Hwa Chong Institution (High School) Sec 3 SMTP Biology 2013 ECOLOGY EFFECTS OF HUMAN ACTIVITIES ON THE ECOSYSTEM Content Energy flow Food chains and webs Carbon cycle Effects of man on the ecosystem Environmental biotechnology Learning outcomes Students should be able to 1 Briefly describe the non‐cyclical nature of energy flow 2 Explain the terms producer, consumer and trophic level in the context of food chains and food webs 3 Explain how energy losses occur along food chains, and discuss the efficiency of energy transfer between trophic levels 4 Describe and interpret pyramids of numbers, biomass and energy 5 Describe how carbon is cycled within an ecosystem and outline the role of forests and oceans as carbon sinks 6 Evaluate the effects of  water pollution by sewage and by inorganic waste  pollution due to insecticides including bioaccumulation up food chains and impact on top carnivores  enrichment of water with nitrates and phosphates 7 Outline the roles of microorganisms in sewage treatment as an example of environmental biotechnology 8 Discuss reasons for conservation of species with reference to the maintenance of biodiversity and how this is done, e.g. management of fisheries and management of timber production 9 *Explain the causes and effects of deforestation and global warming References and Acknowledgements Biology: A Course for ‘O’ Level by Lam Peng Kwan and Eric YK Lam (Federal) GCSE Biology by DG Mackean (John Murray) Advanced Biology: Principles and Applications by CJ Cle.g.g and DG Mackean (John Murray) Advanced Biology through Diagrams by WR Pickering (Oxford University Press) A‐Level Course in Biology by Hoh Yin Kiong (Longman) 1 ECOLOGY 
Ecology encompasses the study of the distribution patterns of organisms, their numbers, their interactions with one another, and their relationships to their environment. 
In other words, ecology is the study of how organisms interact with their physical and biological environments and how these interactions influence the distribution and abundance of living organisms within the biosphere. 
Interactions are necessary because there is only one source of energy (the sun) and all living organisms depend on the flow and harvesting of life‐supporting solar energy through photosynthesis. LEVELS OF ECOLOGICAL ORGANISATION Organisms can be studied at six different levels: individual, population, community, ecosystem, biome and biosphere. Each level is a subset of the next level.  Each species is made up of individuals.  A population is a group of interbreeding individuals of the same species, all occupying a defined area at the same time, e.g. mudskippers living in a mangrove swamp in the Sungei Buloh Wetlands Reserve.  A community is made up of all the different species or all the populations of plants, animals and microorganisms that live and interact in a particular area, e.g. the mangrove swamp habitat has a community made up of mangrove trees, mudskippers, sand flies and microorganisms in the mud.  Different species of a community, together with their non‐living environment, constitute an ecosystem.  An ecosystem is a community of organisms, interacting with one another and their abiotic (non‐living) environment to form a more or less balanced, self‐supporting unit with its own characteristic pattern of energy flow and nutrient cycling. An ecosystem uses both energy and inorganic nutrients.  Energy from the sun enters an ecosystem and flows through it in a linear or non‐cyclic manner. As such, energy has to be constantly supplied to an ecosystem.  Inorganic nutrients are obtained from the physical (abiotic) environment and flows through the ecosystem in a cyclic manner. Thus they are continually recycled, for example, the carbon cycle.  An ecosystem is a part of a biome, e.g. tropical rainforest or sea.  All organisms are restricted to a narrow zone of about 22.4 km called the biosphere, which is the region of Earth’s land, water and air in which organisms can be found. 2 HABITAT  A habitat is the place where an organism lives, i.e. where it obtains its food and shelter, and where it reproduces, e.g. the habitat of the mudskipper is the mud in the mangrove swamps. ENVIRONMENT  An environment means everything in the surroundings of an organism that could possibly influence it. It consists of the non‐living (abiotic) or physical environment and living (biotic) environment. Abiotic factors  The abiotic factors are: climatic factors (light, temperature, water availability, wind) edaphic factors (texture, nutrient status, acidity, moisture content of soil) topographical factors (angle, aspect / direction and altitude of slope)  Light is the ultimate source of energy, thus light intensity affects the distribution and growth of plants and animals.  Temperature influences the rate of all biochemical reactions, and thus, the metabolic activities of organisms. It also influences the rate of evaporation. Plants are adapted to seasonal changes by possessing underground storage organs, shedding of leaves and formation of seeds just before the approach of an unfavourable season.  Water is made available to the land by rainfall. Rainfall distribution over the year is an important limiting factor for organisms. Organisms are adapted to live in dry or wet places, for example,  xerophytes (plants that live in dry areas) reduce rate of transpiration by shedding their leaves, store water in their stems, possess sunken stomata, roll up to reduce surface area exposed to the surroundings  hydrophytes (plants that live in wet areas) have stomata on upper surface of leaf for gaseous exchange and air chambers throughout stem and root  Oxygen is required by aerobic organisms for respiration. Mangrove trees that live in oxygen‐poor mud possess special breathing roots called pneumatophores that arise from the root system and project above the mud surface.  Salinity (salt concentration) is an important factor for aquatic organisms.  The salt concentration of cytoplasmic contents of freshwater organisms is usually higher than that of the surrounding water, so water tends to enter these organisms by osmosis. Protozoa, e.g. Amoeba have contractile vacuoles to remove excess water that enters them by osmosis.  Animals living in sea water tend to lose water by osmosis as the sea water contains a higher concentration of salts than their cells.  pH of water and soil influences types of organisms in such environments. In strong light, photosynthetic activity of plants uses up carbon dioxide in water, making it slightly more alkaline. At night, when photosynthesis ceases and carbon dioxide is produced from respiration, the water turns more acidic. 