Download Chapter 3 Ecosystems and Energy

Chapter 3
Ecosystems and Energy
Lecture Outline:
I. What is Ecology?
A. Ernst Haeckel developed the concept of ecology in the 19th century
i. Ecology literally means “the study of one’s house”; it is the broadest field
within the biological sciences, and is linked to many other disciplines (i.e.,
geology, earth science, chemistry, and physics)
ii. It examines the systems that include interactions among organisms and
between organisms and their abiotic environment
1. The biotic environment includes all living organisms
2. The abiotic environment includes living space, temperature, sunlight,
soil, wind and precipitation
B. Ecologists are most interested in the levels of biological organization that include or
are above the level of the individual organism
i. A group of similar organisms whose members freely interbreed with one
another in the wild to produce fertile offspring is termed a species
ii. A population is a group of organisms of the same species that live in the same
area at the same time
iii. A natural association that consists of all the populations of different species
that live and interact within an area at the same time is called a community
iv. A community and its physical environment comprise an ecosystem
1. An ecosystem is a system in which all of the biological, physical, and
chemical components of an area form a complex, interacting network
of energy flow and materials cycling
2. Ecosystem processes collectively regulate global cycles of water,
carbon, nitrogen, phosphorus, and sulfur essential to the survival of
humans and all other organisms
C. Landscape ecology is a subdiscipline of ecology
i. It studies ecological processes that operate over large areas
ii. A landscape is a region that includes several interacting ecosystems
D. Ecologists who study the biosphere examine global interrelationships among Earth’s
atmosphere, land, water, and organisms
i. The parts of Earth’s atmosphere, ocean, land surface, and soil that contain all
living organisms is termed the biosphere
ii. The atmosphere is a gaseous envelope surrounding Earth
iii. The hydrosphere is Earth’s supply of water
iv. The lithosphere is the soil and rock of Earth’s crust
II. The Energy of Life
A. Energy is the capacity or ability to do work
i. Energy exists in several forms: chemical radiant, thermal, mechanical,
nuclear, and electrical
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ii. Energy can exist as stored energy (potential) or as the energy of motion
(kinetic)
B. The study of energy and its transformations is called thermodynamics
i. In thermodynamics, the word system is used to refer to a group of atoms,
molecules, or objects being studied
1. A closed system is self-contained and isolated; it does not exchange
energy with its surroundings
2. An open system exhibits an exchange of energy with its surroundings
ii. The first law of thermodynamics holds that energy cannot be created or
destroyed, although it can change from one form to another
iii. The second law of thermodynamics holds that when energy is converted from
one form to another, some of it is degraded into heat, a less usable form that
disperses into the environment
1. The less usable energy is more diffuse, or disorganized; entropy is a
measure of this disorder or randomness
2. No process requiring an energy conversion is ever 100% efficient
because much of the energy is dispersed as heat, resulting in an
increase in entropy
C. Photosynthesis and cellular respiration
i. Photosynthesis is the biological process in which light energy from the sun is
captured and transformed into the chemical energy of carbohydrate (glucose)
molecules
1. 6CO2 + 12H2O + radiant energy --> C6H12O6 + 6H2O +6O2
2. Plants, some bacteria, and algae perform photosynthesis
ii. The chemical energy that plants store in carbohydrates and other molecules is
released within cells of plants, animals, or other organisms through cellular
respiration
1. In aerobic cellular respiration, molecules such as glucose are broken
down in the presence of oxygen and water
a. C6H12O6 +6O2 + 6H2O --> 6CO2 + 12H2O + energy
2. Anaerobic bacteria that live in waterlogged soil, stagnant ponds, or
animal intestines respire in the absence of oxygen
D. Chemosynthesis is the process by which energy produced from inorganic raw
materials such as enzymes, hydrogen sulfide and oxygen; water and sulfur/sulfate are
additional byproducts
III. The Flow of Energy Through Ecosystems
A. Energy flow is the passage of energy in a one-way direction through an ecosystem
