Tài liệu MÔI TRƯỜNG KHOA HỌC docx

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, 2010
CONTENTS
2
2
CHAPTER 1: BASIC UNITS OF ECOLOGY
After studying this chapter, you should be able to:
1. Define environment.
2. Define an ecosystem.
3. Identify the components of the biosphere.
4. Describe the living and nonliving components of the environment.
5. Explain that bacteria and fungi are agents of decay.
6. 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, 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.
3
3
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 particles. Chemical change
also occurs. The roots absorb the minerals present.
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.
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.
4
4
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 (CO
2
) in the air and water (H
2
O) 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.
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, it is called Eutrophication (Eutrophication is an increase in the
concentration of chemical nutrients in an ecosystem to an extent that increases
the primary productivity of the ecosystem).
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.
5
5
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 H
2
O 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?
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
6
6
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.
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.
7
7

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.
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.
8
8
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.
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.
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 importance of 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. Identify different nutrients that can be recycled.
9
9
2. Explain the water, carbon and oxygen, nitrogen, and phosphorus cycles.
3. Discuss the importance of each of these cycles.
4. Discuss how people affect these cycles.
5. 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.
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
10
10
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. What happens to the dead bodies of plants and animals in an ecosystem?
3. Define macronutrients and micronutrients.
4. Make a listing of micronutrients and macronutrients, and give their functions?
5. 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)
11
11
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.
12
12
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?

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 CO
2
and water which are
returned into the atmosphere.
13
13
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, CO
2
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.
Plants use CO
2
in the process of photosynthesis. Animals obtain their food
from the plants and release CO
2

though the process of respiration.
Decomposers and burning also release CO
2
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 (CaCO
3
).
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. What are the sources of carbon dioxide?
14
14
2. What are the sources of oxygen?
3. How is carbon released from carbonate rocks into the atmosphere?
4. How are fossil fuels formed?
5. 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.
15

15
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.
16
16
- 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.
17
17
Figure 2.4: The phosphorus cycle

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
18
18
- 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.
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
19
19
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.
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.
20
20
CHAPTER 3: HUMANKIND’S INVENTION WITH NATURE
After studying this chapter, you should be able to
1. Discuss how ancient people affected the environment.
2. Explain the progress made in the field of agriculture.
3. Identify the advances in the area of medicine.
4. Enumerate the new technologies brought about by advances in engineering.
5. Get a glimpse of the bad side of human beings impact on the environment.
6. 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.
21
21
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 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.
22
22
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.
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. Faster- growing 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

23
23
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
24
24
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.
25
25