3 Biotic factors  The biotic environment concerns all living things which an organism comes into contact with. It consists of different species of plants and animals that interact with each other. NICHE  The niche refers to where and how an organism lives within its habitat.  It represents more than just a physical area within a habitat as it includes an organism’s behaviour, interactions with its living (biotic) and non‐living (abiotic) environments, and the role it plays in its habitat, e.g. how it gets its energy and nutrients, how and when it reproduces and how it relates to other species.  An organism’s niche is determined by physical factors (amount of light, oxygen, carbon dioxide, temperature, pH) and biological factors (food requirements, diseases, predators, competitors).  The term fundamental niche refers to the set of resources a population is theoretically capable of using under ideal circumstances in the absence of competition. However, factors such as competition, predation, or limited resources, may force the population to use only a subset of its fundamental niche. The resources a population actually uses are called its realized niche.  According to the Gause’s competitive exclusion principle, two species with similar needs for the same limiting resources cannot coexist in the same place. In other words, two species cannot coexist in a community if their niches are identical.  Separate laboratory cultures of the species Paramecium aurelia and P. caudatum each grew to carrying capacity. However, when two species are grown together, P. aurelia has the competitive edge over P. caudatum in obtaining nutrients, thus the population density of P. caudatum decreased significantly.  Balanus balanoides and Chthamalus stellatus are two types of barnacles that grow on rocks exposed during low tide along the Scottish coast. Balanus fails to survive high on the rocks due to desiccation. Its fundamental niche and realized niche are similar (B1 and B2 below). Even though Chthamalus is concentrated on the upper strata of rocks, when Balanus is removed from the lower strata, the Chthamalus population spread into that area. Thus the realized niche is only a fraction of its fundamental niche (C1 and C2 below). 4 C2
C1 B1 B2 Circumstantial evidence for competition:  Different species are observed to exhibit some niche differences when they coexist in a community. Resource partitioning, in which different species consume slightly different foods or use resources in different ways, reduce interspecific competition, enabling them to coexist within a small geographic area.  Character displacement is the increased morphological differences observed between species when they occur together in the same habitat. Resource partitioning: Five species of warblers Character displacement: Galapagos finches feed in different parts of the spruce tree to display different beak depths on the same avoid competition. island where the different species occur to avoid competition by feeding on seeds of different sizes. 5 FEEDING RELATIO
ONSHIPS OFF AN ECOSY
YSTEM TROPHIC LEVELS means feedin
ng, so troph
hic level reffers to the position p
or stage at whhich organissms obtain Trophic m
their food
d. UENTS OF TR
ROPHIC LEV
VELS CONSTITU
otrophs are mainly greeen plants an
nd photosyn
nthetic bactteria that caan convert 1 Produccers or auto
light eenergy from
m the sun in
nto chemicaal energy which w
they store in thheir organic materials (carboh
hydrates) during photo
osynthesis. TThey manuffacture com
mplex organiic materialss from raw inorgan
nic materials. This is the trophic level that ultimately su pports all otthers. mers or hetterotrophs o
obtain their energy from
m other org
ganisms on w
which they feed. They 2 Consum
requiree continued supplies of organic com
mpounds as food. ores feed di rectly on plaants (produccers). Primarry consumerrs or herbivo
Second
dary consum
mers or carn
nivores feed on herbivorres (primaryy consumerss). mposers or detritivores
d
3 Decom
are made up soil micrroorganismss such as baacteria and fungi that break d
down wastee and decaying organic materials off producers and consum
mers (dead leaves and animal droppings) and return inorganic m
materials to tthe physical environme nt to be use
ed again by plants. green p
AIN AND FO
OOD WEB FOOD CHA
 A food
d chain is th
he linear tra
ansfer of en
nergy in food from plan
nts through a series of organisms with reepeated eatiing and bein
ng eaten. Ea ch stage in aa food chain
n is known aas a trophic level.  Most ffood chains do not hav
ve more thaan 3 to 5 lin
nks due to the inefficie nt transfer of energy. Long fo
ood chains ffunction lesss efficientlyy than shortt ones because of the l oss of energy at each trophicc level. A
A food chain
n  A food
d web or food cycle is a web‐‐like feedin
ng relationsship betweeen the orgganisms of interlocking or inteerconnecting food chainns. 6 
Organisms whose food is obtaained by thee same num
mber of step
ps in the foood chain belong to the same ttrophic levell. A food web
b INTERACTTIONS AMONG ORGANISMS  A pred
dator is a caarnivore thaat feeds on living species. Predators are norm
mally larger than their prey, aand tend to
o kill the pre
ey before t hey eat it. The predato
or‐prey inteeraction maay produce cyclic cchanges in th
he populatio
on size of th e predator aand prey.  A scave
enger is a caarnivore thaat eats the d ead remains of animalss.  Symbio
osis (“living together”) is a term thhat encomp
passes a variety of interractions in which two speciess, a host and
d its symbion
nt, maintainn a close association.  There a
are three geeneral types of symbioti c interactions:  In pa
arasitism, o
one organism
m (the parassite) harms tthe host.  In co
ommensalissm, one parttner benefitts without significantly a
affecting thee other.  In m
mutualism, b
both partnerrs benefit froom the relattionship.  The ke
eystone speccies is the sspecies whicch makes an
n unusually strong impaact on the ccommunity ure. The imp
pact is dispro
oportionatelly large relattive to its ow
wn abundannce. Example
es: structu
 In so
ome communities, keyystone predaators mainttain higher species s
diveersity by red
ducing the densities of strrong compe
etitors, suchh that comp
petitive exclusion of otther speciess does not ur. occu
 Beav
vers constru
uct dams thaat change frree‐flowing sstreams into
o lakes and pponds.  Afric
can elephan
nts uproot extensive fforested arreas, transfo
orming them
m into savannahs or grassslands. 7 NON‐CYCLIC ENERGY FLOW IN AN ECOSYSTEM 
In any ecosystem, the ultimate source of energy is the sun. The flow of energy through the ecosystem is non‐cyclic in nature. The energy released as heat energy to the environment does not return to the same system or organisms that produced it. 
