8 Science Chapter 1

8/7/2019 8 Science Chapter 1

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A scientific investigation of theenvironment

At the end of this chapter, you will be competent to...

• investigate the natural environment and use it productively.

• identify the features in the various built (man made) environmentsand use them productively.

• be concerned about animals that are poisonous to man.

• identify and use international scientific symbols.

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1.1 A scientific investigation of the environmentSri Lanka, although a small country shows a bewildering range of climatic

diversity. Associated with this climatic diversity we get a range of ecosystemdiversity. Forests, grasslands, rivers, streams, springs, mangroves are examplesof some such environments. We are also fortunate in that if we were to visit some of them we do not have to spend a lot of time, distance or money to observe theseenvironments and get first hand experiences. The reason is that we can travel from oneenvironment to another totally different environment in a matter of few hours.

These environments were not built in a day, nor did they appear at random. Theywere built up by the mutual interaction of the living and non-living componentsof a certain area in association with factors such as the climate, rainfall, humidity,temperature and nature of the soil and nutrients. Therefore the living organisms of anenvironment, namely the plants and the animals show remarkable adaptations tosurvive in this environment. In Grade Seven you learnt about the unique interrelationshipsin the environment. The environments you see today have been established over mil-lions of years of time, through processes of evolution and adaptations and results of natural selection.

These environments have affected the livelihood and survival of the humancommunities living close to them. If so the environments of our country areimportant not only biologically but also socially and culturally and can beconsidered as our heritage. Mahaveli ganga, Adam’s Peak mountain range,Sinharaja forest - they are all part of our heritage. This diversity of environments haveto be preserved for future generations. In order to preserve them we have to have aknowledge about them. We have to understand the delicate interrelationships foundthere. The destruction of one species or one condition can have adverse effects on theentire ecosystem. Therefore when utilising them we have to act with a sound scientific

understanding.

There are two main types of ecosystems in our country, namely aquatic ecosystemsand terrestrial ecosystems. Let us study them in more detail.

Do you know?Sinharaja was named as a National heritage in 1988. In 1989 it was named as

a world heritage site.



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1.1.1 Natural aquatic environmentsRivers, streams and inland water bodies are examples of natural fresh water envi-

ronments. Let us investigate about each of these aquatic environments separately.

Rivers

• Most of the rivers begin at the high ground inthe central hills and radiate out, ending up inthe ocean.

• Most rivers are perennial, carrying water all

the year round, although the levels mayfluctuate. Some may even over flow duringthe rainy season.

• Some of small rivers may dry up completelyduring the dry season.

• In the upper reaches the water is pure, clear and fast flowing. It is highly oxygenated.As the river flows down to the plains current is reduced, silt gets collected andwater becomes less clear. As it approaches the coast line, flow is slow, sedimentand silt load is high and water appears muddy.

•

When compared to forests, bio-diversity of rivers is not very high. But there are anumber of species which are adapted to the particular conditions. For example,trout who can survive only in unpoluted water are found in water bodies in NuwaraEliya area. As the river flows down diversity increases, and species such as eelscan be seen.

Some of the uses of rivers are, providing water for our daily needs, providingwater for agricultural activities, producing hydro-power by building dams acrossrivers and as a medium of transport.

Fig 1.1 - A river

Assignment 1• Prepare a list of the uses of rivers.• Find out the rivers and streams around your locality. Investigate the uses

as well as the problems caused by these rivers and streams.

Do you know?81 species of inland fish have been recorded in Sri Lankaof which 27 are endemic.



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River water gets polluted due to human activities such as release of industrialeffluents in to these rivers, destruction of forests and other consequences of urbanisa-tion and industrialisation. This is harmful to us as well as the organisms living in therivers.

Mining of sand from rivers is also a major problem at present. Extensive mining of sand from rivers causes many problems such as slow erosion of the river bank, deep-ening of the river basin, as a result the springs that provide water to the close by wellsdry up, water bed goes down resulting in sea water flowing in, particularly in areasclose to lagoons, accidents to people who use the river for bathing, washing etc.

EstuariesEstuaries are places where the rivers fall in to the sea. (Fig 1.2)Estuaries contain a mixture of saline and fresh water. It can be observed that

the river broadens out and divides into branches. Examples are Kalu ganga andMahaweli ganga. The load of sediment and silt brought down by the river isdeposited at or near the mouth making up triangular deltas.(Fig 1.3) The sediment andsilt deposited here prevent the mixing of sea water and fresh water

.

Estuaries show a greater biodiversity than rivers. Some of the species are freshwater migrants that move from the river into estuaries, marine species, and are perma-nent inhabitants adapted to tolerate low salinity. Many species of fish of economicimportance are common in estuaries. Salmon fish is an example.

Assignment 2Prepare a list of pollutants which get added to water as a result of urbanisation

and industrialisation. Suggest measures that can be taken to minimise their harmfuleffects.

Fig 1.2 - Estuary Fig 1.3 - Delta



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LagoonsLagoons are coastal bodies of brackish

water without permanent connection to the sea,but may be connected to the sea during certainseasons of the year. (Fig 1.4) Lagoons are sepa-rated from the deep sea by sand dunes or coralreefs.

Lagoons too, like estuaries are rich in biodiversity. They are good fishery groundsrich in prawns,crabs and small fish.The mangroves growing in lagoons and estuaries isa valuable resource. They significantly reduce sea erosion.

