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HO CHI MINH UNIVERSITY OF INDUSTRY
INSTITUTE FOR ENVIRONMENTAL ENGINEERING & MANAGEMENT

Compiled by VO DINH LONG

ENVIRONMENTAL SCIENCES
(Specialized English course for Environmental Students)

HO CHI MINH CITY - 2006


CONTENTS

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CHAPTER 1: BASIC UNITS OF ECOLOGY
After studying this chapter, you should be able to:
1.
2.
3.
4.
5.
6.

Define environment.
Define an ecosystem.
Identify the components of the biosphere.
Describe the living and nonliving components of the environment.
Explain that bacteria and fungi are agents of decay.
Discuss the process of photosynthesis.

7. Enumerate the important factors that affect the growth of plants and the survival of animals.
1.1. THE ECOSYSTEM
When God created the world, He said, “Let the earth produces all kinds of plants, those that bear grain
and those that bear fruit”, and it was done. Then He also created animals, including human beings and
provided light. God, therefore, saw to it that everything needed for them to live is found in the world
which He created. He provided space, ways and means by with different organisms can interact with one
another and with their environment.
Part of the world where life operates is known as the biosphere.
The biosphere consists of the air (atmosphere), water (hydrosphere), and earth (lithosphere) where living
things interact with their environment.

Figure 1.1: The biosphere
When you study the interaction or relationship between organisms and their environment, you are
studying an ecosystem. The term ecosystem refers to all the living things and the nonliving things in a
given area. It includes all the plants and animals together with their surroundings. The ecosystem of an
aquarium, for example, consists of the hydrilla and others plants, fish, snails, and other aquatic animals,
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some of which can only be seen under a microscope. It also includes sand and pebbles at the bottom. We
can also include the owner who takes care of the aquarium.
A grassland, too, is an ecosystem. This ecosystem consists of the grass, earthworms, insects, bacteria, soil,
water, sunlight, and other plants and animals that live on it. The pond is another example of an ecosystem.
The forest is a more complex ecosystem. Can you identify some of the components of this ecosystem?
The entire earth can be thought of as an ecosystem. It has an abundance of different kinds of species of
living things which, although separate by great distances, still react with one another and with the
nonliving world.
In a forest ecosystem, interrelationships among its living and nonliving components occur. The branches
and leaves of trees help break the force of the rain. Layers of dead leaves and twins and branches on the

forest floor soak up water and prevent rain from washing soil away. Little water runs off the land. The
roots of trees hold the soil and water on which they depend. Moreover, when the leaves and branches
decay, they become part of the rich topsoil.
The soil is made up of minerals like silica and clay. They come from the breakdown of rocks. There are
spaces between the mineral particles which are filled with air and water. Roots of plants penetrate deeper
into the soil causing physical change. They loosen the tightly packed particle. Chemical change also
occurs. The roots absorb the minerals present.

Figure 1.2: Plant-soil relationship
There are thousands of organisms that live in the soil, like earthworms, that decompose the dead plants
and animals. Some are too small to be seen, but they all help maintain the ecological balance in the soil.

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Figure 1.3: Organisms in the soil
Guide questions
1. What is an ecosystem?
2. How do the living components of an ecosystem affect the nonliving components? Give example.

3. Can a fallen log be considered as an ecosystem? Explain your answer.
1.2. COMPONENTS OF AN ECOSYSTEM
In the preceding section you learned what an ecosystem is. The living component is known as the biotic
and the nonliving component is known as abiotic. The biotic component consists of plants, animals, and
bacteria. The abiotic component includes all the factors of the nonliving environment such as the
substratum, light, rainfall, nutrients, soil, and others. Both the biotic and abiotic components are equally
important in the ecosystem because without one of them the ecosystem would not function.
Insightfulness
The ecosystem consists of the biotic and abiotic components. The biotic components are the plants,
animals, and decomposers. The abiotic components are the non living factors, such as temperature,