Dead parts and bodies of organisms, and egested and excreted materials contain trapped chemical energy. This is released by the activity of decomposers which use some of this energy and the rest is lost as heat energy. Eventually all the energy that enters the biotic part of the ecosystem is lost as heat energy. 
Biological productivity is the rate at which biomass is produced by an ecosystem. It has two components:  Primary productivity is the rate of production of new organic matter by green plants (autotrophs).  Secondary productivity is the rate of production of new organic matter by consumers (heterotrophs). 
Gross primary productivity (GPP) refers to the amount of glucose manufactured during photosynthesis by producers occupying an area of one m2 over a period of one year. 

Some of the glucose manufactured by producers during photosynthesis will be used for respiration. The net primary productivity (NPP) is the amount of biomass formed by producers occupying an area of one m2 over a period of one year. Thus, NPP = GPP – R, where R represents the amount of glucose used for respiration by producers occupying an area of one m2 over a period of one year. Both GPP and NPP are expressed in units of biomass, e.g. kg m‐2 year‐1, or energy, e.g. kJ m‐2 year‐1. 8 
GPP represents only about 1% of the light energy that is available to the producers. The remaining 99% of light energy is lost in the following ways:  Some of the energy hits the ground and not the producers.  Some of the energy is reflected by the waxy cuticle of the leaves.  Some energy is used to evaporate water in transpiration.  Green light is not absorbed by the chlorophyll in the producers.  Photosynthesis is energetically inefficient as it is limited by low carbon dioxide concentration or temperature. energy available to next trophic level TRANSFER OF ENERGY BETWEEN TROPHIC LEVELS  On the average, only about 10% of energy in a trophic level is converted to biomass in the next trophic level.  The transfer of energy from producers to primary consumers (herbivores) is the least efficient, about 1% to 10% of the biomass of the producers. The low level of energy transfer is due to the following:  Some energy trapped in glucose is lost during respiration by the producers as heat energy.  Plants contain cellulose and lignin that may not be completely digested by primary consumers.  Leaves of certain plants may contain poisonous substances such as phenolics and are therefore not consumed by animals.  Certain parts of plants like the roots are not accessible to animals.  Some plants die before they can be eaten (flow of energy to the decomposers).  The transfer of energy from primary consumers to secondary consumers (primary carnivores) is typically 10% to 20% of the biomass of primary consumers. The energy in primary consumers is lost through the following processes:  Loss as heat energy in respiration by the primary consumers.  Excretion (in the urine) by the primary consumers.  Egestion (in the faeces) by the primary consumers.  Certain parts of the primary consumer like bones cannot be eaten.  Death of the primary consumer before it is eaten (flow of energy to the decomposers). 9 
Decomposers such as bacteria and fungi obtain their nutrients and energy from the remains of dead animals and plants. In some ecosystems like the floor of tropical forests, 80% or more of the productivity at any trophic level may be available for the decomposers. 
Ecological efficiency is the percentage of energy transferred from one trophic level to the next, or the ratio of net productivity at one trophic level to that at the level below. It ranges from 5% to 20%. ECOLOGICAL PYRAMIDS 
Food webs give a useful description of feeding relationships in a community. However they are non‐quantitative. Ecological pyramids give a quantification of feeding relationships because they involve obtaining numerical data. PYRAMID OF NUMBERS  This is a bar diagram indicating the relative numbers of organisms at each trophic level at any one time in a given unit area in a food chain.  Characteristics of a typical pyramid of numbers:  Ecosystems are populated by a large number of small animals and a progressively smaller number of larger animals.  Small creatures reproduce faster than larger creatures, so the surplus of small organisms drives the food chain.  Drawback in the use of pyramid of numbers: Each organism is counted as one regardless of their size (e.g. an oak tree is counted as one individual, like an aphid). If the producer is a large tree and an individual tree can support many herbivores, the pyramid of number becomes an inverted pyramid. 10 PYRAMID OF BIOMASS  The pyramid of biomass represents the total biomass of organisms at each trophic level at any one time in a given unit area.  Biomass = number of individuals per unit area  average dry mass of each individual. The unit used is kg m‐2.  The dry matter estimated is the biomass at one particular moment only. This is called the standing crop. A problem arises with organisms with short life cycles; marine phytoplankton may be out‐lived by their predators, zooplankton. Then, for a time, the standing crop of phytoplankton may be smaller than that of its predators. This anomaly arises because no account is being taken of the rate at which the biomass is produced, but only the quantity present at one particular moment.  Limitations of a pyramid of biomass:  The determination of dry mass involves drying the organisms at 100C, and thus is destructive.  A small sample of individuals is normally taken in the determination of dry mass, and this may not be representative of the biomass of all individuals in a population.  Since the standing crop (total biomass at a particular time, rather than over a time interval) is represented, this may result in an inverted pyramid of biomass. PYRAMID OF ENERGY  This represents the flow of energy through each trophic level of an ecosystem per unit area over a given period of time. The length of time is usually one year. The unit used is kJ m‐2 year‐1.  The total energy decreases progressively along the food chain, thus the pyramid of energy is always broad at the base and narrow towards the apex (upright shape).  About 90% of energy is lost when it is transferred from one trophic level to the next. The greatest amount of energy is lost during its transfer from producer to primary consumer.  The pyramid of energy takes into account the productivity, which is the amount of biomass or energy produced over a time interval, whereas standing crop considers the amount of biomass or energy at a particular time.  