STEM
EARTH AND LIFE SCIENCE
FEU Senior High School
GENERAL AIMS OF THE MODULE
This module was created by the faculty members of Far Eastern University High School to
serve as a supplementary instructional material for the students. This module will also serve
as a basis for standardizing the content of Earth and Life Science (ELS) to ensure that every
section will take the same content and same competency since Earth and Life Science is a
core subject as stipulated by the Department of Education.
The module follows the prescribed course content by DepEd with some enhancements as
deemed appropriate by the faculty to ensure that the students meet more than the minimum
requirements. The module for ELS is designed as an independent study module; thus, it will
be equipped with comprehensive content where the reader will obtain the necessary
knowledge prior to class discussion. It is expected for the student to do advanced reading to
be able to participate actively in class.
Structurally, each lesson in the module contains four parts: objectives, subject matter,
evaluation, and activity. The objectives are slightly different from the competencies
stipulated in the DepEd K-12 Curriculum Guide for Earth and Life Science in a sense that they
are more concrete and observable. The subject matter contains the lesson content as
prescribed with some enhancements to ensure smooth transitions between sections. The
evaluation is a 10-item formative assessment to check whether the student understood the
subject matter. Lastly, suggested activities are listed at the end of every lesson where the
student can apply what he/she has learned from the content. The teacher may deviate from
the activity listed as he/she deems appropriate to the needs of the students.
PRACTICAL OBJECTIVES OF THE MODULE
This student module aims to:
1. Equip the student with prior knowledge to help in active class participation;
2. Standardize the content for Earth and Life Science for FEU High School;
3. Provide an independent study material for students who need to do so;
4. Serve as a learning material to make sure that all content for ELS are covered
despite class suspensions.
TEACHING METHODOLOGIES AND STRATEGIES
The teacher should regularly consult this module to make sure that the lesson content will
follow the standard stipulated by the institution. However, regarding teaching
methodologies and strategies, it is left to the creativity and ingenuity of the teacher to design
methods he/she deems appropriate for the needs of her students.
Since Earth and Life Science is a science subject, it is expected for the teacher to construct
methods that will support discovery learning through observation and experimentation.
This will ensure that students will be equipped with science content and skills for doing
science, at the same time having fun learning science. It is also suggested that audio-visual
materials be regularly used since the course is basically a survey of geological and biological
processes.
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EARTH AND LIFE SCIENCE
STEM
FEU Senior High School
UNIT 1
ORIGIN AND STRUCTURE OF THE EARTH
Unit Coverage
Lesson 1: Origin of the Universe
Lesson 2: The Solar System
Lesson 3: Layers and Subsystems of the Earth
UNIT INTRODUCTION
Welcome to Earth and Life Science! This will be your first out of two encounters of science
subjects as a student of Senior High School. Earth and Life Science is an integration of basic
Earth Science and Biology; the other being Physical Science, which is an integration of
Chemistry and Physics. Here in Earth and Life Science (or ELS), you will learn about how the
Earth, and its greatest gift—life, work.
In this unit, you will be familiarized with the world in the biggest perspectives: the universe,
the Solar System, and the planet Earth as a whole.
In Lesson 1, you will be oriented with an introduction to science: what it does and how it is
done, and what are its scopes and limitations. You will also be taught about the different
theories on the origin of the universe. The aim of this lesson is for you to be familiar with
how scientists trace back the distant past using reason and modern technology. It will help
you how to think like a scientist.
In Lesson 2, we will narrow down the discussion to our neighborhood—the Solar System.
Again, we will learn about theories on its origin. This is an appreciation lesson about what
theories were formulated back then and what theory is most popular among scientists today.
You will also be taught about the current information on our Solar System and our neighbors.
How many planets are there in the Solar System? What other bodies are there aside from
planets?
In Lesson 3, we will go to our planet. This is a lesson to refresh you about the layers of the
Earth—the usual crust, mantle, and core—but we will study them here a little more detailed
than your previous grades. We will also study the large-scale interactions happening on our
planet. You will learn that the Earth is composed of basically three features: a solid rock, a
liquid water, and a gaseous atmosphere.
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STEM
EARTH AND LIFE SCIENCE
FEU Senior High School
LESSON 1 – UNIVERSE AND THE SOLAR SYSTEM
OBJECTIVES
At the end of the lesson, you should be able to:
1. State the different hypotheses explaining the origin of the universe;
2. Discuss the story of the Big Bang;
3. Discuss the evidences supporting the Big Bang;
4. Compare and contrast the Big Bang and the Steady State theories;
5. Discuss the String Theory.
SUBJECT MATTER
Introduction to Science
This course will probably
be your first encounter of
science under the Senior
High School Program.
Thus, now would be the
right time for you to know
what Science really is and
appreciate how it works.
Science came from the
Latin word scientia which
means
“knowledge”.
Science is a systematic
body of knowledge that
discovers
the
world
through observation and
collection of facts and
establishes relationships
among these facts by
means of logic and reason. Figure 1.1. Science is basically done through this method. Any judgment
In simpler terms, science that cannot be tested through this method is outside the realm of science.
is done by observing the world through our senses and formulating theories that explain
these observations. The theories are verified through repeated experimentation or testing
and then accepted as long as all observed facts and experimental results satisfy the
conditions of the theory. A single observation that does not fit into the theory is enough to
reject or revise the theory. Hence, Science is not a mere collection of facts but is an active
process of trying to look for explanations on how things work. The entire process is broken
down into smaller steps and is called the scientific method (Figure 1.1).
Since Science relies on repeated experimentations, it is limited only to being testable. Science
cannot prove anything that is not testable. For example, there is no test to tell whether a
philosophical belief is right or wrong; nor whether a work of art is beautiful or not.
Nevertheless, Science still contributes in our daily lives in the sense that it has expanded our
view of the world. In the first steps of our journey in Science, we will try to take a look at the
scientific theories explaining how our Universe came into being.
Creation Myths and Stories
In ancient times, most people tried
to explain natural events as a result
of the action of gods and spirits.
This includes the question on how
the world, the Universe rather,
came into being. A popular theory
of the origin of the universe is the
Biblical account of creation written
Figure 1.2. In the Bible, God created everything—from light to
life—in six days.
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STEM
EARTH AND LIFE SCIENCE
FEU Senior High School
in the book of Genesis where it says that God created everything in six days (Figure 1.2). In
the Tagalog mythology of Malakas at Maganda, God (or Diyos in Filipino) created the entire
world by raising His hand then pointing them down. Shortly, the first man and woman
appeared from inside a bamboo shoot. These are just many examples of creation myths and
stories passed down from generation to generation as a way of perpetuating the culture of a
particular society.
The ancient Greeks were among the first people to use systematic observation and reason to
explain natural events. In fact, they were among the first ones to construct models of the
entire universe. In Earth and Life Science, we will focus on the theories on how the universe
began; models of the universe are discussed under Physical Science.
Theories on the Origin of the Universe
Under this course we will discuss four scientific theories on the origin of the universe,
namely: (1) Big Bang Theory; (2) Steady State Theory; and (3) String Theory.
Big Bang Theory
We will dedicate most of our
discussion of the origin of the
universe in this section
because the Big Bang theory is
the most accepted theory on
how the universe came into
being. So far, the details of this
theory are consistent with the
known laws of physics.
Do you recall a moment when
Figure 1.3. Doppler effect as illustrated by a moving ambulance. The
an ambulance was coming frequency decreases as it moves away and increases as it moves towards
towards you, then away from the observer.
you? You might have noticed
that when it moved away from you, the pitch of its siren became lower. This phenomenon is
called the Doppler effect (Figure 1.3). Waves, when coming from a moving source, decrease
in frequency as it moves away and increase as it moves toward the observer. In the language
of sound, a lower frequency means a lower pitch and a higher frequency means a higher pitch.
A similar phenomenon is also present in light, a wave.
In 1924, Edwin Hubble discovered that stars are not
uniformly distributed in space, as seen by the naked
eye in the night sky. Instead, stars form clusters called
galaxies. The distance of any galaxy from the Earth
can be estimated by measuring the amount of light
the galaxy emits. Through this, Hubble found out that
nearly all galaxies tend to move away from the Earth.
His evidence is based from the fact that the Figure 1.4. Redshift—an illustration of
measured light from galaxies tends to move towards how light also decreases in frequency as it
the red end (lower frequency) of the visible light moves away from the source.
spectrum, a phenomenon called redshift. If you look at Figure 1.4, the illustration of redshift
is similar to that of the Doppler effect in the ambulance siren, implying a source that is
moving away.
With this observation, it was speculated that if the galaxies are moving away from us, there
must have been some point in time when they must have been closer together in the past;
they may have even come from a single point in the beginning. In 1927, George Lemaitre
used this notion of an expanding universe to conceive the Big Bang theory.
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EARTH AND LIFE SCIENCE
FEU Senior High School
The Big Bang theory basically states that about 13.7 billion years ago, everything (every
matter, energy, space and time there is) in the universe started from an infinitely small,
infinitely dense, and infinitely hot entity called a singularity. Where this singularity came
from and why it expanded in the first place is still unknown.
Big Bang theory today also narrates how the fundamental
particles and forces molded the universe as we know it
today. It is summarized as follows:
1. Inflation – the universe exponentially expanded from a
singularity to about 1035 meters in width.
2. Formation of the universe – as the universe
expands, the four fundamental forces separated and
the universe was made of elementary particles such as
quarks, electrons, photons, and neutrinos.
3. Formation of proton and neutron - protons and
neutrons were formed from quarks.
4. Nucleosynthesis – protons and neutrons combined to form the very
first nuclei. One proton and one neutron became hydrogen; two
protons and two neutrons became helium.
5. Radiation era – up to this time, the universe is dominated by
radiation. Through time, this radiation is now in the form of cosmic
microwave background (to be discussed later).
6. Matter domination – at this point,
electrons joined hydrogen and helium to
form the very first atoms.
7. Birth of stars and galaxies – hydrogen
and helium, which are gases, were
produced in large quantities and formed
large masses of gas clouds. Under gravity,
they began to increase mass and ignite to produce stars.
Multiple stars also began to cluster together through gravity to form galaxies.
Hubble’s discovery was not the
only evidence presented to
prove the Big Bang. Two more
proofs,
the
(1)
cosmic
microwave background (CMB)
and (2) the presence of
hydrogen, helium, and lithium in
stars, laid the foundations to
solidify this comprehensive
theory.
In 1960, scientists Arno
Figure 1.5. A map of the sky showing the values of the temperature of
Penzias and Robert Wilson the cosmic microwave background. The temperature only ranges by
tried to construct a radio ±200 microkelvins.
antenna with zero background
noise. However, no matter what point in the sky they point, there is still background noise.
This background noise was speculated to be a remnant energy from the explosion of the Big
Bang. Further data (Figure 1.5) shows that the radiation carries a temperature range of only
±200 microkelvins. This homogeneity suggests that these very distant radiations should
have had interaction in the past. Thus, they might have been so close together back then,
suggesting again the existence of a singularity that once contained all of them together.
Modern technology enabled man to detect what elements are present in stars however far
they are from us. The nucleosynthesis narrative of the Big Bang suggests that stars should be
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FEU Senior High School
made of the simplest atoms hydrogen and helium. True enough, it was found out that stars
indeed contained mostly hydrogen and helium, with little traces of lithium and beryllium.
In its first version, the Big Bang has encountered problems: flatness, monopole, and horizon
problems. These three problems were resolved by an elegant idea called the inflation theory,
proposed by Alan Guth, Andrei Linde, Paul Steinhart, and Andy Albrecht. Through inserting
an exponential inflation in the story of the Big Bang, the problems were resolved and the
theory is back on track. The problems and the solutions are summarized in the table below.
Problem
Expectation (Big
Bang says…)
The universe is curved
Reality (Observation
says…)
The universe is nearly flat
according to sophisticated
measurements
Solution (Big Bang +
Inflation says…)
An exponential inflation
allows a very large curved
universe but we can only
observe the flat geometry. In
the same way that the Earth is
curved but, in our scale, we
perceive it as flat
Monopoles
There should be heavy
stable magnetic
monopoles in the early
universe because of the
very high temperature
There are no magnetic
monopoles detected so far
Horizon
The universe is about
13.7 billion years old.
Everything 13.7 billion
years ago must have
been in contact with
one another
According to the math, the
observable universe is 93
billion light years across. How
can two points 93 billion light
years apart have been in
contact?
An exponential inflation
would have dramatically
decreased the temperature of
the expanding universe, no
longer allowing monopoles to
form
An exponential inflation
faster than the speed of light
will allow these points to
have been in contact 13.7
billion years ago
Flatness
Steady State Theory
A theory opposing the Big Bang was
proposed by Hermann Bondi, Thomas
Gold, and Fred Hoyle in 1948. This
theory states that though the universe
is expanding, matter and energy
density remains the same (Figure
1.6). The discovery of the CMB
debunked this theory because we saw
in Figure 1.5 that the universe is not
constant in composition.
String Theory
Scientists did not stop at the Big Figure 1.6. A comparison of the matter density of Big Bang and
Bang. They wanted to know what Steady State universe. Evidences suggest that the amount of
came before it. However, knowing matter and energy in the universe is constant. Matter is diluted
as space expands.
what came before the Big Bang
would require scientists to be able to come up with a theory that unifies the four fundamental
forces of nature: strong nuclear, weak nuclear, electromagnetic, and gravitational force. The
first three forces were discovered to be produced by elementary particles. Gravity, however,
according to Einstein, is produced by curvature of spacetime, not by particles. In string
theory, elementary particles are said to have been made from the mode of vibration of a
string whose dimensions are smaller than a particle. This theory speculates the existence of
gravitons—particles carrying gravity. The problem with this theory is that its mathematics
can only work in a 10-dimensional space, something that has not yet been observed.
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STEM
EARTH AND LIFE SCIENCE
FEU Senior High School
LESSON 2 – THE SOLAR SYSTEM
OBJECTIVES
At the end of the lesson, you should be able to:
1. State the different hypotheses explaining the origin of the Solar System;
2. Compare and contrast the different hypotheses on the origin of the Solar System;
3. Discuss the story of the Solar Nebular Theory;
4. Identify the regularities of the Solar System;
5. Differentiate planets, asteroids, comets, and dwarf planets;
6. Construct a map of the Solar System extended to the Kuiper belt and Oort cloud; and
7. Classify planets according to composition and position relative to the Sun.
SUBJECT MATTER
Theories on the Origin of the Solar System
The Solar System is just one little speck in the Milky Way Galaxy. The system is made of one
star (the Sun), together with the planets and other heavenly bodies surrounding it. There are
many theories regarding the origin of the Solar System, which are presented in chronological
order they were proposed. Among them one theory stands out because it is consistent with
the known laws of physics.
Vortex Theory
Rene Descartes, a French mathematician and physicist, was
one of the first proponents in constructing a model on the
origin of the Solar System. In his model (Figure 2.1), the
system came into being by the vortex motion of solar
materials. The vortices are interlocked and influences the
motions of one another.
Buffon’s Collision Theory
George Louis Leclerc, Comte de Buffon is a French naturalist
who proposed that the planets were formed due to a collision
between the Sun and a giant comet. The debris from the
collision formed the planets that rotate in the same
direction as they revolved around the Sun.
Figure 2.1. Descartes’ depiction
of the Solar System run by
interlocked vortices.
Kant-Laplace Nebular Theory
Grounding on the vortex idea of Descartes, Immanuel Kant
and Pierre Simon Laplace proposed the nebular theory
(Figure 2.2). In this theory, it was speculated that a great
cloud of gas and dust (called nebula) began to collapse due
to intense gravity. As it collapsed, it spun rapidly until it
became a flattened disk. Local regions around the Sun
began to condense into planets due to gravity as well.
One major flaw of this theory is that it assumes that the Figure 2.2. The steps of Solar
Sun should be spinning rapidly until now. It was found out, System formation according to Kant
however, that the Sun is spinning more slowly than the and Laplace.
planets. For their theory to be correct, either the Sun has to be faster or the planets have to
be slower.
Jean-Jeffreys Tidal Theory
A relatively simple model was proposed by Sir James Hopwood Jeans and Harold Jeffreys
(Figure 2.3). According to their model, a massive star traveled near enough from the Sun to
tear out some of its surface through gravitational attraction. These surface substances
condensed and became protoplanets (lit. “before planets”). Eventually they attracted other
bodies to form planets.
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Solar Nebular Theory
The most convincing theory is the Solar Nebular Theory (SNT)
because it follows the current known laws of physics and its
mechanism allows the existence of exoplanets—planets
outside the Solar System revolving around another star.
In the SNT, the solar system was formerly a collection of
hydrogen and helium gas cloud. This cloud, probably due to a
violent disturbance like the explosion of a nearby star, began
to collapse under its own gravity. The center of the cloud began
to shrink and spin into a rapidly rotating disk. The
gravitational energy generated turned into heat energy,
causing the center to glow and thus forming the Sun.
The remaining gas and dust around the Sun formed the
solar nebula. Grain-sized particles accreted into
centimeter-sized ones which later on grew into large bodies
called planetesimals. Coalescing planetesimals formed the
protoplanets.
Figure 2.3. A massive star tore
out some parts of the Sun. These
parts condensed and became
protoplanets.
It was also speculated that there was a time when the Sun shed a lot of energy and dissipated
all the remaining gas around it. The first four planets, Mercury, Venus, Earth and Mars, were
too near the Sun and failed to catch the gas due to the high temperature. The last four, Jupiter,
Saturn, Uranus, and Neptune, were far and cool enough to condense the gas and attract it
through gravity. The first four are therefore rocky or terrestrial planets; the last four are the
gas giants.
Exploring the Solar System
The Solar System is elegant; it has remarkable regularities. In fact, it is these regularities that
caught the attention of the ancient Greeks to change their way of thinking about the cosmos.
At first, they thought that the heavens are governed by the will of the gods; however, after
observing regularities in the heavens, they started to think that these events are not
controlled by supernatural beings but by natural laws. This gave birth to science.
Some of the observed regularities of the Solar System are the following:
1. The orbits of all planets are almost in the same plane.
2. The orbits are elliptical rather than perfectly circular.
3. The plane of the orbits follows the Sun’s plane of rotation.
4. All planets revolve around the Sun counterclockwise. All planets except Venus and
Uranus rotate counterclockwise.
5. The planets contain almost all the rotational motion of the Solar System.
6. The Solar System contains asteroids and comets.
Aside from the Sun and the eight planets, the Solar
System also contains bodies called asteroids and comets.
An asteroid (Figure 2.4) is a rocky material that has no
atmosphere but orbit around the Sun just like planets.
Most of the asteroids in the system are found between
Mars and Jupiter, in a region called asteroid belt. This
belt is probably a remnant of the early Solar System. The
asteroids failed to form as planets because Jupiter’s
strong gravity keeps on pulling them apart.
Figure 2.4. An asteroid is a rocky body
with no atmosphere but can orbit
around the Sun.
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Comets (Figure 2.5), on the other hand, are composed
mainly of ice (frozen water and gas) and dust (carbon or
silicon). They are popularly seen as meteor showers. Just
like asteroids, they orbit the Sun as well. As they go near the
Sun, in a point called perihelion, their frozen gas sublimes
and glows as a spectacular tail and we see it on Earth as a
glowing meteor shower.
Comets have two sources: the Kuiper belt and the Oort
cloud (Figure 2.6). The Kuiper belt is the outermost region
of the Solar System, located somewhere
beyond Neptune. It is sometimes called
the “final frontier”. Comets coming from
this region orbits the Sun every less than
200 years and are called short period
comets. The Oort cloud is beyond the
Kuiper belt and is the source of long
period comets.
As we conclude our discussion on the
Solar System, we will get back to the
classical entities comprising the system:
the eight planets. They are classified
according to composition and position.
Figure 2.5. A comet is made of
frozen gas that glows and sublimes
upon approaching the Sun.
Figure 2.6. A map of the Solar System showing the
location of the Kuiper belt and the Oort cloud.
For composition, the planets are divided
into two: rocky and gaseous. They are also
known as terrestrial and Jovian planets,
respectively. Our section on solar nebular
theory already explained why we have the
first four planets as rocky planets and the
last four as gaseous ones.
For position, we classify planets into outer
and inner planets, with the asteroid belt
giving the boundary. Incidentally, the rocky
planets are also the inner planets and the
gaseous ones are the outer planets. You
may refer to Figure 2.7.
Figure 2.7. A map of the Solar System showing the
relative location of the eight planets and the five dwarf
planets.
As a bonus, let us introduce the five dwarf
planets of the Solar System: Pluto, Eris,
Haumea, Makemake, and Ceres (Figure
2.8). Ceres is located in the asteroid belt
and the rest are beyond Neptune. A dwarf
Figure 2.8. The five dwarf planets and their sizes relative
planet is a body that assumes a round to the Moon.
shape, orbits around the Sun, but has not
cleared its neighborhood around it. On August 24, 2006, Pluto was reclassified from a planet
into a dwarf planet.