water, and others. The abiotic affect the biotic components and vice versa.
1.2.1. Green plants
Green plants are known as the producers. They capture the energy from the sun and together with carbon
dioxide (CO2) in the air and water (H2O) convert together those into food energy. Since plants are able to
manufacture their own food, they are also known as autotrophs (or self-nourishing). These plants are able
to manufacture food though the process of photosynthesis, which will be explained in the next section.
Green plants also take substances, such as nitrogen and sulfur from the environment and convert those
into plant materials that can be used by other organisms as food. These green plants further provide
oxygen which is taken in by humans and animals in the process of respiration. For these reasons, all life,
whether in the pond, forest, or grassland, depend on green plants.
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You might think that green plants consist only of the trees or big plants that you see around. The other
producers are invisible to your eyes. These are the microscopic drifting plants which are greater sources of
food than the big plants that you can see. We call these microscopic plants phytoplankton. When they
become too abundant, they can give a pond or a body of water a green color.
Have you ever seen a pond or a lake with green surface?
Guide questions
1. What are producers?
2. What do producers perform in an ecosystem?

3. What are phytoplanktons?
1.2.2. Animals
Animals, or the consumers, obtain their food from plants or other animals. Because of this, they are also
known as heterotrophs, which means that they feed on others and cannot manufacture their own food,
unlike the green plants.
There are three different types of consumers, namely, the herbivores, the carnivores, and the omnivores.

Figure 1.4: There are three different types of consumers

The herbivores are those that eat plants only. For example, the caterpillar that feeds on leaves is an
herbivore while the snake that eats the caterpillar is a carnivore. Omnivores eat both plants and animals. A
human being is a good example of an omnivore.
Through the process of respiration, animals combine the food they eat with oxygen to produce CO 2 and
H2O which are used by plants in the photosynthesis process. Animals also convert the materials of the
plant bodies into the materials that make-up their own bodies. All the energy produced and used by
animals comes from the plants.
Guide questions
1. What are consumers?
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2. What are the three types of consumers? and give one example for each type.
1.2.3. Bacteria and fungi as agents of decay
Have you ever observed what happen to leaves that fall on the ground?
After some time, the leaves wither, break down into smaller pieces, decay, and finally become part of the
soil. What do you think is responsible for this change?
Have you heard of the word decomposer? What do you think does a decomposer do?
Decomposers make-up the third biotic component of the ecosystem. They use the bodies of dead animals
and plants for their food. The materials contained in these dead bodies are broken down by the
decomposers, thus they get the energy they need and release the minerals and other nutrients back into the
environment for use again by other organisms. Bacteria are among the most abundant decomposers while
fungi are known to be the fast-acting decomposers.
Decomposers are found everywhere. In the pond, they are abundant at the bottom where the remains of
the dead organisms (plants and animals) settle. On land, they abound on the surface of the soil where the
dead bodies of plants and animals are found.
Each of the three groups of the biotic component of the ecosystem - producers (plants), consumers
(animals), and decomposers (bacteria and fungi) - has its own specific function or task to perform.

Figure 1.5: Relationship among biotic component of the ecosystem

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The work performed by an organism is known as its ecological niche, while the place where the organism
lives in the ecosystem is known as its ecological habitat.
Guide questions

1. What are producers?
2. Give examples of producers?
3. What do decomposers perform in the ecosystem?
1.2.4. Nonliving factors
The nonliving factors of the environment make-up abiotic component of the ecosystem. These include the
chemical and physical factors in the environment, such as light, temperature, water, pH (acidity), wind,
chemical nutrients, salinity (saltiness), soil, and others. Organisms are affected by the biotic factors
simultaneously but, of course, different species of organisms are affected differently. For example, lichens
may not survive when temperature gets very high but cactus may.
Different organisms thrive in different conditions. There are animals, like the earthworms, which favor
wet condition, while others, like ants, prefer drier conditions. Some plants, such as cactus, grow best in
sandy soil while tomatoes grow best in loamy soil.
As a whole, these environmental factors not only provide essential energy and materials but also
determine the kind of organisms that will inhabit the area. Hence, they provide the conditions necessary
for the survival of the organisms.
Guide questions
1. What are the components of an ecosystem?
2. Give examples for each component of the ecosystem.
3. In general, what are the functions of these components?

