Multiple choice questions: -

1. Asterias belong to: 

(a) Echinoidea                                               (b) Asteroidea 

(c) Ophiurodea                                              (d) Holothuroidea 

2. Common name of Asterias: 

(a) Brittle star                                                (b) Star fish 

(c) Sea pentagon                                            (d) Basket star 

3. Locomotory organs of starfish: 

(a) Polian vesicles                                         (b) Podia 

 (c) Both  (a) and (b)                                     (d) None of these 

4. Characteristic feature of echinoderm: 

(a) Haemal system                                        (b) Water vascular or ambulacral system 

(c) Both (a) and (b)                                       (d) None of these 

5. Larval stage in life history of starfish: 

(a) Dipleurula                                               (b) Bipinnaria 

(c) Brachiolaria                                            (d) All of the above 

6. The eggs of Asterias are: 

(a) Macrolecithal                                          (b) Microlecithal 

(c) Megalecithal                                           (d) Oligolecithal 

7. Excretory products: 

(a) Urea and creatine                                    (b) Ammonia 

(c) Urea                                                        (d) Uric acid 

8. Which of the following phyla is found only in sea water? 

(a) Annelida                                                  (b) Arthropoda 

(c) Mollusca                                                 (d) Echinodermata 

9. Most fragile arms are of: 

(a) Star fish                                                    (b) Sea urchin 

(c) Brittle star                                                (d) none of these 

10. Tube feet are locomotory in function and also perform additional: 

(a) Excretory function                                          (b) Feeding function 

(c) Protective function                                          (d) All the above 

💥Answer key:-  

1. B   2. B  3. B  4.C  5. D  6. B 7. A  8.D   9.C  10.B