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STEM
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FEU Senior High School
LESSON 3 – LAYERS AND SUBSYSTEMS OF THE EARTH
OBJECTIVES
At the end of the lesson, you should be able to:
1. Discuss how the Earth ended up with layers;
2. Differentiate the layers of the Earth in terms of composition;
3. Identify the boundaries of the four basic layers.
4. Describe the four subsystems of the Earth;
5. Differentiate the layers of the atmosphere.
SUBJECT MATTER
Layers of the Earth
The Earth is not a uniform sphere. It has layers on its surface which we know to be the land,
the sea, and the sky. We will explore them in detail in the next lesson. The interior of the
Earth is not uniform as well. It is made up of different layers just like the surface. In this
lesson, we will study them in detail.
Recall how the planets were formed following
the Solar Nebular Theory. Clumps of gas and
dust accreted to form planetesimals; they, in
turn, accreted further to form the protoplanet.
Lastly, more accretion has given the body
enough gravity to assume a round shape and
become a planet.
However, planet formation did not stop there.
Considering that the gas and dust are of
different
compositions,
differentiation
occurred. Materials of high density such as iron
and nickel began to sink at the bottommost
part of the planet while lighter ones such as
silica, aluminum, and the gases stayed on top.
In the end, we have a layered planet. You can
visualize this phenomenon by mixing oil and
water then shaking it. Observe that oil and
water will still separate with the water at the
bottom and the oil on top.
Figure 3.1. A cutaway of Earth showing the four
basic layers.
The Earth has four basic layers (Figure 3.1):
inner core, outer core, mantle, and crust.
These layers have boundaries in them, called
discontinuities. The Lehmann discontinuity
is between the outer and inner core; the
Gutenberg is between the core and the
mantle; and the Mohorovicic is between the
mantle and the crust (Figure 3.2).
The inner core is made of solid iron and Figure 3.2. A cutaway of Earth showing the three
nickel. Despite the high temperature boundaries.
(~6000˚C) inside the core, the immense
pressure it experiences prevents it from turning into liquid. This concept works in the same
way that a pressure cooker can be used to cook beef because the immense pressure will
prevent the water from turning into steam inside the cooker, allowing less time to cook the
beef. The outer core, on the other hand, is also made from liquid iron and nickel because the
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pressure is not enough to make it solid. The molten metal state of the outer core is speculated
to be responsible for the Earth’s magnetic field, which is used to make compasses work.
The mantle (Figure 3.3) is the thickest layer of
the Earth, making 83% of the Earth’s volume
and 67% of its mass. It is made of silicon, iron,
magnesium, and oxygen. Activities inside the
mantle have direct implications in the
deformation and movement of the crust. Mantle
activities
cause
earthquakes,
volcanic
eruptions, and continental drift.
The mantle is divided into the upper and lower
mantle due to differences in pressure. The
lower mantle is plastic and very hot. The upper Figure 3.3. The mantle of the Earth highlighting
the layers within.
mantle is further divided into two layers: the
asthenosphere and the lithosphere, with the latter encompassing the crust as well.
In the asthenosphere, rocks are mechanically weak but can slowly flow. It is said that the
asthenosphere exhibits a convection current that drives the movements of the lithosphere
and the Earth’s crust. The lithosphere is composed of the rigid rocks of the upper mantle and
the crust. The rigid lithosphere is moved by the circulation of the asthenosphere, much like
a paper boat is moved by the water current. We will study the dynamics of the asthenosphere
and lithosphere and its implications on the Earth’s crust in Lesson 6.
The crust is the topmost layer of the Earth. It is the layer where we live and is divided into
two: oceanic and continental crust. The oceanic crust is the ocean floor, thin but dense; the
continental crust is thick but less dense than the oceanic crust. It is for this reason that water
does not seep into the mantle but can seep in the soils of the continent and return ultimately
to the ocean.
Subsystems of the Earth
The Earth is a unique planet. It has
land, it has liquid water, and it has
an atmosphere. The interplay of
these three systems of the planet
paved the way for energy flow and
eventually create the fourth
subsystem: the biosphere. In this
section, we will study each system
in detail and how it affects the
energy flow in the Earth. Figure
3.4 shows the relative scope of
each subsystem.
Figure 3.4. The subsystems of the Earth.
Hydrosphere
The hydrosphere is a key system of the Earth because the
presence of liquid water made life as we know it possible. In
fact, scientists look for the presence of liquid water in other
planets when they try to see if the planet is hospitable for life.
The planet Earth is labeled as the “blue planet” (Figure 3.5)
because it has plenty of water. Almost 97% of the hydrosphere
is saltwater; 2% is contributed by the polar ice caps; and the
remaining 1% is fresh water and ground water.
Figure 3.5. A blue planet.
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Lithosphere
The lithosphere, also known as the
geosphere, is the system of the
Earth consisting of all rocks and
minerals in it, including until the
upper mantle. We have fully
described the layers beneath the
Earth in the previous lesson. Today,
we will briefly describe the
lithosphere on the surface of the
Earth. The lithosphere is not one
big ball of rock. It is like a broken
dining plate loosely glued together.
These plates, called tectonic plates,
Figure 3.6. The major and minor tectonic plates of the Earth.
move against each other in three
The arrows show relative movements of the plates.
possible directions: converging,
diverging, or sliding past each other. Figure 3.6 shows the major and minor plates of the
Earth. The movements, according to the plate tectonics theory, are caused by the convection
current of the asthenosphere. We will study them in detail in Lesson 6.
Atmosphere
The atmosphere is the
gaseous layer of the
Earth. It is composed
of approximately 78%
nitrogen, 21% oxygen,
and
<1%
carbon
dioxide while the rest
are trace amounts of
neon,
helium,
methane, krypton, and
hydrogen gases. The
atmosphere of the
early Earth was not a
habitable
one.
Volcanic eruptions Figure 3.7. The different layers of the atmosphere. A zoom-in of the lowest layers
produced
water are shown together with some examples of activities in those layers.
vapor,
carbon
dioxide, and other gases, but no oxygen present. When the early Earth cooled, water vapor
condensed, forming the oceans. The evolution of the photosynthetic bacteria called
cyanobacteria paved the way for an oxygen mass production for the atmosphere. Oxygen also
created ozone (O3), which made land habitable for terrestrial life.
The atmosphere has layers (Figure 3.7). The lowest layer is the troposphere. This is the layer
where terrestrial life and weather systems (due to weather cloud formation) are possible. In
the troposphere, the temperature decreases as you go higher.
The next layer is the stratosphere, where the ozone layer is found. Its temperature increases
as you go higher because the ozone absorbs the ultraviolet radiation. This is also the layer
where passenger airplanes and jets fly because there is no weather in the stratosphere.
The middle layer is called the mesosphere (from the word meso- which means “middle”) and
is only characterized by a decreasing temperature as the altitude increases, just like in the
troposphere.
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The thermosphere is a vast layer characterized by increasing temperature with increasing
altitude and the presence of the ionosphere and magnetosphere. Together, these two layers
help with the formation of the spectacular auroras in the polar regions. The ions in the
ionosphere also forms a layer that bounces radio signals back to Earth.
Finally, the exosphere (from the word exo- which means “outside”) is the outermost layer of
the atmosphere. Orbiting satellites are found here.
Biosphere
The biosphere is a subsystem from the highest layer of the atmosphere to the lowest point
of the Earth where the conditions necessary to sustain life as we know it are present. Details
of life processes in the biosphere will be discussed in the last lesson of the last unit.
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UNIT 2
EARTH MATERIALS AND PROCESSES
Unit Coverage
Lesson 4: Rocks and Minerals
Lesson 5: Exogenic Processes
Lesson 6: Endogenic Processes
Lesson 7: History of the Earth
UNIT INTRODUCTION
Congratulations! You are done with the first unit. In the next unit, we are going to study the
Earth in detail: its composition, its processes, and its history.
In Lesson 4, be prepared for studying rocks and minerals. How rocks differ from minerals,
how minerals and rocks are formed, how to classify rocks, and in the end, having known all
these, discuss the rock cycle. Once you get through this lesson, you will never see rocks the
same way again.
In Lesson 5, we will study the processes that occur on the surface of the Earth. You might be
already familiar with these processes; but this time, we will review them in such a way that
you can confidently predict the story behind a rock formation on the surface of the planet.
You will understand why glacial mountains are sharp and steep, why beaches are sandy, why
how landslides occur, and so on.
In Lesson 6, we will go down the inside of the Earth. Again, you might have studied them
back in your previous years; but we are going to review them in more detail here. At the end
of this lesson, you can explain why the continents appear as they are today, why are there
formations such as the Pacific Ring of Fire and the Mid-Atlantic Ridge, and how volcanoes
erupt.
We will close Earth Science with an overview of the Earth’s history. We will learn about
different types of fossils and how they are used to reconstruct Earth’s history even before
the time of man came. The last section, the Geologic Time Scale, which is a timeline of history
of life on Earth, will serve as your preparation for the next two units of Life Science.
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LESSON 4 – ROCKS AND MINERALS
OBJECTIVES
At the end of the lesson, you should be able to:
1. Differentiate a rock and a mineral;
2. Identify the properties of a mineral;
3. Explain how igneous, sedimentary, and metamorphic rocks are formed;
4. Classify rocks into igneous, sedimentary, or metamorphic;
5. Discuss the rock cycle.
SUBJECT MATTER
Recall the lesson on the Solar System. The planet Earth is a terrestrial planet. This means that
our home is a ball of rock. In this new unit, we will discuss how rocks are formed and how
they shape our planet. We will start our discussion on minerals.
Minerals
Mineral is the most common solid material found on Earth. Earth’s land and oceans all rest
on layers of rock made of minerals. Minerals make up rocks. Strictly speaking, a mineral has
to have all of the four features as follows: (1) naturally occurring; (2) has a definite chemical
composition; (3) its atoms or molecules are arranged in a definite pattern, forming crystals;
and (4) it is inorganic (not made of organic or carbon-based compounds). There are several
thousand known minerals, a hundred of which constitute rocks—the so-called rock-forming
minerals.
Figure 4.1. Different colors of quartz due to impurities.
Since minerals have uniform composition, they have
definite properties. In fact, scientists use these
properties to identify an unknown mineral. Common
properties of minerals are shown below:
1. Color and streak – minerals come in different
colors; however, impurities can change the color of
a mineral. Color is therefore not a foolproof way to
identify a mineral (Figure 4.1). Streak is the color of
the mineral in powdered form (Figure 4.2). It is
Figure 4.2. Cinnabar streak. Notice
more reliable than mere inspection of color.
2. Luster – may be metallic or non-metallic. A shiny how the streak differs from the apparent
color of cinnabar.
non-metallic is said to be glassy, while a dull one is
said to be earthy.
3. Hardness – defined as the resistance of a mineral from being scratched. A hardness scale
called Mohs index of hardness was developed by Friedrich Mohs, a German mineralogist.
The hardness of diamond is set at 10, while talc, the softest mineral, is set at 1.
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4. Cleavage – a property of a mineral to
split into pieces that have flat
surfaces (Figure 4.3). The flat surface
is said to be the mineral’s plane of
weakness.
5. Density – mass per unit volume of
the mineral. The density of a mineral
is measured relative to the density of
water (1 g/cm3).
Rocks make up the solid layer of the
Earth’s crust. They are usually
aggregates of minerals. Some rocks are
composed of only one mineral. Quartzite
Figure 4.3. Muscovite has cleavage in one direction;
is entirely made of quartz (silicon feldspar has two; halite has three.
dioxide, SiO2); limestone is entirely
calcium carbonate (CaCO3). Most rocks, however, are made of more than one mineral. Rocks
are classified according to how they were formed. There are three classes of rocks, namely:
(1) igneous, (2) sedimentary, and (3) metamorphic.
Types of Rocks
Igneous rocks are formed from solidification of molten rock material (or magma). Rocks can
solidify either above or beneath the surface of the Earth. Rocks that solidified above the
surface are said to be extrusive igneous or volcanic rocks (Figure 4.4a), since they almost
always come from volcanoes. Those that solidified below are called intrusive igneous or
plutonic rocks (Figure 4.4b), from the Roman god of the underworld, Pluto, since they solidify
underground.
Figure 4.4a. Obsidian: extrusive
igneous; glassy texture
Figure 4.4b. Diorite: intrusive igneous;
coarse-grained
Sedimentary rocks are formed by the accumulation of materials called sediments. They are
classified according to the type of sediment that formed them. There are three types of
sedimentary rocks.
The ordinary sedimentary rocks are called clastic sedimentary rocks, formed from
mechanically weathered debris. Examples include sandstone (Figure 4.5a), siltstone, and
conglomerate.
Those rocks formed through precipitation of dissolved minerals are called chemical
sedimentary rocks. Examples include hematite (Figure 4.5b) and limestone.
Lastly, sedimentary rocks that are formed from accumulation of plant or animal debris are
called organic sedimentary rocks. Examples include limestone from shells and corals and coal
(Figure 4.5c) from plants. Limestone is made of calcium carbonate while coal is made of
carbon.
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Figure 4.5a. Sandstone: clastic
sedimentary rock
Figure 4.5b. Hematite: chemical
sedimentary rock
FEU Senior High School
Figure 4.5c. Coal: organic
sedimentary rock
Metamorphic rocks are “modified” rocks due to heat, pressure, or chemical processes. Thus,
any region of the Earth with intense heat or pressure might be a source of metamorphic rocks.
These rocks can be foliated (layered or banded) or non-foliated. An example of a foliated
metamorphic rock is gneiss (Figure 4.6a); an example of a non-foliated metamorphic rock is
marble (Figure 4.6b), which came from a metamorphosed limestone.
Figure 4.6a. Gneiss: foliated
metamorphic rock
Figure 4.6b. Marble: non-foliated
metamorphic rock
Rock Cycle
The three types of rocks discussed earlier
in this lesson can change from one type to
another depending on the conditions of its
environment. The processes that change
the rock and the resulting rock from these
processes are illustrated in a diagram
called the rock cycle (Figure 4.7).
Let us start from magma. All magma turns
into igneous rocks because, by definition,
igneous rock is cooled or hardened
magma. Igneous rocks can be subjected to
either weathering and erosion or heat and
pressure. All rocks subjected to
weathering and erosion become sediments,
tiny debris of rocky materials. These tiny
Figure 4.7. The rock cycle highlights the processes that
debris can undergo compaction and the rocks can undergo to change from one type to another.
cementation to form sedimentary rocks.
Finally, igneous and sedimentary rocks subjected to heat and pressure turn into
metamorphic rocks. All three types of rocks can melt and turn into magma, and the cycle is
completed.
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LESSON 5 – EXOGENIC PROCESSES
OBJECTIVES
At the end of the lesson, you should be able to:
1. Differentiate exogenic and endogenic process;
2. Compare and contrast the different exogenic processes;
3. Infer the exogenic process that took place in a given rock or land formation.
SUBJECT MATTER
In the previous lesson, we discussed the processes occurring in rocks. In this lesson and the
next, we are going to discuss about processes that affects larger scales such as rock and land
formations. We call these processes geological processes. Geological processes are classified
into exogenic and endogenic processes. Exogenic processes include weathering, erosion, mass
wasting, and deposition. Together, exogenic processes shape the Earth’s landscape.
Weathering
You may have encountered the concept of weathering as early as your elementary school
days. We are going to recall this concept and provide some examples of weathering in
everyday action. Weathering is simply defined as a process that leads to breaking down of
rocks into smaller and smaller pieces. One particular importance of this process is that it
produces soil for our plants to survive as well as release nutrients such as potassium and
phosphorus, which are found mainly from broken down rocks. Weathering is divided into
two types: physical and chemical weathering.
Physical Weathering
Physical weathering is where rock is broken down without altering its mineral composition.
Agents of physical weathering include ice, temperature, pressure release, and plants.
Frost Wedging
Ice can cause weathering because of freeze-thaw
cycle, a process that occurs when temperature
changes between below and above freezing point.
This phenomenon is common in high mountainous
regions where rocks and ice are both present.
During the day, for example, temperature is above
freezing point. Water can then seep into small
spaces inside rocks. During the night, temperature
may go below freezing point, turning water into ice.
One unique property of water is that it expands as
Figure 5.1. Expansion of water upon
it freezes. The expansion will generate a force that freezing generates a force enough to break
pushes the surrounding rock aside, creating cracks rocks slowly.
and effectively breaking the rock. Because this type
of weathering results in wedge-shaped rocks caused by
ice, this process is also called frost wedging (Figure 5.1).
Insolation Weathering
Temperature can also break a rock because of extreme
temperature changes. When a material is heated, it
expands. When it is cooled, it contracts. Rocks that are
exposed on the surface is subject to the changing
temperature of day and night. During the day, rocks
expand due to the fact that they are exposed to the sun.
during the night, the temperature drops, and the rocks
contract. The repeated expansion and contraction
creates stress that eventually breaks the rock. In other
Figure 5.2. Repeated expansion and
contraction due to extreme temperature
can stress a rock and cause it to break.
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terms, this type of weathering is
called insolation weathering since
it is the sun’s radiation which
heats the rock (Figure 5.2).
Pressure Release
In some not-so-familiar cases,
rocks can also be broken down by
pressure
release.
This
is
particularly evident in plutonic
rocks such as granite domes.
Recall from Lesson 4 that plutonic
rocks form beneath the Earth’s
surface. Thus, they are subjected to Figure 5.3. Pressure release due to erosion of overlying rock
causes the plutonic rock to undergo expansion and sheeting.
pressure caused by overlying rocks.
If these overlying rocks are carried away, the pressure is released, expanding the rock
formation and creating fractures in the process (sheeting). This type of weathering is also
called unloading (Figure 5.3).
Biological Weathering
Our last example of physical weathering might be the
most familiar to you—biological weathering (Figure 5.4).
Simply put, this is a weathering mechanism exhibited by
plants (and sometimes animals). When plant roots seep
through the soil or a rock, the roots act like wedges to
gradually break the rocks.
Figure 5.4. Plant roots breaking the
pavement.
Chemical Weathering
Unlike physical weathering which only involves breaking down of rocks into smaller pieces,
chemical weathering, involves altering the rock’s mineral composition; in other words, it
involves chemical change. Practical examples of chemical weathering are carbonation and
oxidation.
Carbonation
Carbonation is the dissolution of limestone in acidic
water. In chemical terms, the calcium carbonate (CaCO3)
present in limestone reacts with the acidic water to form
carbonic acid (H2CO3). Carbonic acid is unstable, leaving
behind water (H2O) and carbon dioxide (CO2). This type
of weathering is particularly responsible for the
formation of stalactites and stalagmites in limestone
caves (Figure 5.5).
Figure 5.5. Limestone caves are
formed by dissolution of limestone in
acidic water.
Oxidation
Oxidation is evident in rocks rich in iron such as hematite. As you
have learned in your previous years, rust is formed by reaction
of iron with oxygen in the atmosphere (or sometimes in water).
Rocks rich in iron undergo chemical weathering to form a
characteristic color that indicates rusting (Figure 5.6). In this
case, the mineral iron (Fe) turns into ferric oxide (Fe2O3).
Erosion
Weathering alone is not enough to shape the Earth’s landscape.
The weathered particles, or rock debris, are removed from the
point where they were broken down by weathering and then
transported elsewhere. The process of removing these rock
Figure 5.6. Hematite
rusting as evidence of
oxidation of iron mineral.
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debris loose from their point of origin and transporting them to another location is called
erosion. Erosion can be classified in two ways: (1) depending on the agent; and (2) depending
on the type of transportation. We will discuss both classifications.
Agents of Erosion
One very important agent of erosion is running water. Running water, which is mostly found
in streams, rivers, and coastlines, can shape soil, valleys, riverbanks, coastlines, and seaside
cliffs (Figure 5.7a).
Glacier is also an important agent, though glaciers are not readily observed in the Philippines.
Glaciers shape the slope of glacial mountainous regions by plucking the surface through frost
wedging. Glacial erosion causes the characteristic sharp rocks of glacial mountains (Figure
5.7b).
Wind, which is formed from the travelling of air from an area of high pressure to low
pressure, can erode soft rocks, dust, sand, and sometimes volcanic ash. An evident action of
wind erosion is the formation of sand dunes in Paoay, Ilocos Norte (Figure 5.7c).
Figure 5.7a. Natural arch
formation due to coastal erosion
Figure 5.7b. Characteristic sharp
and steep mountains due to glacial
erosion.
Figure 5.7c. Sand forming strips
and dunes as a result of wind
erosion.
Types of Transportation
Aside from the agent of erosion, the manner of being transported from one place to another
is also classified. There are four ways of transporting eroded material. In Figure 5.8, all four
ways are exemplified in a typical river:
 Solution – material is dissolved and carried along by water. This is the manner of
transport common in limestone cave formation.
 Suspension – material is carried along by water, air, or ice.
 Traction – materials move by rolling along the surface.
