Topic 15 – Relationships of organisms with one
another and with the environment
15.1 – Energy flow, 15.2 – Food chain and Food Web, 15.3 – Carbon Cycle,
15.4 – Nitrogen Cycle, 15.5 – parasitism,
15.6 – Effects of humans on the ecosystem,
15.7 – Pollution, 15.8 – Conservation.
SUFEATIN SURHAN  BIOLOGY MSPSBS  2010
SYLLABUS CHECKLIST
Candidates should be able to:
(a) state that the Sun is the principal source of energy input to biological systems;
(b) describe the non-cyclical nature of energy flow;
(c) define the following terms and establish the relationship of each in food webs: producer, consumer,
herbivore, carnivore, decomposer, food chain;
(d) describe energy losses between trophic levels and infer the advantages of short food chains;
(e) describe and interpret pyramids of numbers and biomasses;
(f) describe and state the importance of the carbon cycle;
(g) describe the nitrogen cycle in making available nitrogen for plant and animal protein; including the
role of bacteria in nitrogen fixation, decomposition and nitrification (details of denitrification and
the names of individual bacteria are not required);
(h) understand the role of the mosquito as a vector of disease;
(i) describe the malaria pathogen as an example of a parasite and describe the transmission and
control of the malarial pathogen (details of the life cycle of the pathogen are not required);
(j) describe the effects of humans on the ecosystem with emphasis on examples of international
importance (tropical rain forests, oceans and important rivers);
(k) describe the consequences of deforestation in terms of its effect on soil stability, climate and local
human populations;
(l) evaluate the effects of:
water pollution by sewage, by inorganic waste and by nitrogen-containing fertilizers;
air pollution by greenhouse gases (carbon dioxide and methane), contributing to global warming;
air pollution by acidic gases (sulphur dioxide and oxides of nitrogen), contributing to acid rain;
pollution due to insecticides;
(m) discuss reasons for conservation of species with reference to
management of fisheries and management of timber production;
(n) discuss reasons for recycling materials, with reference to named examples.
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maintenance of
biodiversity,
Ecology: energy flow in an ecosystem

Ecology is the study of the relationships between living organisms and the natural environment.

The natural environment of an organism consists of all factors found in its surroundings that affect it.
These include:

Abiotic (non-living) factors that make up the physical (non-living) environment.
They
determine the type of living organisms that are found in the habitat. These factors include
light (source of energy for living organisms), water (rainfall), temperature, oxygen, salinity
and pH of soil or water.

Biotic (living) factors, i.e. all other living organisms which an organism comes in contact with
in its habitat.

A habitat is a place where an organism lives and carries out all its activities such as feeding and
reproduction. Habitats may be small or large.

Ecological niche is the function of an organism or the role it plays in the habitat.

A population is a group of individuals of the same species living and reproducing in a given area.

A community is made up of different populations of organisms (communities) and their non-living
environment. It is a self-supporting unit and mush have the following components:

A constant source of energy (usually sunlight);

Food producers – autotrophs to convert this energy into the chemical energy of food;

Food consumers – organisms that feed on other living organisms including food producers;

Decomposers – organisms whose activity enables recycling of materials between living
organisms and the non-living environment. This simply means that decomposers break down
organic matter (remains of dead organisms and their excretory products) into simple inorganic
substances (carbon dioxide, water, nitrates, etc.) that go back into the non-living
environment to be reused by autotrophs.

Green plants trap sunlight and convert it into chemical energy (food) during photosynthesis in the
following way:

Plants use some of the chemical energy in this food for their own living activities, i.e. to do work.
The rest of the chemical energy in food is passed on to other organisms.

Animals get their energy source (food) by feeding on plants or other animals.

Decomposers get their energy source (food) by feeding on dead plants and animals.