From the above, you may have realised that estuaries and lagoons provide ampleemployment opportunities.

Let us investigate how the lagoon environment can be protected while using themfor our use.

Since a large amount of fishery resources are obtained from lagoons, their watershould be kept clean and protected from pollution. Due to the development of townsaround estuaries and lagoons, a large amount of industrial and domestic waste getsreleased to these water bodies. Further these uniqe sorroundings attract tourists, as a

result of which tourists centres are being established. Therefore it is important to usethese environments optimally. Accordingly,• avoiding distructive methods of fishing.• minimising pollution by mineral oils.• minimising pollution by soaps, detergents, shampoos and other domestic and

industrial effluents being added to water.

RiverineRiverines are the environment found on the two sides of a river. Rivers overflow

during rainy seasons and form flood plains. This is associated with rivers. The soil hereis very rich since silt and other organic sediments collect here. Therefore in seasonswhen there is no rain, these areas are used for cultivation. Also the clay soil found inthese areas are used for the tile and brick industry. Therefore riverine environmentsare economically very useful for human beings.

Inland watersNatural ponds and lakes belong to this group. These are ecosystems containing

fresh water. Such inland ponds and lakes can be seen in the dry zone as well as the wetzone of Sri Lanka.

Fig 1.4 - Lagoon



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Tanks are man made inland water bodies. Theydo not belong to the above category. Inland waterbodies provide habitats for aquatic animals andamphibians as well as their food, breeding groundsand provide protection.

Fish, frogs, toads, reptiles, birds and water snakesare inhabitants of these water bodies. Lotus, waterlilies and various other plants which are used as foodand medicines are also some valuable resources foundin these waters.

OceansLarge percent of the earth’s surface is covered by

oceans. Although ocean water has a high salinity andcannot be used for drinking purposes, it provides ahabitat for many living organisms.

Some such organisms are sea weeds (Algae),fish, starfish, coral polyps and sea anemone.(Fig 1.6)

Many marine forms such as fish and other animalsprovide food for man. Example Tuna, Shark, Seer,Sprats, Loligo, Cuttle fish and species of bivalves.

Marine plants are used in the production of food, pharmaceutical drugs, toothpaste and paints. Example Algae and diatoms.

The high concentration of salts provide a good source of various salts.Example Common salt (Sodium chloride)

Epsom salt (Magnesium sulphate)Electricity is generated using the energy in ocean waves as well as the tides. There-

fore you would have seen that the ocean is a store of resources. The extent of oceanbelonging to Sri Lanka is many times the extent of the land, yet we have not utilised thisresource fully.

Let us now consider some terrestrial habitats. We shall consider only theforests and the grasslands in this respect.

Fig 1.5 Inland water

Fig 1.6 marine organism

Assignment 3Prepare an article for a wall chart on the theme “ The ways in which wecould make use of the ocean.”



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1.1.2 Natural terrestrial environmentsVarious types of forests and grasslands belong to this group called natural

terrestrial environments.

Tropical rain forests

These are also called wet ever greenforests. They are found in highlands of 900 m. above sea level. The annual rainfall

is above 2000 mm, and the temparatureis high. Therefore there is a hot - wetclimate here. Within the forests, humidityis high. Almost no dry season. Manystreams and rivers can be seen. Large treesare about 40 m. tall, thickly branched andform a canopy. (Fig 1.7) Trees show distinct stratification into three layers. If youexamine a profile of these forests the stratification can be seen easily. (Fig 1.8) Exam-ples of these forests are Sinharaja, Kitulgala and Kanneliya, forests.

Many creepers and lianas wind around thetree trunks which are covered with epiphytes.Little undergrowth is found as light penetrationis low. Many economically important trees suchas Dipterocarpus (Hora), “Keena”, “Kaledel”,Berrya (Halmilla) and “Nadun” are found. Theundergrowth consists of mainly ferns,selaginella and some seedlings and undecayedlayer of plant leaves can be seen on the ground.

Animal diversity is high consisting of many endemic and original species of birdsand insects.

Tropical rain forests can be considered as a uniqe environment for retaining the“Gene pool” of our country. Only a small area of this type of forest cover is remainingin Sri Lanka at present.

Fig 1.7 Sinharaja forest

Fig 1.8 - A profile of tropical rain forest



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Montane forests

These are found at heights of 900 m.above sea level. Annual rainfall of about 4000mm. Area is subjected to strong winds. There-fore trees are short and stunted. Trunks aretwisted and gnarled. Top of the trees form aflat canopy. (Fig 1.9) No stratification.Leaves are small. Common plants are “Walsapu”, “Veralu”, “Mihiriya” and “Dan”varieties.Due to the coolness tree trunks are moist. Hence they are covered withlichen, mosses and epiphytes.

Some species of monkeys, wild boar, deer, giant squirrel, loris and sambhur, aswell as many species of fish, amphibian, lizards and birds are found here.

Examples of montane forests are Pidurutalagala, Adam’s Peak, Kikiliyamana,Knuckles range, Horton plains and Pattipola forests reserve. Most montane forestsare the water catchments for many rivers. Therefore it is our responsibility to protectthem for the future generation.

Dry Mixed Evergreen ForestsThese are also known as Monsoon forests.

They are located at around 900 m above sea levelin the dry zone. Temperature is more than 30 de-grees Celcius (30 oC) with an annual rainfall of about 1250 - 1900 mm.Long drought period fromMay - September when the rainfall may be about150 mm is found. These are found in the dry, butnot xerophytic areas of the counrtry.