B. Producers, consumers, and decomposers
i. Producers (aka autotrophs)
1. In photosynthesis, producers use the energy from sunlight to make
organic molecules from carbon dioxide and water
2. Plants, algae and certain types of bacteria are important producers
ii. Consumers (aka heterotrophs)
1. Consumers obtain energy when they eat producers or other consumers
a. Consumers that eat producers are primary consumers
(herbivores)
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b. Secondary consumers (carnivore) eat primary consumers
c. Tertiary consumers (top carnivores) eat secondary consumers
2. Omnivores eat a variety of organisms
3. Detritus feeders (detritivores) consume organic matter that includes
animal carcasses, leaf litter, and feces
iii. Decomposers (aka saprotrophs)
1. Wastes and dead organic material from producers and consumers
supply decomposers (i.e., bacteria, fungi) with energy
2. Bacteria and fungi are important decomposers
C. The path of energy flow: who eats whom in ecosystems
i. In an ecosystem, energy flow occurs in food chains, in which energy from
food passes from one organism to the next in a sequence
1. Energy enters ecosystems from an external source (the sun), flows
linearly, and exits as heat loss
2. Each level in a food chain is termed a trophic level
a. Producers (photosynthetic organisms) form the first trophic
level
b. Primary consumers (herbivores) form the second trophic level
c. Secondary consumers (carnivores) form the third trophic level
d. Decomposers occur at every step in a food chain
ii. Simple food chains rarely occur in nature, a food web is a more realistic model
D. Ecological pyramids
i. Ecological pyramids graphically represent the relative energy values of each
trophic level
1. A pyramid of numbers show the number of organisms at each trophic
level in a given ecosystem
2. A pyramid of biomass illustrates the total biomass at each successive
trophic level
a. Biomass is a quantitative estimate of the total mass of living
material
b. Biomass indicates the amount of fixed energy at a particular
time
3. A pyramid of energy illustrates the energy content, often expressed as
kilocalories per square meter per year, of the biomass at each trophic
level
E. Ecosystem productivity
i. The gross primary productivity (GPP) of an ecosystem is the rate at which
energy is captured during photosynthesis
ii. Net primary productivity (NPP) is the energy in plant tissues after cellular
respiration has occurred
1. Only the energy represented by NPP is available as food for an
ecosystem’s consumers
2. Ecosystems differ strikingly in their productivities (NPP)
iii. Human impact on NPP
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1. Humans consume far more of Earth’s resources than any other of the
millions of animal species (approximately 32% of the annual NPP of
land-based ecosystems)
2. Humans only represent 0.5% of the total biomass of all consumers on
Earth
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Answers to Thinking About the Environment
End of Chapter Questions:
1. Draw a food web containing organisms found in a Chesapeake Bay salt marsh.
Ans: Answers will vary
2. Distinguish among Earth's four realms: atmosphere, hydrosphere, lithosphere, and biosphere.
Ans: The atmosphere is the gaseous envelope surrounding Earth; the hydrosphere is Earth's
supply of water—liquid and frozen, fresh and salty; and the lithosphere is the soil and rock of
Earth's crust. The organisms of the biosphere—Earth's communities, ecosystems, and
landscapes—depend on one another and on the other realms of Earth's physical environment: the
atmosphere, hydrosphere, and lithosphere.
3. Which scientist—a population ecologist or a landscape ecologist—would be most likely to
study broad-scale environmental issues and land management problems? Explain your answer.
Ans: Landscape ecology is a subdiscipline of ecology that studies ecological processes that
operate over large areas. Landscape ecologists examine the connections among ecosystems
found in a particular region. Landscapes, are based on larger land areas that include several
ecosystems. Population ecologists work on a smaller scale A population ecologist might study a
population of polar bears or a population of marsh grass.
4. What are two examples of resources that ecosystems require from the abiotic environment?
Ans: Resources that ecosystems require from the abiotic environment include any of the
following: living space, temperature, sunlight, soil, wind, and precipitation.