However, to construct a pyramid of energy, one needs to combust the organisms. This is destructive and will affect the food chain. 11 NUTRIENT CYCLING IN NATURE While the Earth receives a continuous supply of solar energy, the supply of minerals is limited, so living systems must be able to recycle the chemical constituents of life, e.g. carbon and nitrogen. CARBON CYCLE  The carbon dioxide concentration in the atmosphere remains relatively constant. The various processes by which carbon, in the form of carbon dioxide, is removed and restored to the atmosphere constitute the carbon cycle. In this cycle, carbon cycles between the biotic and abiotic components of the ecosystem. (A) Natural removal of carbon dioxide from the atmosphere – photosynthesis  During photosynthesis, green plants absorb carbon dioxide from the atmosphere and use it to manufacture carbohydrates like glucose. When animals feed on green plants, the organic carbon compounds become part of their bodies. (B) Natural release of carbon dioxide into the atmosphere – respiration, decomposition / decay  Respiration: When living organisms respire, organic carbon compounds like glucose are broken down and carbon dioxide is released into the environment.  Decomposition or decay: Saprophytic fungi and bacteria commonly feed on dead and decaying plants and animals or their faeces or urine. The process of decomposition involves (i) Hydrolysis of complex organic matter in dead and decaying matter by enzymes secreted by saprophytic microorganisms (decomposers) into simple organic matter (ii) Simple organic matter, e.g. simple sugars (glucose) are absorbed into the microorganisms by diffusion (iii) When the microorganisms respire, simple sugars are broken down and carbon dioxide is released into the atmosphere. (C) Carbon reservoirs or storage  A carbon sink is an area that stores carbon compounds for an indefinite period, more than it releases. In other words, it is a carbon reservoir. 12 

The tw
wo main carb
bon sinks are oceans annd forests. C
Carbon sinkss remove ca rbon dioxide from the atmosp
phere and th
his helps to reduce ratee of global w
warming. The role of oceanss as carbon sinks are drriven by two
o processes, namely th e solubility pump and biological pump. pump is a physicochemical processs that transp
ports carbonn dioxide, ass dissolved  Thee solubility p
on, from the ocean’s surrface to the interior. inorrganic carbo

c
dioxxide fixed by photosyynthesis is  Thee biological pump is a process by which carbon nsferred to deep ocean
ns as dead organisms such as phyytoplanktonn or algae, skeletal s
or tran
faeccal material, resulting in sequesttration (storage) of ca
arbon for loong periodss of time. Perm
manent seq
questration may be in the form of organic matter or ccalcium carrbonate. A fracction of organic carbon
n transporteed by the biological b
pu
ump to the seafloor iss buried in ano
oxic conditions under sediments to fform fossil ffuels, e.g. oil and naturaal gas. Forestss are also im
mportant caarbon sinks. Atmospherric carbon d
dioxide is abbsorbed by plants and used in
n photosynthesis. In forrests, a largee amount off carbon com
mpounds is stored in trees. When the treees die, theeir remains may be burried deep in
n the groun
nd. In anaeerobic or higghly acidic conditiions such ass waterloggged soils, deecomposition may not be complette, thus deaad remains are sub
bjected to caarbonificatio
on – physicaal processess that transform them innto fossil fuels such as coal. 
The Kyyoto Protoccol is a pro
otocol to thhe United Nations N
Framework Coonvention on o Climate Changee. It was firrst adopted in 1997 onn Kyoto, Jap
pan. It is aim
med at reduucing green
nhouse gas emissio
ons, for example, carbo
on dioxide. SSingapore joined the Kyo
oto Protocool in 2006. Th
he primary greenh
house gas in Singapore is carbonn dioxide generated g
frrom energyy consumpttion. Thus, Singapore has mad
de it compulsory for all air‐conditio
oners and refrigerators tto be energyy efficient.
here – combbustion (D) Humaan activitiess that releasse carbon diioxide into tthe atmosph
 Burning of fossil fu
uels like coal and naturaal gas releases carbon dioxide into tthe atmosph
here. 13 Importance of the carbon cycle  It ensures that there is a continuous supply of inorganic carbon dioxide for plants to carry out photosynthesis that converts solar energy into chemical energy which other non‐photosynthetic organisms depend on.  It enables a linear flow of energy through the ecosystem since the organic carbon compounds contain trapped energy that is passed from one trophic level to the next. THE EFFECTS OF HUMAN ACTIVITIES ON THE ECOSYSTEM 
Natural resources are resources supplied by nature. Renewable natural resources such as air, water, soil, forests and wildlife can be replaced in the ecosystem. On the other hand, non‐
renewable natural resources such as fossil fuels take many years to form, thus they cannot be replaced once they are used. 
An ecosystem consists of groups of organisms that interact with each other and with the environment in which they live. An ecosystem is self‐sustained and stable only when certain conditions exist:  A constant input of light energy  Presence of producers that capture light energy, convert it to chemical energy which is stored in organic compounds  The cycling of matter from the environment into living organisms and back to the environment again 
With the development of agriculture, it is possible to support large populations, thus the balance between humans and their environment is upset. 
An increasing population has three main effects on the environment.  Intensification of agriculture – leads to the destruction of forests and wildlife habitats to grow more food plants  Urbanization – crowding leads to problems of waste disposal and pollution of atmosphere when fuels are burned for transport and heating  Industrialization – leads to air pollution when gases and wastes are released DEFORESTATION Deforestation is the rapid destruction of forests and woodland. CAUSES OF DEFORESTATION  Logging Forests are cut to obtain timber for lumber and paper production. 14 
Gathering fuel wood In many parts of the world, wood is a major energy source and is used for firewood. Some of this wood is converted to charcoal to be used as fuel. 
Slash‐and‐burn or “shifting” agriculture The farmer cuts the trees, tills the land for a few years, then abandons it and leaves it fallow for up to 7 years for the forest to regenerate. The land is needed for growing crops such as rice. 