All living organisms – plants, animals and decomposers – break down food during cellular respiration
to release the chemical energy in it for their living activities. In the course of carrying out their
living activities, chemical energy is eventually changed to heat energy and lost to the non-living
environment.
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NOTE: Heat energy is considered as waste energy since living organisms cannot use it. Only light
energy (in the case of photosynthetic organisms) and chemical energy in food can be taken in by
living organisms and used to do work.

In an ecosystem, therefore, plants trap the sun’s energy and pass it on to all the other living
organisms in it.
Eventually, however, all the energy trapped by plants is lost to the non-living
environment as heat energy. This heat energy cannot re-enter the world of living organisms. Thus,
energy flow in an ecosystem is a one-way or non-cyclical flow. It cannot be recycled.
Food chain and food webs

The organisms in an ecosystem can be grouped according to their functions in it.

Producers: these are mainly the green plants. They use light energy to manufacture complex
organic food substances from simple inorganic raw materials via photosynthesis.
Since their
function is to manufacture food, they are known as food producers.

Consumers: these obtain their energy from other organisms upon which they feed.
Animals
function as consumers.
Consumers consist of:
i.
Herbivores: these feed directly on plants and so function as primary consumers. Examples
include cows, goats, rabbits, water snails, caterpillars, insect pollinators (butterflies and
bees), and birds.
ii.
Carnivores: these feed on other organisms.
Those that feed on primary consumers are
known as secondary consumers, and those that feed on secondary consumers are known as
tertiary consumers, and so on. Examples of carnivores include tigers, dogs, snakes, hawks,
frogs, spiders and dragonfly nymphs.
iii.
Scavengers and parasites: scavengers feed on dead organisms, e.g. hyenas, crows and
vultures. Parasites feed on the living tissue of organisms that are alive. Aphids (insects that
suck plant juices), ticks and female mosquitoes (suck our blood0 are external parasites. The
malaria-causing protozoan and disease-causing bacteria are internal parasites. Both
scavengers and parasites are also consumers.
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iv.
Predators and prey: a predator is a consumer organism that feeds on another consumer
organism, the prey. Thus, when a hawk feeds on a snake, the hawk is the predator while
the snake is the prey.

Decomposers: these feed on dead organisms and breakdown the complex nutrients locked up in
them into simple inorganic substances which are returned to the non-living environment (air, siol
and water) to be used again by producers.

A food chain shows the transfer of energy and materials (i.e. food) from organism to organism along a
feeding pathway. Each stage along this pathway is known as a trophic (feeding) level. The following
are examples of food chains and trophic levels.

In an ecosystem, numerous food chains are present. These are often linked in various ways. For
example,

the same type of plant (e.g. maize) may be fed upon by different types of organisms (e.g. aphids,
rats);

the same type of primary consumer (e.g. grasshopper) may feed on different types of plants (e.g.
grass, maize);

the same type of secondary consumer (e.g. owl) may prey on different types of animals (e.g.
mice, snakes, lizards).
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
By eating different types of plants or animals, a consumer has a better chance of surviving in an
ecosystem. This is because if one of its food sources is destroyed, it still has other sources that it can
eat.

The complex feeding relationship that results in a community when two or more food chains
become linked is known as a food web. A simple example of a food web found in a garden is given
below:

Energy transfer in food chains: In the food chain below, the grass provides all the animals in the
chain with food (chemical energy).

About 90% of the chemical energy (food) the grass makes is used for its activities and lost as heat.
Only about 10% is converted into new tissue and storage material in the grass. This is the amount
of chemical angry available for the next link in the food chain.

When the rat feeds on grass, a large amount of food passes through its food canal undigested, and
is egested. Of the absorbed food, a certain amount is used for the rat’s activities and eventually
lost as heat and as waste. Usually about 10% or less of the chemical energy the rat obtains from
the grass is converted into new tissue in the rat’s body. This then is the amount available for the
next link in the food chain.

