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Chapter 2
Principles of Ecology:
Matter, Energy, and Life
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Learning Outcomes
After studying this chapter, you should be able to answer the following
questions:
• What are systems, and how do feedback loops regulate them?
• Chemical bonds hold atoms and molecules together. What would
our world be like if there were no chemical bonds, or if they
were so strong they never broke apart?
• Ecologists say there is no “away” to throw things, and that
everything in the universe tends to slow down and fall apart.
What do they mean?
• All living things—except for some unusual organisms living in
extreme conditions—depend on the sun as their ultimate energy
source. Explain.
• What qualities make water so unique and essential for life as we
know it?
• Why are big, fierce animals rare?
• How and why do elements such as carbon, nitrogen, phosphate,
and sulfur cycle through ecosystems?
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Most institutions demand unqualified
faith; but the institution of science
makes skepticism a virtue.
–Robert King Merton
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2.1 Systems Describe Interactions
• A system is a network of
interdependent components and
processes
• For example, an ecosystem might
consist of countless animals,
plants, and their physical
surroundings.
• Keeping track of all the elements
and their relationships in an
ecosystem would probably be an
impossible task
• To simplify an ecosystem, we use
feeding relationships such as those
between plants, herbivores,
carnivores, and decomposers
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Systems can be described in terms
of their characteristics
• Open systems are those that receive inputs from their surroundings
and produce outputs that leave the system.
– Almost all natural systems are open systems
• A closed system exchanges no energy or matter with its
surroundings.
• Pseudo-closed systems exchange only a little energy but no matter
with their surroundings.
• Throughput is a term we can use to describe the energy and matter
that flow into, through, and out of a system.
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• An increase in the state variable leads to further increases in
the same variable, is called a positive feedback.
• Negative feedback results in a decrease in the causative
variable.
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• When positive feedbacks accelerate out of control,
the system can become unstable and even collapse.
– A term for this process in wetlands is eutrophication
(chapter 10), the excessive growth of plants, in response
to excessive nutrients, which leads to biological collapse
(at least temporarily) of a wetland system.
• In contrast, a negative feedback has a dampening
effect.
– too many fish in a pond leads to food scarcity, which
leads to fish mortality.
2.2 Elements of Life
PRINCIPLES OF MATTER AND ENERGY
• Matter - Has mass and takes up space.
– Three phases
• Solid
• Liquid
• Gas
• Law of Conservation of Matter
– Under normal conditions, matter cannot be created
or destroyed.
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BUILDING BLOCKS OF LIFE
• Atom - Smallest particle that exhibits the
characteristics of an element.
– Protons - Positively charged.
– Electrons - Negatively charged.
– Neutrons - Neutral.
• Ions - Charged atoms.
– Cations - Positive charge.
– Anion - Negative charge.
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Carbon-12 Atom
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BUILDING BLOCKS OF LIFE CONT’D
• Isotope - Atoms of a single element that differ in
atomic mass.
– Radioactive isotopes spontaneously decay or shed
subatomic particles.
• Half Life
• Molecule
– Group of atoms that can exist as an individual unit and that
has unique properties.
• Compound
– A molecule containing different kinds of atoms.
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Chemical Bonding
• Ionic Bond - Formed when an atom loses or
gains one or more electrons.
• Covalent Bond - Formed when two or more
atoms share electrons.
– Energy is needed to break chemical bonds.
– Energy is released when bonds are formed.
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Chemical Reactions
• Reactions start with reactants and produce
products.
– Oxidation - A molecule or atom loses an electron.
– Reduction - A molecule or atom gains an electron.
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pH: Acids, Bases, and Buffers
• Substances that readily give up hydrogen ions
in water are known as acids.
• Substances that readily bond with H ions are
called bases or alkaline substances.
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Acids
• Substances that readily give up hydrogen ions in water are
known as acids. Hydrochloric acid, for example, dissociates in
water to form H+ and Cl- ions.