Urbanization Forests are cleared for development such as housing, industrialization and infrastructure such as roads and railroads. 
Cattle ranching In order to raise cattle to supply the US demand for hamburgers and hotdogs, cattle ranchers in Central America are clearing away tropical forests and converting the newly opened areas to grazing land. EFFECTS OF DEFORESTATION  Soil erosion  The leaf canopy of the trees in tropical rainforests protects the soil from the impact of the falling rain. The roots of the trees hold soil and water.  The removal of trees exposes the soil directly to the force of the rain.  Topsoil, the most fertile layer, is washed away during heavy rain, especially on steep slopes.  Sheet erosion occurs when the whole of the topsoil is washed down a slope by heavy rain.  Gully erosion occurs when rainwater flows down hillsides in small channels which gradually widen and deepen as more soil is washed off, forming gullies.  Lowland flooding  Eroded soil due to deforestation may be deposited in rivers and streams, blocking the flow of water.  Water levels in rivers rise rapidly, causing floods.  Desertification  Sunlight falls directly onto the soil. Water evaporates rapidly from the soil which then hardens.  With the topsoil eroded, plant life cannot be supported. The land becomes barren.  The destruction of land leading to desert‐like conditions is called desertification.  Climate change  Deforestation reduces transpiration, resulting in fewer clouds and reduced rainfall.  On the global scale, deforestation and burning of wood cause progressive warming of the Earth because of excessive carbon dioxide released. 15 
Loss off cultural divversity  Thee world’s forests, particu
ularly rainfo rests, are ho
ome to overr 10 million ttribal people
e.  Deforestation ccauses the e
extinction off forest dwe
ellers, e.g. B
Brazil lost 877 tribes betw
ween 1900 and
d 1950. 
Loss off natural hab
bitats and biodiversity
 Trop
pical forestss contain an enormous ddiversity of species.  Desstruction of ttropical fore
est destroys a large num
mber of diffe
erent specie s.  Man
ny plant species that have h
medic inal properties, e.g. th
he Madagasscan periwin
nkle which ds one of th
yield
he most pote
ent anti‐leukkaemia druggs, will be exxtinct. POLLUTION
N Pollution is the proceess by which
h harmful suubstances aare added to
o the enviroonment in th
he form of gases, wastes and cheemicals. The
ese harmful substances are called p
pollutants. 16 WATER POLLUTION Human activity sometimes pollutes streams, rivers, lakes and even coastal waters. This affects the living organisms in the water and sometimes poisons humans or infects them with disease. (A) WATER POLLUTION BY INORGANIC WASTES  Inorganic wastes consist of acids, alkalis and heavy metal ions (mercury, copper, lead, cadmium, nickel). Cadmium and nickel are carcinogenic chemicals. Mercury causes brain damage and deformities.  Many of these compounds tend to accumulate in aquatic organisms, and are passed along food chains. They become concentrated and build up to toxic levels in the bodies of the final consumers, thus causing harmful effects in them.  The case of mercury poisoning in Minamata Bay, Japan:  In 1952, many people in Minamata Bay in Southern Japan died or became seriously ill as a result of mercury poisoning. A factory has been discharging mercury into the bay as part of its waste.  Although the mercury concentration in the sea was low, its concentration was increased as it passed through the food chain. By the time it reached the people of Minamata Bay, in the fish and other seafood which formed a large part of their diet, it was concentrated enough to cause brain damage, deformity and death. (B) WATER POLLUTION BY SEWAGE  Sewage is waste water from toilets and sinks of households and industries. It is made up of water, organic matter (faeces, urine) and inorganic matter.  Untreated sewage discharged into rivers and lakes contains bacteria. Bacteria grow and multiply rapidly using up the oxygen in the water. Anaerobic bacteria then continue breaking down the organic wastes releasing foul‐smelling gases like hydrogen sulfide and ammonia. People who use water bodies polluted by sewage may become infected with diseases like cholera and typhoid.  Untreated sewage also contains phosphates and nitrates, which are nutrients for algae. This can lead to eutrophication. 17 (C)

EUTROPHICATION Eutrophication is the enrichment of natural waters with nutrients (nitrates and phosphates) that enable the water to support an increasing amount of algae and plant life. 
The following processes are main causes of eutrophication:  Excessive chemical fertilizers containing nitrates and phosphates are not absorbed by crops and are washed away by rainwater into nearby rivers and lakes, causing eutrophication.  Untreated sewage contains nitrates and phosphates. 
Effects of eutrophication:  Nitrates and phosphates are used in the synthesis of proteins and nucleic acids, respectively. Thus excessive growth of algae (algal blooms) occurs.  Overgrowth of algae and floating water plants prevents sunlight from reaching the submerged plants. Submerged algae die due to overcrowding and lack of sunlight.  When the algae die, the aerobic bacteria and fungi that decompose them use oxygen to do so; this lessens the supply of oxygen to fish and other organisms which die due to lack of oxygen. 
The degree of pollution of river water is often measured by its biochemical oxygen demand (BOD). This is the amount of oxygen needed by aerobic microorganisms to decompose or break down organic matter in water polluted by sewage in a fixed period of time. The higher the BOD, the more polluted the water is likely to be. It is possible to reduce eutrophication by using detergents with less phosphates, using agricultural fertilizers that do not dissolve so easily, and using animal wastes on the land instead of letting them reach rivers. (D) WATER POLLUTION BY OIL SPILLS  In 1989, a tanker called the Exxon Valdez ran onto Bligh Reef in Prince William Sound, Alaska, and 11 million gallons of crude oil spilled into the sea.  Around 400 000 sea birds were killed by the oil and the populations of killer whales, sea otters and harbour seals, among others, were badly affected. 