4. Can an ecosystem exists without one of its components? Justify your answer.
Vocabulary

Autotroph: Organism that is self-nourishing; one that can produce its own food.
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Hetertrop: Organisms that feeds on others and cannot manufacture its own food.
Biological magnification: Accumulation or increase of chemical substances on organisms in succeeding
higher trophic levels.
Biomass: Amount of organic materials in plants or animals from which energy can be derived.
Energy: Capacity to do work
Energy content: The amount of energy available for doing work. For example, the amount of energy in
fuel available for powering a motor vehicle.
Food chain: Energy pathway which proceeds from the producers to the consumers.
Food web: Series of interrelated food chains in an ecosystem.
Pyramid of energy: Representation of the organic content in each trophic level.
Biosphere: Portion of the earth and its environment within which life in any of its form is manifested.
Photosynthesis: Process of manufacturing food by green plants in the presence of sunlight.
Atmosphere: Layer of air surrounding the earth.
Hydrosphere: The part of the Earth composed of water including clouds, oceans, seas, ice caps, glaciers,
lakes, rivers, underground water supplies, and atmospheric water vapor.
Lithosphere: The outer, rigid shell of the Earth, situated above the atmosphere and containing the crust,
continents and plates or the solid part of the earth’s surface
Grassland biome: Community where grass is abundant while trees are scarce and where mostly
herbivores and rodents dwell.
Carnivore: Animals that get food from killing and eating other animals.
Herbivore: Organisms that eat plants only.
Omnivore: Organisms that consume both plants and animals
Biotic factor: Living component of the ecosystem which includes plants, animals, and bacteria.
Biotic potential: Reproductive capacity of the living components of the ecosystem.
Producer (autotroph): Green plant or organism that, performs photosynthesis.
Consumer: Organism that feeds on other organisms.

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Decomposer (also known as microconsumer): Organism which breaks down nonliving organic material;
example are bacteria and fungi.
Environment: Sum of all external forces and conditions acting on an organism or a community of
organisms.

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CHAPTER 2
MATERIALS AND NUTRIENT CYCLES
The energy that flows into an ecosystem cannot be recycled. Once the energy is used, it is lost. But it
much be constantly repeatedly replenished if the ecosystem is to continuously function.
The important chemical nutrients, however, are used repeatedly. They are cycled between the living and
nonliving components of the ecosystem. Generally, they begin in the abiotic part of the ecosystem (water,
land, and air). Then, they enter to the bodies of plants and animals and return into the abiotic environment.
The movement of these materials and nutrients between the living and nonliving environment clearly
shows the interrelatedness of the abiotic and biotic components in an ecosystem. Among these recycled
materials and nutrients are carbon, oxygen, water, nitrogen, and phosphorus.
After studying this chapter, you should be able to
1.
2.
3.
4.
5.

Identify different nutrients that can be recycled.
Explain the water, carbon and oxygen, nitrogen, and phosphorus cycles.

Discuss the importance of each of these cycles.
Discuss how people affect these cycles.
Differentiate micronutrients from macronutrients

