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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.
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.
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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.
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.
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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 (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.
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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
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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 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.
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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
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.
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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.
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.
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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.
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. Identify different nutrients that can be recycled.
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
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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
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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. 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)
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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.
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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.
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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?
2. What are the sources of oxygen?
3. How is carbon released from carbonate rocks into the atmosphere?

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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.
Figure
2.3: The
Nitrogen
Cycle
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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.
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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
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- 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 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?
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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.
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Nutrient: Substance taken by a cell from its environment and used in catabolic or anabolic
reactions.
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.
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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 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.
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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. 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 living better food, live in more
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