The snake is more efficient at digesting the food in the rat’s tissue. (Plant tissue is more difficult
to digest than animal tissue because of its indigestible cellulose content.) Roughly about 10% or
more of the chemical energy the snake obtains by feeding on the rat is converted into new tissue
in the snake’s body, and is available to the next link in the chain. The transfer of chemical
energy from the snake to the hawk also results in the same kind of losses.
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
In the above food chain, let us assume that the grass contains 20 000kJ available for the next link
in the chain. If energy losses are about 90% at each step, the energy flow is as follows:

Food chains are short: as chemical energy is transferred from one trophic level to the next, there is a
loss of energy so that the total amount of energy decreases progressively down a food chain. As a
result, a food chain is short. In most ecosystems, the chemical energy manufactures by the producer
is completely dissipated into the surroundings by the fourth or fifth trophic level.
Pyramid of numbers, biomass and energy

The food chain in the previous page can be represented graphically by plotting

the number,

the biomass, and

the energy content
of organisms at each trophic level.

These graphs are known as ecological pyramids. Usually, ecological pyramids have a broad base and
a narrow apex, indicating a progressive decrease in numbers, biomass and energy from the first
trophic level to the final trophic level.

Pyramid of number represents the number of individuals at each trophic level of a food chain at
a particular time. The number of individual organisms (population size) decreases progressively
up the trophic levels in the food chain. At the same time, there is an increase in the body size of
individuals up the chain.

Pyramid of biomass represents the total wet or dry mass of the organisms in each trophic level.
Biomass takes into account both the body size of the individual organisms and their numbers. It is
measured in grams per square metre (g/m2) of the habitat as follows:
body size (g) x number of organisms found in one square metre of habitat (m2)
Thus, a pyramid of biomass gives a more accurate picture of the relationships in a food chain than
a pyramid of numbers. The example below shows how a pyramid of numbers can be misleading.
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Pyramid of biomass for the above food chain would show a broad base since one tree has a large
biomass to support the other populations. Most pyramids of biomass show an upright pyramid
with a broad base tapering towards the apex. This indicates that the biomass of the organisms
gets smaller and smaller at each trophic level, starting with level 1.
NOTE: Body size of organisms may increase progressively along a food chain, but biomass (size x
numbers) usually shows a progressive decrease along a food chain.

Pyramid of energy represents the rate of energy flow in a food chain.
Each horizontal bar
represents the amount of energy in kilojoules (kJ) in one square metre (m2) of the habitat that
flows through that trophic level of the food chain in a year. Thus energy flow is measured in
kJ/m2/yr.
This is the best way of representing relationships between organisms in the various trophic levels
of a food chain. A pyramid of energy is always upright (broad base tapering to a narrow apex),
showing that the amount of stored chemical energy gets smaller and smaller at each trophic
level, starting with level 1.
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Nutrient cycling in nature

A functioning ecosystem uses both energy and inorganic nutrients. As energy flow is one-way, it is
constantly being supplied by the sun from outside the ecosystem.

Inorganic nutrients, however, need not be supplied from outside as they can be recycled within the
ecosystem.
Carbon, nitrogen and water are the main nutrients which are necessary for the
maintenance of life.
The cycling of these nutrients is brought about by physical, chemical and
biological processes.
(A) Carbon Cycle

This refers to the processes by which carbon, in the form of carbon dioxide, is removed and restored
to the atmosphere. These processes maintain its amount in the atmosphere at a constant level of
0.03% by volume.


Process that removes carbon dioxide: photosynthesis

Processes that set free carbon dioxide: respiration, decay and combustion
Importance of the carbon cycle: Cycling of carbon is essential for an ecosystem to function because:

it ensures a linear flow of energy through the ecosystem as solar energy is trapped in carbon
compounds.

it enables a continuous supply of inorganic carbon in the form of carbon dioxide which is readily
used by plants during photosynthesis (an ultimate process which traps solar energy).