2.1. IMPORTANCE OF THE NUTRIENT CYCLES
The energy from the sun flows to the plant goes to the herbivore that eats the plant, to the carnivore, and
to the last consumer until the energy is lost into the ecosystem. The energy does not go back to the source.
It cannot be used over and over again.
In contrast, when the bodies of dead plants and animals decompose, they are changed into nutrients
through the action of bacteria and fungi. The nutrients are stored in the abiotic environment like the soil.
The nutrients can be used again by the plants. The plants are eaten by the animals and when the animals
die, they decompose into nutrients. These nutrients can be used over and over again. In this way, a cycle
of nutrients is formed.
The cycle of nutrients is an important process that takes place in the ecosystem. Through the cycle of
nutrients, the organic compounds found in the bodies of organisms are converted into inorganic
compounds which serve as nutrients to the other organisms. In both processes of energy flow and nutrient
cycles, the plants provide the link by which the biotic and abiotic components interact with one another.
Insightfulness
Energy cannot be recycled. When using, it is lost into the ecosystem.
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The nutrients in an ecosystem can be used over and over again. They are cycled beginning from the
nonliving environment: air, water, and soil. Then, these substances are taken in by the producers and are
passed on through several consumers. They are returned to the nonliving environment by decomposers.
Nutrients may be classified into two types, namely, the macronutrients and the micronutrients. The
macronutrients are those that are required by the organisms in large quantities. Examples are carbon,
hydrogen, oxygen, and nitrogen. Sulfur, phosphorus, and potassium are also macronutrients but are
needed by organisms in smaller quantities. The micronutrients are needed in very small amounts. They are
also essential to life. Examples are copper, zinc, iron, and boron.

The macronutrients are the major components of fats and carbohydrates. They make-up the cell structures
of plants and animals. The cell walls of plants, for example, are made up of a very rigid substance called
the cellulose. Cellulose is made up of these three elements with a ratio of 7.2 carbons, 1 hydrogen and 8
oxygen. This substance makes the cell walls very firm and rigid. It adds strength to the plant.
Nitrogen, carbon, hydrogen, and oxygen are the building blocks of proteins. Phosphorus makes up many
nucleic acids and is also essential for the transformation of energy in the cells.
The micronutrients are as important as the macronutrients. Magnesium, for example, is necessary in the
production of chlorophyll.
Guide questions

1. What happens to the energy from the sun when it enters to an ecosystem?
2.
3.
4.
5.

What happens to the dead bodies of plants and animals in an ecosystem?
Define macronutrients and micronutrients.
Make a listing of micronutrients and macronutrients, and give their functions?
What are the components of cellulose?

2.2 THE WATER CYCLE
As with any cycle, the water cycle has neither beginning nor end. However, it is useful to choose a
starting point. Let us begin with water vapor in the atmosphere.
a)

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b)

Figure 2.1: The water cycle
When water in the atmosphere reaches saturation (the highest amount of moisture that the air can hold), it
falls as rain. This falls directly to the land and bodies of water like the oceans and seas. Some runs off the
surface of the land into rivers. The rain that falls on the land is absorbed by plants through the roots and
drank by animals. Some penetrates the soil and becomes part of the underground water, which eventually
empties into the oceans. The processes of condensation and precipitation are responsible for the return of
water from the atmosphere into the land and other bodies of water.
The water from the land and other bodies of water returns to the atmosphere through the process of
evaporation. Plants return the water by the process known as transpiration, while animals do this through
respiration. Water accumulates again in the atmosphere as clouds and falls as rain.
Guide questions
1. What is saturation?
2. What is evaporation?
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3. What is respiration?
4. Trace the pathway of the water cycle.
2.3. THE CARBON AND OXYGEN CYCLE
Much of the carbon in the environment exists in the form of carbon dioxide. Plants absorb this gas though
the leaves and use in the process of photosynthesis. Oxygen is given off during this process. Animals and
other consumers obtain their food as well as their oxygen needs from plants. In the process of respiration,
the food is broken down into CO2 and water which are returned into the atmosphere.

Figure 2.2: The carbon and oxygen cycles
When the animals and plants die, their bodies and waters are broken down by the decomposers. In this
process, CO2 is produced and returned to the atmosphere. Sometimes dead organisms fail to decompose
quickly. When this happens, the dead bodies change to coal, oil, and gas which become fossil fuels after a
long time. When burned, fossil fuels release carbon dioxide into the atmosphere.

Insightfulness
Carbon dioxide is present in the atmosphere from wastes, dead bodies of organisms, and fossil fuels.