 Saltation – materials move from the surface to the medium in quick, repeated cycles, as
if they are jumping.
Mass Wasting
Figure 5.8. All four types of transportation are present in a typical
river.
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One type of erosion is the mass movement of rocks termed as mass wasting. You can call a
process mass wasting if it involves mass movement of rocks along a slope. Mass wasting is
classified into three categories depending on the materials involved and the nature of
movement (Figure 5.9):
Figure 5.9. Four basic types of mass wasting.




Fall – occurs when a mass of rock becomes dislodged and freely falls along a steep cliff.
Flow – occurs when a mass of rock becomes either saturated with water or too granular
that they appear to flow instead of sliding.
Translational slide – occurs when the mass slides along a well-defined surface.
Rotational slide – also known as slump; involves sliding of mass along a concave,
upward curved surface.
Deposition
We are now down to the last type of exogenic process: deposition. The first three processes
involve breaking down and wearing away of rocks. This time, we will discuss what happens
when rocks are accumulated instead of broken apart.
Deposition can form delta (Figure 5.10a). Delta forms when the water from a river
approaches a slow-moving water such as a lake or a sea. When the water from the river slows
down, it loses its capacity to carry sediments. The sediments are then deposited in the seabed.
Another formation is called alluvial fan (Figure 5.10b). Alluvial fans are formed when a
stream from a mountain approaches a gently sloping plain. Just like the case in delta, water
loses velocity as well as its capacity to carry sediments. The sediments are then deposited in
a fan-shaped manner.
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Figure 5.10a. Delta forms as river deposits its
sediments in the seabed.
FEU Senior High School
Figure 5.10b. Alluvial fan forms as river deposits its
sediments on a gently sloping plain.
Together, exogenic processes shape the Earth’s surface and landscape. In the next lesson, we
will discuss processes that shape the Earth’s continents and formations such as mountain
ranges, island arcs, volcanoes, and ocean basins.
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LESSON 6 – ENDOGENIC PROCESSES
OBJECTIVES
At the end of the lesson, you should be able to:
1. Discuss the continental drift and plate tectonics theories;
2. Compare and contrast the different types of plate boundaries;
3. Identify the geographical features formed by the different types of plate boundaries;
4. Compare and contrast the different types of folds and faults;
5. Explain magmatism and volcanism.
SUBJECT MATTER
Continental Drift Theory
From our lesson in Lesson 6, we learned that
the lithosphere of the Earth is like a paper
boat being moved by the convection currents
of the asthenosphere. In this lesson, we are
going to discuss the details of this
phenomenon. Let us jump start the lesson by
asking, “How did we realize that the
lithosphere is moving? We do not feel the
movement of the crust after all.” The
speculation that the Earth’s crust is moving
did not start from being actually able to
observe its movement, but because the
continents form a fitting jigsaw puzzle when
connected together. You can readily observe
the fit by looking at the matching shapes of
South America’s east coast and Africa’s west
coast. It is this observation that made a
German geophysicist and meteorologist
Alfred Wegener to formulate the continental
drift theory (Figure 6.1).
Figure 6.1. Illustration of the continental drift theory.
The continental drift theory states that all
the continents of the planet were
once
joined
in
a
single
supercontinent called Pangea (lit.
“all of Earth”). 200 million years ago,
Pangea split into two major
continents named Laurasia and
Gondwanaland. The continents
continued to split apart and
arranged into the seven continents
we know today.
Aside from the apparent jigsaw
puzzle fit of the continents, there was
another evidence at hand. It was
found out that fossils of ancient Figure 6.2. Fossils of reptiles and plants are found across
reptiles and plants were found across continents, suggesting that the latter were once joined.
continents (Figure 6.2), strongly suggesting
that these continents were once joined since
W
reptiles and plants cannot cross oceans.
The theory was nearly convincing, but it failed to provide explanation as to how did the
continents move. This question was left unanswered until another theory in the 1960s was
developed—the plate tectonics theory.
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Plate Tectonics Theory
This comprehensive theory that encompasses all endogenic processes was developed in
1960s. This theory explains the movement of the continents, as well as presence of
geographical features such as volcanoes, mountain ranges, islands, and mid-ocean ridges.
According to this theory, the crust is composed of broken plates of rocks like broken pieces
of dinner plate loosely interconnected. These plates move together in three ways: converging,
diverging, or sliding past each other. Figure 6.3 shows the major and minor plates of the
Earth’s crust, together with the type of boundary and movement of the plates relative to each
other.
Figure 6.3. Plate tectonics theory states that the crust is composed of broken plates such as the map shown
above. These plates move relative to each other in three ways: converging, diverging, or sliding past each other.
The plates are moved by the convection currents present in the asthenosphere. The currents
make the tectonic plates seem like a paper boat drifting to the direction of the water current.
Convection is a heat transfer mechanism caused by the fact that warm fluid rises and cool
fluid sinks. Since the core is hotter than the crust, the liquid rock of the asthenosphere rises
up to the crust. After it reaches the crust, the temperature is cooler, and the liquid rock sinks
again. As seen in Figure 6.4, convection currents cause convergent, divergent, and transform
plate boundaries, to be discussed next.
Figure 6.4. Convection currents are caused by the difference in temperature of the core and
the crust. Convection currents can create all three types of plate boundaries.
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Plate Boundaries
Plate boundaries lie between adjacent tectonic plates. They can be classified into three types
depending on the relative movement of the plates.
Convergent boundaries are those whose plates collide against each other. They can be found
both on continents and oceans. Thus, convergent boundaries can be classified further into
three types: oceanic-oceanic, oceanic-continental, and continental-continental (Figure 6.5).
Oceanic-oceanic boundaries create island arcs as a result of volcanic activity between the
two colliding plates. Oceanic-continental boundaries, for the same reason, create volcanic
arcs. Continental-continental boundaries create mountain ranges instead because two plates
collide head-on without magma formation. The volcanic activity mentioned is present only
in boundaries where oceanic crust is present because its thinness allows for better friction;
thus, more heat and more possibility of magma formation.
Figure 6.5. Convergent boundaries are classified into three: oceanic-oceanic, oceanic-continental, and
continental-continental. They form island arc, volcanic arc, and mountain range, respectively.
Divergent boundaries are most common in
oceans and are responsible for the phenomenon
called seafloor spreading. Divergent boundaries
are caused by two plates moving apart from
each other. As a result, magma upwells from the
asthenosphere to fill in the gap, forming ocean
ridges. One prominent divergent boundary in
the world forms the Mid-Atlantic Ridge.
Transform boundaries are commonly found
between two divergent boundaries side-to-side
with each other, creating a sliding force between
the two plates. Transform boundaries cause
earthquakes.
Figure 6.6. Divergent boundaries form ocean
ridges. In this figure, two divergent boundaries
side-to-side created a transform boundary.
Folding and Faulting
Tectonic forces can create folds and faults in the Earth’s rock layers (strata). Folds are formed
when the force causes no breakage in the strata, while faults are created when there is a
breakage.
Folds (Figure 6.7) are classified into two: linear and circular folds. Linear folds are further
classified into anticlines and synclines. Anticlines are linear folds projecting upwards while
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synclines are linear folds projecting downwards. Circular folds are classified into domes and
basins. Domes are circular folds whose strata project upwards, leaving the youngest strata at
the peripheries and the oldest strata at the center. Basins, on the other hand, project
downwards, leaving the oldest strata at the peripheries and the youngest strata at the center.
We will discuss how to determine older and younger rocks in the next lesson.
Figure 6.7. The different types of folds.
Faults (Figure 6.8) are similar to plate boundaries. They are characterized by a break in the
rock layers and these layers move relative to each other. Just like the plate boundaries, faults
are also classified into three, together with the force responsible for such movements.
Fault
Normal
Reverse
Transform
Force
Tension
Compression
Shear
Magmatism and Volcanism
Magmatism is the process of
forming magma, usually inside a
volcano. As discussed on plate
boundaries, magma is formed in
regions where there is friction that
generates enough heat to melt the
plastic rocks lying under the
lithosphere. Volcanism, on the other
hand, is the surface discharge of
magma.
Volcanic eruption is a violent
discharge of magma together with Figure 6.8. The different types of faults.
gases and volcanic dusts. However, volcanoes vary in their degree of eruption. Some
volcanoes can destroy everything around it in a matter of minutes while some seep lava
quietly that you can walk around it. The severity of eruption lies mainly on the magma
composition of the volcano. The more viscous the magma, the more violent the volcanic
eruption.
How does a volcano erupt at all? The force of a volcanic eruption comes from the internal gas
pressure inside the magma. Magma, besides being made of molten rock, contains a lot of
dissolved gases. Recall in your basic chemistry lessons that gases flow from an area of high
pressure to area of low pressure. In a volcano, there are two pressure systems acting: the
confining pressure which is basically the pressure applied by the rocks against the magma;
and vapor pressure, the internal gas pressure inside the magma. As long as the confining
pressure is greater than the vapor pressure, no eruption will take place. However, once the
vapor pressure becomes greater, the volcano will erupt. Making the vapor pressure greater
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than the confining pressure can be done in two ways: (1) increase vapor pressure; or (2)
decrease confining pressure.
To better visualize volcanic eruption, use a bottle of soft drink. The liquid has dissolved gases
in it; the liquid has vapor pressure. In order for the soft drink not to compromise its taste, a
confining pressure of air is included in the bottle to prevent the gases from escaping. Once
you shake the bottle, the gases will distribute throughout the liquid. Once you open the bottle,
the confining pressure will decrease, initiating an “eruption”. In the case of a volcano, the
escaping gases carry magma with them, initiating volcanic eruption.
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LESSON 7 – HISTORY OF THE EARTH
OBJECTIVES
At the end of the lesson, you should be able to:
1. Apply the different laws of stratigraphy in relative dating of rocks;
2. Describe the concept of absolute dating;
3. Contrast the different types of fossils;
4. Discuss the geologic time scale.
SUBJECT MATTER
Laws of Stratigraphy
In the last lesson we have mentioned about “younger” and “older” strata or rock layers. In
this lesson we will now discuss how to determine age of rocks. To do this, scientists have
come up with scientific ways to identify the age of rocks. We have two general techniques of
dating rocks: relative and absolute dating.
Relative dating is a comparative method of determining the age of rocks. For a given series
of rock layers, one simply has to rank the layers from oldest to youngest. Relative dating does
not generate a numerical age of a given rock layer. This method of dating uses the laws of
stratigraphy.



Law of Superposition – developed by Nicolaus Steno. This law states that younger rock
layers are atop the older layers (Figure 7.1a).
Law of Original Horizontality – developed by Steno. This law states that layers of
sedimentary rock are originally deposited in horizontal layers (Figure 7.1b). However,
endogenic processes can alter the original horizontal layers.
Law of Cross-Cutting Relationships – developed by Steno. This law states that the
cross-cutting rock is younger than the layer(s) it cross-cuts (Figure 7.1c).
Figure 7.1a. Law of superposition
implies that the light-colored rock
layer is younger than the darkcolored rock layer.
Figure 7.1b. Law of original
horizontality states that rock layers
are originally deposited in nearly
horizontal layers, unless acted upon
by endogenic processes.
Figure 7.1c. The cross-cutting
intrusion, labeled C, is younger than
the intruded rocks A and B.

Law of Included Fragments – states that the included rock
fragment is older than the including rock fragment.

Law of Faunal Succession – developed by William Smith. This
law made use of the observation that fossil plants and animals
succeed each other in time in a predictable manner. This law
implies that rocks from different geographical locations can be Figure 7.2. Law of
relatively dated by using the age of fossils contained in the included fragments
implies that the pebbles
rocks. The older the fossil, the older the rock. This law is cemented in this rock
considered valid because of the assumption that biological should be older than the
evolution is nonrepetitive and orderly. For example, if you cementing rock.
discovered a T-Rex fossil on a rock layer in Manila and
discovered another T-Rex fossil on a rock layer in Tokyo, then you can conclude that the
rock layers in Manila and Tokyo where the T-Rex fossil lied are of relatively the same age.
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Through technology, science has come up not only with a method of comparing rock layers
using the laws of stratigraphy. Today, scientists can come up with a good estimate of a rock’s
absolute age in thousands, millions, or even billion years ago. This method is called absolute
dating and uses the concept of radioactivity to generate the numerical age of a given rock. A
radioactive element turns half of itself into another element (e.g. uranium turning into lead)
in a constant period of time. This duration is called half-life. By knowing both the half-life of
an element and how much of the element remains in a given rock, we can determine the
absolute age of the rock. Figure 7.3 visualizes this concept.
Figure 7.3. The amount of a radioactive element (represented by black dots) runs out by half every
half-life. In this example, the remaining amount is shown after ten half-lives.
Fossils
Back then people had thought that the Earth formed 6 000 years ago. However, the discovery
of fossils, principles of geology, and the technology of absolute dating suggested that the
Earth should be older than 6 000 years; it should even be around 4.6 billion years old,
following the age of the oldest rocks ever recorded on our planet. Fossils are familiar to us
not for their contribution to the history of the Earth but for their industrial use as source of
fuels. In this section, we will classify fossils according to how they were formed. Figure 7.4
shows six different kinds of fossils.
(A)
(B)
(C)
(D)
(E)
(F)
Figure 7.4. The different types of fossil: (A) mold fossil; (b) cast fossil; (C) carbon fossil; (D) petrified fossil; (E)
trace fossil; and (F) true form fossil.






Mold fossil – forms when a hard part of an animal imprints on a soft rock
Cast fossil – forms when minerals fill in the mold, imitating the shape of the animal
Carbon fossil – forms when the remains of a dead plant leave carbon films onto rocks
Petrified fossil – forms when minerals replace a dead organism’s parts
Trace fossil – not really made of organismal remains but can show hints of its activity
(e.g. footprints)
True form fossil – forms when an organism becomes trapped in amber or ice, preserving
all its original features
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Geologic Time Scale
Through the collective efforts of geologists and biologists, we now have an idea about what
lifeforms were dominant across different times on our planet. The diagram illustrating this
idea is called geologic time scale. Figure 7.5 shows a typical geologic time scale, though
different sources show different details of the time scale.
Figure 7.5. A typical geologic time scale. In this scale, time is divided into eons, eras, and periods. It
also shows different evolutionary events across different times.
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UNIT 3
PROCESSES OF LIFE
Unit Coverage
Lesson 8: Introduction to Life Science
Lesson 9: Bioenergetics
Lesson 10: Perpetuation of Life
UNIT INTRODUCTION
You are now done with Earth Science! And today, you will start with Life Science, or more
popularly known as Biology. Students fear Biology because of the stigma that this subject
requires a sharp memory due to lots of terms to memorize. Indeed, that is true. However,
more than just memorizing, Life Science will help you understand your environment better.
After this unit and the next, you will feel that you see things that other people do not normally
see.
Specifically, in this unit, we will start with an introduction to life science, then discuss the
two major metabolic pathways of life: photosynthesis and cellular respiration. Lastly, we will
study how life is perpetuated on Earth. Prepare yourself for another round of explaining
illustrations and diagrams.
In Lesson 8, we will explore the more “abstract” side of life science: the themes in the study
of life and the characteristics of a living thing.
In Lesson 9, we will discuss photosynthesis and cellular respiration in greater detail. This
will be a lot of brainwork. But don’t worry for we have also prepared cool experiments for
this lesson—cool enough that you will experience being a legit scientist.
We will close this unit by studying how life is made possible in this world. How do we become
a full-grown human from a single cell? What’s with this word called DNA? How do other
organisms multiply themselves? Lesson 10 is a transition from life on a small scale to the
next unit, which is discussion of life on a larger scale.
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LESSON 8 – INTRODUCTION TO LIFE SCIENCE
OBJECTIVES
At the end of the lesson, you should be able to:
1. Discuss the origin of life based on emerging pieces of evidence;
2. Discuss the evolution of life using sample organisms;
3. Identify the different characteristics of life;
4. Describe how unifying themes in the study of life show the connections among living
things and how they interact with each other and with their environment.
SUBJECT MATTER
Theories on the Origin of Life
In this unit and the next we will discuss life science—also known as biology. In this
introduction, you will be provided with the basic history on how life evolved on Earth. There
are several theories regarding the origin of life, some of which are discussed below:
Panspermia Theory
This theory came from the words pan and sperma (lit. “all seed”). This theory states that the
seed of life was present in meteors in space. These meteors landed on different planets but
life only flourished on Earth because our planet contained a habitable environment and
made life possible.
Further, according to this theory, the seed of life is amino acid (Figure 8.1), the building block
of proteins. Proteins play a major on cell processes. Evidences supporting this theory
include: (1) it was found out that certain strains of bacteria
can survive in space; and (2) there were amino acids found
in meteorites.
Divine Creation Theory
The account that life was created by a supernatural being.
This is the most popular theory on the origin of life and
different cultures have different stories to tell how life was
created.
Figure 8.1. Amino acids were
found in meteorites. Amino acids
are building blocks of proteins,
which play a major part on life
processes.
One popular account of creation was the six days of creation
written in the Book of Genesis, the first book of the Bible. In
this story, God created everything in six days, starting from light until the creation of man.
Nonliving Matter Origin
The most accepted theory to date; this theory states that life began as a series of chemical
reactions of organic (carbon-based) compounds. These compounds eventually became
larger and created biomolecules; biomolecules assembled to produce the very first cells.
Long ago, people believed in the concept of vitalism, the belief that forces governing life is
distinct and independent from forces that govern the physical sciences. However, the MillerUrey experiment debunked the concept of vitalism. In the said experiment, urea, an organic
compound, was produced from atmospheric gases energized by lightning. This suggested
that organic compounds can be created from inorganic ones.
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Figure 8.2. Miller-Urey experiment simulates the early Earth. It showed that
inorganic gases produced organic compounds through electrical sparks.
Evolution of Life
Now that we have a picture of how life began, we can now discuss how life evolved as we
know it today. In the beginning, organic compounds were produced from inorganic ones, as
simulated by the Miller-Urey experiment. The first biomolecules were created from the
organic compounds that formed, and eventually these biomolecules were enveloped in
compartments known as cells.
Figure 8.3a. Hydrothermal vents
are home to chemosynthetic
bacteria.
Figure 8.3b. Cyanobacteria made
life possible on the waters and their
surface through photosynthesis.
Figure 8.3c. Bacteria evolved and
paved the way for unicellular
eukaryotes called protists.
Figure 8.3d. Evolution produced the biodiversity of life.
The very first existing cells, called bacteria, are believed to have evolved in deep-sea
environments called hydrothermal vents. Here, the primary process of producing food for
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life is called chemosynthesis (Figure 8.3a). Eventually, a group of bacteria called
cyanobacteria was able to develop the process of photosynthesis near the surface of the seas
(Figure 8.3b). Through this process, sunlight became a source of energy and produced
oxygen. With oxygen filling in the waters and the atmosphere, life flourished in the waters of
the Earth. Lifeforms included unicellular eukaryotes (Figure 8.3c), algae, and aquatic animals.
Eventually life came on land and led to the diverse forms we know today as fungi, plants, and
terrestrial animals (Figure 8.3d). For you to be familiar with the details of how life evolved
through time, you may consider revisiting the geologic time scale from the previous lesson.
Characteristics of Life
Scientists are in continuous search for life outside Earth. To guide them, they use the
following characteristics to tell if an unidentified being is indeed a living thing.
Cellular Organization
All lifeforms, in their most basic
structure, are made of cells.
Every life process is ultimately
caused by cellular activities,
including how we obtain energy
from the environment, move our
muscles, reproduce our own
kind, and even thinking. Figure
8.4 shows an animal and a plant
cell.
Figure 8.4. On the left are epithelial cells of the cheeks; on the right
are onion cells. Cell action provides the basis for the processes of life.
Metabolism
Defined as the sum total of all biochemical processes of an organism. For lifeforms to survive,
their body should become a large factory of chemical processes. We will study the two
fundamental metabolic processes of life in the Lesson 9.
Homeostasis
Being a large factory of chemical reactions is not enough for a lifeform. It should be able to
regulate this factory to optimal levels to ensure survival. A complex process called feedback
mechanisms help regulate the organism’s metabolism. We will encounter different
mechanisms of regulation in Lesson 11.
Reproduction and Heredity
One essential characteristic of life is its ability to
perpetuate itself and produce offspring (Figure
8.5). Division of cells to form new cells is the
foundation of reproduction, growth, and repair.
Special instructions on how to divide and
differentiate the cell, perhaps the most
remarkable feat of life, is stored in a very long
molecule called the DNA. The DNA also contains
heritable information about the organism. This
Figure 8.5. Life has ability to reproduce its
long molecule can also change along the way, own kind, as seen with this bear with her cubs.
making evolution and diversification of life
possible. We will study how life is perpetuated in Lesson 10.