18 SEWAGE TREATMENT VIA ENVIRONMENTAL BIOTECHNOLOGY 
Sewage contains organic wastes such as faeces and urine, and inorganic wastes such as chemicals discharged from factories. Sewage is treated in water reclamation plants. 

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The activated sludge process refers to biological treatment processes that use suspended growth of microorganisms to remove BOD and suspended solids. At the plant, the sewage first passes through metal grids or mechanical screens to remove large solids such as stones, paper and other debris. This is followed by grit settling tanks to settle out and remove heavier sandy materials. The wastewater which is now free of debris and sandy materials is drained into primary settling tanks (primary clarifier). Solid pollutants in suspension settle to the bottom of the tank and are removed as sludge. Light materials such as scum and grease float to the surface of the tank. The sewage is then channelled to aeration tanks, where it is mixed with aerobic microorganisms (known as activated sludge) such as bacteria and fungi that digest organic pollutants in the sewage into harmless, soluble substances. The tank is aerated by bubbling air through it. 
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In aeration tanks, microorganisms cause the tiny suspended organic particles to clump together (flocculate). The bacteria in the clumps produce extracellular enzymes which digest the organic solids. The soluble products are absorbed by the bacteria and used for growth. The sewage in the aeration tank is sent to the trickling filter where the sewage is sprayed onto the surface of a filter bed. The sewage trickles through the filter bed which removes bacteria. The sewage is now treated. The final effluent meets the discharge standards of 20 mg/l biochemical oxygen demand (BOD) and 30 mg/l total suspended solids (TSS). The sludge removed from the settling tanks is treated in the anaerobic sludge digester, where the sludge is digested by anaerobic bacteria. Methane and carbon dioxide gas are produced. Methane can be used to generate electricity for the plant. The treated sludge is dewatered to remove the water content, before being used as fertiliser or incinerated. 19 http://watertreatmentprocess.net/wp‐content/uploads/2010/02/sewage‐treatment‐process‐designs.jpg POLLUTION DUE TO PESTICIDES 
A pesticide is a chemical that destroys agricultural pests or competitors. Types of pesticides:  Plants with compete with the crop plant for root space, soil minerals and sunlight are killed by chemicals called herbicides.  The crop plants are protected against fungus diseases by spraying them with chemicals called fungicides.  To destroy insects which eat and damage the plants, the crops are sprayed with insecticides. INSECTICIDES ‐ Substances used as insecticides include pyrethroids, organochlorines, organophosphates and carbamates. Organophosphates and carbamates are particularly toxic. Problems with the use of insecticides  As well as killing the intended pest, known as the target species, they often kill useful pollinating insects, or even predators and parasites of the target species. The farmer is forced to spray more frequently because the natural predators of the target species have been wiped out.  The target species may acquire resistance to the insecticide. Increased dosages are necessary. 
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Bioaccumulation and biomagnification  Some insecticides, e.g. DDT (dichlorodiphenyltrichloroethane) are non‐biodegradable. They cannot be broken down by microorganisms, thus they persist for a long time in the soil, get washed by rainwater to nearby water bodies and accumulate in the bodies of aquatic organisms.  DDT is much more soluble in fat than in water so once ingested they remain in the fatty tissues of animals, and it is not excreted. DDT accumulates in the bodies of consumers. If the consumers keep on consuming food that contains DDT, the concentration of DDT will further increase in their bodies. This is called bioaccumulation.  The insecticide is being passed along food chains, increasing in concentration in the bodies of organisms along the trophic levels. This process is called bioamplification or biomagnification.  The use of DDT as an insecticide and aldrin and dieldrin as seed dressings eaten by pigeons led to the accumulation of organochlorine residues within the falcons. These concentrated organochlorines caused the birds to lay eggs with thinner shells that were more likely to break before hatching. HERBICIDES ‐ Many herbicides break down rapidly, being biodegradable, and are only poisonous to animals when absorbed or ingested at high concentrations. FUNGICIDES ‐ Copper salts have been used to protect grapevines against fungi. More recently a number of carbon‐based fungicides, such as zineb and benomyl, have been developed. Difference between bioaccumulation and biomagnification: Bioaccumulation is defined as the increase in concentration of a substance in an organism. Biomagnification or bioamplification refers to the increase in concentration of a substance in a food chain, not an organism. 21 CONSERVATION DEFINITION OF CONSERVATION  Conservation refers to the attempts by humans to preserve organisms or environments that are at risk as a result of human activity.  Conservation involves:  the preservation of endangered habitats and species of plants and animals  the management of ecosystems, e.g. grassland has to be managed in some way, otherwise succession occurs and the grassland becomes invaded by bushes and trees  the restoration of damaged habitats, a process known as reclamation  the controlled production of useful materials from the living environment such as crop fields and fisheries  the controlled use of natural resources like water, fossil fuels and minerals so that they are not used up  the control or elimination of environmental pollution REASONS FOR CONSERVATION To maintain biodiversity by preventing the extinction of species  Biodiversity refers to the range of species that are present in a particular ecosystem.  