• acid rain, acid mine drainage, and many other environmental
problems involving acids are caused by an abundance of H+
ions
• In general, acids cause environmental damage because the H+
ions react readily with living tissues (such as your skin or
tissues of fish larvae) and with nonliving substances (such as
the limestone on buildings, which erodes under acid rain).
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Bases
• Substances that readily bond with H+ ions are called
bases or alkaline substances. Sodium hydroxide
(NaOH), for example, releases hydroxide ions (OH-)
that bond with H+ ions in water.
• Buffers are substances that accept or release
hydrogen ions. A solution can be neutralized by
adding buffers
– alkaline rock can buffer acidic precipitation, decreasing its
acidity. Lakes with acidic bedrock, such as granite, are
especially vulnerable to acid rain because they have little
buffering capacity.
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pH
• We describe the strength
of an acid and base by its
pH, the negative
logarithm of its
concentration of H+ ions
(fig. 2.7). Acids have a pH
below 7; bases have a pH
greater than 7. A solution
of exactly pH 7 is
“neutral.” Because the pH
scale is logarithmic, pH 6
represents ten times
more hydrogen ions in
solution than pH 7.
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The four major groups
of organic molecules
•
Figure 2.8 The four major groups
of organic molecules are based on
repeating subunits of these
carbon-based structures.
• Basic structures are shown for
(a) butyric acid (a building
block of lipids) and a
hydrocarbon,
(b) a simple carbohydrate,
(c) a protein,
(d) a nucleic acid.
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Lipids
• Lipids (including fats and oils) store energy for
cells, and they provide the core of cell
membranes and other structures.
• Many hormones are also lipids.
• Lipids do not readily dissolve in water, and
their basic structure is a chain of carbon
atoms with attached hydrogen atoms. This
structure makes them part of the family of
hydrocarbons (fig. 2.8a).
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Carbohydrates
• Carbohydrates (including sugars, starches, and
cellulose) also store energy and provide
structure to cells.
• Like lipids, carbohydrates have a basic
structure of carbon atoms, but hydroxide (OH)
groups replace half the hydrogen atoms in
their basic structure, and they usually consist
of long chains of nucleic acids.
• Glucose (fig. 2.8b) is an example of a very
simple sugar.
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Proteins & Nucleic Acids
• A protein is an organic compound that contains many
amino acids. Each amino acid contains an amino group
(NH2) and a carboxyl group (COOH).
• All enzymes are proteins that act as catalysts for chemical
reactions.
• Nucleic acids are another group of acids that consist of a
phosphate group, a nitrogenous base and a pentose sugar.
Nucleic acids form the building blocks of DNA
(deoxyribonucleic acid) or RNA (ribonucleic acid).
• DNA and in some cases RNA contains the genetic code of
living organisms. RNA of different kinds are involved in the
process of protein synthesis.
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Cells are the
fundamental units
of life
• All living organisms are
composed of cells, minute
compartments within
which the processes of life
are carried out (fig. 2.10).
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Cells
• Most higher organisms (plants, fungi, and animals) are
multicellular, usually with many different cell varieties.
• Your body, for instance, is composed of several trillion cells of
about two hundred distinct types.
• Every cell is surrounded by a thin but dynamic membrane of
lipid and protein that receives information about the exterior
world and regulates the flow of materials between the cell and
its environment. Inside, cells are subdivided into tiny organelles
and subcellular particles that provide the machinery for life.
• Some of these organelles store and release energy. Others
manage and distribute information. Still others create the
internal structure that gives the cell its shape and allows it to
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fulfill its role.
Nutrients
A few different elements are especially important for life:
• Carbon (C) is captured from air by green plants, and oxygen (O) and
hydrogen (H) derive from air or water.
• The most important additional elements are nitrogen (N) and phosphorus
(P), which are essential parts of the complex proteins, lipids, sugars, and
nucleic acids. Some protein also require Sulfur (S).
• Plants must extract these elements from their environment. Low levels of N
and P often limit growth in ecosystems where they are scarce. Abundance
of N and P can cause eutrophication that can destabilize an ecosystem.