Unifying Themes in the Study of Life
In studying life, scientists have come up with general principles that encompass the world of
the living. These themes are essential to be put into consideration when you study how life
works. Some of the themes are given as follows:
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Levels of Organization – all lifeforms are organized in the following manner:
CELL  TISSUE  ORGAN  ORGAN SYSTEM  ORGANISM  POPULATION 
COMMUNITY  ECOSYSTEM
Check Figure 8.6 to see how each level of organization is made from the previous level. It is
important to take note that as you go up a level, there are emergent properties which cannot
be inferred by merely studying the previous level. The whole is not just the sum of its parts.
For example, memory works by complex networks of nerve tissues. If a blow to the head
disrupts the network, though the individual nerve cells are still present, memory can be
affected.
Figure 8.6. The different levels of organization.
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Flow of Energy
Life persists on Earth because of
energy flow all the way from the Sun to
the plants, to the herbivores, to the
carnivores, and to the decomposers.
The flow of energy is commonly
illustrated using an energy pyramid
(Figure 8.7). All lifeforms use energy to
perform life activities.
Interaction
A lifeform cannot survive by itself. It
needs to interact with its environment,
including other lifeforms. For example,
we need to eat food to provide
ourselves with energy for growth and Figure 8.7. Flow of energy across the biosphere is illustrated
other life processes; we use animal and as a pyramid. Less energy is obtained as an organism goes on
top of the food chain.
plant fibers to cloth ourselves. All
organisms also interact with the environment as
exemplified by the different nutrient cycles to be
tackled in Lesson 14. In Figure 8.8 you will see the
mutualism between a clownfish and a sea anemone.
Structure and Function
One wonderful thing about life is that there is a
correlation between a structure and its function. It
will be easier for us to understand how a body part
works by inspecting how it looks. This theme works
at all levels of biological organization.
An example given in Figure 8.9 is the
different shapes and sizes of finch
beak depending on the food these
birds eat. This was discovered by
Charles Darwin as he traveled on the
islands of Galapagos. This observation
led him into thinking about the most
revolutionary theme in the history of
biology: evolution.
Figure 8.8. Mutual interaction between a
clownfish and a sea anemone.
Evolution
Perhaps the one core theme in all of
biology. This theme accounts for the
vast diversity of life as we know it. As Figure 8.9. Darwin discovered that finches of the Galapagos
stated by Theodosius Dobzhansky, islands have adapted different beak shapes and sizes that
correspond to their diet.
“Nothing in biology makes sense
except in the light of evolution.” Life has been evolving and diversifying on Earth since life
itself first appeared. But along with the diversity, shared features can be seen among
organisms. The shared features of two organisms can be explained by the idea that they
shared a common ancestor; and along the way as life went on the heritable variations
occurred along the way. We will discuss evolution in greater detail in Lesson 13.
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LESSON 9 – BIOENERGETICS
OBJECTIVES
At the end of the lesson, you should be able to:
1. Differentiate a prokaryotic and a eukaryotic cell;
2. Identify the parts of the chloroplast and the mitochondrion;
3. Discuss the stages of photosynthesis;
4. Discuss the stages of cellular respiration.
SUBJECT MATTER
Bioenergetics concerns itself on how cells, the basic unit of life, harness energy to facilitate
life’s day-to-day activities. For recall purposes, we will study the differences between two
types of cells. Their structural differences have implications on how they harness the energy
they need to survive. The Venn diagram in Figure 9.1 shows the similarities and differences
Figure 9.1. On the left-hand side are illustrations of a typical prokaryotic and eukaryotic cell. On the right-hand
side is a Venn diagram showing the similarities and differences between the two types of cells.
a prokaryotic and a eukaryotic cell.
You may recall from your high school biology about the two most fundamental cellular
processes: photosynthesis and cellular respiration. They are fundamental in a sense that these
two are responsible for the energy flow in the living world. Photosynthesis harnesses energy
from the sun to make food; cellular respiration uses food and oxygen to produce energy
which the organism can use for its activities.
Photosynthesis
Photosynthesis occurs inside the
eukaryotic
cell’s
chloroplast.
In
prokaryotes, the process may occur in
specialized pigmented structures called
plastids or within the organism’s
pigmented cell membranes. The parts of
the chloroplast are highlighted in Figure
9.2. It consists of coin-shaped structures
called thylakoids, stacked together as a
granum. The grana are inside the fluidfilled cavity called the stroma, covered by
the double membrane of the chloroplast.
Photosynthesis is a process of obtaining
energy from the sun and converting it to
food. The food is for the organism’s use
Figure 9.2. The chloroplast—an important organelle for
photosynthesis.
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as well as other organisms who feeds on the producer. In chemical terms, the equation is as
follows:
6CO2 + 6H2O + light energy  C6H12O6 + 6O2
The equation says that the photosynthetic organism needs carbon dioxide, water, and light
energy to produce glucose and oxygen. We will now discuss photosynthesis in detail.
An overview of photosynthesis is in
Figure 9.3. Light reactions need light and
water to produce oxygen, ATP, and
NADPH. The Calvin Cycle then needs
carbon dioxide, ATP, and NADPH to
produce glucose. The used-up ATP and
NADPH, now in form of ADP and NADP+ is
now ready for another round of light
reaction.
Figure 9.3. An overview of photosynthesis. It is divided
into light reactions and the Calvin cycle.
Light-Dependent Reactions (in thylakoid)
1. Light excites the chlorophyll molecules present in the photosystem. This causes the
photosystem to release electrons. The electrons will travel all the way to the primary
electron acceptor (Figure 9.4, left).
Figure 9.4. Light excites chlorophyll molecules inside the photosystem, causing the molecules to release
electrons. The electrons will be shuttled (yellow arrows) across a series of proteins until it reaches NADP + to form
NADPH. Meanwhile, H+ ions build up (red arrows) and spins the ATP synthase to produce ATP.
2. The electrons will be relayed from the primary electron acceptor to a series of
proteins until they are finally captured by NADP+, forming NADPH (Figure 9.4, right).
3. The lost electrons in the photosystem will be replaced by the electrons of water;
after losing its electrons, water will become oxygen.
4. Meanwhile as electrons are shuttled through the proteins, a concentration of H+
builds up in the thylakoid space. This creates a concentration gradient that makes an
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ATP synthase turn like a turbine, generating energy in form of ATP. ATP and NADPH
will go to the next phase—the Calvin Cycle (Figure 9.5).
Light-Independent Reactions
(in stroma)
1. Ribulose
bisphosphate
(RuBP), a five-carbon
molecule, will combine
with CO2 to form a 6carbon compound.
2. The compound will break
into
two
3-carbon
molecules
called
3phosphoglycerate (PGA).
3. A series of redox reactions
through ATP and NADPH,
produced earlier in the
light-dependent reactions,
will
turn
PGA
into
glyceraldehyde-3phosphate (PGAL), still a 3carbon molecule.
Figure 9.5. The Calvin cycle is divided into three stages: carbon
fixation, reduction, and regeneration of RuBP.
4. Steps 1-3 will occur three times, producing a total of six PGAL molecules. For
accounting purposes, take note that we now have a total 18 carbons (3 carbons of
PGAL x 6 PGAL produced).
5. Since steps 1-3 occurred three times, we used up 15 carbons (5 carbons of RuBP x 3
RuBP used). 5 PGAL molecules will be used to regenerate 3 RuBP molecules. The
remaining PGAL molecule will be set aside.
6. Once again, steps 1-5 will occur, adding another 1 net unit of PGAL for a total of 2
PGAL molecules. We now have two 3-carbon PGAL for a total of 6 carbons.
7. These 6 carbons will be used to produce 1 unit of glucose (C6H12O6).
Cellular Respiration
Cellular respiration is a process of breaking down
food to obtain energy that the cell can use. The
energy harvested from this process can be used for
various purposes such as movement, transport of
substances, and creation of chemicals which the cell
can use to grow and divide. The process takes place
in the eukaryotic cell’s mitochondria. In
prokaryotes, the process occurs in the cell
membrane. The parts of the mitochondria are
illustrated in Figure 9.6. It has two spaces, the
intermembrane space and mitochondrial matrix.
Between these two is the inner membrane. Just like
the chloroplast, the mitochondrion is covered by
double membrane.
Figure 9.6. The mitochondrion and its parts.
The energy generated by cellular respiration can be used to power the organism’s life
processes. The equation for cellular respiration is as follows:
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C6H12O6 + 6O2  6CO2 + 6H2O + energy (ATP)
The equation says that glucose and oxygen is used to produce carbon dioxide, water, and
most importantly, energy in form of ATP. The equation is almost exactly the reverse of
photosynthesis. The details of the process, however, differs substantially. We will now
discuss cellular respiration in detail. Take note of the amounts of materials produced as they
will be used later in the lesson to count how many molecules of ATP will be produced in one
molecule of glucose.
Glycolysis
Glucose will be split using 2 ATP molecules.
Ultimately, glucose will end up as 2 pyruvate
molecules (Figure 9.7). The table below
summarizes what we used and what we
produced in this reaction:
Requires
2 ATP
1 glucose
Produces
2 pyruvates
2 NADH
4 ATP (a net of 2 ATP)
In a specific process called aerobic respiration,
pyruvate will go into the mitochondria. Here, the
next stage of reactions takes place.
Pyruvate Oxidation
One pyruvate molecule will be oxidized by a
molecule called NAD+ and combine with
coenzyme A to produce CO2, NADH, and acetylCoA (Figure 9.8).
Requires
2 pyruvates (from glycolysis)
Figure 9.7. A summary of glycolysis.
Produces
2 CO2
2 NADH
2 acetyl-CoA
Krebs Cycle
The acetyl-CoA produced from pyruvate oxidation will
further go into a process called the Krebs cycle. This
process is also known as tricarboxylic acid (TCA) cycle
or citric acid cycle (Figure 9.9).
Acetyl-CoA will be used as a reactant to turn oxalate
into citrate. The cycle goes on and ultimately return
to oxalate. In the process, CO2, NADH, FADH2, and
ATP are produced. Since there are two acetyl-CoA
from the previous stage, there will be two cycles of
Krebs cycle, producing the following amounts of
products:
Figure 9.8. Pyruvate oxidation.
Requires
2 acetyl-CoA (from
pyruvate oxidation)
Produces
4 CO2
2 ATP
2 FADH2
6 NADH
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Figure 9.9. The Krebs cycle produces a variety of products.
Oxidative Phosphorylation
This pathway is similar to the electron transport chain we encountered back in
photosynthesis. The idea is that electrons are transported across a series of proteins,
creating a concentration gradient of H+, and using this gradient to generate energy in form
of ATP (Figure 9.10).
Electron carriers NADH and FADH2 produced from the three previous stages will now shuttle
their electrons into the chain. The final carrier of the electrons is oxygen, after which it will
turn into water.
Figure 9.10. Oxidative phosphorylation mass produces ATP by continuously pumping
H+ ions from the energy of electrons.
On the average, 1 NADH molecule can produce 3 ATPs while an FADH2 can produce 2 ATPs.
With this information, calculate how much ATP is generated by one molecule of glucose.
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LESSON 10 – PERPETUATION OF LIFE
OBJECTIVES
At the end of the lesson, you should be able to:
1. Differentiate sexual and asexual reproduction;
2. Compare and contrast different reproductive methods of plants and animals;
3. Discuss the central dogma of molecular biology;
4. Discuss the advantages and disadvantages of GMOs.
SUBJECT MATTER
In this lesson we will discuss how life is maintained through time. The idea is that despite
the fact that an individual’s lifespan is short and organisms die, they reproduce offspring for
the next generations to come; life is therefore perpetuated as long as organisms reproduce.
Sexual vs. Asexual Reproduction
There are two primary types of reproduction: sexual and asexual. In sexual reproduction, a
male parent will produce sperm cells with half of its DNA inside the cell and a female parent
will produce an egg cell with half of its DNA inside the egg as well. Since the sperm and egg
cells contain only one half of the original DNA of the producer, they are called haploid cells.
The sperm and egg will combine in a process
called fertilization, producing a new organism
with two sets of DNAs, one set from the father and
another set from the mother. Since the fertilized
egg has now a paired set of DNAs, it is now called
a diploid cell. Figure 10.1 summarizes sexual
reproduction. One advantage of sexual
reproduction is that it allows “shuffling” of genes,
which provides more opportunity for the
population to become adapted to its changing
environment.
Figure 10.1. In fertilization, two haploid cells,
sperm and egg, will combine their nuclei to
produce a diploid cell, called zygote.
In asexual reproduction (Figure 10.2), a cell or a part of the
organism may bud off and grow to produce a new organism.
Since there are no combinations and segregations involved,
the genes of the offspring are identical to the parent. One
advantage of asexual reproduction is that it is fast and allows
selection of favorable traits. For example, a plant that yields
big fruits may be asexually reproduced to ensure that its
offspring will all be big fruit-bearers as well.
Plant Sexual Reproduction
In sexual reproduction, plants exhibit the complex cycle called
alternation of generations. In this cycle, a plant undergoes two
phases, or generations: a haploid generation called
gametophyte; and a diploid one called sporophyte. In
discussing plant sexual reproduction, we will survey three
groups of plants: mosses, ferns, and flowering plants.
Figure 10.2. Asexual
reproduction in different species
of protozoa.
Mosses
Mosses are the simplest of plants for they have no true roots, stem, and leaves; yet, their
sexual reproductive cycle is complex just like any other plant. Its life cycle is outlined below
and illustrated in Figure 10.3:
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1. The sporophyte produces two types of spores: one male and one female.
2. The male will grow into an antheridium and produce sperm cells. The female will
grow into an archegonium and produce egg cells. The two cells can unite when there
is water for the sperm to swim (e.g. raindrop).
3. The fertilized egg will grow into a new generation of sporophytes within the female
gametophyte.
Figure 10.3. Sexual life cycle of a moss.
Figure 10.4. Sexual life cycle of a fern.
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Ferns
Ferns are nonflowering vascular spore-bearing plants. In evolutionary terms, they are
considered to be somewhat between the mosses and the seed-bearing plants. Their life cycle
exhibits alternation of generations outlined below and illustrated in Figure 10.4:
1. The sporophyte contains spores underneath its leaves. The spores, when dispersed
and planted, germinates into a heart-shaped gametophyte.
2. The gametophyte contains both an antheridium and archegonium. Through
fertilization, an egg can grow inside the archegonium and grow into a new
sporophyte.
Flowering Plants
From the word itself, flowering plants make use of flowers for sexual reproduction. In
flowering plants, the two gametes will combine in a process called double fertilization, which
occurs inside a flower. The process is as follows and illustrated in Figure 10.5:
1. It starts in flowers, where anthers contain pollen grains with sperm cells inside and
the ovary houses the embryo sac with an egg cell inside.
2. A pollinator such as an insect will put the pollen grain over the stigma of a flower.
After pollination, the two sperm cells from the pollen grain will travel along the tube.
One sperm will fertilize the egg and another will combine with the two polar nuclei,
resulting in a triploid (3n) endosperm. The fertilized egg will use the endosperm as
food source.
3. The fertilized egg will develop into a fruit with a seed (or seeds). The seed, with the
right conditions, can grow into a whole new sporophyte.
Figure 10.5. Sexual life cycle of a flowering plant.
Plant Asexual Reproduction
Fortunately, plants can be reproduced asexually. The capability of plants to reproduce
asexually has been used to maintain food quality and food security. Some of the asexual
reproductive methods of plants include layering, fragmentation, stem cutting, and grafting
(Figure 10.6). Not all species of plants can be reproduced asexually, however.
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(A)
(B)
(C)
(D)
Figure 10.6. (A) Strawberries can be propagated using runners; (B) Kalanchoe leaves can grow into a new plant
when planted; (C) Stem cutting propagation in a plant; (D) Grafting to get a favorable shoot and root system.
Layering
Plants with so-called runners or stolon can be reproduced asexually by burying the runners
in soil. Hormones in the plant will enable the runners to develop into a whole new
plant, which can be separated from the parent plant by simply cutting the runner. Strawberry
is an example of a plant that can be reproduced by layering.
Fragmentation
The plant Kalanchoe exhibit fragmentation. That is, a fragment of a plant can grow into a
whole new plant. In Kalanchoe, a bud can tear off its leaf and grow into a whole new plant
identical to its parent.
Stem Cutting
Some plants can grow roots if their stem is cut at an angle and planted in sandy soil. Growth
enhancers are added to ensure optimal growth of the new plant.
Grafting
Grafting is a method where the stem of one plant is attached to the stem of another plant.
This is particularly useful if the traits one wants for a plant is exhibited by separate plants.
In the example given, a plant with large flowers was grafted into a plant with large roots. As
a result, we have a plant with large flowers and durable root system.
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Animal Asexual Reproduction
Reproductive mechanisms of animals are easier to understand. We start our discussion with
the asexual means of reproduction. There are four examples presented here: binary fission,
fragmentation, regeneration, and parthenogenesis (Figure 10.7).
(A)
(B)
(D)
(C)
Figure 10.7. (A) Dugesia may reproduce asexually by being divided into half; (B) A young Hydra can develop
within the parent’s body; (C) Sea stars exhibiting regeneration; (D) Bees can turn haploid egg cells into a whole
new organism.
Binary Fission
In binary fission, the animal will simply break into two halves. One half will grow into a whole
organism while the other half will grow into a whole one as well. This is exhibited by
flatworms such as Dugesia.
Budding
Budding is similar to binary fission but the animal does not break in half. In budding, the
offspring will grow on the body of the parent and will eventually break off. This is exhibited
by hydras.
Regeneration
Regeneration is exhibited by sea stars (or starfish). If an arm was broken off, as long as part
of its central nerve ring is present in the broken arm, the arm can grow into a whole new sea
star.
Parthenogenesis
Parthenogenesis is rather special. It is a process wherein the parent produces an offspring
without fertilization. We will pay attention to the parthenogenesis exhibited by bees. The
queen bee is the sole parent in a colony of bees. The queen may lay either a fertilized or an
unfertilized egg. If the egg is fertilized by a male drone, the resulting offspring will be female.
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If the egg is unfertilized (underwent parthenogenesis), the offspring is male. The role of the
male in a colony is merely a fertilizer for the queen’s eggs. All worker bees are females.
Animal Sexual Reproduction
You may be familiar with the way animals reproduce sexually, since we humans are classified
under animals. We are going to explore four categories of sexual reproduction on animals
(Figure 10.8).
(A)
(B)
(C)
(D)
Figure 10.8. (A) In frogs, the female lays eggs in the pond while the male ejects sperm cells into the pond; (B)
Male tortoise ejecting his sperm cells inside the female’s body; (C) The two earthworms are fertilizing each other’s
eggs; (D) Clownfish sexual life cycle shown.
Fertilization
External fertilization is simply union of sperm and egg cells outside the female body. This is
evident in frogs. The female lays eggs into a body of water while the male is over her,
simultaneously ejecting sperm to fertilize the eggs upon touching the water. Tadpoles will
then develop in the pond.
Internal fertilization is where the union takes place inside the female body. This is observed
in terrestrial animals including humans.
Hermaphroditism
In the animal kingdom, some species have both male and female organs in their bodies. They
are called hermaphrodites, from the Greek gods Hermes and Aphrodite. Hermaphrodites can
be divided into two categories: simultaneous and sequential hermaphrodites.
Simultaneous hermaphroditism is a mechanism where an animal can both be male and female
at the same time. In earthworms, their reproductive mechanism will result in both
individuals getting their eggs fertilized by their partner.
Sequential hermaphroditism is a method where the animal, though both male and female sex
organs are present, does not use them at the same time. The animal switches sex based on
environmental and behavioral factors. An example of an animal that exhibits this is the
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clownfish. In a school of clownfish, there is one female and one male, while the rest are
neither. If the female dies, the male becomes the female, while one of the undifferentiated
fish in the group will become the next male.
Central Dogma of Molecular Biology
Have you wondered how an app you play in your smartphone works? Or how any computer
game or office application software works? These programs are actually expressions of
thousand to million lines of codes of computer language. In the most basic level, computers
work by interpreting a very long sequence of 1’s and 0’s.
In biology, life is maintained by expressing the genes coded in DNA, a very long sequence of
four letters, and perpetuated by replicating the same genes and passing them on to the
offspring. These processes constitute what we call central dogma of molecular biology. It is
central because all lifeforms perform these processes. The overview of central dogma is
illustrated in Figure 10.9. DNA is transcribed into RNA; RNA is then translated into proteins.
Proteins perform many functions in our body, ranging from digestion, movement, transport,
and production of physical features like hair and eye color.
Figure 10.9. An overview of central dogma. Gene expression involves translating DNA into
proteins. This is analogous to computer programs working through translation of codes and a
long sequence of 1’s and 0’s.
DNA: The Basic Instructions for Life
Figure 10.10. DNA structure is made of nucleotides with any of the four bases A, C, G and T.
DNA exhibits complementary base pairing to assume a double helix shape.