Decomposition in nature: Decomposers play a vital role in the cycling of nutrients in ecosystems.
Although they are not shown in most food chains, they form the link between

the producers and consumers in the biotic environment, and

the abiotic environment,
in all food chains.
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The following diagram shows how decomposers link the biotic and abiotic environments.
(B) Nitrogen Cycle

Decomposition involves the conversion by bacteria of proteins to amino acids, and the conversion of
amino acids and urea to ammonium ions. This process usually takes place in the soil.

Ammonium ions contain nitrogen atoms but before plants can absorb nitrogen from the soil, it must
be in the form of nitrate ions.
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
Nitrifying bacteria converts ammonium ions first into nitrites and then into nitrates. This is
nitrification.

Plants absorb the nitrates and use them together with the carbohydrates made by photosynthesis to
make amino acids and then proteins.

Animals eat the protein in plants and excrete e.g. urea in urine.

Both plants and animals die, and decomposition releases ammonium ions again.

Atmospheric nitrogen (79% in the air) cannot be used either by plants or animals in its gaseous form
but it is used by some bacteria (the nitrogen fixing bacteria).

These bacteria are found in two forms:

Those which live freely in the soil

Those which live in swellings called nodules on the roots of peas, beans and other leguminous
plants. This is a form of symbiotic relationship. Therefore, legumes are often used to enrich
poorly fertilized soil.

Nitrogen fixation by these bacteria changes the atmospheric nitrogen into ammonium ions, which are
in turn made into nitrates by nitrifying bacteria.

Nitrogen fixation also occurs when lightning passes through the nitrogen in the air

Nitrogen is oxidized into nitrogen oxides (NOx), which are dissolved by rainwater into nitrites and
nitrates in the soil.

Denitrifying bacteria are present in poorly aerated soil such as waterlogged soil. Such soil has an
anaerobic condition, which is suitable for such bacteria.

They convert nitrates in the soil into nitrogen gas, which is then lost to the atmosphere. This
results in loss of fertility of the soil.
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Parasitism

A parasite is an organism that lives in or another organism called the host from which it obtains food.
The relationship between a parasite and its host is called parasitism.
In this relationship, the
parasite tends to cause diseases and/or death to its host.

A pathogen is an organism that causes diseases in an organism. The malarial parasite is a pathogen.

A vector (of diseases) refers to a living organism that transmits a disease-causing parasite from one
individual organism (man, animal or plant) to another.

The malarial parasite is a parasitic protozoan called Plasmodium.

Plasmodium is transmitted to a human host by the bite of an infected female Anopheles mosquito
– the vector of the malarial parasite.

Plasmoduim has a complicated life cycle with many stages that occur in two hosts – the Anopheles
mosquito and the human being. The asexual part of the cycle occurs in humans while the sexual
part occurs in mosquitoes.

In humans, the parasites first go to the liver. Then they invade red blood cells and cause the
cells to burst. This and the toxins the parasites produce cause any of the symptoms of malaria
(cyclic occurrence of chills and fever, headache and nausea). The secondary effects are anaemia
(due to red blood cell destruction) and jaundice.
NOTE: Malaria may also be transmitted by transfusion of infected blood.