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Plants use CO2 in the process of photosynthesis. Animals obtain their food from the plants and release
CO2 though the process of respiration. Decomposers and burning also release CO2 into the environment.
Erupting volcanoes emit carbon dioxide. The eruption of the volcano supplies fresh carbon to the
atmosphere from the deeper part of the interior of the earth.
Carbon dioxide combines with water and forms calcium carbonate (CaCO3). This compound is used in the
production of shells of animals like clams and oysters. When shelled organisms die, the calcium carbonate
may dissolve or form part of carbonate rocks serve as an buffer environment and storing carbon for many
years. During the process of weathering, carbon dioxide is again released into the environment.
Guide questions
1.
2.
3.
4.
5.

What are the sources of carbon dioxide?
What are the sources of oxygen?
How is carbon released from carbonate rocks into the atmosphere?
How are fossil fuels formed?
What two important processes are involved in the cycle of carbon and oxygen? Discuss these
processes.

2.4. THE NITROGEN CYCLE
Nitrogen is an element crucial to life. It is an important component of proteins and nucleic acids. The

nitrogen gas constitutes about 78 percent of the air in the atmosphere. However, it cannot be used directly
by plants and animals. Plants use it in the form of nitrates.

You inhale large quantities of nitrogen but it remains in your body unchanged.

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Figure 2.3: The Nitrogen Cycle
Nitrogen in the atmosphere is converted into nitrates in two ways: (1) by the action of lightning and (2) by
action of specialized organisms. Electrical activity (lightning) during thunderstorms converts nitrogen into
nitrates but only a small amount. The nitrates produced by this process fall to the earth with the rain.
The organisms that convert nitrogen are bacteria, algae, and fungi, of which bacteria is the most
important. Nitrogen-fixing bacteria directly convert nitrogen into nitrates though the process called
nitrogen fixation. Examples of nitrogen-fixing bacteria are the Rhizobium, which live in the roots of
legumes like beans, peas, and peanuts. The association between Rhizobium and legumes forms swollen
areas within the roots called nodules. Nitrates are formed within the nodules. The compounds are then
used by the plants to build proteins, or remain in the soil as fertilizers. Because of this, legumes are
important crop rotation as they help maintain soil fertility. This explains why farmers plant legumes in
soil before they plant new crops.
Decomposers break down the protein in the bodies of plants, animals, and their wastes. In this process,
ammonia is produced. Ammonia may be used directly by some plants but others cannot. They have to
transform this into nitrates through the nitrogen-fixing bacteria. This process converting ammonia to
nitrates is known as nitrification. The plants are then able to obtain nitrates to synthesize amino acids and
proteins.
The nitrates produced by the nitrogen-fixing bacteria are converted into nitrites by another group of
bacteria called nitrite bacteria. Nitrites are converted into nitrogen by the denitrifying the bacteria in a
process called denitration. Denitration completes the cycle of nitrogen.
Insightfulness
-

The most complex of the nutrient cycles is the nitrogen cycle. It involves many microorganisms.

-

Nitrogen cannot be used directly by the plants. It has to be transformed into nitrates.

-

Lightning, nitrogen-fixing bacteria, and decomposers convert nitrogen into nitrates.
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-

Denitrifying bacteria convert nitrites into nitrogen, thus completing the nitrogen cycle.

-

Plants use nitrogen for the synthesis of amino acids and proteins.

What will happen if the nitrates are not absorbed by plants? Is this beneficial to the soil?
If nitrates are not absorbed by plants, they are washed away by heavy rains. This process is called
leaching. Leaching drains the soil of its nutrients which are ultimately lost into the rivers and shallow
marine sediments. These nitrates enter the marine food chain and are returned to land by the droppings of
seabirds. These droppings are known as guano, which were once a major world supply of fertilizer.
Guide questions
1. What is the important of nitrogen?
2. What is the useful form of nitrogen?