• If you fertilize your plants, these two nutrients, along with potassium (K),
are probably the main ingredients in your fertilizer. These elements often
occur in the form of nitrate (NO3), ammonium (NH4), and phosphate (PO4).
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2.3 Energy
• Energy is the ability to do work such as moving
matter over a distance or causing a heat transfer
between two objects at different temperatures.
• Energy can take many different forms. Heat, light,
electricity, and chemical energy are examples that
we all experience.
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Kinetic Energy
• The energy contained in moving objects is
called kinetic energy.
• Examples of kinetic energy
– A rock rolling down a hill,
– the wind blowing through the trees,
– water flowing over a dam (fig. 2.11),
– electrons speeding around the nucleus of
an atom are all.
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Potential Energy
• Potential energy is stored energy that is latent but available for use.
– Chemical energy stored in the food that you eat and the gasoline that you put into your
car are also examples of potential energy that can be released to do useful work.
– Energy is often measured in units of heat (calories) or work (joules). One joule (J) is the
work done when one kilogram is accelerated at one meter per second. One calorie is the
amount of energy needed to heat one gram of pure water one degree Celsius. A calorie
can also be measured as 4.184 J.
• A rock poised at the top of a hill and water stored behind a dam are
examples of potential energy.
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Energy continued…
• Heat describes the energy that can be transferred between objects of
different temperature.
• The first law of thermodynamics states that energy is conserved.
• The second law of thermodynamics states that, with each successive
energy transfer or transformation in a system, less energy is available to do
work.
• The second law recognizes that disorder, or entropy, tends to increase in all
natural systems. Consequently, there is always less useful energy available
when you finish a process than there was before you started.
• Organisms are highly organized, both structurally and metabolically.
Constant care and maintenance is required to keep up this organization, and
a continual supply of energy is required to maintain these processes. Every
time some energy is used by a cell to do work, some of that energy is
dissipated or lost as heat.
• If cellular energy supplies are interrupted or depleted, the result—sooner or
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later—is death.
2.4 Energy for Life:
Green plants get energy from the sun
• Green plants are often called primary producers
because they create carbohydrates and other
compounds using just sunlight, air, and water.
• Nearly all organisms on the earth’s surface depend on
solar radiation for life-sustaining energy, which is
captured by green plants, algae, and some bacteria in a
process called photosynthesis.
• Photosynthesis converts radiant energy into useful,
high-quality chemical energy in the bonds that hold
together organic molecules.
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The electromagnetic spectrum
• Of the energy that reaches the earth’s surface,
photosynthesis uses only certain wavelengths, mainly red
and blue light
• Half of the energy plants absorb is used in evaporating
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water
How does photosynthesis capture energy?
• In chloroplasts,
chlorophyll is
involved with two
interconnected
cycles of chemical
reactions, the lightdependent & the
light-independent
reactions.
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Photosynthesis
• Photosynthesis begins with light dependent reactions:
– Enzymes split water molecules and release molecular
oxygen (O2).
– Adenosine triphosphate (ATP) and nicotinamide adenine
dinucleotide phosphate (NADPH) are also created
• In light-independent reactions enzymes extract energy
from ATP and NADPH to add carbon atoms (from carbon
dioxide) to simple sugar molecules, such as glucose.
– These molecules provide the building blocks for larger,
more complex organic molecules.
Respiration & Photosynthesis
• Animals (like us) eat
plants—or other animals
that have eaten plants—
and break down the
organic molecules in our
food through cellular
respiration to obtain
energy (fig. 2.15).
Photosynthesis
6H2O + 6CO2 + sun  C6H12O6 (sugar) + 6O2
Cellular Respiration
C6H12O6+6O2  6H2O + 6CO2 + energy
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2.5 From Species to Ecosystems
• Species - All organisms genetically similar enough to breed
and produce live, fertile offspring in nature (e.g., Human
being).