Life cycle of mosquitoes: Mosquitoes, like Anopheles, undergo complete metamorphosis (i.e. egg,
larva, pupa and adult) as shown:
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Causative agent
A unicellular microorganism (single cell), Plasmodium
Nutrition
Parasites i.e. feed on haemoglobin (proteins) in RBCs
Vector (carrier)
Female Anopheles mosquitoes
Transmission
After inserting its proboscis into the skin, a mosquito injects its saliva first to stop
the blood from clotting around the wound.
The initially uninfected mosquito sucks blood containing the parasites from an
infected person (usually at night). Female mosquitoes require blood for the
development of their eggs.
The parasites reproduce in the gut of the mosquito and then migrate to the salivary
gland of the mosquito.
When this mosquito bites the next person who is healthy, it injects the saliva as
well as the parasites into this person, thus infecting this second individual.
Target cells
Plasmodium attacks liver cells first and then the red blood cells.
Sign & symptoms
Intermittent high fever
Chills
Shivering / paroxysms
Profuse sweating
Anaemia (due to destruction of red blood cells)
Treatment
By taking anti-malarial drugs such as quinine, which kill any Plasmodium parasites
in the body.
Control methods
1. By controlling the mosquito vector population
(a) Cover water tanks with netting to stop mosquitoes from laying their eggs in
the water
(b) Empty containers and drains and fill any areas where water can collect to
eliminate mosquito breeding grounds
(c) Drain swamps where mosquitoes lay their eggs
(d) Introduce larva-eating fishes such as Tilapia and guppies into the swamps to
feed on mosquito larvae (biological method)
(e) Cover the surface of water with light oil. Larvae cannot then use the water
film from which they hang as they breathe air from the atmosphere. The
larvae therefore suffocate.
(f) Spray insecticides over stagnant water to kill any mosquito larvae in it.
(g) Spray insecticides on walls and roofs of houses as well as in any dark
corners. The residual insecticides on the sprayed walls and roofs remain
active for several days, hence killing any mosquitoes which rest there.
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2. By avoiding mosquito bites
(a) Place nets over door and windows
(b) Sleep under mosquito nets
(c) Wear clothes which cover wrists and ankles especially in the evenings, when
mosquitoes are most active.
(d) Use insect repellant sprays
3. By treating the parasites in the blood
(a) Provide anti-malarial drugs to patients suffering from malaria and also
isolate them to prevent from spreading the disease (to prevent from
infecting mosquitoes).
(b) Take prophylactic drugs as preventative measures to kill the parasite if it
enters the bloodstream, especially before travelling to areas with high cases
of malaria.
(A) Deforestation


EFFECTS OF MAN ON THE ECOSYSTEM
Deforestation is defined as the clearing of large areas of forest. We do this:

To provide land for crop cultivation, cattle grazing and urban development;

To provide timber – wood is used for construction, making paper, firewood; and

For fibres.
Effects of deforestation: The main effects are on soil, water retention, climate, local populations
and natural habitats.

On soil: Deforestation causes soil erosion. This is the wearing away and removal of fertile topsoil
from an area by wind and water (rainfall). It makes the soil poor and useless for crop cultivation.
Forests protect soil in the following ways:
i. They provide a protective cover for the soil against win and rain.
ii. They act as windbreakers, reducing wind speeds and checking the erosion of the surrounding
land.
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
On water retention: Deforestation tends to increase flooding. This is because the roots of forest
trees hold rainwater and release it gradually to the soil below and to the nearby streams and lakes.
Cutting down trees lets rainwater rush into nearby water bodies, resulting in flash floods.
Soil
carried by the rushing water causes silting of streams. This contributes greatly to floods.

On Climate: Deforestation tends to decrease rainfall. This is because forests release a lot of water
into the atmosphere via transpiration. Cutting down forests results in drier air, leading to a decrease
in rainfall and a drier climate in the region. This encourages the formation and spread of deserts
(desertification). This effect is especially serious in the tropics where land exposed by deforestation
tends to become poor rapidly (result of soil erosion and high rate of humus break-down) and so
cannot support plant growth.

On local human population: Deforestation has short-term good effects and long-term bad effects on
the local human population.
(a) Initially, deforestation provides jobs related to forestry-activities and products such as logging
and timber processing. These come to an end when the forests are gone.
(b) The locals can farm or rear livestock on the cleared land. This again is not profitable, especially
in the tropics, as the soil becomes poor very rapidly. They also have to face frequent floods.
(c) When farming activities fail, the local population may be forced to go to nearby towns for jobs.
As they are unskilled, finding jobs would be difficult. Most of them end up living in slums, and
may become a social problem.
(d) Deforestation deprives native tribes who live in forests of their homes. Such people find it hard
to adapt to a life outside the forest. Often, many die – something that has happened to many
native tribes living in tropical rainforests all over the world.