The activities of humans have already caused the extinction of many species of plants and animals, leading to lower biodiversity. Many more are faced with extinction and are classified as  threatened species – fairly abundant but face serious threats to their survival, e.g. African elephant  endangered species – these need human protection for their survival, e.g. white rhinoceros  The maintenance of a large gene pool is important as many wild plants and animals possess favourable genes. By selectively crossbreeding the economically important plants with their wild relatives, the yield and vigour can be improved, e.g. better resistance to diseases or drought. Economic reasons  Many plants of the tropical rainforest are sources of  raw materials for industries, e.g. rattan, fibres (fabrics from cotton plants and ropes from coconut husk), rubber (from latex of rubber trees) and oils  medicinal drugs like quinine (an anti‐malarial drug from the bark of Chincona) and vinblastine (anti‐leukaemia drug derived from the Madagascar rosy periwinkle)  natural insecticides like pyrethrum found in chrysanthemum  food plants like maize, rice, pineapple and banana 22 To maintain a stable and balanced ecosystem  This prevents disruption of major cycles such as the carbon cycle. Aesthetic reasons  Conservation preserves the natural scenery and wildlife for people to appreciate and relax, providing one of the aesthetic pleasures in life. It also maintains the natural resources for outdoor recreational activities such as fishing and hiking. CONSERVATION OF FISHING GROUNDS (MANAGEMENT OF FISHERIES)  Rivers, oceans and lakes constitute fishing grounds. If the number of fish removed from a population exceeds the number of young fish reaching maturity, then the population will decline.  Over‐fishing has reduced stocks of many fish species, e.g. herring in the North Sea, halibut in the Pacific and anchovies off the Peruvian coast.  Most fishing gear used in commercial fishing catches marine life indiscriminately. It does not distinguish between targeted and non‐targeted catch, e.g. immature organisms or unwanted species. Examples:  Drift nets trap all marine life indiscriminately.  Prawn trawlers drag large fishing nets along the bottom of the sea.  Scallop dredges scrape the seabed, destroying the coral reefs.  Measures of conservation: (1) Manage the fishing industry  Ban use of drift nets that indiscriminately traps all forms of sea life.  Use nets of a certain mesh size so that immature fish are left to breed, and only mature fish above a certain size are caught.  Fixed effort harvesting is a management system whereby the size of the fishing fleet and the number of days at sea (period of fishing) are regulated.  Restrict the mass of a species that any one nation may catch. The maximum sustainable yield is the greatest mass of fish that may be removed without reducing the population over the years.  Ban harvesting of endangered species. (2) Manage a natural ecosystem by raising endangered species in hatcheries and releasing them into fishing grounds where the fish population is decreasing. (3) Create and manage artificial ecosystems.  Inland fish farms usually raise trout or salmon using fresh water taken from a river and led through ponds. The polluted effluent to be returned to the river is first passed through settling tanks to prevent eutrophication and pollution.  Offshore fish farms use floating cages sited in estuaries. - Fish cages should be moved frequently to prevent the settling of fish faeces on the sea bed. 23 - Antibiotics are used to control diseases that may spread rapidly when a single species is grown at a high density. - Escaped fish may interbreed with the wild stock. Characteristics inbred into the farmed fish are unlikely to be beneficial in the natural environment, so the entire wild population may be weakened. CONSERVATION OF FORESTS (MANAGEMENT OF TIMBER PRODUCTION) Methods of conservation: (1) Forest management  Prevent indiscriminate cutting down of forest trees (tree felling).  Selective cutting – Only selected species of trees, or mature trees in certain blocks or strips are cut at a regulated rate, leaving the surrounded area untouched.  Reforestation – replant quick‐growing species to replace the trees that were cut down for timber.  Develop genetically superior trees that are faster‐growing, better‐grained, disease‐resistant, insect‐resistant and drought‐resistant.  Remove diseased or dead trees.  Check trees regularly and control insects and diseases that harm them. (2) Find wood substitutes  Plastic and other materials may be substituted for wood in packaging.  Fibrous waste in sugarcane can be used to manufacture paper. (3) Reduce demand  Recycle paper CONSERVATION OF SOILS  Soil loss can be reduced by keeping soil covered with vegetation.  Conservation techniques:  Strip cropping – alternate rows of crops (e.g. beans) and cover plants (e.g. grass) planted to prevent soil erosion  Terracing – flat areas dug into the hillside to prevent water erosion  Contour ploughing – rows of crop follow contour of land to prevent water erosion  Wind breaks – grow rows of trees to prevent wind erosion  Crop rotation – grow different crops in succeeding harvests to minimize reduction of soil nutrient, e.g. legumes can restore soil nitrates 24 APPENDIX AIR POLLUTION 
Air pollution is caused by  natural occurrences such as biological decay, forest fires or volcanic eruptions  human activities 
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Air pollution due to human activities include  exhaust fumes from motor vehicles  chimney fumes from factories where fossil fuel is burnt  burning of garbage  the use of chlorofluorocarbons in foam packaging Air pollution results mainly from the incomplete burning of fuels such as coal, oil, petrol and wood. 
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Factories produce smoke and sulphur dioxide; cars produce lead compounds, carbon monoxide and the oxides of nitrogen which lead to smog. SULPHUR DIOXIDE AND OXIDES OF NITROGEN Burning of fossil fuels, e.g. coal, oil and natural gases, releases sulphur dioxide (SO2) and oxides of nitrogen into the air. 