Most plants found here are those which can withstand long periods of drought.No marked stratification. Perennial as well as deciduous plants can be found. Treesare short (20 m). Barks are thick and trunks are twisted. Roots penetrate deep intothe soil. Space between trees is fairly big, hence the forest is not very dark. It has awell grown undergrowth. Common plants are “Weera”, “Palu”, “Burutha”(Satin wood),“Kaluwara”, “Kalumediriya”, “Welang”, “Halmilla”, “Kohomba”(Margosa), “Kolon”,“Kon” etc. (Fig 1.10)

Fig 1.9 - A profile of montane forest

Fig 1.10 - A profile of dry mixedever green forest



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Animals such as leopards, deer, bear, different species of monkeys, giant squirrelscan be seen. Good location for elephants. Examples of these forests are found inAnuradhapura, Polonnaruwa, Batticaloa, and Ampara district.

This ecosystem would have once covered most of the dry zone land, but now it isreduced to a small extent.

Thorny shrubs and woods

These ecosystems are found in the aridzone, northwest and south east of the is-land. Temperatures are higher than 34 de-grees Celcius (34 oC), and annual rainfall isbelow 1250 mm. Prolonged drought periodfrom May - September. Therefore these arecalled xerophytic areas. Soil is dry andsandy. Humidity is low.

Plants in these regions are adapted to withstand the environmental conditions pre-vailing here. Some such adaptations are fleshy leaves, reduced number of leaves,stems store water, stems become photosynthetic and leaves and stems posses latex.Some examples of plant types are “Nawahandi”(Euphorbia), “Daluk”,“Pathok”(Cactus), “Komarika”(Aloe), “Kaneru”, “Andera”, “Eraminiya”. This typeof vegetation can be found in Mannar, Kilinochchi, Mulativu, Hambantotadistricts.Wilpattu, Bundala sanctuaries,Madu area, Chundikulam, Madunagala.

Weerawila and Tissa are sanctuaries belonging to this catogory.

We have already studied about the natural forests of Sri Lanka, we can nowinvestigate how such ecosystems progressed into the major succession in the aboveareas of the country.

Fig 1.11 - Thorny shrubs and woods

If you get an opportunity to travel from Colombo to Badulla by train, you canobserve some of the above environments and note how they change from the lowcountry to the highlands.



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1.1.3 Natural grasslandsGrasslands exhibit characteristics between a forest and a desert. Grasslands

associated with a forest may show a few large trees. Horton planes is an example of this. Grasslands can be found in every type of climatic zone. They are of four types;

• Wet Patanas• Dry Patanas• Damana and Talawe• VillusGasslands are important ecosystems as they are the main catchment areas as well

as grazing grounds for animals. It is our responsibility to preserve them.

Wet patanas

They are located arround 2000 m. above sealevel. Rainfall is high and well distributed. Thereforethey are moist throughout the year. These are closeto the forests, (Fig 1.12) hence the dominant spe-cies is often is a Montane forest tree type. Someexamples of wet patanas are Horton planes, Elk

planes, Moon planes, Sita eliya, Bogawanthalawaand Bopath thalawa. Apart from grass, there areisolated trees. Dominants are Ma Ratmal Rhodedendron. The main trunks and branchesof these trees are covered with the epiphyte Usnea (Old man’s beard). In additionCyperus species and the fern Pteridum are commonly found. Soil is rich in humus.

Dry Patanas

Welimada plateau, Knuckles, Deniyayaand Rakwana are examples of dry patanas.

Except for small patches of forests in thevalleys, the rest of the area is covered withthis type of grasslands. The characteristicgrass variety is Mana (Cymbopogan nardus)(Fig 1.13). Dry patanas are more extensivelyspread out than wet patanas. Very often inthe dry season the grass catch fire resulting in the soil being exposed and consequentlygetting eroded.

Fig 1.12 - Wet patanas

Fig 1.13 - Dry patanas



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Damana and TalawaThese grasslands are a consequence of chena

cultivation. The grasslands of the low country dryzone are called Damana (Fig 1.14) and those in thelow country wet zone are called Talawa (Fig 1.15).They can be seen in Polonnaruwa, Welikande,Trincomalee and Kalutara districts. The vegetationconsists of grasses such as Mana, Iluk and Bata(Cane) as well as trees such as Diwul,Palu, Mylaand Madan. This ecosystem has a diversity of largegrazing and browsing animals like the deer, buffalo

and is a popular habitat of elephants.

VillusThese are wet grasslands found in the

flood plains of the rivers in the dry zone. Inareas where flooding occurs, villus areformed in the abandoned ponds, lakes andlarge water bodies. Villus are highly fertileecosystems.

It is very high in biodiversity and den-

sity, comprising of large animals such as el-ephants, deer, buffalo, leopards, foxes, ot-ters and birds such as peacocks, jungle fowl,storks, “Seru”, king fishers and hawks and a large range of fish, amphibians and rep-tiles.

After the rainy season, the villu areas get filled with water plants and make abeautiful scene with the encircling forests. (Fig. 1.16) They are a fine attraction fortourists. The villus filled with fish is a rich fishery resource for the villagers. The mostextensive villus of Sri Lanka are in the Mahaveli flood plains. Villu grasslands are finegrounds for cattle farming. Examples are the cattle farms of Tamankaduwa.

WetlandsThese are located at a lower level in comparison with the other water bodies.