3. How is nitrogen converted into nitrates?
4. What is nitrogen fixation?
5. Differentiate between nitrification and denitrification.
6. Explain leaching. What is its role in the nitrogen cycle?
2.5. THE PHOSPHORUS CYCLE
Phosphorus is essential to life. It is a component of the cell membranes, nucleic acids, and adenosine
triphosphate – the energy currency of the cell.

Figure 2.4: The phosphorus cycle

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Phosphorus is found naturally in the environment in the form of phosphates. Phosphates in the soil come
from phosphate rocks. Though the process of weathering, the phosphates are incorporated into the soil in
soluble or insoluble forms. The plants absorb the phosphate and use it for protein synthesis. The animals
obtain phosphate from the plants they eat. When the plants and animals die, decomposition brings back
the phosphate into the soil.
Phosphate in the soil may be washed away into shallow marine sediments by means of leaching. It may
also reach the deep ocean sediments. From the shallow marine sediments, the phosphates are returned to
the soil in the form of guano deposits of marine fish and sediments. Phosphates in the deep ocean
sediments are recycled back to the soil by means of upwelling. If upwelling does not take place, the
phosphate becomes incorporated into the phosphate rocks.
Phosphate rocks are mined to be used in the manufacture of phosphate fertilizers. Though leaching, the
phosphorus in these fertilizers is lost from the soil. Human therefore hasten the rate of loss of available
phosphate. This can have serious effects on the supply of phosphorus for agriculture in the future.
Insightfulness

-

Phosphorus presents in soil in the form of phosphates. Though weathering, phosphate rocks
contribute to the amount of phosphate in the soil.

-

Phosphate is taken in by plants and passed on the food chain. When plants and animals die, the

-

bacteria convert the dead bodies into phosphates and return them into the soil.
Guano deposits are good sources of phosphates.

Human activities have altered the cycle of materials in the environment. When people cut down trees or
destroy forest in one area, rainwater continues to flow until it finally reaches the sea instead of rising to
the atmosphere and falling again on the forests. The massive destruction of the forests changes the
environmental conditions, so that forests may never recover at all.

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Figure 2.5: Eutrophication
Similarly, deforestation also affects the mount of nitrates in the soil though leaching. This loss of nitrogen
limits the growth of plants and pollutes groundwater.
The phosphorus cycle has also been disrupted by the activities of humans especially in the water
ecosystem. People use a lot of agricultural fertilizers and detergents of which phosphates are major
components. When the phosphates from fertilizers and detergents run off into lakes, they stimulate the
rapid growth of algae and other aquatic plants causing algae bloom. This condition is known as
eutrophication.
As the plants age and die, decomposition takes place and use up so much oxygen causing the death of fish
and other animals.

Guide questions
1. What is the importance of phosphorus?
2. What processes are involved in the cycle of phosphorus?
3. In what ways have people altered the cycle of nutrients in the environments?

4. Define algae bloom. How does it lead to eutrophication?
5. What are the effects of eutrophication?
VOCABULARY
Algae bloom: Very rapid growth of algae in surface waters due to increase in inorganic nutrients,
especially phosphorus and nitrogens.
Conservation: Process of reducing the use of resources through recycling, decreased demand, and
increased efficiency use.
Denitrifying bacteria: Bacteria that convert nitrates into nitrogen gas.
Denitrification: Process that convert nitrates into nitrogen gas.
Eutrophication: Accumulation of nutrients in a lake or pond due to human intervention or nature causes.
Evaporation: The process of the change in the state of a liquid or solid to a gas or vapor. Vanishing of
the surface of a liquid to the atmosphere.
Leaching: The process by which nutrient chemicals or contaminants are dissolved and carried away by
water, or are moved into a lower layer of soil.
Nitrate: Inorganic anion containing three oxygen atoms and one nitrogen atom.

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Nitrogen fixation: A process whereby nitrogen fixing bacteria living in mutualistic associations with
plants convert atmospheric nitrogen to nitrogen compounds that plants can utilize directly.
Bacteria: Group of single - celled organisms responsible for functions like that decay of organic
materials and nutrient recycling.
Nutrient: Substance taken by a cell from its environment and used in catabolic or anabolic reactions.