• Population - All members of a species that live in the same area
at the same time (e.g., Al-Ain human population).
• Biological Community - All populations living and interacting
in an area (e.g., Al-Ain human population + all other animal and
plant populations).
• Ecosystem - A biological community and its physical
environment.
– Its environment includes
• Abiotic factors (nonliving components), such as climate, water, minerals,
and sunlight,
• Biotic factors, such as organisms
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Food Webs and Trophic Levels
• Productivity refers to the amount of biomass
produced in a given area during a given time.
– Primary Producers - Photosynthesize.
– Consumers - Eat other organisms.
• Food Webs are series of interconnected food
chains in an ecosystem.
– Trophic Level refers to an individual’s feeding
position in an ecosystem.
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Food chains, food webs, and
trophic levels link species
• Photosynthesis (and rarely chemosynthesis) is the base of
all ecosystems. Organisms that photosynthesize, mainly
green plants and algae, are therefore known as producers.
• In ecosystems, some consumers feed on a single species,
but most consumers have multiple food sources. Similarly,
some species are prey to a single kind of predator, but
many species in an ecosystem are beset by several types of
predators and parasites. In this way, individual food chains
become interconnected to form a food web.
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Food chains, food webs, and
trophic levels link species
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Trophic Levels
•Organisms can also be identified by
the kinds of food they consume:
–Herbivores - Eat plants.
–Carnivores - Eat flesh.
–Omnivores - Eat plants and animals
(e.g., humans).
–Detritivores - Eat detritus (e.g, ants)
–Scavengers- clean up dead
carcasses of larger animals (e.g.,
crows, jackals)
–Decomposers - Breakdown complex
organic matter into simpler
compounds
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Ecological pyramids describe trophic levels
• Most ecosystems have huge number of primary producers
supporting a smaller number of herbivores, supporting a
smaller number of secondary consumers.
• Second law of thermodynamics.
• Ecosystems not 100% efficient.
• 10% Rule
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Energy flow in food webs
• Why is there so much less energy in each successive level in figure
2.18?
– some of the food that organisms eat is undigested and doesn’t provide usable
energy
– energy is not destroyed, but it is converted and degraded as it moves through
an ecosystem. Much of the energy that is absorbed is converted to heat or
kinetic energy in the daily processes of living, and thus isn’t stored as biomass
that can be eaten.
• predators don’t operate at 100% efficiency. A general rule of thumb is
that only about 10% of the energy in one consumer level is
represented in the next higher level.
• The amount of energy available is often expressed in biomass. For
example, it generally takes about 100 kg of clover to make 10 kg of
rabbit and 10 kg of rabbit to make 1 kg of fox.
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A numbers pyramid
• The total number of
organisms and the
total amount of
biomass in each
successive trophic
level of an ecosystem
also may form
pyramids (figs. 2.19,
2.20) similar to those
describing energy
content.
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2.6 Biogeochemical Cycles and
Life Processes
• The elements and compounds that sustain us are
cycled endlessly through living things and through
the environment.
• Substances can move quickly or slowly: you might
store carbon for hours or days, while carbon is
stored in the earth for millions of years.
• When human activity alters flow rates or storage
times in these natural cycles, overwhelming the
environment’s ability to process them, these
materials can become pollutants.
• On a global scale, this movement is referred to as
biogeochemical cycling.
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Biogeochemical Cycles and
Life Processes
• Substances can move quickly or slowly: you
might store carbon for hours or days, while
carbon is stored in the earth for millions of
years.
• These materials can become pollutants. --When?
– If human activity alters flow rates or storage times
in these natural cycles (e.g., sulfur, nitrogen, carbon
dioxide, and phosphorus.
The hydrologic cycle
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The hydrologic cycle
• Most of the earth’s water is stored in the oceans, but
solar energy continually evaporates this water, and
winds distribute water vapor around the globe.
• Water that condenses over land surfaces, in the form
of rain, snow, or fog, supports all terrestrial (landbased) ecosystems.