The basic instructions for life are in the form of DNA (Figure 10.10). DNA stands for
deoxyribonucleic acid. It is made up of a long series of building blocks called nucleotides. A
nucleotide has any of the four bases: adenine, thymine, guanine, and cytosine. DNA has a
shape of a double helix held together by hydrogen bonds. As a double-stranded molecule,
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DNA exhibits complementary base pairing. A always partners with T and C always partners
with G.
Replication
The objective of DNA replication is to produce exact copies of DNA prior to cell division to
ensure that the daughter cells will be genetically identical. DNA replication takes place by
unwinding the double helix structure into two strands. New nucleotides will then fill in the
strands by complementary base pairing. Thus, in one copy, half came from the original strand
while the other half is newly made. This concept is called semi-conservative replication. See
the parent DNA in Figure 10.11. This DNA will split, and incoming nucleotides (light blue)
will fill in the single-strand. Notice how the two daughter DNA is exactly alike with the parent
DNA because of complementary base pairing.
Figure 10.11. DNA replication follows a semi-conservative manner. One half of the new DNA
comes from the parent DNA. Complementary base pairing guides the replication process.
Transcription
Before we proceed to transcription,
let us introduce a molecule similar to
DNA: the RNA. RNA stands for
ribonucleic acid. It differs from DNA in
the following aspects (Figure 10.12):
1. It has ribose sugar instead of
deoxyribose;
2. It only occurs as a singlestranded molecule;
3. It has no thymine (T) but
instead it has uracil (U). Uracil
is complementary to adenine.
Figure 10.12. A comparison of DNA and RNA. Note that RNA
is single-stranded and has bases A, C, G and U.
For gene expression, DNA is first transcribed into the single-stranded RNA. This enables the
instructions to get out of the nucleus while the original copy is protected inside the cell. As
an analogy, take a very rare book inside a library. The book cannot be taken out of the library
for it should be protected. So instead of taking it out, you just transcribed the important
contents of the book. You take the transcription with you and keep the original book inside
the library.
Transcription follows complementary base pairing. In Figure 10.13, the RNA (light blue) is
transcribed from a single strand of DNA called the template strand. The template strand is
complementary to the RNA transcript.
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Figure 10.13. Transcription of a template strand produces an RNA. In eukaryotic cells, this RNA will be
processed further before exiting the nucleus.
In eukaryotic cells, the RNA will exit from the nucleus through the nuclear pore. However,
before going outside, the RNA undergoes modifications that involve splicing of some
portions of the transcript and putting protections at both ends of the RNA. Once outside the
nucleus, the RNA is ready for translation.
Translation
The transcript will be read by a ribosome to produce protein, the biomolecule that can play
many roles in the organism ranging from enzyme production to expression of physical traits.
In translation, the ribosome will find the first AUG sequence it will encounter; then, the
transcript will be read in three letters called a codon. The ribosome will continue translation
until it reaches any of the three stop codons: UGA, UAG, and UAA. Take for example the given
sequence below:
5’-UACCAGUCGUCGAUGGAAUCUAGGGUCUAUCGUAUCUGAUCG-3’
The reading will always start on the first AUG encountered. All other sequences before the
AUG will not be translated. The first AUG is highlighted below.
5’-UACCAGUCGUCGAUGGAAUCUAGGGUCUAUCGUAUCUGAUCG-3’
After AUG, the ribosome will start reading in threes until it encounters any of the three stop
codons. The range of RNA to be translated is highlighted below.
5’-UACCAGUCGUCGAUG|GAA|UCU|AGG|GUC|UAU|CGU|AUC|UGAUCG-3’
To determine which amino acids will result
from the sequence, a translation code
called the Universal Genetic Code is used. It
is universal because it is the code for all
known lifeforms. An example of the
Universal Genetic Code is shown in Figure
10.14. Following the Genetic Code, we will
produce the following sequence of amino
acids:
Met—Glu—Ser—Arg—Val—Tyr—Arg—Ile
The amino acid sequence produced will
fold into its proper shape and perform its
function as a protein.
Figure 10.14. The Universal Genetic Code shows
which among the 20 amino acids will be produced per
codon.
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Genetic Engineering
Recent breakthroughs in science and technology now enables artificial modification of genes
to favor encoding of a desired protein (and eventually, a desirable character). An example
given in Figure 10.15 is the production of insulin through genetic engineering. Through this
method, insulin becomes more affordable and medication for people with diabetes can easily
accessed. Genetic engineering is commonly done using the following steps:
1. A plasmid DNA from a bacterium will be extracted and cut;
2. The desired DNA from a human cell will be extracted and cut as well;
3. The cut human DNA will be ligated to the plasmid DNA;
4. The plasmid DNA, now called recombinant DNA, will be introduced to a bacterium;
5. The bacteria will then express the DNA with insulin and produce insulin.
Figure 10.15. Production of human insulin through genetic engineering.
Genetic engineering has a wide variety of applications, including medicine, research, and
agriculture. In agriculture, it is used to improve food quality and security. An example is the
production of Bt corn which is a genetically modified organism (GMO) resistant to corn pests.
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UNIT 4
DIVERSITY OF LIFE
Unit Coverage
Lesson 11: How Animals Survive
Lesson 12: How Plants Survive
Lesson 13: The Process of Evolution
Lesson 14: Interaction and Interdependence
UNIT INTRODUCTION
Welcome to the last and the longest unit in this module: Unit 4. This is the longest unit
because two long lessons, How Animals and Plants Survive, are here. However long they may
be, you might these two as the most practical lessons in this module.
We will kick off the unit with the longest lesson: How Animals Survive. This is a survey of
how ten body systems differ across different groups of animals. Well, that’s a lot! But the
payoff of this lesson is that you will see animals in a very special lens: the lens of a student
with extensive knowledge in animal survival. You will appreciate the different adaptations
made for different animals for different environments. You will see the beauty in the
diversity of animals. You will finally understand why an animal has this or that structure, and
why the structure would not work for other animals.
A good follow-up will be How Plants Survive. This is a general overview of plant anatomy
and a survey of different plant organ adaptations. After this lesson, you can readily infer the
biology of a plant just by looking at its physical characteristics. If you have a passion for
plants, this might be the lesson for you.
Lesson 13 will be a short discussion on evolution: its evidences and its implications. We will
survey the different evidences supporting this theory and how it is used as a central theme
in the study of life. You will be acquainted with an overview of classification of organisms
and appreciate that evolution is what made life diverse on Earth.
Lastly, in Lesson 14, we will study the biggest organization of life: ecology. We will tackle
how lifeforms are in harmony with other lifeforms as well as with the nonliving environment.
We will survey different principles of an ecosystem, as well as different terrestrial and
aquatic biomes to give you an idea about what type of organisms can live in that area.
As you finish this module, we hope that you will be equipped with the necessary scientific
skills to explain what is going on around you and to discover what else is not yet explained
to you.
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LESSON 11 – HOW ANIMALS SURVIVE
OBJECTIVES
At the end of the lesson, you should be able to:
1. Explain the different processes involved in the various organ systems;
2. Describe the general and unique characteristics of the different organ systems in
ensuring animal survival;
3. Relate animal structure with its function.
SUBJECT MATTER
This lesson is a survey of different organ systems of different groups of animals. And that’s a
lot. This lesson will probably be the longest among the 13 lessons included in this module.
Don’t worry! Though memorization is inevitably part of biology, we will do our best to
memorize with understanding. We will give meaning to everything we encounter in this
lesson to help you retain the material. Once you master this lesson, for every animal you
encounter, you will have an idea on how they survive. You will be useful in zoo educational
tours. You will never see animals the same way again.
Animal Nutrition
The most basic need of any animal, including humans, is food. All animals must consume food
in order to survive. All types of food must provide the animal with the following:
 Chemical energy to fuel life processes
 Organic building blocks for biosynthesis
 Essential nutrients to provide materials that the body needs but cannot produce
The process of taking in food, breaking it down, and using it to maintain life is called nutrition.
You may be familiar with the terms carbohydrates, fats, proteins, vitamins and minerals.
Scientists have used these terms to divide our diet depending on which of the three items
they provide for an animal’s body.
Carbohydrates and fats typically play the role of providing chemical energy for the body. As
what you have learned in Lesson 9, chemical energy comes in form of ATP, which is normally
produced from glucose, an example of a carbohydrate. ATPs act as energy source to sustain
life’s activities.
However, energy is useless if there is nothing to build and process. An animal needs a source
of organic carbon and nitrogen in order to grow by building and repairing itself. Sources of
these include carbohydrates, fats, and proteins.
Finally, animals also require essential nutrients—molecules that they need but cannot
synthesize. They are classified into essential amino acids, essential fatty acids, vitamins, and
minerals.
Vitamins are organic molecules that have diverse functions and are required in small
amounts.
 Vitamin B – water-soluble; has many forms (1, 2, 3, 5, 6, 7, 9 and 12); commonly used
as coenzymes
 Vitamin C – water-soluble; required for production of connective tissue
 Vitamin A – fat-soluble; incorporated in the visual pigments of the eye
 Vitamin D – fat-soluble; for calcium absorption and bone formation
 Vitamin E – fat-soluble; an antioxidant
 Vitamin K – fat-soluble; for blood clotting
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Minerals are inorganic molecules that primarily function as cofactors, maintaining nerve
function, and body salt balance. One example of a mineral is iron, which is used by
hemoglobin to grab oxygen gas from the air in the lungs.
Now that you are familiar with the things the body basically needs, we will discuss how
animals obtain these needs.
Animal Digestion
Food processing is a basic
function of all animals. It is
divided into four steps
shown in Figure 11.1. The
basic principle is that food is
broken down, the nutrients
are assimilated by the body,
and the unwanted materials
are taken out.
Ingestion is the process of
taking in food. We will Figure 11.1. The four steps of food processing.
enumerate four types of
feeding mechanisms:
 Suspension feeders – also known as filter feeders; most aquatic animals are filter
feeders by eating small organisms or food particles suspended in water. Examples
include baleen whales, clams and oysters.
 Substrate feeders – animals that live in or on their food source. Examples include
leaf miner caterpillar, moth larva, and maggots.
 Fluid feeders – suck nutrient-rich fluid from a living host (or a mutualist). Examples
include mosquitoes, hummingbirds, and bees.
 Bulk feeders – those who eat relatively large pieces of food. Their adaptations
include tentacles, pincers, claws, fangs, jaws, and teeth.
Digestion is the process of breaking down food into its simplest forms and absorbing them
to be used by the body. Many animals have a compartmentalized digestive system in order
to process the food efficiently. The digestive system runs like a conveyor system in a
factory—it is a long highway and every specific process is confined in a certain area.
There are two types of digestive compartments:
 Incomplete – the food enters and exit in one common
path; evident in Hydra, where a gastrovascular cavity
processes food extracellularly. The hydra takes in its prey
via its tentacles. The cells lining its cavity contain
hydrolytic enzymes and engulfing cells. The undigested
material exits to the mouth as well. An incomplete
digestive system is also present in some flatworms like the
planarians.
 Complete – the food enters through a one-way tube called
the alimentary canal. An advantage of a complete digestive
system is that the animal can ingest food while digesting
earlier meals.
Figure 11.2. Hydra has an
incomplete digestive system.
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Figure 11.3. A complete digestive system illustrated by the earthworm, grasshopper, and bird.
In an earthworm, a muscular pharynx sucks food in through the mouth. The food passes
through the esophagus and is moistened in the crop. A structure called gizzard contains small
bits of sand that aid in mechanical digestion of food. Finally, digestion and absorption are
done by the intestine.
A grasshopper, which we will choose to represent some insects, has a digestive tract divided
into three regions: foregut, midgut, and hindgut. Again, food is moistened in the crop. Gastric
cecae in the midgut function in digestion and
absorption.
Bird digestive system is similar to the earthworm.
The crop is still used to store food and the gizzard
is for mechanical digestion. Chemical digestion
occurs in the intestine as well.
Mammalian Digestive System
The mammalian digestive system has an
alimentary canal and accessory organs that secrete
digestive glands into the canal. The human
digestive system is illustrated in Figure 11.4 while
the functions of major structures are summarized
in the table below.
Structure
Mouth
Salivary gland
Stomach
Liver
Gall bladder
Pancreas
Small intestine
Large intestine
Function
Takes in food
Secretes saliva
Mechanically digests food
Produces bile
Stores bile
Secretes insulin
Chemically digests food;
absorbs nutrients
Absorbs water
Figure 11.4. A diagram of the human
digestive system.
Carnivore vs. Herbivore Digestive System
As our part of introduction to life science, we said that structure fits function. This theme is
evident in the digestive system of animals. Carnivores are those who eat meat while
herbivores are those who eat plants. Plants are harder to digest than meat because of the
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tough material present in plant cells such as
cellulose. Thus, the digestive system of
herbivores is generally longer than carnivores.
This is to allow a longer period in digesting the
material and extracting the nutrients in it. An
example comparison is the system of a coyote (a
carnivore) and a koala (an herbivore) in Figure
11.5.
Animal Circulation
As animals, we need oxygen to sustain cellular
respiration. Cellular respiration involves the
intake of oxygen gas and release of carbon
dioxide as its by-product. The process is called
cellular respiration because it is performed by Figure 11.5. A comparison of coyote and koala
every cell in the body. Thus, every cell in the body digestive system. A koala has a longer digestive
system since it is an herbivore.
must have access for gas exchange. In order to
accomplish this, nature offers two solutions: (1) keeping all cells of the animal in direct
contact with the environment; and (2) a circulatory system that moves fluids between each
cell’s immediate surroundings and the tissues where exchange with the environment occurs.
Direct contact with the environment can be done by either having a gastrovascular cavity or
a flat body shape. The former is illustrated in cnidarians such as jellies and hydras. In hydra
(Figure 11.2), the gastrovascular cavity makes it
possible to bathe both its outer and inner cells to the
fluid environment. For jellies (Figure 11.6), a more
elaborate branching pattern called circular canal and
radial canals help diffuse the nutrients and wastes
across cells. The flat body shape is illustrated by
Figure 11.6. A jelly has a circular canal
flatworms. Its flat shape can facilitate diffusion
and radial canals in order to circulate
because its entire body is in contact with the external
materials throughout its body.
environment.
The second adaptation (i.e. circulatory system) has
two types: open and closed (Figure 11.7). A
circulatory system has three basic components: a
circulatory fluid, a set of vessels, and a muscular pump (heart).
Figure 11.7. Open vs. closed circulatory system. An open circulatory system has
hemolymph while a closed one has blood and interstitial fluid.
Arthropods (insects, spiders, crabs, etc.) and most mollusks (snails and shellfish) have an
open circulatory system. In this system, the circulatory fluid is called hemolymph. The
hemolymph serves a dual function as the circulatory fluid and the fluid that bathes the body
cells (the interstitial fluid). Contraction of tubular hearts circulates the hemolymph into
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sinuses surrounding the organs. It is within these sinuses that chemical exchange occurs
between the hemolymph and the body cells. Relaxation of the heart draws the hemolymph
back to the pores for another round of circulation. For an open circulatory system to work
effectively, body movements are necessary for the organism.
The closed circulatory system is a familiar one because it is present in the human body. In a
closed system, a circulatory fluid called blood is confined to vessels and is distinct from the
interstitial fluid. Chemical exchange occurs between blood and the interstitial fluid, as well
as between interstitial fluid and body cells. Ringworms, cephalopods (octopus and squids),
and all vertebrates have a closed circulatory system.
An advantage of an open circulatory system is that it is less costly in terms of energy
expenditure because it only requires a low pressure to circulate the hemolymph. On the
other hand, closed circulatory systems are useful for relatively larger and more active
animals.
Vertebrate Circulatory System
The circulatory system of all vertebrates has two main parts: a muscular pump called the
heart and the blood vessels. There are three main types of blood vessels: arteries, capillaries,
and veins. Arteries carry blood away from the heart; within organs, arteries form smaller
vessels called arterioles, which then diverge to form capillaries. In capillaries, chemical
exchange occurs via diffusion, including gas exchange. Downstream, the capillaries converge
to form venules, and venules converge into veins. Veins carry blood back to the heart.
Figure 11.8. Single circulation vs. double circulation.
The hearts of
all
vertebrates contain two or more muscular chambers. The chamber that receives blood is
called atrium; the one that pumps blood is called ventricle. In vertebrates, there are basically
two types of circulation: single and double circulation (Figure 11.8).
Single circulation is evident in sharks, rays, and bony fishes. The heart only has two
chambers: one atrium and one ventricle. Oxygen-poor blood is collected into an atrium and
passed on to the ventricle. The ventricle then pumps the blood for oxygenation in the gill
capillaries. In the gills, oxygen is diffused into the blood. The capillaries will then converge
into arteries which will carry blood into body capillaries. Blood then returns to the heart.
Amphibians, reptiles, and mammals exhibit double circulation; however, the number of
chambers per group varies. In a double circuit, the circuit is divided into pulmonary and
systemic circuits. In pulmonary circuit, one pump of the heart delivers oxygen-poor blood
into the gas exchange tissues (mainly the lungs) and returns the now oxygen-rich blood to
the heart. In systemic circuit, the oxygen-rich blood is delivered from the heart into the
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different body capillaries, where there is chemical exchange. The now oxygen-poor blood
will return to the heart for another pulmonary circuit.
A summary of classification of circulatory systems is illustrated in Figure 11.9.
Animal
Circulation
Direct
Contact
Flat Shape
Circulatory
System
Bathed
Cells
Open
Figure 11.9. Summary of circulation mechanisms.
Closed
Single
Circuit
Double
Circuit
Gas Exchange
If the circulatory system concentrates on transporting gases and nutrients across cells,
respiratory systems concentrate on facilitating gas exchange between the animal and its
external environment. To understand better the principles of gas exchange, it is good to
understand that a gas always diffuses from a region of higher partial pressure to a region of
lower partial pressure.
One adaptation for respiration is the presence of respiratory surfaces. From the term itself,
the surface of the animal contains the respiratory organs. Two major requirements for this
to work are: (1) the surface should be large and thin; and (2) the surface should be moist
because cell transport only works in aqueous media. This adaptation, however, will not
simply work for animals with larger bodies. For these animals, there are three available
adaptations: gills, tracheae, and lungs.
Gills
Gills are folds of the body surface
that are suspended in the water. This
is particularly evident for aquatic
animals. For gill-bearing animals,
they either move their gills through
the water or move the water through
their gills. Though gills are present
in many aquatic animals such as sea
stars, octopuses, squids, and
bivalves, we will only discuss gills of
bony fishes.
Figure 11.10. Countercurrent exchange in fish gills. Notice how
the %O2 of the water is always greater than the %O2 in the blood
capillary, facilitating diffusion at every point in the gills.
Gills are more popularly known in
bony fishes. The low concentration
of oxygen in water calls for an efficient respiratory organ and gills can fulfill such demand.
The arrangement of gills in the fish allow for a mechanism called countercurrent exchange
(Figure 11.10). Under this phenomenon, the blood flows in the direction opposite to that of
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water passing over the gills. At each
point in the exchange the blood
oxygen is always less than the water
oxygen, facilitating diffusion at
every point in the gills.
Tracheal system
In insects, the adaptation is called a
tracheal system (Figure 11.11). the
system is made up air tubes that
branch throughout the body. The Figure 11.11. The tracheal system of an insect showing the
largest tubes, called the tracheae, spiracles, tracheae, and air sacs.
connect to external openings called
spiracles. Air sacs are available for organs requiring a large supply of oxygen, such as the
wings. Tracheal systems are enough to facilitate gas exchange without the help of the insect’s
open circulatory system.
Lungs
The third adaptation is
present
in
terrestrial
vertebrates: the lungs.
Lungs
are
localized
respiratory organs that is
ventilated using a variety of
mechanisms.
For
this
section, we will explore
three types of ventilation:
amphibian, avian, and
mammalian.
Figure 11.12. The mechanism of respiration for amphibians is positive
An amphibian breathes via pressure breathing where air is pushed into the lungs. Amphibians can also
positive pressure breathing breathe through their skin.
(Figure 11.12). In this
mechanism, lungs are inflated with forced
airflow. Here are the steps:
1. During inhalation, muscles lower the flow
of the oral cavity, drawing in air through
its nostrils.
2. The floor of the oral cavity rises, forcing air
down the trachea.
3. During exhalation, air is forced back out by
the recoil of lungs and by compression of
the muscular body wall and the floor of the
mouth drops.
4. Nostrils open and the floor of the mouth
rises, letting the exhaled air escape.
Avian lungs use a more efficient mechanism for
breathing in a sense that the airflow is
unidirectional (Figure 11.13); thus, fresh air does
not mix with air that has been used already. Here
are the steps:
1. During first inhalation, fresh air fills the
posterior air sac.
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2. During the first exhalation, the fresh air fills the lungs and the parabronchi facilitates
gas exchange.
3. During the second inhalation, air passes through the lungs and fills the anterior air
sacs.
4. During the second exhalation, air exits from the anterior air sacs and pushed out of
the body.