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CHAPTER 3
HUMANKIND’S INVENTION WITH NATURE
After studying this chapter, you should be able to
1.
2.
3.
4.
5.
6.

Discuss how ancient people affected the environment.
Explain the progress made in the field of agriculture.
Identify the advances in the area of medicine.
Enumerate the new technologies brought about by advances in engineering.
Get a glimpse of the bad side of human beings impact on the environment.
Enumerate some bad effects of modern technologies.

3.1. BALANCE OF NATURE
Scientists estimated that the earth is already around three billion years old, and it will exists for another
three billion years. The life of the earth depends mainly on the sun. If the gravitational pull of the sun
remains constant, the earth will continue to revolve around the sun in its present speed. There is a delicate
balance between the centrifugal force of the earth as is goes around the sun.
If the sun continue to shine the way it is now, then the earth will continue to receive radiant energy needed
by the living creatures. Again, there is a delicate balance here. Too much sunshine will make the earth too
hot for most living beings to survive. In short, the balance of nature is so delicate that any action that
might upset such balance could have catastrophic results.
For millions of years, this balance of nature has been maintained. The animals that antedated humans for

thousands of year did not really disturb the environment. The effect they made on the environment was
minimal and Mother Nature easily recovered.
During the dawn of civilization, humans and the predators lived in very similar ways. Both hunted for
food and dwelt in natural habitats, like caves. With this kind of life, they did not alter the environment.
But, since humans were more intelligent and more cunning, plus the fact that they walked erect and made
use of their hands, they were able to invent weapons to help them. Axe from stones and spears from sharp
object made them better hunters than the animals. And when they learned the use of fire, they cooked their
food with it, warmed their bodies by it, and heated a lot of things to help them survive. That was when
humans proved their superiority over animals.
When they learned to eat green leafy vegetables and learned how to cultivate them, they started to alter
the environment. They made clearings in the forests and planted vegetables. When the land was no longer
that fertile, they abandoned the place and cleared other lands. That was the beginning of forest
destruction. Then they learned how to domesticate animals and lived in a permanent dwelling which was
made of the products of the environment, like wood for the structure and leaves for roofing. They had to
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change the environment some more. Fortunately, there were not so many people at that time, so the
environment was able to recover. The balance of nature remained.
As the population increased and the needs of people became more complex, they put greater and greater
pressure on the environment. Larger houses were constructed from different materials, strong fences to
protect them from enemies, irrigation canals for agriculture, and large enclosures for animals, all these
required more change in the environment. But even then, there was no serious damage to the environment
from which nature was unable to recover. It could be said then that by and large, humans lives for many,
many years in harmony with the environment.
The rise in civilization of the Sumerians, the Babylonians, the Egyptians, the Greeks, and the Romans
placed additional burden on Mother Earth, especially in the terms of land used for public buildings,
monuments, and, of course, houses. With more lands used for agriculture and the upkeep of animals,
especially those used in war, changes in the environment became more permanent. But even then, they
were not causes for worry.

It was only during the rapid progress in knowledge about the world, followed by the so-called industrial
revolution, when humans made greater impact on the environment.
Guide questions
1. Explain in details the meaning of balance of nature

2. Name some ways by which humans upset the balance of nature.
3.2. PROGRESS IN AGRICULTURE, ENGINEERING, AND MEDICINE
Because of their superior intelligence, aided by the virtues of curiosity, imagination, and creativity,
humans were able to discover the many laws of nature, and they used this knowledge to control parts of
nature mostly for the benefit of humankind, in general.
In the field of agriculture, the knowledge of genetics produced larger and better varieties of fruits and
vegetables. These varieties gave better yields per area planted and were more resistant to diseases. Some
examples will be enumerated to highlight the point.
Better yielding varieties of rice, wheat, and potatoes have resulted in bumper harvest in many parts of the
world. As the direct consequence, the problem of feeding the growing populations was partly solves by
these discoveries.
Scientists were able to breed seedless grapes and seedless papayas. Mangoes are now harvested all year
round. And perhaps, the other fruits may soon be grown seedless, like melons, and watermelons. Large
varieties of guavas and Santo are now in abundance.