On natural habitats: Deforestation destroys the natural habitats of many organisms that dwell in
forests. Many species of plants and animals are completely wiped-out in the process.
(B) Pollution

Pollution is the addition of materials to the environment that damages or defiles it, making it
undesirable or unfit for life. The materials that cause pollution are known as pollutants.
Air pollution

Air pollution: This may be caused by forest fires, volcanic eruptions, biological decay and human
activities. Human activities include


burning of garbage and fossil fuels;

the producing of exhaust from motor vehicles (using petrol and diesel);

the producing of exhaust from power plants, factories and mining centres (using diesel and coal);

the use of chlorofluorocarbons (CFCs) in foam packing, cooling agents and aerosol sprays.
Pollutants: The most important air pollutants are carbon monoxide, carbon dioxide, oxides of
nitrogen, sulphur dioxide and CFCs.
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
Air pollution due to sulphur dioxide: Sulphur dioxide is produced by burning low-grade petroleum
fuels and coal. The main sources that emit this gas are electrical power stations, factories and
mining centres that use coal as fuel.

Sulphur dioxide is an acidic gas which dissolves readily in moist air to form an acid.
(a) It enters plants via stomata on leaves and damages the internal tissues of leaves causing them
to drop off. Lichens are especially sensitive to this pollutant. Their growth is greatly reduced
in areas where the sulphur dioxide level is high. This characteristic of lichens is used to
monitor the level of this gas in the air in industrial areas.
(b) In humans, the gas irritates and damages the sensitive lining of the eyes, air passages and
lungs. Prolonged exposure to the gas is linked with respiratory diseases like lung cancer and
bronchitis.

Sulphur dioxide dissolves in rainwater to give rise to acid rain.
(a) When acid rain falls on vegetation, it reduces their growth and damages their leaves. Forests
have been destroyed by this rain.
(b) When acid rain falls on buildings, it corrodes the metallic and marble structures.
(c) Acid rain dissolves aluminum salts in soil causing them to build up to toxic levels in
underground water supplies. This affects our sources of drinking water. When this water
flows into ponds and lakes it slowly kills plant and animal life in them.

Air pollution due to oxides of carbon: Main source of carbon monoxide is from the exhaust of motor
vehicles. Carbon monoxide has a great affinity for haemoglobin, thus reducing the capacity of blood
to transport oxygen round the body. It is fatal in high concentrations.
Carbon dioxide is released during combustion of fossil fuels. It causes the greenhouse effect – high
levels of carbon dioxide prevent heat (infrared rays) from escaping into space. This may lead to
global warming causing climate changes and flooding (triggered by melting of ice caps).

Air pollution due to CFCs: CFCs deplete the ozone layer high up in the earth’s atmosphere by
reacting with ozone and breaking it down. The ozone layer acts as a shield that prevents most of the
ultraviolet radiation in sunlight from reaching the earth’s surface. Depletion of this layer exposes all
living organisms on earth to the harmful effects of ultraviolet radiation. In humans, these effects
include sunburns, skin cancers, cataracts and mutations (damage to DNA).

Ways of reducing air pollution:

To reduce sulphur dioxide pollution,
(a) ensure proper maintenance of chimneys emitting exhaust, and fit them with filters;
(b) remove sulphur compounds from low grade fuel oil and coal;
(c) treat the waste gases of industries of industries to remove the gas.
15

Use less of cars

Use non-fossil fuels and use less of fossil fuels

Use ozone-friendly products to prevent ozone depletion
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Water pollution


Water pollution: This is caused by

treating water bodies as dumping places for untreated sewage and factory wastes;

washing of fertilizers and pesticides by rainwater into nearby water bodies.
Pollution by sewage: Sewage contains organic matter like faeces and urine. Its effects in water
bodies are as follows:

Sewage contains bacteria that cause water-borne diseases like cholera, typhoid and dysentery.
Using sewage-polluted water leads to outbreaks of these diseases.