Finally,
we
have
the
mammalian lungs. In contrast
to amphibian lungs, we breathe
by negative pressure breathing
(Figure 11.14). We pull air into
the lungs. By the contraction of
the muscle called diaphragm,
the lungs expand, causing the
pressure inside the lungs to
become lower than the outside
of the body. Since gas travels
Figure 11.14. Negative pressure breathing in mammalian lungs.
from a region of higher
pressure to lower pressure, air
then fills in the lungs.
Relaxation of the diaphragm increases the air pressure, forcing out the air outside the body.
Since there is only one tube, fresh air mixes with used air, making mammalian lungs less
efficient than avian lungs.
Immune System
Animals are active organisms. They are
exposed to the harshness of the
environment and this includes exposure
to pathogens, disease-causing organisms,
such as bacteria, fungi, and viruses.
Fortunately, animals evolved ways to
prevent or counterattack invading
pathogens to ensure survival. The
collection of mechanisms an animal uses
to prevent diseases is called the immune
system.
Figure 11.15. An overview of the immune system.
The basic logic of the immune system is
the ability of the body to recognize your
own cells against cells that are not of your
own; the ability to distinguish self from non-self. The immune system is divided into two
categories, shown in Figure 11.15: innate immunity and adaptive immunity. Innate immunity
is available for all animals while the adaptive one is exclusive for vertebrates.
Innate immunity can recognize a broad range of pathogens and rapidly responds to them.
The first line of innate immunity includes the physical barriers (skin, mucus, and secretions)
that fight off pathogens before they enter our body. It is for this reason that you experience
common cold (sipon) whenever you are about to get sick because your nose secretes plenty
of mucus to prevent entry of pathogens.
In case that the pathogens get through the physical barriers and enter the body, internal
defenses take over. They include the following:
 Macrophages – eat cells of pathogens
Figure 11.13. Avian lungs are equipped with air
 Natural killer cells – lyse cells by sacs that collectively function to prevent air
mixing inside the lungs.
releasing chemicals
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Interferons – inhibit spreading of viruses
Inflammatory response – a series of reactions that leads to the defense of a localized
infection (Figure 11.16)
Figure 11.16. An inflammatory response following an injury.
Inflammatory response happens following an injury. Chemical signals such as histamine and
prostaglandins are released at the site of injury, dilating the blood vessels and attracting
more phagocytic cells to come to rescue. The phagocytes will destroy the pathogens and
blood clotting will follow to heal the wound. Taking antihistamines (for prevention of allergic
reactions) can impair this mechanism.
It is important to remember that the internal defenses mentioned above are part of innate
immunity. Thus, they respond to a broad range of cells and respond the same way for any
other pathogens. However, if they fail to kill the pathogens, the adaptive immunity finally
takes the last stand.
Adaptive Immunity
The adaptive immune response (Figure 11.17) is present in vertebrates. Unlike innate
immunity, this mechanism exhibits specificity; an adaptive immunity for one infection might
not work for another. However, the adaptive immunity can work over long periods of time,
responsible for how we become immune to certain infections following an initial exposure.
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The adaptive immune response is divided into two, depending on their mode of action: cellmediated and humoral (antibody-mediated) response. However, it is important to take note
that the adaptive immune response uses these two mechanisms simultaneously. As we go
along the steps, look at Figure 11.17 while reading. You can also watch videos online in order
to understand how the adaptive immune response works step-by-step.
Before we start, it is also important to take note what an antigen is. An antigen is any
substance capable of initiating an immune response. It is often present on the surfaces of
suspected pathogens. For example, some people are allergic to pollen grains because of
antigens on its surface. An antigen is necessary to initiate an adaptive immune response.
Here are the steps:
1. An antigen-presenting cell will engulf the pathogen and expose its antigen
2. Presenting the antigen will trigger an “alarm” for the entire body; helper T cells will
communicate with the antigen-presenting cell
3. The helper T cell will secrete chemicals to call for B cells and T cells and command
them to multiply. After this, B cell and T cell pathways will take place.
B cell pathway
1. B cells will multiply into plasma cells and
memory B cells
2. Plasma cells carry antibodies which they will
secrete to label the pathogens
3. Antibody-labeled pathogens can be easily
detected by the immune cells for attack and
destruction
4. Memory B cells will contain “memory” of the
antigen of the pathogen for secondary
immune response
T cell pathway
1. T cells will multiply into cytotoxic T cells and
memory T cells
2. Cytotoxic T cells will secrete chemicals that
will lyse the cells infected by pathogens
3. Memory T cells will contain “memory” of the
antigen of the pathogen for secondary
immune response
B cell pathway is useful for pathogens who thrives outside body cells. T cell pathway is useful
for pathogens who thrive inside body cells.
The secondary immune response triggers when the host is attacked by the same pathogen
for the second time. During secondary immune response, the memory cells will merely
multiply fast into either plasma cells or cytotoxic T cells, initiating an immune defense so fast
that we no longer feel the symptoms of the pathogen. In that sense, we are then called
“immune” to the pathogen. One concrete illustration of this phenomenon is the bulutong or
chickenpox, a viral infection caused by Varicella. Once exposed to chickenpox, our body has
manufactured memory cells that live for several decades which will multiply immediately
upon subsequent exposures to chickenpox.
The secondary immune response is also used for practical purposes such as production of
vaccines. When a vaccine is introduced, your body is exposed to an antigen of the pathogen,
initiating a response without feeling the symptoms. When the real pathogen invades your
body, your memory cells would immediately proliferate B cells and T cells.
Osmoregulation
Aside from balancing the temperature between the organism and the environment, we face
the challenge of balancing our body fluids through uptake and loss of water and solutes. This
process is called osmoregulation. Osmoregulation is necessary to keep the cells from
shrinking or swelling, as is the case during osmosis. First, let us explore how different
animals face their osmotic challenges.
Osmotic
Figure 11.17. An overview of the adaptive immune response.
Challenges
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We are going to survey three broad groups of organisms in terms of facing osmotic
challenges: marine animals, freshwater animals, and land animals.
Marine animals face the challenge of
a salty environment. To adapt, it
excretes a concentrated urine with
plenty of salt and little water.
Freshwater animals, on the other
hand, face the challenge of an
environment with too much water
and little salt. To adapt, it excretes a
very dilute urine with little salt and Figure 11.18. Difference in salt and water balance between a
plenty of water. Figure 11.18 shows freshwater fish and a marine fish.
the difference in osmoregulation
between a marine and a freshwater fish.
For terrestrial animals, different adaptations have arisen to maintain one goal: prevent
dehydration. Notable adaptations include waxy exoskeleton of insects, hard shells of snails,
and layers of dead, keratinized skin cells of mammals.
Nitrogenous Wastes
As discussed in animal nutrition, animals take in organic nitrogen. Likewise, unwanted
nitrogenous products brought by breakdown of protein and nucleic acids have to be excreted.
Different animals excrete organic nitrogen in different forms: ammonia, urea, or uric acid.
The forms mentioned vary in toxicity, water amount, and energy requirements.
 Ammonia – a highly toxic substance in high concentrations; thus, only animals who
thrive in environment with plenty of water excrete ammonia.
 Urea – a derivative of ammonia; this is a water-soluble non-toxic substance that uses
less water than ammonia. Animals with more or less sustainable water supply such
as mammals and amphibians excrete urea.
 Uric acid – an insoluble non-toxic substance with very little water. Animals who have
limited water supply such as reptiles (except turtles) and birds excrete uric acid.
Survey of Excretory Systems
Now that we have surveyed the
different osmotic challenges and
nitrogenous wastes, it is time for us to
explore the various excretory systems
developed through the course of
evolution.
Figure 11.19. Flame bulb system in flatworms. The cap cell
Protonephridia
Flatworms have excretory systems sweeps to filter the fluid and the tubule cell collects the
filtrate.
called protonephridia (Figure 11.19).
Protonephridia consist of a network of dead-end tubules. Each dead-end is capped by flame
bulbs. The flame bulb works like a flickering flame by
sweeping its cilia to draw water and solutes from the
flatworm’s fluids. The filtered fluid is then collected
by the tubule cell and is eliminated into the
environment through openings in body wall.
Metanephridia
Annelids such as earthworms have metanephridia
(Figure 11.20), excretory systems that directly collect
filtrate from the body cavity. Each segment of an
earthworm has a metanephridium and is
characterized by tubules enveloped by a capillary
Figure 11.20. Metanephridia of an
earthworm.
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network. Each tubule opens from a ciliated opening to the coelom and exits to the external
environment. If protonephridia act like a sweep, metanephridia act like a vacuum cleaner.
Further, the capillary network can reabsorb needed material and secrete unwanted material
into the metanephridia.
Malpighian tubules
In insects, the excretory system is composed of
Malpighian tubules (Figure 11.21). Under this
system, salt and nitrogenous wastes from the
hemolymph enter the tubules by diffusion. As a
consequence of osmosis, water will also enter the
tubules and mix with the feces in the digestive
system. Towards the hindgut, reabsorption of ions
and organic molecules will take place. Again, water
will be reabsorbed by osmosis, leaving behind uric
acid and feces for elimination.
Nephrons
Figure 11.21. Malpighian tubules of
All vertebrates have an excretory system composed of insects.
nephrons, which are located inside a specialized organ
called a kidney. To give you a general idea, urine is formed from the kidneys and delivered
into the rest of the urinary system for excretion. In this section, we will study the kidney and
how it forms urine in detail.
Figure 11.22. Kidney organization. A kidney has functional units called nephrons. The parts of an
individual nephron are also shown.
Looking at Figure 11.22, you will see that the kidney is made of several nephrons. Urine
formation happens inside these nephrons, outlined in the following steps:
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1. Filtration – blood from the afferent arteriole of the renal artery will be delivered into
the glomerulus. Here, the tiny spaces cause blood pressure to increase, filtering the
blood. The filtrate is collected by the Bowman’s capsule and is collected by the
proximal tubule. The filtered blood will exit through the efferent arteriole.
2. Reabsorption – the main role of the proximal tubule is to reabsorb materials filtered
but are still needed by the body for fluid balance. The filtrate will then travel to the
Loop of Henle. The Loop of Henle also functions for reabsorption of water and salt.
3. Secretion – after the Loop of Henle, the filtrate will flow into the distal tubule. Here,
materials that were not filtered by the blood will be secreted into the urine. Finally,
the urine is ready for collection.
4. Excretion – urine will be collected by collecting tubules, which all converge into a
ureter. The two ureters from the two kidneys will gather urine into the urinary
bladder for storage prior to urination. The urethra opens into the external
environment.
Endocrine System
To ensure that the body works in balance and harmony, signaling systems have evolved over
animals. To do this, signaling molecules called hormones are secreted by certain organs and
delivered to target cells to evoke specific responses.
Have you ever experienced a fight-or-flight situation? The extra boost of energy you obtained
for “emergency purposes” was triggered by hormones called adrenaline by acting on your
liver to produce more glucose. Mechanisms like this will be discussed under the endocrine
system, since this system secretes the best-known hormones of the animal body.
Cell Signaling
Before proceeding to a survey of
major body hormones, let us first
discuss cell signaling, the way cells
communicate with one another.
There are three basic types of cell
signaling
(Figure
11.23),
depending on the relationship
between the transmitting cell and
the receiving cell.



Autocrine – a mechanism
where the hormone acts on the Figure 11.23. Three basic types of cell signaling: autocrine,
same cell that produced it. paracrine, and endocrine signaling.
Examples of processes under
autocrine signaling include growth factors that regulate cell division and differentiation.
Paracrine – a mechanism where a cell releases a signal molecule that diffuses through
the extracellular fluid and acts on nearby cells only. The secretion of histamine of white
blood cells is an example of paracrine signaling since it acts on nearby blood vessels to
promote vasodilation.
Endocrine – a mechanism where the signal molecule travels to the bloodstream and acts
on cells at a distance from the secreting cell. The adrenaline rush is an example of
endocrine signaling since the adrenal glands secrete the hormone which acts on distant
organs such as the liver and muscles. A special category called neuroendocrine signaling
is used if the secreting cell is a neuron (nerve cell). The hypothalamus and pituitary
glands exhibit neuroendocrine signaling.
Endocrine Glands
Now that we know how endocrine glands work, we are now ready to enumerate the different
endocrine glands of the body and what functions they perform. Figure 11.24 shows the
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location of the different endocrine glands of the human body. A table below also summarizes
the endocrine glands, their hormones, and their functions.
Figure 11.24. The different endocrine glands of the human
body.
Endocrine Gland
Hypothalamus
Hormone
Various
Anterior pituitary gland
Thyroid-stimulating hormone
(TSH)
Adrenocorticotropic hormone
(ACTH)
Follicle-stimulating hormone
(FSH)
Luteinizing hormone (LH)
Prolactin (PRL)
Posterior pituitary gland
Growth hormone (GH)
Melanocyte-stimulating
hormone (MSH)
Endorphins
Antidiuretic hormone (ADH)
Oxytocin
Pineal gland
Melatonin
Thyroid gland
Parathyroid gland
Thymus
Adrenal glands
Calcitonin
Parathyroid hormone (PTH)
Thymosin
Epinephrine and
norepinephrine
Insulin
Glucagon
Estradiol
Pancreas
Ovaries
Progesterone
Testes
Testosterone
Oxytocin
Action
Regulates anterior pituitary
gland
Regulates thyroid glands
Regulates adrenal glands
Regulates female sex hormones;
Sperm production
Regulates male sex hormones;
Ovulation
Stimulates breast development
and milk secretion
Stimulates bone growth
Promotes skin darkening
Inhibits perception of pain
Promotes water reabsorption in
kidneys
Promotes uterine contractions
and milk secretion
Synchronizes biological clock
with day length
Decreases blood calcium
Increases blood calcium
Promotes maturation of T cells
“Fight-or-flight” response
Decreases blood sugar
Increases blood sugar
Promotes secondary sexual
characteristics
Prepares and maintains uterine
lining
Promotes secondary sexual
characteristics
Promotes uterine contractions
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Nervous System
All living organisms should be able to detect changes in its external and internal
environment; further, they should be able to respond to these changes accordingly to assure
survival. To do this, communication between the animal’s organ systems is vital. So far, we
have learned about cell communication through the use of chemicals such as hormones.
However, the response rate of this method of communication is too slow. Due to this, a
system that can act at greater speeds evolved—the nervous system.
Survey of Nervous Systems
Figure 11.25. A survey of invertebrate nervous systems and the nervous system of a salamander, a vertebrate.
Looking at Figure 11.25, you will see that different groups of invertebrates have different
organization of their nervous systems. As an example, cnidarians such as hydra and jellies
have nerve nets and sea stars have a central nerve ring. Through the course of evolution,
nerves become more concentrated on the anterior part of the organism, a concept called
cephalization. Cephalization is evident from the planarians up to the chordates. In the next
section, we will study the vertebrate nervous system.
Vertebrate Nervous System
The vertebrate nervous system is organized as shown in Figure 11.26. For the purposes of
this subject, we will focus more on the functions of each division rather than their structural
differences.
Central and Peripheral Nervous System
The two major divisions of the nervous system are the central and peripheral nervous
systems. Simply, the central nervous system is composed of the brain and the spinal cord.
The rest of the nerves of the body is under the peripheral nervous system.
The task of the central nervous system (CNS) is to integrate incoming sensory information
from the peripheral nervous system into their corresponding responses. The peripheral
nervous system collects information, transmits the information into the CNS, and carries out
the response.
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Figure 11.26. Organization of the vertebrate nervous system.
Afferent and Efferent Division
Going back to the peripheral nervous system, take note that its function is both to transmit
signals into the CNS and to carry out the necessary response as deemed appropriate by the
CNS. The collection of nerves that transmit sensory and visceral information into the CNS is
classified under afferent division while the collection that carries out the corresponding
response is under efferent division.
Somatic and Autonomic Nervous System
The efferent division is further divided into two, depending on the types of response carried
out. The somatic nervous system (from soma, meaning “body”) carries out responses that are
voluntary and under conscious control. Typically, these voluntary movements are carried
out by our skeletal muscles as moving your body is a voluntary response. The autonomic
nervous system carries out responses that are “automatic”, or involuntary.
The enteric nervous system is an independent division of the autonomic nervous system
which is connected to the walls of the digestive tract. This nervous system responds based
on digestive stimuli and hormones. We will discuss parasympathetic and sympathetic
nervous systems next.
Parasympathetic and Sympathetic Nervous System
The autonomic nervous system is divided into two systems with opposing functions but are
always active: parasympathetic and sympathetic nervous system. The parasympathetic
nervous system predominates during relaxed, quiet situations—the “rest and digest”
system; the sympathetic nervous system predominates in times of stress, danger, or
strenuous physical activities—the “fight or flight” system.
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The table below enumerates some of the organs where the autonomic nervous system acts
upon together with the corresponding opposing responses of the parasympathetic and
sympathetic nervous systems. You can easily guess the action just by thinking about how
your body would react in a stressful or in a quiet situation.
Organ
Eyes
Salivary glands
Heart
Lungs
Stomach
Liver
Intestines
Bladder
Genitals
Parasympathetic Division
Constricts pupils
Stimulates salivation
Decreases heart rate
Constricts airways
Stimulates stomach activity
Inhibits glucose release
Stimulates activity
Stimulates contraction
Stimulates arousal
Sympathetic Division
Dilates pupils
Inhibits salivation
Increases heart rate
Dilates airways
Inhibits stomach activity
Stimulates glucose release
Inhibits activity
Relaxes bladder
Inhibits arousal
The Body in Motion
For the last section of our lesson, we will study the mechanisms of movement of different
groups of organisms. We will start with studying how the vertebrate skeletal muscle works
and we will finish with surveying different skeletal systems and how they help in moving the
body.
Vertebrate Skeletal Muscle
Vertebrate skeletal muscles connect to the bones of the skeleton through structures called
tendons. Figure 11.27 displays the functional level of organization of a skeletal muscle.
Skeletal muscles are made of individual muscle bundles; each muscle bundle is made of
multiple muscle fibers (muscle cell). A muscle cell is composed of individual myofibrils.
Finally, a myofibril is composed of interconnected sarcomeres.
Figure 11.27. Organization of a vertebrate skeletal muscle.
To easily understand how a vertebrate skeletal muscle facilitates body movement, just
remember that muscles move by shortening (contracting), not by elongating. You can flex
your arm because of the shortening of your biceps; you can then extend your arm because of
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the shortening of your triceps. But how do our muscles contract? Muscles contraction is
explained by a mechanism called sliding filament model.
Sliding Filament Model
Figure 11.28. A simplified sliding filament model.
Shown in Figure 11.28 is a single sarcomere, similar to that shown in Figure 11.27. An
individual sarcomere is made of thin filaments called actin and thick filaments called myosin.
The sliding filament model is outlined in the steps below:
1. Initially, the actin fibers on the opposite sides of myosin fibers are far apart.
2. Through a nerve signal, calcium (Ca2+) ions will be released into the sarcomeres;
opening the binding sites for myosin “heads” to bind to the actin fibers.
3. Upon binding, ATP will be used by the myosin heads to “pull” the actin fibers together.
4. This pulling action effectively shortens the entire muscle for body movement.
For better understanding of the mechanism of muscle contraction, you may watch any video
of the sliding filament model online.
Skeletal Systems
Skeletal systems do not only provide protection and support for the animal’s soft tissues but
also provide a framework against which muscles work to move parts of the body. In this
section, we will survey three types of skeletal systems.
Hydrostatic skeleton
A hydrostatic skeleton is a structure composed of
muscles and an incompressible body fluid, no rigid
support is involved. This type of skeleton works
from the principle that fluids flow from an area of
high pressure to low pressure. Animals with
hydrostatic skeleton include cnidarians, flatworms,
ringworms, and roundworms.
Figure 11.29 shows how the hydrostatic skeleton
aids for the locomotion of a typical ringworm.
Initially, the longitudinal muscles will contract,
shortening the body part and filling it with fluid.
Next, the circular muscle will contract, extending
the skeleton and moving the worm forward.
Figure 11.29. Locomotion of a ringworm.
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Exoskeleton
An exoskeleton is a hard, external body covering such as the shell of mollusks or the chitinous
exoskeleton of arthropods. The exoskeleton serves multiple functions including protecting
the internal organs, preventing dehydration, and providing a framework against which a
muscle can exert force.
Endoskeleton
In contrast to the exoskeleton, an endoskeleton still protects internal organs and provides
framework against which a muscle can exert force; but, an endoskeleton is located inside the
organism’s body. Also, vertebrate endoskeletons serve as a repository of calcium and
phosphate as well as manufacturing site of white and red blood cells.
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LESSON 12 – HOW PLANTS SURVIVE
OBJECTIVES
At the end of the lesson, you should be able to:
1. Describe the different meristematic tissues;
2. Discuss the three types of plant tissue systems;
3. Describe the structure of monocot and dicot root, stem and leaf;
4. Discuss some adaptations of roots, stems and leaves.
SUBJECT MATTER
Basic Plant Structure
If you will look at your surroundings, you will realize that plants vary greatly in terms of
physical appearance. Some plants have fruits and flowers, some plants are bushy, some
plants are tall, among other characteristics. However diverse they may be, all plants have a
basic two-part body plan: a root system and a shoot system. Typically, the root system is
underground while the shoot system is aboveground.