Water from the surrounding areas flow into these and collect here. Wetlands have ahigh soil water level. Once maximum water has been absorbed, the remaining watercollects and remains as a surface layer of water.

Fig 1.16 - A beautiful scenery of a Villu

Fig 1.14 - Damana

Fig 1.15 - Thalawa



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Examples are Muthurajawela,Bellanwila - Aththidiya and Bundalareserves.The marshes and otherwetlands of Sri Lanka are homelandto many animals and plants. Manyreeds, grasses and small shrubs canbe seen here.

In the past wetlands were con-sidered as unfertile, mosquito breed-ing and unimportant lands and was

often used for dumping and filling forvarious constructions. However now their importance has been recognised and theyare named as protected areas. By studying the illustration given below you will under-stand why a wetland is considered as an important eco system.

The contribution of forests for the maintanance of organisms is very important.Forests are the catchment areas for rivers. Forests contribute directly for maintainingthe water cycle and to provide a favourable climate. As you learnt in grade 7, the firstlink in a food chain are plants. Forests provide habitats, food and breeding groundsfor a variety of organisms as well as maintain the oxygen - carbon dioxide balance in

the atmosphere.

By now you would have understood the importance of rivers, streams, oceans,forests, grasslands and the other environments (which we have investigated in thischapter) for our survival. Therefore it is our duty to protect the wild life and theseresources, contribute in following the rules and reglations reguarding the environment,avoid adding substances that are harmful to the environment, finally avoid using envi-ronmental resources indiscriminately.

Fig 1.17 - Bundala reserve

Acts as a sponge for water(Prevent flooding /Overflow)

Wetlands/Marshes

Improves natural beauty

Removes poisonous

pollutants

Provides a habitat

for wild life



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1.2 Using built environments productively

1.2.1 Agricultural environments

Man started changing the environment he lived in to suit his requirements from theearly periods of civilization. In the earlier peroids he depended mainly on huntinganimals for food but this gradually changed to a dependence on plant crops whichmade him the pioneer of agricultural ecosystems.

Fig 2.18 - Some agricultural ecosystems

When converting the natural environment to an agricultural system, man makesthe following changes.

Examples where land is specially prepared for agriculture are seen in teacultivation, paddy cultivation, and vegetable plantations. Wet Patana areas of NuwaraEliya, Sita Eliya, have been used for potato cultivations.

Allocation of land for animal farming resulted in grasslands. Due to constantgrazing by animals a plant succession did not take place in these areas. An example is

the animal farm in Ambewela.

A chena cultivation A paddy field

A tea estate A coconut cultivation A rubber cultivation

Assignment - 4Select any of the agricultural ecosystems stated above and list the special

features found in it.

An animal farm



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Check whether the following are included in your list.1. Same type of crop grown in a large area of land.

2. Soil is prepared to suit a particular crop.3. Using machinery and removing cover crops.4. Providing irrigation facilities.5. Providing transport facilities.

Now let us consider how maximum production is obtained from an agriculturalsystem. It will be useful to compare an agricultural system with a natural environment.In order to figure this out you will have to recall what you learnt in Grade 7.

In order to get maximum benefit from an agricultural system a great deal of attentionand commitment is needed. Water and suitable fertilizers have to be provided as andwhen needed. If some disease is detected it must be controlled immediately since theentire crop can be destroyed quickly.

If the same crop is grown continuously the harvest will get reduced. Hence methodssuch as crop rotation and multi-crop agriculture have to be practise.

Agricultural environment Natural environment

1. Land has to be prepared beforecultivation.

2. One or two selected crops are grown.3. Nutrients are removed from the plot when

the harvest is removed from the land.4. Need to add fertilizer.5. Need to provide water artificially.6. Need to adopt various strategies to

control pests.7. Need to take action to preserve soil.8. Food chains are simple.

1. Prepared by natural means.

2. High diversity of plants.3. Nutrients are retained as products

are not removed.4. No need for extra fertilizer.5. Water is available naturally.6. Pests are controlled naturally.

7. Soil is naturally preserved.8. Food chains are complex.

Assignment - 5Grow some crop that you like in your home garden. Prepare a small plot for

this or grow it in a pot. Maintain a diary about how it was maintained till it startedbearing.



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1.2.2 Industrial environments

The word factory is a familiar word to you from the time you were small. Recallthe various industries in your locality.

Rubber and tea factories, factories for making synthetic clothes, tile factories,brick factories, cement block factories are some examples. An industrial environmentis a system where all factors necessary for the production of a certain product such asthe machinery, raw materials, labour and energy resources are collectively used to getout the finished product.

Industries are essential for a country to develop. Industries produce many thingswhich are needed for the development of the quality of life of the people. Substances

such as the tooth brush you use, soaps, medical drugs, garments, processed foods,sanitary substances, furniture and even energy are produced in specially designed manmade industrial environments.

The products of such industries, just as they are useful may also have certainharmful effects on us too.

1. Noise generated from the factories2. The poisonous gases, smoke and dust given out3. Excess of heat given out and being released to the atmosphere4. Release of unhealthy chemicals are some examples.Due to the above reasons an industrial environment may not be very suitable for

residential purposes.In order to minimize the harmful effects it is necessary to get the approval of the

relevant state authorities and to maintain the approved standards when constructingand maintaining an industry.