• Living organisms emit the moisture they have
consumed through respiration and perspiration.
• Eventually this moisture reenters the atmosphere or
enters lakes and streams, from which it ultimately
returns to the ocean again.
The carbon cycle
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The carbon cycle
• Carbon serves a dual purpose for organisms: (1) it
is a structural component of organic molecules,
and (2) chemical bonds in carbon compounds
provide metabolic energy.
• The carbon cycle begins with photosynthetic
organisms taking up carbon dioxide (CO2).
– This is called carbon-fixation because carbon is changed
from gaseous CO2 to less mobile organic molecules.
• Once a carbon atom is incorporated into organic
compounds, its path to recycling may be very quick
or extremely slow. Explain this.
The nitrogen cycle
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The nitrogen cycle
• Nitrogen provides organisms with amino acids, peptides, and
proteins.
• (Nitrogen is a primary component of many household and
agricultural fertilizers.)
• Nitrogen makes up about 78% of the air, but plants cannot use
N2, the stable diatomic molecule in air.
• The key to N cycle is nitrogen-fixing bacteria (including some
blue-green algae or cyanobacteria).
– These organisms combine gaseous N2 with hydrogen to make
ammonia (NH3).
– Other bacteria then combine ammonia with oxygen to form nitrites
(NO2 –).
– Another group of bacteria converts nitrites to nitrates (NO3 –), which
green plants can absorb and use.
The nitrogen cycle
– After plant cells absorb nitrates, the nitrates are reduced
to ammonium (NH4), which cells use to build amino
acids that become the building blocks for peptides and
proteins.
– Why members of the bean family (legumes) are
especially useful in agriculture?
– How N reenters the soil environment?
– Through the decomposition of dead organisms (by fungi and
bacteria) ammonia is released and ammonium ions are then
available for nitrate formation.
– How does N reenter the atmosphere, completing the
cycle?
– Denitrifying bacteria break down nitrates into N2 and nitrous
oxide (N2O), gases that return to the atmosphere.
The phosphorus cycle
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The phosphorus cycle
• At the cellular level, energy-rich phosphorus-containing compounds
are primary participants in energy-transfer reactions
• How phosphorus is a major contributor to water pollution?
– Abundant phosphorus stimulates lush plant and algal growth in water bodies
(eutrophication)
• The phosphorus cycle begins when phosphorus compounds leach
from rocks and minerals over long periods of time.
• Why phosphorous is usually transported in water? … It has no
atmospheric form.
• Producer organisms take in inorganic phosphorus, incorporate it
into organic molecules, and then pass it on to consumers.
• Phosphorus returns to the environment by decomposition.
Practice Quiz
1. What two problems did Arcata, California, solve with its constructed
wetland?
2. What are systems and how do feedback loops regulate them?
3. Your body contains vast numbers of carbon atoms. How is it possible that
some of these carbons may have been part of the body of a prehistoric
creature?
4. List six unique properties of water. Describe, briefly, how each of these
properties makes water essential to life as we know it.
5. What is DNA, and why is it important?
6. The oceans store a vast amount of heat, but this huge reservoir of energy is
of little use to humans. Explain the difference between high-quality and lowquality energy.
7. In the biosphere, matter follows circular pathways, while energy flows in a
linear fashion. Explain.
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Practice Quiz continued…
8. Which wavelengths do our eyes respond to, and why? (Refer to fig. 2.13.)
What is the ratio of short ultraviolet wavelengths to microwave lengths?
9. Where do extremophiles live? How do they get the energy they need for
survival?
10. Ecosystems require energy to function. From where does this energy
come? Where does it go?
11. How do green plants capture energy, and what do they do with it?
12. Define the terms species, population, and biological community.
13. Why are big fierce animals rare?
14. Most ecosystems can be visualized as a pyramid with many
organisms in the lowest trophic levels and only a few individuals at the top.
Give an example of an inverted numbers pyramid.
15. What is the ratio of human-caused carbon releases into the atmosphere
shown in figure 2.22
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