Sewage can be broken down by microorganisms, i.e. it is biodegradable.
During this
decomposition process, microbial activity
i.
uses up oxygen causing the oxygen level in water to drop;
ii.
releases carbon dioxide;
iii.
releases nitrates and phosphates – inorganic nutrients that accelerate the growth of algae
and water plants.
This profuse plant growth is known as eutrophication. Algae have a short life span and soon
die, producing more organic matter for decay. The resulting increase in microbial activity
causes the oxygen level in water to drop further. Aquatic animals like fish die when this
happens. Sewage plus the bodies of dead aquatic animals cause the oxygen level to drop
drastically killing even the most hardy organisms. When this happens, the water body turns
into a stinking, lifeless and unsightly scene.
Biochemical Oxygen Demand (BOD) is used to measure pollution of water bodies by
microorganisms. BOD is the amount of oxygen bacteria need to break down the organic
matter in a water sample in a fixed period of time.

Pollution by inorganic wastes from factories: These wastes include acids, alkalis and heavy metals
like mercury, copper, lead, cadmium and nickel. Cadmium and nickel are carcinogenic chemicals,
while mercury causes brain damage.
Many of these chemical compounds tend to accumulate in aquatic organisms, and are passed along
food chains. They become concentrated in the bodies of the final consumers. Eventually, they build
up to toxic levels in the bodies of the consumers and harm them.
This is known as biological
amplification.
Example of biological amplification: This was what happened when factories around Minamata Bay in
Japan emptied mercury waste into the bay. The mercury was passed along the following food chain:
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The villagers who ate the fish over a period of time were seriously harmed – about 45 people died
while 120 were seriously ill.

Pollution by fertilizers: Fertilizers used in farming get into water bodies and cause eutrophication.

Pollution due to pesticides: These are chemicals used to kill pests that harm crops, farm animals
and humans. They include insecticides and herbicides.

Insecticides sprayed on crops not only kill the pests but also kill beneficial insects (e.g.
pollinating agents, and insects that feed on crop pests).

Certain insecticides like DDT are non-biodegradable. They become washed by rainwater into
nearby water bodies. There, they accumulate in the bodies of the aquatic organisms and are
passed along the food chain, to become concentrated in the body of the final consumer
(biological amplification)
A well-studied example is the build-up of DDT in eagles. This build-up caused the eagles to lay eggs
with thin shells, which broke easily. As a result, the eagle population decreased.


Certain insecticides sprayed on fruits and vegetables are carcinogenic.
Prevention of water pollution: This can be done in the following ways:

Treating sewage in sewage plants first before discharging the effluent into water bodies. This
kills harmful microorganisms and removes organic wastes.

Treating factory wastes before emptying them into water bodies.
In this process, toxic
compounds are removed.

Use more organic manure (by recycling crop and animal wastes) and reduce the use of inorganic
fertilizers.

Alternatives to the use of insecticides in agriculture: One method is to use insects that prey on
insect pests – this is known as biological control. However, care must be taken to ensure that the
introduced insect predator does not upset the ecosystem to create more problems.

CONSERVATION
Definition of conservation: To conserve something means to protect it and keep it in a healthy
condition. Today, conservation means to ensure a high quality of life for humans by the wise use of
the natural environment. This definition is very broad and includes:
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
the protection of nature, i.e. wildlife and forests to enrich our lives;

the controlled production of useful materials from the living environment such as crop fields and
fisheries;


the controlled use of fossil fuels and minerals; and

the control or elimination of environmental pollution.
Conservation of species: We are threatening the existence of many species by

destroying their habitats, e.g. deforestation especially of the rainforest which has a wealth of
plant and animal species;


polluting their environment; and

hunting them indiscriminatingly for their products.
Our activities have already caused the extinction of many species of plants and animals. Many more
are faced with extinction and are classed as

threatened species – fairly abundant but face serious threats to their survival, e.g. African
elephant;


endangered species – these need human protection for survival, e.g. white rhinoceros.
We have to conserve plant and animal species for the following reasons:

Ecological importance: Each species has a role (function) to play in maintaining the delicate
balance in ecosystems. Just removing one species would upset this balance.