The Central Environment Authority, Provincial councils and other local govermentauthorities are organizations working for this purpose. Also laws and regulations havebeen enforced regarding the raw materials used for the industry, release of factoryeffluent, health and protection of the work force.

If you or any of your neighbours have been subjected to the ill-effects of an industrialenvironments, you have the right to seek legal aid !

Assignment - 6Find out information about organizations such as the Central Environment

Authority, Urban Development Authority etc. Write a short essay on how we cancontribute to help them to perform their functions more efficiently.



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From the above discussion it is prominantthat the industrial environment has to be properly

maintained without polution in order to getoptimum benifits.

1.2.3 Human settlements

In mans unending efforts to change the envi-ronment, constructing modern settlements takea special place. Establishment of settlements associated with agricultural developmentprojects started with Independence in Sri Lanka. Example , Gal Oya settlement.

As an example of rural settlements, the establishment of settlements associatedwith the Maha Weli project can be quoted.

At the beginning these settlements there were adequate basic facilities. With timethe population increased and problems arose. As an example space was limited, sanitaryfacilities were not sufficient, and social and cultural differences were seen.

Urban settlements were born due to people migrating to the cities for variousneeds as well as many development projects being established in the cities. Here againland and other facilities became limited creating many problems.

Fig 1.19 - Well planned Industrialenvironment

Lack of space

Diseases rising to

epidemic levelSocial and cultural

problems

Insufficientsanitary facilities

Improper sewagedisposal

Insufficientlight

Unorganisedurban

settlements

Insufficientventilation Damage due to

sudden fires

Floodingduring rain



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As a remedy for the above problems plans are being drawn to build better plannedhousing complexes. Accordingly, high rise flats are planned so that maximum use is

made of the existing land unlike in the unorganized settlements such as the slums.Therefore our motto for tomorrow should be ‘ planned cities’.

Fig. 1.20 - Unplanned urban settlement Fig. 1.21 - Planned urban settlement

From the discussion so far, you should be now able to understand how to makeoptimum use of agricultural, industrial and human settlements productively and

scientifically.

Assignment - 7Construct a model of a planned settlement using throw away materials.In planning the above model make use of the criteria given below:1. Making optimum use of the land2. Sufficient light and ventilation3. Adequate sanitary facilities4. Road ways and water supply5. Recreation and sports facilities6. Safety and protection7. Other daily requirements



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1.3 - Animal’s which are poisonous to man

Sri Lanka is a very fortunate country blessed with a rich biodiversity. People of this country, over a long period in the history have maintained amicable relationshipswith plants and animals, and lived in harmony with the environment. However, therehave been experiences of various types of harm from animals, in various degrees. Inthis context, harm from poisonous snakes is predominant.

Snakes are carnivorous animals predating on live prey. The purpose of the poisonor venom of the snake is to paralyse the prey so that it is easily swallowed. It alsoserves as a protection from enemies. Attacks on human beings is mostly due to human

activities which disturb their habitats or life activities. Hence it is important to understandtheir habits in order not only to protect ourselves but also to protect the snakes sincethey are exceedingly valuable in maintaining the natural balance of the environment.

1.3.1 Snakes

Snakes rank high among poisonous animals in Sri Lanka. Snakes are reptiles whoare legless, hence creep along the ground. They are carnivorous sometimes feeding onprey which are much larger than its mouth. Their mouth and jaws are specially adaptedfor this purpose. The lower jaw consisting of two halves is fastened by an elasticligament which can stretch enabling the mouth to be opened wide to admit any largeprey into the mouth. Before the prey is taken into the mouth it is often paralysed by thevenom secreted by the poison glands.

Poison glands are modifiedsalivary glands and their ducts openat the base of the two canine teethon either side of the mouth. Thispoison is sent out by a canal and

injected into the body of the preyby the canine teeth, which are called‘fangs’. Poison fangs are found onlyin poisonous snakes.

Fig 1. 22 - Poisonous teeth and Poisonous glandsof snkes

sheath of teeth

poisonous gland

nasal opening

poison duct

teeth

tongue



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Snake poison or venom is a protein solution. It contains enzymes and water. Theseaffect the nervous system of the prey. Hence it helps to paralyse the prey as well as in

digestion.

Ninty six species of snakes have been detected in Sri Lanka. Among these onlyfive species are highly poisonous.

They are; i) Cobraii) Two species of kraitsiii) Two species of vipers

Features and habits of the above snakes.

1. Cobra• Can be found anywhere in Sri Lanka.• Length: about 130 - 200 cm.• Special features: Upper side of the body is light brown,

or grey-black. There are white or yellow stripes atintervals. It has a hood which can be expanded. Thereare two black spots on the underside of the hood,and a “ m ”shaped mark on the upper side.

• Habits: During the day it gets about looking for food,while at night time they hide in termite hills, rat holesor piles of firewood.

2. Indian Krait (Common Krait)

• Length: About 90 - 110 cm.• Special features; Highly poisonous species of snake.

Upper side of the body is blackish brown. Body is

shiny as if well oiled. It even preys on other nonpoisonous snakes.• Habits: Gets about in the night looking for food. During

the day hides under decaying leaves, loose soil ordry grass. Fond of watery habitats.

Fig 1. 23

Fig 1. 24

Do you know?The anti-venom vaccine that is given to snake bite victims is also used to prepare

drugs for leprosy, asthma and measles.



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3. Sri Lankan Krait• Length: About 90 cm.• Special features: Highly poisonous snake. Body is

blackish purple. Has ring-like white bands across thebody.