These two plant systems are composed of organs
which are the roots, stem, leaves, and sometimes
flowers and fruits. These organs, in turn, are made of
tissues. For visualization of the organ system and the
organs, take a look at Figure 12.1. You may need to go
back to this illustration for reference when we discuss
plant growth and development.
Plant tissues may grow up to a certain extent
(determinate growth) or perpetually (indeterminate
growth). Those tissues that exhibit determinate
growth are called permanent tissues while those that
exhibit indeterminate growth are called meristematic
tissues. We will explore meristematic tissues first.
Figure 12.1. Two-part body plan of a plant.
Meristematic Tissues and Plant Growth
Meristems are responsible for the plant’s growth both in terms of length and girth. An
increase in length is caused by apical meristems (Figure 12.2) at the tip of the plant’s axillary
buds, apical buds, and roots. This growth is called primary growth. There are two types of
apical meristems: shoot apical and root apical meristems.
Figure 12.2. The shoot apical meristem (left) and the root apical meristem. The primary meristems
indicated will give rise to the three types of tissue systems: dermal, ground, and vascular tissues.
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Notable parts of the shoot apical meristem include the following:
 Axillary bud – grows into new shoot meristems; responsible for branching of trees.
 Node – part of a shoot where leaves grow.
 Primary meristems – gives rise to the three types of permanent tissues: dermal,
ground, and vascular tissues. They will be discussed later.
 Young leaf – also called leaf primordium; gives rise to leaves.
Notable parts of the root apical meristem include the following:
 Root cap – protects the root from abrasion due to the roughness of the soil.
 Primary meristems – similar to that of the shoot apical meristem.
 Root hair – present in root cells far from the root apical meristem; helps to absorb
water and minerals from the soil.
Some plants, especially woody plants, exhibit secondary growth (growth in diameter). This
mechanism is facilitated by meristematic cylindrical tissues called lateral meristems (Figure
12.3). There are two types of lateral meristems: vascular cambium and cork cambium. The
vascular cambium gives rise to the secondary vascular tissues (xylem and phloem) while the
cork cambium gives rise to the bark—the protective covering of a woody plant.
Figure 12.3. Vascular cambium and cork cambium thickens the plant.
Permanent Tissues
Permanent tissues arise at the mature sites of the plant—giving rise to cells with specialized
functions rather than merely dividing cells. Permanent tissues are broadly classified into
three: ground, vascular, and dermal tissues. We will study ground tissues first.
Ground Tissues
Ground tissues originate from ground meristems. These tissues are structurally simple; they
are made of a simple cluster of plant cells. There are three types of ground tissues:
parenchyma, collenchyma, and sclerenchyma. Each type has a distinctive cell wall structure
and thus perform various functions.
(A)
(B)
(C)
Figure 12.4. Different types of ground tissue: (A) parenchyma; (B) collenchyma; and (C) sclerenchyma (cells
with red wall).
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Parenchyma
Most of the soft, moist cells of the plant are made of parenchyma. The flesh of an apple and a
potato tuber are made of parenchyma. Structurally, parenchyma cells have uniformly thin
cell walls (Figure 12.4a). They are alive at maturity and primarily function for storage and
short-distance transport, among others.
Collenchyma
Collenchyma cells provide flexible support for the plant. Examples include leaf petiole and
the stalk of a celery. They are alive at maturity and have unevenly thick cell wall (Figure
12.4b).
Sclerenchyma
Sclerenchyma cells provide rigid support and protection due to its cell wall being encased in
a substance called lignin (Figure 12.4c). However, since sclerenchyma is encased in lignin, it
can no longer take up nutrients; thus, they are dead at maturity. Sclerenchyma cells are
present in the hard shells of walnuts and coconuts.
Vascular Tissues
Vascular tissues originate from the procambium. Vascular tissues are more complex than
ground tissues for the former is specialized in long-distance transport. Vascular tissues may
be either xylem or phloem. Their differences are highlighted in Figure 12.5.
Xylem
The xylem is a vascular tissue that
conducts water and minerals in one
way only: from the soil upward
from the plant’s roots to the shoot.
Water and minerals travel because
of the negative pressure during
transpiration and water’s capillary
action. Xylem cells are lignified;
thus, they are dead at maturity.
Phloem
Phloem conducts food and organic
molecules throughout the plant.
Figure 12.5. Comparison between xylem and phloem.
Unlike the xylem, the phloem can
transport materials in a two-way route because it works on the principle of concentration
gradient: solutes travel from an area of high concentration to an area of low concentration.
Commonly, the travel comes from the leaves to the roots and fruits, and other parts of the
plant that store food. Phloem cells are living for they assist in the transport of sugars.
Dermal Tissues
Dermal tissues, also known as the epidermis, originate from protoderm. Epidermis envelops
the outer surface of the plant except at the very tips of the shoot and the absorptive parts of
the roots. Through the course of evolution, plants have developed dermal tissues that serve
diverse functions including protection, absorption, and gas exchange.
(A)
(B)
(C)
Figure 12.6. (A) Microscope image of stomata; (B) trichomes of Cannabis leaf; (C) root hairs from a young seed.
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Stomata
Stomata (Figure 12.6a) are responsible for the intake of carbon dioxide and release of oxygen
gas and water vapor. It has two kidney-shaped guard cells that open and close depending on
environmental conditions. Stomata are present on the surface of leaves.
Trichomes
Trichomes are hair-like projections present in leaves and stems. The main goals of trichomes
are: (1) to deter predators by giving the leaves a hairy appearance which makes the predator
lose appetite; and (2) to keep the plant cool by reflecting light (white color effectively reflects
light). In Figure 12.6b, the trichomes of Cannabis secretes tetrahydrocannabinol (THC) which
naturally protects the plant against insect pests.
Root hairs
Root hairs are simply extensions of root epidermal cells with the primary objective of
increasing the surface area of the roots for maximum water and mineral absorption. Figure
12.6c illustrates developing root hairs in a germinating seed. Root hairs are present in the
most delicate tips of the roots.
Monocot vs. Dicot Plants
In this section, we will study the structural differences in the plant organs of the two major
groups of angiosperms: monocots and dicots. This section will help you readily identify if a
flowering plant is monocot or dicot just by observing its physical characteristics. Figure 12.7
summarizes their physical differences.
Figure 12.7. Comparison of monocots and dicots using five different plant structures.
Plant Organs
We will conclude this lesson by enumerating some of the many adaptations of plant organs
that perform specialized functions.
Roots
If you have eaten food like radish (labanos), carrot, or sweet potato (kamote), then you have
eaten a plant root. These roots are specialized for storage. But the more familiar function of
the root to you is its job to anchor the plant to the soil and absorb water and minerals.
There are two basic types of root systems: taproot and fibrous root. A taproot system
consists of a thick root with smaller, lateral roots. Radish and carrots have a taproot
system—the one you actually eat is the taproot itself!
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A fibrous root system, on the other hand, have multiple smaller-sized roots branching from
a central point. Grasses and sweet potatoes have a fibrous root system.
Some plants developed roots with functions other than anchorage and water transport. As
you have read, carrots, radishes, and sweet potatoes have roots adapted for storage. Figure
12.8 illustrates some specialized root systems and adaptations. Notable examples include
the following:
 Prop roots – aerial roots that support the entire plant aboveground; they show up in
plants that grow in shallow and unstable soil.
 Storage root – present in carrots, radishes, and similar plants; the root stores water
and food.
 Pneumatophores – present in mangroves which live in swamps; the roots are
projecting upward above the water to obtain oxygen for the roots below the water
surface.
 Buttress roots – aerial roots that support the trunks of very tall trees.
 Strangling root – a type of aerial root present in strangler fig; the roots grow towards
the ground while wrapping around a host tree.
(A)
(B)
(C)
(D)
(E)
Figure 12.8. Some root adaptations: (A) prop roots; (B) storage roots; (C) pneumatophores; (D) buttress roots;
and (E) strangling roots.
Stems
A stem may sound easy for you to define because you can readily see it in every plant you
encounter. A stem is technically defined as a structure that raises and separates the leaves
to expose them to sunlight. Going back to Figure 12.1, a stem is an alternating series of nodes;
each node has a leaf and an axillary bud; and a stem has a terminal point called the apical bud.
Apical buds increase the height of the stem while axillary buds provide lateral shoots to cover
more canopy for photosynthesis. In Figure 12.7, take note that monocot stems have scattered
vascular bundles while dicot stems have vascular bundles arranged in a ring.
Some plants have stems with additional functions (Figure 12.9). We will survey them below:
 Rhizome – present in ginger; it is a horizontally-growing stem that grows
underground. Vertical shoots may emerge from the axillary buds of the rhizome.
 Bulb – present in onion; bulbs are stems that grow vertically underground with
enlarged modified leaves for storage.
 Stolon – present in strawberries; horizontally-growing shoots that grow along the
soil surface. Stolons can be used for asexual reproduction.
 Tuber – present in potatoes; tubers are enlarged rhizomes or stolons. They are
specialized for storing food for use during off seasons.
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(A)
(B)
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(C)
(D)
Figure 12.9. Some stem adaptations: (A) rhizomes; (B) bulbs; (C) stolons; and (D) tubers. Take note that in (B),
the stem is only the small yellowish-brown portion just above the base; the flesh are modified leaves.
Leaves
Leaves are the primary photosynthetic organs of a plant. Leaves vary in shape and sizes
across different plants; they are even used to classify a species of plant. A leaf consists of a
flattened blade and a stalk called a petiole (Figure 12.1). Many monocots, however, lack
petioles and instead their leaves envelop the stem in a sheath. You can observe this in a corn
or a banana plant.
Leaves, too, have specialized adaptations. The flesh of an onion in Figure 12.9 is actually a
specialized fleshy leaf. We will survey four more adaptations in this section. They are
illustrated in Figure 12.10.
 Tendrils – specialized leaves (sometimes stems) that are sensitive to touch; they
cling to an object at the point of contact.
 Spines – present in cacti; the green flesh of the cactus is actually a photosynthetic
stem while the spines serve as specialized leaves.
 Reproductive leaves – present in Kalanchoe; the leaves that fall off from its edge can
grow into genetically identical Kalanchoe plant.
 Bracts – often mistaken as petals, bracts are colored leaves that attract pollinators;
they are present in bougainvillea and poinsettia.
(A)
(B)
(C)
(D)
Figure 12.10. Some leaf adaptations: (A) tendrils; (B) spines; (C) reproductive leaves; and (D) bracts.
Upon finishing this lesson, you are now equipped with the basic knowledge required to
appreciate the diversity of plants. you can readily identify the plant’s parts, state whether it
is a monocot or a dicot, and describe some of a plant’s adaptations. Ultimately, you can infer
the biology of a certain plant just by looking at its remarkable features.
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LESSON 13 – THE PROCESS OF EVOLUTION
OBJECTIVES
At the end of the lesson, you should be able to:
1. Describe the different evidences of evolution;
2. Discuss the origin and extinction of species in light of natural selection and descent
with modification;
3. Describe how the present system of classification of organisms is based on
evolutionary relationships.
SUBJECT MATTER
The theory of evolution is a central theme in biology, though many people still do not accept
the theory which was popularized by Charles Darwin in his book On the Origin of Species
published in 1859. In this lesson we will explore three aspects of evolution: (1) its evidences;
(2) its power to explain the diversity of life today; and (3) evolution being the basis for
classification of all organisms.
Evidences of Evolution
Basically, evolution states that species change over time. New species appear from
preexisting species through descent with modification and natural selection. According to
Darwin, the process of evolution takes thousands to millions of years to occur. Through the
works of scientists over the years, several evidences were used to validate Darwin’s theory
and somehow reconstruct the process of evolution. We are going to explore these evidences.
Fossil Record
The fossil record documents the patterns of evolution. It shows how present-day organisms
were different from the organisms in the past and how changes have occurred from ancestral
organisms to the present-day ones. For example, Figure 13.1 shows that the modern horse
Equus evolved from a smaller horse-like animal Eohippus some 55 million years ago. More
fossils revealed transitional species such as the Mesohippus and Merychippus which shows
that the modern-day horse started from a smaller, 4-toed animal and eventually got larger
with reduced number of toes.
Figure 13.1. Fossil record shows how the modern-day horse descended from an ancestral horse.
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Homologous Structures
Have you ever seen a cat forelimb,
a bat wing, and a whale flipper?
Compared to the human arm, you
might think that the structures
mentioned appear quite different
from each other and are of
different functions: human arm is
for grabbing; cat forelimb is for
walking; bat wing is for flying; and
whale flipper is for swimming.
Figure 13.2. The bones of the human arm, cat forelimb, whale
Surprisingly, if we look at the flipper, and bat wing are strikingly similar in arrangement.
bones of these structures, you will
find that the way the bones are arranged are strikingly similar (Figure 13.2). Structures like
these are homologous structures. Homologous structures are those structures believed to
have a common ancestry due to similarity in structure. Therefore, the four animals must have
all descended from a common ancestor.
However, there are also structures with striking resemblance and function but are from
different ancestry called analogous structures. For example, the wing of an insect and the
wings of a bat are analogous structures. Insect wings are thought to have originated from an
ancestral gill. Analogous structures appear if natural selection brings two different groups of
organisms to evolve a common adaptation due to the same environmental challenges they
face.
Vestigial Structures
There are some structures
found in living things with
no apparent function. these
are known as vestigial
structures. It is said that
these
structures
are
homologous to structures
useful in other species,
especially ancestral ones.
For example, humans have
Figure 13.3. Whales have a vestigial pelvic bone, suggesting that they
a vestigial tailbone, which descended from tetrapod mammals.
is homologous to a
functional tailbone of ancestral apes; whales have a vestigial pelvic bone (Figure 13.3), which
is homologous to a functional pelvic bone of ancestral tetrapod mammal.
Similarity of Embryos
Embryos are unborn or unhatched
animals in its earliest phases of
development. Look at Figure 13.4,
what do you notice about the embryos?
They look very similar to one another.
All of them have tails and gill slits. This
suggests that these animals, which are
all from different groups of
vertebrates, had a common ancestor.
Figure 13.4. Embryos of fish, salamander, tortoise, chick,
rabbit, and human are very similar.
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Biochemical Evidence
Cytochrome c is a protein found in the membranes of the mitochondria. As you already know,
mitochondria are found in almost all eukaryotes. Surprisingly, even distant groups of
organisms show similar amino acid sequence of cytochrome c, which led scientists to believe
that eukaryotes all had a common ancestor. Scientists use the amino acid sequence of
cytochrome c to determine the number of differences in the sequence between two
organisms; then they use this data to infer how distant the two organisms are in terms of
evolutionary relationship. For example, humans and dogs differ by 13 amino acids while
humans and snakes differ by 20. Humans are thus closer to dogs than they are to snakes.
Chimpanzee and humans have identical cytochrome c, indicating a very close evolutionary
relationship between chimpanzees and humans.
Origin and Extinction of Species
Now that we have learned about the evidences of evolution, let us now study how evolution
exactly works. Evolution has been identified as the driving force towards the diversity of life
we witness today.
Evolution basically works because of two observations: (1) there are variations in heritable
traits within a population; and (2) organisms produce more offspring than the environment
can support. From these two principles, Darwin inferred that due to limited resources and
environmental challenges, only those organisms who “fit” with the environment can survive
and populate.
We will simulate how new species emerge by using colored circles. In the biological species
concept, species is defined as a group of populations having the capacity to interbreed and
bear fertile offspring. In simple terms, if two individuals cannot bear a fertile offspring, then
they are of different species. We take the larger circle as the environment and the smaller
circles as the species in a small population (Figure 13.5):
A. Suppose we have a population of a certain species thriving in a given locality.
B. Then, some of the individuals migrated to new different environments and
reproduced. Take note that as they reproduced, new traits emerged.
C. One day, a predator appeared and hunted for these individuals. The predator eats any
individual it can easily see.
D. Only those who blended with the environment survived. In the end, we have different
localities having differentiated individuals. In the long run, as new environmental
challenges arise, more traits might appear, until the individuals are so distinct that
they can no longer interbreed and hence can be classified as different species.
(A)
(B)
(C)
(D)
Figure 13.5. Simplified simulation of evolution.
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However, life does not only produce new species. It also erases some species from the planet.
That is why we no longer see the species on the fossil record. Scientists have come up with
ideas about how extinction occurs. One cause is attributed to changes in global climate and
atmosphere, such that the environment is no longer capable of supporting a wide variety of
organisms that once thrived there because their adaptations all of a sudden were no longer
fit for survival. Today, human activities such as overhunting and pollution are the major
causes of extinction of some species.
Classification of Organisms
As early as during the time of Aristotle, the Father of Biology, humans have classified
different living things. That is the reason we have terms such as “plants” and “animals” and
so on. Aristotle also believed that organisms can be classified based on a “natural scale”.
Today, since biologists are convinced with the idea of Darwin that all living things share a
common ancestor, classification of all living things on Earth are now based on evolutionary
relationships. That is, organisms are classified according to the degree of similarity of their
physical, chemical, and behavioral characteristics; or, simply, according to shared ancestry.
Shared ancestry between groups of organisms can be illustrated using a cladogram.
Figure 13.6. A cladogram of vertebrates. Shown in red lines are the shared
characteristics of the groups (e.g. primates, rodents and rabbits all have hair).
Figure 13.6 is an example of a cladogram, which appears like a branching tree. Using the
cladogram, we can say that sharks and ray-finned fishes are related because their common
ancestor had vertebrae. However, ray-finned fishes and amphibians are more closely related
because their common ancestor had both vertebrae and a bony skeleton.
Aside from cladograms, organisms are classified according to a standard developed by the
Swedish botanist Carl von Linné, more popularly known as Carolus Linnaeus. He introduced
the system of using a standard two-word Latin name to every organism, known as the
scientific name. Scientists generally classify organisms into seven categories in increasing
degree of shared characteristics:
Kingdom
Phylum
Class
Order
Family
Genus
Species
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Organisms of the same order have more shared characteristics than organisms of the same
class; organisms within the same family have more shared characteristics than organisms of
the same order, and so on. For example, cats and dogs belong to the same order: Order
Carnivora (mammals who are carnivores). Cats and humans belong to the same class: Class
Mammalia (animals who produce milk), but not to the same order (humans are of the Order
Primata). Therefore, cats are more closely related to dogs than they are to humans.
EVALUATION
Choose the letter of the best answer.
1. Bat wing, whale flipper, human arm and cat forelimb are __________ structures.
A. Analogous
C. Homologous
B. Ancestral
D. Vestigial
2. The wings of an insect and the wings of a bird are __________ structures.
A. Analogous
C. Homologous
B. Ancestral
D. Vestigial
3. The human appendix, whale pelvic bone and snake femur are __________ structures.
A. Analogous
C. Homologous
B. Ancestral
D. Vestigial
4. Who devised the binomial nomenclature system of naming organisms?
A. Alfred Russell Wallace
C. Carolus Linnaeus
B. Aristotle
D. Charles Darwin
5. Which evidence of evolution suggests that chimpanzees and humans are 99% similar?
A. Biochemical evidence
C. Homologous structures
B. Fossil record
D. Vestigial structures
6. What evidence of evolution suggests that horses today came from an ancestral four-toed
ungulate?
A. Biochemical evidence
C. Homologous structures
B. Fossil record
D. Vestigial structures
7. A species is correctly defined as two individuals who __________.
A. Can produce a fertile offspring
C. Live in a given area
B. Eat the same food
D. Look very similar
8. Cat and tiger belong to the same genus. Cat and dog belong to the same order. Which two
animals are more closely related than the other?
A. Cat and dog
C. Dog and tiger
B. Cat and tiger
D. All three are equally related
9. Which characteristic is shared by ray-finned fishes, amphibians, mammals, and birds?
A. Ability to produce milk
C. Bony skeleton
B. Amniotic egg
D. Four limbs
10. Which of the following categories is the most inclusive?
A. Class
C. Genus
B. Family
D. Order
ACTIVITY
Research: Construct a cladogram using these five plants: apple, corn, fern, moss, pine tree.
Make sure to write the shared characteristics in a branch similar to that of Figure 13.6. Do
this on a ½ short bond paper.
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LESSON 14 – INTERACTION AND INTERDEPENDENCE
OBJECTIVES
At the end of the lesson, you should be able to:
1. Describe the different principles of an ecosystem;
2. Explain the interplay of biotic potential and environmental resistance in relation to
population growth;
3. Describe the different types of terrestrial and aquatic biomes.
SUBJECT MATTER
Principles of Ecology
In this lesson we will study lifeforms not as individual units but as they interact with their
environment. Interdependence among organisms occur in every location where life is
possible: in deserts, rainforests, meadows, and even the oceans. The study of interaction of
living organisms among themselves and their nonliving environment is called ecology. We
will review the different principles of ecology, principles governing ecosystems, in this
section.