Economic importance: Many plants especially of the tropical rainforest are sources of raw
materials for industries, medicinal drugs, natural insecticides and food.
(a) Raw materials for industries: These include rattan, timber, fibres, rubber and oils. The wild
rubber tree was cultivated and the latex tapped from it is used to produce rubber. Rattan
and timber are used for making furniture. Fibres from jute, hemp and cotton are used for
making rope and cloth.
Oil from oil palm and sunflower are used for making soap and
margarine.
(b) Medicinal drugs: Quinine (used to treat malaria) and morphine (pain-suppressing drug) are
from plants, while the Madagascar periwinkle plant has chemicals that may cure leukemia.
One species of the poison-dart frogs of South America produces a chemical that is a more
powerful analgesic than morphine. Another species produces a toxin that may have a use as a
cardiac stimulant for heart attack patients.
(c) Chemicals that repel insects: Pyrethrum, the chemical found in chrysanthemum flower, is
used in many insecticides industries.
(d) Food-producing plants: Maize, rice, pineapple and banana were developed from wild-type
rainforest plants.

Scientific importance: In selective breeding, economically important plants are often crossed
with their wild relatives. This tends to increase vigour, yield and resistance to diseases and
adverse conditions. It is extremely important to prevent the extinction of these plant species as
they are important in crop improvement. Today, over 25 000 such wild plant species are on the
verge of extinction.
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
Aesthetic importance: The beauty of nature – its spectacular forest and fascinating wildlife – is
our heritage. Conserving it enriches our life and is essential for our emotional and mental health.

Measures taken to conserve species: These include education (to appreciate and care for nature),
setting up of parks, reserves and sanctuaries, and introduction of conservation laws.
RECYCLING

Recycling: This involves recovering used materials and reusing them for other purposes. Materials
like waste water, waste paper and scrap metal can be recycled.

The reasons for recycling materials are as follows:
(a) to conserve natural resources like water, forests and metals;
(b) to reduce the problem of waste disposal; and
(c) to save energy.

Recycling conserves natural resources:
(a) Freshwater is a precious resource (98% of the earth’s water is salty). Water shortage is a
serious problem in many countries. This is due to an ever increasing population, deforestation
and pollution of freshwater bodies. One way of conserving freshwater is to recycle water
from sewage and use it in industries for washing rubbish chutes and watering roadside plants.
(b) Forests are another natural resource that is vanishing rapidly. We cut down large areas of
coniferous forests to produce wood pulp which is used for making paper. By recycling paper,
we can conserve a part of our forests.
(c) Metals are non-renewable resources. We can conserve them by recycling metal scraps.

Recycling reduces the problem of waste disposal: Disposal of garbage is a serious problem
today. Garbage is normally burned in incinerators or buried in landfills. By recycling waste, we
can reduce the amount of garbage that needs to be burned or buried, thus reducing
environmental pollution.

Recycling saves energy: Recycling saves a lot of energy. For example, it is much cheaper to use
scrap iron to make steel than to mine the iron ore and extract it.
Thus recycling not only conserves the material that is being recycled, it also conserves fossil fuels
like coal and petroleum which are used to supply the energy in most industrial processes. Cutting
down the amount of fossil fuels used is important for the following reasons:
(a) It cannot be recycled.
(b) Its supply is dwindling rapidly.
(c) Its use is also a major cause of air pollution.
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