• Habits: Looks for prey in the night. During the day hidesunder rotting leaves, logs or piles of stones. Whenfrightened, coils up and hides the head in the coil.

4. Saw-Scaled viper• Length: About 30 - 45 cm.• Special features: Head is triangular. Has a white bird’s

foot shaped mark on the head. Upper side of the body

is grey- brown and has diamond shaped marks. .• Habits: Nocturnal. During the day hides in loose soil,drying leaves or shrubs. It jumps forward when attackinga prey and recoils to the original position.

5. Russell’s Viper• Highly poisonous snake.• Length: About 80 - 120 cm.• Special features: Upper part of the body is reddish-brown.

The under-side is yellowish - white. In the centre of the

body, and on either side there are three rows of black dots.• Habits: A special feature about this snake is their loud

hisses as a warning sign before striking. More active inthe night but can be seen during the day as well.

Identifying highly poisonous snakesIt is important to be able to identify poisonous species of snakes from the non-poisonousspecies. The following features are useful for identifying these species• Shape of the head.• Nature of the scales on the upper side of the head, body and tail.• Nature of the tail and body features

Fig 1. 25

Fig 1. 26

Fig 1. 27

The venom of saw scaled viper and Russell’s viper travel slowly along the blood,and cause harm to the blood system. The symptoms of these snake bites areblood in urine, bleeding from gums, bleeding under the skin, vomiting blood, bloodin the faeces, severe pain around the wound and swelling.



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Mildly poisonus and non-poisonous snakes

Several species are mildly poisonous, and the symptoms of their stings are festeringaround the wound, severe pain and swelling. This situation persists for a few days. Itmay affect the kidneys but is not fatal. Eg. “Polong Thelissa”, “Mukal ang Thelissa”,“Pala Polanga”

Certain other species such as Catsnake (Mapila), Mal Karawala, Ahatulla havevery lightly poisonous venom. They cause a slight pain, slight swelling which wears outafter a few hours.

Non-poisonous snakes

In Sri Lanka there are 59 species of non-poisonous snakes. The myth that ‘Snakesare poisonous’ make people destroy any snake they meet. Therefore it is important tobe able to identify the non-poisonous types. Even the non-poisonous types arecarnivorous Some of them such as python, rattle snake and checkered keel ball swallowtheir whole prey.

Vipers

TriangularSmallShort, blunt

Body features

1. Shape of head2. Nature of scales3. Tail

Cobra and Kraits

Shape of a spoonLargeLong

Table 1.1

Now let us find out about the mildly poisonous and non-poisonous types of snakes.

Do you know ?Deaths due to the venom of Merrems

hump nosed viper have been reported.Although considered as a highly poisonousspecies, it is a mildly poisonous, nocturnal type.

Fig 1. 28 - Merrems hump nosed viper

Assignment - 8

Get information from your elders about the various ideas they have about snakes.Using books and other resources (teachers) identify the myths from the aboveinformation and prepare a booklet.



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What we can do to prevent snake bites

Sri Lanka, being a country with lush greenery will harbour snakes in any part of the country. Paddy fields, bushes and jungles provide the necessary food, warmth andprotection for snakes. Therefore our first focus should be to protect ourselves fromthe snakes around us, instead of indiscriminate killing of these snakes which is a preciousgift of nature. We can carry out a few but important practices for this purpose.

The reason for the presence of snakes around us and getting exposed to theirstings and bites are largely due to our own neglect. Therefore it is important to followsome simple precautionary measures to avoid harm from snakes. Some of them are asfollows;

• Keep our environments clean - There are many piles of rubbish around us. Leftover food is part of the rubbish. Rats and toads gather around these in search of food. Snakes chase after these prey and get into rubbish heaps for this reason.

• Avoid collecting piles of used newspapers, books etc. Snakes also like all otherreptiles prefer warmth. The warmth inside piles of newspapers etc. may attractsnakes.

• Clean up old termite hills, rat holes around your house for they can attract snakes.• Do not pile up left over bricks, tiles in your back garden. They provide the necessary

warmth and protection for snakes.• Use correct protective gear when walking around places where snakes may be

found. When walking around in the night carry a torch and wear protective boots.• When walking on grass or shrubs, make a noise on the ground or beat the ground

with a stick. Although snakes have little hearing they are extremely sensitive tovibrations on the ground. Therefore, snakes creep away from such places for theirown protection.

It is important to be aware of what treatment should be taken in case of snakebites or stings.

What can be done when bitten or stung by a snake ?

In case of bites from strongly or mildly poisonous snakes, remove the patientimmediately to a state hospital. Follwing first-aids can be given until the proper treatmentis made available.• Reassure the victim• Make him comfortable to avoid any fear of excitment• Loosen the clothes if they are tight.



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• Wash the wound well with soap and water. Cover with a clean piece of cloth (toprevent bacterial infection).

• If the bite is in the foot, do not move it, lift the victim when taking him to hospital.

What not to be done when bitten or stung by a snake ?• Do not suck out the blood from the wound with your mouth.• If the patient is unconsious, avoid giving anything orally.• Do not give king coconut, young coconut, fruit juice or drinks which contain alcohol.• Do not cut around the wound, put constricting bands or give Aspirin as a sedative.

The polyvalent anti-venom serum used in hospitals can be used for all five types of snakes. It is given only when symptoms begin to appear.