The Environment
Lifeforms do not survive by themselves. For example, plants provide food and shelter for
animals; animals that eat plants can then provide a source of food for other animals. The
environment is divided into two factors: biotic and abiotic factors. Biotic factors are the living
things in an organism’s environment; abiotic factors are the nonliving ones such as water,
soil, and nutrients.
Levels of Organization
We have previously studied the levels of organization back in the Introduction to Life Science
(Figure 9.6). We will study them here in greater detail by defining the terms which you have
to familiarize:
 Organism – an individual living thing; may be a single cell or a multicellular
individual.
 Population – a group of organisms of the same species which can interbreed and live
in a given area.
 Biotic community – a collection of populations of different species that live in the
same place.
 Ecosystem – a biological community together with its nonliving environment.
 Biome – a collection of ecosystems sharing the same climate and type of community.
Examples of biomes include deserts, rainforests, and tundra.
 Biosphere – the layer of Earth that supports life.
Ecological Interactions
The terms are used to describe the setting of interaction. In this section, we will add terms
that describe the interaction itself.
 Habitat – the place where an organism lives; for example, the habitat of a marine fish
is the open ocean.
 Niche – the roles or position that an organism plays in the environment; a niche is
composed of the organism’s habitat, activities, and resource demands.
The following terms are what we call community interactions; that is, interaction between
two different species. There are five different community interactions. You may refer to
Figure 14.1 to better visualize how each interaction works.
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(A)
(B)
(C)
(D)
(E)
(F)
Figure 14.1. The different types of community interactions. C-F have a special category called symbiosis because
they are long-term relationships.





Predation – where one organism kills and feeds the other. In Figure 14.1a, the
cheetah chases for the deer for mealtime.
Competition – where two organisms compete for a limited resource. A resource may
be food, shelter, or mate. Competition may be intraspecific (same species) or
interspecific (different species). In Figure 14.1b, two antelopes compete against each
other, possibly for mate.
Parasitism – a type of symbiosis where one organism is harmed while the other
benefits. In Figure 14.1c, the mosquito sucks blood from the human to feed itself. The
human may be harmed because blood is drained from him at the same time viral
diseases may be acquired.
Mutualism – a type of symbiosis where both organisms benefit from the interaction.
In Figure 14.1d, the bee benefits from the flower by eating nectar; the flower benefits
by allowing the bee to serve as a pollinator. In Figure 14.1e, the carabao egret finds a
rest station over the carabao; the carabao benefits from the egret because the latter
feeds on the ticks and lice on the carabao’s body.
Commensalism – a type of symbiosis where one organism benefits while the other
is neither benefited nor harmed. In Figure 14.1f, the remora clings to the shark for a
free ride; the shark is not affected by the presence of the remora.
Flow of Matter and Energy
Perhaps the most useful knowledge for introductory ecology is the study of flow of matter
and energy, which are represented by illustrations of cycles and pyramids.
Energy in the ecosystem ultimately comes from sunlight through photosynthesis (in some
cases, inorganic chemicals such as sulfur). Other organisms who cannot make their own food
obtain energy through feeding on other organisms. Let us define some more terms regarding
how organisms obtain their energy:
 Autotrophs – organisms which can make their own food either through
photosynthesis (plants, algae, etc.) or chemosynthesis (sulfur bacteria, etc.)
 Heterotrophs – organisms that feed on other organisms and may be classified into
subgroups:
o Herbivores – those who feed on plants
o Carnivores – those who feed on meat
o Omnivores – those who feed both on plant and meat
o Decomposers – those who feed on decaying matter to break down organic
compounds for reuse of autotrophs
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Energy flow in an ecosystem can therefore be illustrated using a diagram called the food
chain. Using Figure 14.2, a food chain is composed arrows indicating which organism feed
on the other. As an example, the food chain shows that grasshopper feeds on grass; and the
frog feeds on the grasshopper.
Figure 14.2. A typical food chain.
Multiple food chains can be interlinked
in one diagram called food web. A food
web can illustrate whether an organism
feeds on more than one organism. Food
webs are useful in analyzing which
species will be affected if the
population of a certain species runs out.
For example, using Figure 14.3, if the
grasshopper population runs out, rat
population will be dramatically
affected; but the frog population can
still manage to survive because it still
has dragonfly, butterfly, and fruit fly to
eat.
Food chains and food webs show how
organisms obtain their energy.
However, it does not show how much
energy is obtained by that organism. To
illustrate how much an organism
obtains upon feeding on another,
diagrams called energy pyramids are
used.
Figure 14.3. A food web is made of interconnected food
chains.
A typical energy pyramid is shown in
Figure 14.4. It shows the “Rule of Ten”,
which states that as an organism goes
up a trophic level, it can only obtain
10% of the energy of the organism that
it fed on. Energy is not transferred
100% because most of the energy is
used by the consumed organism for its
daily activities and is released in the
form of heat.
We will take on more complex Figure 14.4. An energy pyramid shows how much energy is
ecological processes by analyzing obtained by an organism at each trophic level.
nutrient cycles and understanding how
key substances such as carbon, nitrogen, and water are cycled throughout the ecosystem.
Organisms constantly need a supply of organic carbon, organic nitrogen, and water to sustain
its life activities.
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Nitrogen Cycle
Nitrogen gas (N2) composes 78% of
the atmosphere. Ultimately, all
nitrogen is taken from here and
returned here; for this reason, we have
the nitrogen cycle (Figure 14.5). The
processes are outlined as follows:
1. Nitrogen fixation – nitrogen in the
atmosphere is useless for life.
Fortunately,
nitrogen-fixing
bacteria such as those present in
legumes biochemically convert
atmospheric nitrogen (N2) into
ammonium ions (NH4+).
2. Ammonification – decaying plants
and animals and animal wastes are
decomposed by bacteria and fungi Figure 14.5. The nitrogen cycle showing the interaction and
interdependence of organisms in cycling the nitrogen content
to produce ammonium as well.
of the Earth.
3. Nitrification – nitrifying bacteria
can convert ammonium ions into nitrites (NO2-) or nitrates (NO3-).
4. Assimilation – plants can absorb nitrates for their own use. Herbivores can assimilate
this nitrogen in other forms to build their own body. Proteins and nucleic acids have
nitrogen.
5. Denitrification – if the nitrates and nitrites unused by plants will be converted back to
nitrogen gas (N2) by denitrifying bacteria.
Carbon Cycle
Life as we know it is based on the compounds formed by the element carbon. Carbon is a
constituent of what we call organic compounds, substances essential for life. Thus, organisms
need a source of carbon compounds for survival. The process of carbon exchange among
organisms and the environment is highlighted in a diagram called carbon cycle (Figure 14.6).
The processes are outlined below:
1. Photosynthesis – carbon dioxide
2.
3.
4.
5.
(CO2) from the atmosphere is taken
by plants and other photosynthetic
microorganisms and convert them
into food such as glucose (C6H12O6).
Respiration and assimilation –
animals
and
other
nonphotosynthetic organisms take
oxygen and food. Waste products
include CO2 and other carbon
compounds.
Decomposition
–
decaying
organisms have carbon remains Figure 14.6. The carbon cycle highlighting the carbon stores
that go into the soil to become fossil on the different subsystems of the Earth and how carbon is
fuel, organic matter, or marine cycled across these systems.
deposits.
Fossil fuel emissions – burning of carbon deposits results in the release of carbon
dioxide into the atmosphere.
Diffusion – carbon dioxide from the atmosphere may be dissolved into the oceans,
increasing ocean acidity.
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Water Cycle
Finally, we have water, the molecule essential to all life on Earth. You may have encountered
the water cycle (Figure 14.7), or the hydrologic cycle, during your days in the elementary
school. Today, we will review the cycle together with some added steps for better
understanding.
The ocean contains about
97% of the water of the Earth.
It will serve as the terminal
station of our water cycle,
outlined as follows:
1. Evaporation – surface
ocean
waters,
upon
reaching
a
certain
temperature, will turn
into water vapor and
become suspended in the
atmosphere
Figure 14.7. The water cycle showing the five key steps: evaporation,
2. Condensation - the water condensation, precipitation, runoff, and transpiration.
vapor,
due
to
low
atmospheric temperature, will turn into liquid once again but this time the water droplets
are still suspended on the atmosphere. In simple language, water vapor turns into clouds.
3. Precipitation – when the air cannot hold the water anymore, the droplets will fall back
either to the oceans or the ground in form of rain or snow.
4. Runoff – water that precipitated to the ground will eventually return to the ocean in form
of rivers, streams, or groundwater.
5. Transpiration – water that precipitated to the ground and absorbed by plant roots will
evaporate to the atmosphere. A special term called transpiration is used because its
mechanism is slightly different from that of ordinary evaporation.
Population Growth
In this section, we will tackle the dynamics of a population. These are discussed under the
discipline population ecology. You will understand how a population grows and what factors
limit the growth of a population. First, let us look into factors that add or reduce the
population size.
𝑁𝑒𝑤 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑠𝑖𝑧𝑒 = 𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑠𝑖𝑧𝑒 + (𝑏𝑖𝑟𝑡ℎ + 𝑒𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛) − (𝑑𝑒𝑎𝑡ℎ + 𝑖𝑚𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛)
A population size can increase with birth and emigration (when species come into the area).
It can decrease with death and immigration (when species leave the area). With these data,
you can calculate the population growth rate, which is as follows:
𝑃𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑔𝑟𝑜𝑤𝑡ℎ 𝑟𝑎𝑡𝑒 =
𝑛𝑒𝑤 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑠𝑖𝑧𝑒 − 𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑠𝑖𝑧𝑒
𝑥 100
𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑠𝑖𝑧𝑒
For example, if a previous population of 50 deer increased with 2 deer, then you have a
population growth rate of 4%.
Common sense will tell you that a population cannot grow indefinitely due to limited
resources. Use this as your guiding principle to help you better understand the dynamics of
population growth. First, let us define two simple terms regarding population growth:
 Biotic potential – defined as the maximum capacity of an organism to reproduce
under ideal environmental conditions.
 Environmental resistance – any factor that restricts an organism from realizing its
biotic potential such as food supply, weather and climate, and predators.
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In a simple statement, an organism can realize its biotic potential if there is no environmental
resistance. Population growth typically behaves in two ways: exponential growth and
logistic growth (Figure 14.8).
Figure 14.8. Exponential and logistic growth.
Exponential growth is a J-shaped curve exhibited by a population that increases in size
indefinitely. This type of growth can take place if the environmental conditions are ideal; that
is, the biotic potential is realized. You will notice that the curve has a shallow slope at first
called the lag phase; this is the case because the reproducing organisms are still few at that
time. However, as time goes by, the size will suddenly increase because there will be plenty
of reproducing organisms.
Just like exponential growth, logistic growth experiences a lag phase first, followed by an
exponential growth. However, the carrying capacity of the environment restricts the growth
from increasing indefinitely. Once the carrying capacity is reached, the population stops
growing due to the limited resources the environment can offer. Logistic growth is exhibited
by populations who experience environmental resistance.
Biomes
Let us close ELS by taking you into an adventure. Here, you will see the different biomes that
the Earth offers for you.
Terrestrial Biomes
Terrestrial
biomes
are
mostly designed by the
amount of precipitation and
the average temperature
that
the
environment
experiences throughout a
year. Average temperature is
dictated by the region’s
latitude while the amount of
precipitation is dictated by
the global wind patterns that
the region experiences.
Figure 14.9 displays the
biome distribution across Figure 14.9. Biome distribution across different latitudes.
different latitudes. You may notice that more or less the biomes form a horizontal band
depending on the latitude. We will survey the major biomes of the planet.
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(A)
(B)
(C)
(D)
(E)
(F)
Figure 14.10. A survey of major terrestrial biomes.
Tropical rainforest
Tropical rainforest (Figure 14.10a) is characterized by warm temperature and large amount
of rainfall. Thus, this biome obtains constant water and energy supply. For this reason, this
is the biome with the best diversity among all terrestrial biomes. Here, there are broadleaved trees make up the canopy while mosses, ferns and other shorter plants make up the
understory. The Philippines has a lot of tropical rainforests but they are now in danger of
depletion due to urban development and illegal logging.
Tropical savanna
A tropical savanna (or savannah in British, Figure 14.10b) is characterized by warm
temperature just like the tropical rainforest but receives less rainfall; for this reason,
savanna is characterized by vast grasslands with few trees because the precipitation is not
plenty enough to support tall trees. Tropical savannas are common in Africa, Australia, and
South America, where they commonly lie between deserts and tropical rainforests.
Desert
A desert (Figure 14.10c) experiences hot days and cold nights because of very little
precipitation. Deserts commonly lie at around 30˚ latitude where global wind circulations
produce high pressure areas, preventing the formation of clouds. With this condition,
organisms adapted to very little water such as cacti and camels thrive.
Temperate deciduous forest
The temperate regions, or those regions which experience the four seasons, can also support
trees as long as there is sufficient amount of rainfall. Temperate deciduous forests (Figure
14.10d) are characterized by trees that shed leaves during autumn in preparation for winter
and regenerate leaves during the spring due to warm temperature and plentiful rainfall.
Coniferous forest
While temperate deciduous forests shed their leaves during autumn, there are forests that
lie at higher latitudes with trees that do not shed leaves at all. Thus, they are called evergreen
forests (Figure 14.10e). Evergreen forests are composed of coniferous trees which grow
upwards and have needle-like leaves. Growing upward is necessary to reach maximum
sunlight while needle-like leaves prevent snow from putting weight or covering the leaves;
these two are adaptations for surviving the snowy winter season.
Tundra
Tundra (Figure 14.10f) are located in higher latitudes which experience cold temperature
and rainfall only plenty enough to support small plants. Also, tundra have a layer of
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permanently frozen soil below the surface called the permafrost. Thus, only shallow-rooted
plants can grow here.
Aquatic Biomes
Aquatic biomes are typically divided into two: freshwater and marine biomes. Freshwater
biomes are characterized by freshwater (tubig tabang) such as lakes and rivers while marine
biomes have salty water (tubig alat) such as seas and oceans.
Freshwater
A freshwater habitat such as a
lake is divided into layers
shown in Figure 14.11.
Horizontally, a lake has two
zones: littoral and limnetic
zone. The zone with a
substratum (or “land part”)
and may be filled with plants
is called the littoral zone. The
limnetic zone is open surface
water.
Vertically, the lake has three
Figure 14.11. Layers of a freshwater ecosystem such as a lake.
zones:
 Photic zone – reached by
sunlight; thus, photosynthesis can work here. Many freshwater fishes also thrive in
the photic zone because the planktons are there.
 Profundal zone – cannot be reached with enough sunlight; thus, only a limited
number of species can thrive here.
 Benthic zone – organisms who cling to the sandy substratum live here. They are
collectively called benthic macroinvertebrates or benthos.
Marine
The ocean is an example of a saltwater member of the hydrosphere. It can also be divided
into horizontal and vertical zones (Figure 14.12).
Figure 14.12. Horizontal and vertical zones of the ocean, a marine biome.
There are three horizontal zones:
 Intertidal zone – may be submerged or not depending on whether it is high tide or
low tide. Organisms living here are adapted for changing water level.
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Neritic zone – is a portion of shallow but constant water. Seaweeds and some corals
live here.
Oceanic zone – is the portion of the open ocean.
Vertically, the ocean is divided into four zones:
 Pelagic zone – is constantly exposed to sunlight. Just like the photic zone of the lake,
photosynthetic organisms such as phytoplankton can live here.
 Bathyal zone – is known as the twilight zone, where light penetration is low. Aquatic
organisms adapted to a low light environment can thrive here.
 Abyssal zone – is a dark environment. Organisms that live here generally lack eyes.
This is also the habitat of the popular anglerfish.
 Hadal zone – not shown in the diagram, hydrothermal vents are located here.
Hydrothermal vents are said to be the very first site for evolution of life.
Print References
Biggs, A. et al. (2017). Glencoe Biology: Teacher Edition. United States of America: McGraw-Hill
Education.
Reece, J. et al. (2011). Campbell Biology, 9th ed. China: Pearson Education Inc.
Religioso, T.F. and Vengco, L.G. (2016). You and the Natural World Series: Earth and Life Science. Quezon
City, Philippines: Phoenix Publishing House, Inc.
Russell, P.J., Hertz, P.E., and McMillan, B. (2017). Biology: The Dynamic Science, 4th ed. Canada: Cengage
Learning.
VanPutte, et al. (2016). Seeley’s Essentials of Anatomy & Physiology, 9th ed. Singapore: Mc-Graw Hill
Education.
Online References
van Andel, T.H. and Murphy, J.B. (2018). Plate tectonics. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/plate-tectonics
Belmont, P. (2018). Water cycle. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar593940
Bierman, P. R. (2018). Weathering. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar596280
Butterfield, D. A. (2018). Hydrothermal vent. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar263970
Cherkauer, D. S. (2018). Hydrosphere. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar269400
Cloos, M. (2018). Mantle. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar342950
Cloos, M. (2018). Plate tectonics. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar434175
Cloos, M. (2018). Rock. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar472260
CrashCourse. (2017). “Astrophysics and Cosmology: Crash Course Physics #46”. Retrieved from
https://www.youtube.com/watch?v=VYxYuaDvdM0
CrashCourse. (2015). “Introduction to the Solar System: Crash Course Astronomy #9”. Retrieved from
https://www.youtube.com/watch?v=TKM0P3XlMNA
Page | 91
STEM
EARTH AND LIFE SCIENCE
FEU Senior High School
Dauben, J. W. (2018). Science. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar495860
Dodelson, S. (2018). Big bang. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar702079
Dodelson, S. (2018). Inflation theory. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar749366
Dutch, S. I. (2018). Pangaea. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar751397
The Editors of Encyclopaedia Britannica (2016). Antigen. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/antigen
The Editors of Encyclopaedia Britannica (2007). Biotic potential. In Encyclopaedia Britannica. Retrieved
from https://www.britannica.com/science/biotic-potential
The Editors of Encyclopaedia Britannica (2018). Erosion. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/erosion-geology
The Editors of Encyclopaedia Britannica (2016). Fold. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/fold
The Editors of Encyclopaedia Britannica (2018). Geologic time. In Encyclopaedia Britannica. Retrieved
from https://www.britannica.com/science/geologic-time
The Editors of Encyclopaedia Britannica (2016). Law of Faunal Succession. In Encyclopaedia Britannica.
Retrieved from https://www.britannica.com/science/law-of-faunal-succession
The Editors of Encyclopaedia Britannica. (2018). Nitrogen cycle. In Encyclopaedia Britannica. Retrieved
from https://www.britannica.com/science/nitrogen-cycle
The Editors of Encyclopaedia Britannica (2014). Stratigraphy. In Encyclopaedia Britannica. Retrieved
from https://www.britannica.com/science/stratigraphy-geology
The Editors of Encyclopaedia Britannica. (2018). Water cycle. In Encyclopaedia Britannica. Retrieved
from https://www.britannica.com/science/water-cycle
The Editors of Encyclopaedia Britannica (2016). Weathering. In Encyclopaedia Britannica. Retrieved
from https://www.britannica.com/science/weathering-geology
Erulkar, S.D. and Lentz, T.L. (2018). Nervous system. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/nervous-system
Hames, W. (2018). Mineral. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar363040
Harris, T. (2001). How Volcanoes Work. In HowStuffWorks.com. Retrieved from
https://science.howstuffworks.com/nature/natural-disasters/volcano.htm
King, H. (2018). Pictures of Sedimentary Rocks. In Geology.com. Retrieved from
https://geology.com/rocks/sedimentary-rocks.shtml
Klein, C. (2018). Mineral. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/mineral-chemical-compound
Kurzgesagt – In a Nutshell. (2018). “String Theory Explained – What is The True Nature of Reality?”
Retrieved from https://www.youtube.com/watch?v=Da-2h2B4faU
Laflen, J. M. (2018). Erosion. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar184160
Page | 92
STEM
EARTH AND LIFE SCIENCE
FEU Senior High School
PBS Space Time. (2016). “How Cosmic Inflation Flattened the Universe | Space Time | PBS Digital
Studios”. Retrieved from https://www.youtube.com/watch?v=blSTTFS8Uco
Pielke, R.A. (2017). Atmosphere. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/atmosphere
Reiners, W. A. (2018). Nitrogen cycle. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar392420
Rogers, K. (2014). Abiogenesis. In Encyclopaedia Britannica. Retrieved from
https://www.britannica.com/science/abiogenesis
Rubin, K. H. (2018). Rock cycle. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar754990
Schlosser C. (2018). Carbon cycle. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar754404
Yaffe, M. P. (2018). Mitochondria. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar749188
Zerega, N. (2018). Plant. In World Book Advanced. Retrieved from
http://worldbookonline.com/advanced/article?id=ar433620
Page | 93