Sulphur dioxide at high concentrations has damaging effects on plants and animals.  It penetrates the leaves through the stomata, damaging the internal tissues of the leaves.  Lichens are particularly sensitive to sulphur dioxide. Their growth is greatly reduced in areas where the sulphur dioxide level is high and this is used to monitor the level of this gas in industrial areas.  In humans, it irritates and damages the sensitive lining of the eyes, air passages and lungs. Prolonged exposure is linked to respiratory diseases. What is acid rain?  Acid rain encompasses both wet (rain, snow, fog) and dry (particulate) acidic depositions that occur near and downwind of areas where major emissions of sulphur dioxide and nitrogen oxides result from the burning of fossil fuels.  All rainfall is slightly acidic; water reacts with atmospheric carbon dioxide to produce weak carbonic acid which has a pH of about 5.6. Acid rain is defined as precipitation in which the pH is below 5.6. It is alarming that in Wheeling, West Virginia, rainfall has been measured with a pH of 1.5, almost similar to stomach acid! 25 Cause of acid rain  Sulphur dioxide and nitrogen oxides released into the atmosphere, primarily from power plants that burn fossil fuels, are transformed by reactions with oxygen and water vapour to form sulphuric acid and nitric acid, respectively. Effects of acid rain  It affects the ability of trees to tolerate cold temperatures, and the weakened trees are killed by cold conditions or become more susceptible to diseases.  It acidifies lakes, damaging and killing fish embryos and affecting adult reproduction.  It leaches ions of metals, such as aluminium, lead, mercury and calcium, from the soils and rocks and discharges them into rivers and lakes. Aluminium ions are damaging to fish as it clogs up the gills and cause suffocation.  Acid rain damages building materials, especially limestone, sandstone and marble. Classical buildings such as the Acropolis in Athens, Greece show considerable decay. SMOG  Smog is a mixture of smoke and fog. Sulphur dioxide is the main component of smog. (B) CARBON MONOXIDE  This gas is a product of combustion in engines of cars and trucks. When inhaled, carbon monoxide combines with haemoglobin to form a stable compound, carboxyhaemoglobin, that reduces the oxygen‐carrying capacity of blood. 26 (C)
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CHLOROFLUOROCARBONS (CFCs) These are used as aerosol propellants, as cooling agents in refrigerators and in foam packaging. The chlorine from CFCs reacts with ozone and reduces its concentration in the ozone layer. As the ozone layer filters out much ultraviolet radiation in sunlight, its depletion causes more ultraviolet radiation to reach the Earth’s surface, thus leading to increased incidence of skin cancer. (D) LEAD  Compounds of lead are mixed with petrol to improve the performance of cars. Lead is expelled with the exhaust gases into the air. High concentrations of lead in the body may cause cramps, loss of control of hands and feet and even coma and death. (F) CARBON DIOXIDE  Greenhouse effect:  Sunlight that reaches Earth warms the atmosphere and surface. Some of the heat is reradiated as infrared radiation.  Water vapour and greenhouse gases (carbon dioxide, CFCs, methane) warm Earth’s atmosphere as they trap some of the heat energy radiating from Earth.  This is a natural phenomenon that keeps temperature of Earth warm for living things to thrive (or else Earth’s surface would probably be at ‐18C!).  Global warming:  Massive release of carbon dioxide from the combustion of fossil fuels such as coal leads to global warming by enhancing the natural greenhouse effect of the atmosphere.  Global temperatures have risen by over 0.5C, leading to the melting of polar ice caps, rise in sea levels and flooding of low‐lying areas. (G) SMOKE  This consists of tiny particles of carbon and tar which come from burning coal. When these particles settle they blacken buildings, damage the leaves of trees and cuts down amount of sunlight reaching the ground. (H) PARTICULATES  Exhaust gases, particularly from diesels, contain microscopic particles coated with hydrocarbons. These particles cause death, especially in people suffering from emphysema and bronchitis. CONTROL OF AIR POLLUTION  Vehicles have catalytic converters fitted to their exhaust systems to remove most of the nitrogen oxides, carbon monoxide and unburned hydrocarbons by converting them into harmless compounds like carbon dioxide, water, nitrogen and oxygen. 27 
Following burning of coal, material rich in calcium carbonate is injected into the gases. Calcium carbonate reacts with sulphur dioxide, producing calcium sulphate as sludge. This removes sulphur dioxide from the emissions. This method is known as scrubbing. 
Use low‐sulphur coal to reduce emission of sulphur dioxide. 
Convert coal that is high in sulphur into a gas to remove the sulphur. This is known as coal gasification. 
Use alternatives to burning coal and oil, such as solar or wind energy. 
Use ozone‐friendly products to prevent ozone depletion. RECYCLING OF MATERIALS Non‐renewable and renewable resources  Non‐renewable resources are mineral resources such as coal, oil, aluminium, iron, lead and tin that cannot be renewed once they are used up.  Renewable resources are materials derived from plants, or sources of energy that do not come from fossil fuels. Renewable sources of energy (other than plant products) are hydroelectric power, wind power, tidal power and wave power. Recycling  To recycle is to process waste materials in order to make useful products, e.g. waste water, wastepaper and scrap metal.  Reasons for recycling materials: (1) Recycling conserves natural resources. Water  Freshwater is a precious resource as 98% of the earth’s water is salty.  Although 70% of the Earth’s surface is covered by water, we make use of only 1% of water in our homes, on farms and in industries.  Water can be recycled from sewage and used in industries.  In Singapore, water that is discharged after sewage treatment undergoes further treatment.  The final product is clear and odourless water used for industrial purposes, for flushing toilets, washing rubbish chutes and watering roadside plants. 28 Paper (trees)  Trees (forests) are another natural resource that is lost at a rapid rate as they are cut down to make wood pulp for making paper. Paper can be recycled to conserve the world’s forests. Metals  Metals are non‐renewable resources and can be conserved by recycling metal scraps, metal tins and lids. (2) Recycling reduces waste pollution.  Disposal of garbage is a serious problem. Garbage can be burnt in incinerators or buried in landfills. The latter method is preferred as burning releases dangerous gases into the air.  Most landfills are almost filled and there may not be enough space for more landfills.  One way of reducing the pollution that results from the disposal of garbage is to recycle the waste.  Garbage items that can be recycled include paper, glass, bottles, plastic containers, metal cans and waste food. (3) Recycling saves energy and money.  Recycling paper uses up 64% less energy than making new paper, hence it is generally cheaper to recycle paper than to make new paper.  It is cheaper to use scrap iron to make steel than to mine the iron ore and extract it.  Recycling not only conserves the material that is being recycled; it also conserves fossil fuels like coal which is used to supply the energy in most industrial processes.  Cutting down the use of fossil fuels used is important because they cannot be recycled, their supply is dwindling rapidly and their use is a major cause of air pollution. 29