1.3.2 Other poisonous animals

Among the poisonous animals around us Arthropods play an important part. Somesuch Arthropods are wasps, hornets, bee, centipede, scorpion and tarantula.

Wasps, hornets and bees are herbivores feeding on plant nectar. Therefore theirpoison is only for protection. They introduce poison into our bodies with their ‘sting’placed at the posterior end of their body. When they sting the darts of the sting remainin the body of the victim.

Fig 1. 29

wasp hornets bee

Centipede Scorpion Tarantula



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Bee poison is not fatal, but wasps and hornets poison may be fairly lethal, sometimemay even cause death. As soon as a bee stings, removing the darts from the wound

can relieve the pain.Wasps and bees collect honey in their hives. As long as we do not disturb them,

they do no harm to us. By trying to collect honey from these hives, people get attackedby these bees and wasps. Further, in order to chase them away, people try to destroytheir colonies and get attacked by these insects.

Centipede is a carnivorous animal. Centipedes have poisons stings to anesthetisethe prey as well as for their own protection. They remain inactive during the day, hidingunder stones or rotting leaves and become active in the night. So, most people getstung by centipedes at night time.

Scorpion too is carnivorous. It is a solitary, nocturnal arthropod. It remains inactiveduring the day under rotting logs of trees, rubbish heaps and stones. Poison is sent outby a sting at the end of the tail. It too helps to anaesthetise the prey, digest it, as well asfor protection. When man becomes a challenge they may sting them too.

Tarantula is a highly poisonous arthropod. The most poisonous forms have hairson their body. They can be found on coconut trees, palm trees etc. A special featureabout spiders is their habit of moving towards a danger.

In order to prevent or minimise harm from poisonous animal we need tounderstand their habits and life activities.

The poisonous animals which we mentioned above seem to be harmful to man,but we cannot forget their environmental importance.

Assignment - 9Find out about traditional remedial methods in your town/village for stings by

poisonous Arthropods

Assignment - 10Construct a poster showing the ways of preventing or minimising harm from

poisonous snakes and arthropods.



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1.3.3 The environmental importance of poisonous animals

The population of members of any species remain at a level that can be supportedby the environment. This is called balance in nature. Nature itself has certain ways bywhich this balance is maintained. Presence of carnivorous reptiles and other poisonousanimals are one way which helps to maintain the environmental balance.

Carnivorous animals do a predatory function. Predators prevent the population of their prey increasing beyond control.

Example;

• Number of pests are kept under control by being eaten by snakes, tarantulas andcentipedes.

• Number of rats, frogs, lizards and small snakes are kept under control by poisonoussnakes eating them.

• Insects such as bees and wasps help in pollination of flowers which is importantfor producing fruits.

So, it is clear that all the poisonous animals we learnt before are part of a foodchain. They also contribute to increasing the bio-diversity in our environment.

So, by destroying such animals we do a lot of harm to our environment. You mayby now understand the importance of protecting ourselves from them while consideringthem as our eco-friends.



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1.4 International Scientific symbolsPay attention to the symbols indicated below;

1 2 3What is the message or order conveyed by each of the above symbols?They are stated below;

1. Bus stop2. Pedestrian crossing for children ahead3. Hospital

Just like you, any person in any corner of the rest of the world too, willunderstand the above message or order in exactly the same way as you.

Man has being using symbols to communicate information in the past too.These symbols were unique to each country, nationality, different groups, dif-

ferent areas. Communication among people of different countries have become closer,due to current trends in globalisation.

Therefore there is a need for developing these symbols according to in-ternational standards to be acceptable to any citizen in any part of the world.This enables any person in any country, nationality, whether literate or illiterateto understand the messages given by these symbols.

There is a need to understand and act according to the various messagesgiven by symbols in our dealings with places delivering services and goods,dealing with equipment, travelling to foreign countries and seeking employmentin various institutions. Therefore it is important to be knowledgeable about thesesymbols.

Assignment - 11• Note the symbols indicated in various places and in labels of various

packed goods and write them down.• Try to understand the messages that are communicated by these symbols.



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In this chapter, let us consider some common symbols used in scientific laborato-ries, factories, medical field and in communicating weather information.

1.4.1 Symbols associated with scientific laboratories

A laboratory is a place where various kinds of chemicals, glassware and otherequipment as well as water and electricity are being used. In working under suchenvironment, there is a tendency for various accidents to occur.

Many persons work in laboratories. Therefore such places should be maintained

methodically. You should be especialy more concerned regarding safety and disci-pline when working in a laboratory. Proper laboratory practices will reduce the numberof accidents and help to maintain the condition.

The use of symbols in laboratories is largely concerned with messagesregarding the safety and orderly maintenance of the laboratory.

Examine table 1.2 showing some symbols used in laboratories and the messagesconveyed by each of the symbols.

Fig 2.30 - Students engaged in an experiment inside school laboratory



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Assignment - 12

• Examine the labels on the bottles / packing of chemicals in your schoollaboratory and try to identify the above symbols indicated in them.

• List out the properties of the substance as indicated by the symbol.

Table 1.2 - Some symbols used in Chemistry laboratories

Substance which can explode on cathing firerubbing or shock.

Oxidising (These substances provide oxygen which allowsother substances to burn more fiercely).

Highly inflammable.

Toxic. (These substances can kill. They may act when youswallow them, or breathe them in or absorb them through yourskin).

Irritant (These substances are not corrosive but can causereddening or blistering of skin).