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In the field of medicine, doctor and the scientists were able to discover the cure for many diseases, thus
prolonging and preserving producing healthier babies. The end result of all these are a much faster rate of
population increase.
In the field of animal science, researchers were able to improve the breed of animals used for food. Fastergrowing chickens and pigs and cultured fish are some good examples. Artificial hatching of eggs was
invented. All these resulted in more food for the fast-growing population of the world.
In the field of engineering, scientists invented better means of transportation on land, at sea, and in the air.
The more recent inventions include the bullet train that can run up to 500 kilometers (km) per hour,

airplanes that can carry up to 700 passengers, and large ships powered by nuclear fuel.
Landscapes have been altered to improve services to the people. For instance, dams were built to produce
electricity for homes and factories. Oil, coal, and other fossil fuels were mined to power these new
inventions.
For more comfort at home, scientists invented artificial lighting, air-conditioning systems, refrigerator to
preserve food better, radio and television for faster and better dissemination of information and for
entertainment, and all those electric gadgets in the kitchen to the delight of many housewives.
In the field of food technology, we can choose from a very wide variety of food available in the market,
caned goods of all kinds, powered milk, packed lunches, preserved fruits and vegetables, and many
others.
All there may be considered as the good impact humans have made on the environment. As a result of
these inventions and new technology, people are living better food, live in more comfortable homes, enjoy
their vacations more, get better health services, travel faster, and dress better. In short, they can do a lot
better than their ancestors.
3.3. ADVERSE EFFECTS OF PEOPLE’S ACTIVITIES
Humankind’s intervention with nature has its adverse effects too. These include the pollution produced by
modern technology and its ill effects on the environment (disruption of the atmosphere which causes
greenhouse effect, ozone depletion and acid rain); among others; pollution of the water system,
deforestation, improper disposal of solid wastes, as well as nuclear wastes; and noise pollution.
3.3.1. The greenhouse effect

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Figure 3.1: The greenhouse effect
Too much carbon dioxide and other gases emitted by factories are accumulating in the atmosphere. These
gases allow sunlight to penetrate the earth’s atmosphere but unfortunately, they also trap radiant heat and
revert its escape into outer space.
The immediate consequence is global warming, which is better known as the green-house effect. The rise
in the average temperature of the earth could have serious consequences. Among them is the melting of

ice and glaciers in the North and South poles. This will raise the water level in many areas of the world,
resulting in the submersion of the low-lying coastal towns and cities.

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3.3.2. Ozone depletion
High above the earth’s atmosphere, between 15 and 59 km above the earth, is a layer of ozone (O 3). It is
formed when ultraviolet radiation (UV) splits a molecule of oxygen (O2), and the free oxygen atoms (O)
combine with other oxygen molecules. Ozone acts as a filter in the upper atmosphere, preventing the
harmful ultraviolet radiation of the sun from reaching the earth. Scientists discovered that compounds of
carbon such as carbon dioxide (CO2) and chloroflofuorocarbons (CFCs), nitrogen oxides (NO) and
methane break up ozone molecules, thereby gradually depleting it.

Figure 3.2: Ozone depletion
In fact a large ozone hole was discovered above the tip of South America. The people directly below it
may experience skin irritations and soreness in their eyes. This may be due to the higher intensity of
harmful ultraviolet radiations hitting them.
Ozone levels, on the average, have declined by around 2 percent between 1969 and 1988. But in some
parts of the world, the decrease in much higher. For example, in Melbourne of Australia, ozone levels
dropped by as much as 10 percent in 1987, causing a 20 percent increase in ultraviolet radiation reaching
the ground.
3.3.3. Acid rain
Sulfur and nitrogen oxides are released from industrial factories, electrical power plants, smelting plants,
and motor vehicles.

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