Corrosive (These substances attack and destroy living tissue,including eyes and skin).

Eye wash (If some chemical enters the eye, a place for washingthe eye).

Emergency shower (A place for washing the body if a chemicalcomes in contact with the body or in case of burns).

Symbol Message conveyed by the symbol



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1.4.2 Symbols associated with factories

The symbols used in factories help to ensure the protection of the workers of thefactory as well as visitors coming from outside. In addition they also give a directiontowards the orderly maintenance of the factory. Some such symbols and the messagesconveyed by each is given in the table below. (Table 1.3)

No Smoking

No Entry

Do not touch

No eating or drinking

Fire Exit

Eye protection must be worn

Wear protectors

Switch off when not in use.

Symbol Message / Order

Table 1.3 - Some symbols associated with factories



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1.4.3 Symbols associated with weather informationInformation regarding weather conditions are constantly provided to the public

through media. In the communication of this information many symbols are used. Somesuch common symbols and the messages communicated by them are given in the tablebelow

Do you knowMeteologists use certain symbols of International standard to record and map

out information regarding the weather.Indicated below are some such symbols.

Light showers expected

Normal or heavy rain

,Symbol Weather information

Symbol Weather Information

Clear sky (night)

Sunny

Light rain shower (day)

Drizzle

Heavy rain

Thunder storm

Heavy snow

Table 1.4 - Symbols used to interpret weather information



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1.4.4 Symbols associated with the medical fieldSymbols associated with the medical field convey messages to ensure the safety

and orderliness of the employees, patients, visitors and places such as hospitals,operation theatres, medical laboratories.

Wear masks

Wear gloves

Wash your hands

Danger, Biological hazard. Eg, Place where pathogenicmicroorganisms experiments are conducted.

Radioactive. Eg. Place where X-rays are used. Emission

of harmful rays.

Symbol Message / Order conveyed by the symbol

Table 1.5 - Symbols used in the medical field

The above descriptions of symbols were those commonly used in certain fields only.Although they are indicated for specific fields, they can be used as and when necessaryin any other field too.

There are many more symbols that are in use, other than those you just studied.Identifying these symbols, acting accordingly will ensure your own personal safety,safety of others, your environment as well as ensure the orderly maintenance of theinstitutions concerned. Therefore it is vital that you act with a knowledge of the use of symbols.

Assignment 13• Identify places in your school, class room, laboratory where symbols can be put

up in order to make such places safer and orderly.• Construct some boards with appropriate symbols and place in suitable places in

the school with the permission of your principal.



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Exercises

(1) Students of Grade 8 joined a field trip to observe different types of ecosys-tems. Given below is a report prepared by them regarding the differenthabitats.

Observations Eco system Observations Ecosystems

01. Tree tops show clearstratification. Groundlayers are dark. Manystreams and waterways.

02 Plants with fleshy leaves.Posses thorns. Fewleaves. Dry winds.Strong, intense sunlight.

03. Plants are stunted.

Trunks are hoisted withknots. Epiphytes growon the trunks. Plantssuch as walsapu, dan,olives(Veralu) andkeena are common.

04. Trees spread far apart.Undercover not verydark. Has good under-

growth. Many trees of economic importance.

05. Has a grass cover.Few trees growingrandemly. Good

water seepage. Coolclimate, and windy.

06. Ocean is seperatedfrom a sandy dune.Water is salty. Prawns& crabs abdundant.Sonneratia and nearthe shore.

07. Fresh water habitat.

Water does not flow.Many reeds along theedges. Frogs, water -snakes and fish areabundant. Flowerssuch as Olu & Manelare common.

08. Thin plant cover onground. Tall bushesfar apart. Dominants

are Mana and Iluk grass varieties.

Select the suitable ecosystem that fits the description from those given below:

Montane forest, Tropical rain forest, Wet Patana, Dry Patana, Damana, Villu,Thorny shrubs and woods, Talawa, Dry mixed evergreen forests, inland waters,lagoons.



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(2) When we travel along the main roads in Sri lanka we come across morecultivated areas than natural forest areas.

I. Name the most common type of tree used for re forestation in theTalawe grasslands in the low country wet zone.

II. What type of plants have been selected for reforestation in the upcountry areas?

III. A single brown - hopper infecting a paddy field can destroy the entirefield, but an insect infectation to a natural forest will not destroy theentire forst. Give a scientific explanation for the above phenomenon.

(3) State the factors we should be concerned about as Sri lankan when constructing an industrial environment.

(4) Read the following statement by several students on observing serpentin the school premises.

I. It is wrong to let it go, because there is a saying that ‘ Anyone who letsa poisonous snake get away is a fool’.

II. All snakes are not poisonous - so let us let him stay.III. Snakes hover aound the school because of the rubbish heaps we collect.IV. Let us knock the ground with a stick. Then it will go.

V. Even if the snake is poisonous, it has a significant environmental value.

State briefly, your ideas about each of the above statements.

(5) Identify the given symbols and answer the following questions.

I. Write in order, the message given by each of the above symbols.II. Write down one location where each of the above symbols should be

exhibited.III. In a place where the symbol a is exhibited, there is a heap of broken articles

strewn around. Explain briefly the hazards that can be caused by this.IV. What are things you should not do in a location where b. is exhibited.V. ‘Sometimes indicating messages by symbols is more effective than by

writing’ - Give your ideas about this statement.

bca

Documents

8 Science Chapter 1