5. Give two examples of potential energy, and in each case tell how it is converted to kinetic
energy.
Ans: Energy can exist as stored energy—called potential energy—or as kinetic energy, the
energy of motion. Think of potential energy as an arrow on a drawn bow, which equals the work
the archer did when drawing the bow to its position. When the string is released, the bow's
potential energy is converted to the arrow's kinetic energy of motion. Similarly, the cordgrass
that a meadow vole eats has chemical potential energy in the bonds of its molecules; as
molecular bonds are broken, this energy is converted to kinetic energy and heat as the meadow
vole swims in the salt marsh. Thus, energy changes from one form to another.
6. How are the following forms of energy significant to organisms in ecosystems: (a) radiant
energy, (b) mechanical energy, (c) chemical energy, (d) thermal energy?
Ans: Radiant energy is energy, such as radio waves, visible light, and X rays, which is
transmitted as electromagnetic waves. Radiant energy is significant for providing energy for
photosynthesis and visible light for sight. Mechanical energy is energy in the movement of
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matter, necessary for animals capturing food. Chemical energy is energy stored in the bonds of
molecules; for example, food contains chemical energy. Thermal energy is heat energy that
flows from an object with a higher temperature (the heat source) to an object with a lower
temperature (the heat sink). Within ecosystems and organisms the different forms of energy are
necessary for biological work such as growing, moving, reproducing, and maintaining and
repairing damaged tissues.
7. State the first and second laws of thermodynamics.
Ans: According to the first law of thermodynamics, energy cannot be created or destroyed,
although it can change from one form to another. According to the second law of
thermodynamics, when energy is converted from one form to another, some of it is degraded into
heat, a less usable form that disperses into the environment.
8. How is the first law of thermodynamics related to the movement of an automobile?
Ans: The gasoline that you put in your automobile has potential energy stored as chemical
energy in its molecular bonds. As gasoline is burned it releases energy, part of this energy is
captured and transformed into mechanical energy to move the car forward. The remainder of the
energy is lost as heat energy. The first law of thermodynamics explains how chemical energy
converts to mechanical energy.
9. Give an example of a natural process in which order becomes increasingly disordered.
Ans: As a result of the second law of thermodynamics, no process requiring an energy
conversion is ever 100% efficient because much of the energy is dispersed as heat, resulting in
an increase in entropy. An automobile engine, which converts the chemical energy of gasoline to
mechanical energy, is between 20 and 30% efficient. That is, only 20 to 30% of the original
energy stored in the chemical bonds of the gasoline molecules is actually transformed into
mechanical energy, or work. In our cells, energy use for metabolism is about 40% efficient, with
the remaining energy given to the surroundings as heat.
10. Why do deep-sea organisms cluster around hydrothermal vents? What is their energy source?
Ans: Deep-sea hydrothermal vents provide super heated water (exceeding 200°C, or 392°F)
which supports bacteria as primary producers. These bacteria obtain energy and make
carbohydrate molecules from inorganic raw materials by chemosynthesis. Chemosynthetic
bacteria possess enzymes that cause the inorganic molecule hydrogen sulfide to react with
oxygen, producing water and sulfur or sulfate. Such chemical reactions provide the energy to
support these bacteria and other organisms in deep-ocean hydrothermal vents.
11. Give an example of a herbivore, a carnivore, and an omnivore.
Ans: Rabbits and deer are examples of herbivores. Lions, lizards, and spiders are examples of
carnivores. Bears, pigs, and humans are examples of omnivores.
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12. Why is the concept of a food web generally preferred over a food chain?
Ans: Simple food chains rarely occur in nature because few organisms eat just one kind of
organism. More typically, the flow of energy and materials through an ecosystem takes place in
accordance with a range of food choices for each organism involved. In an ecosystem of average
complexity, numerous alternative pathways are possible. A hawk eating a rabbit is a different
energy pathway than a hawk eating a snake. A food web is a more realistic model of the flow of
energy and materials through an ecosystem.
13. Could you construct a balanced ecosystem that contained only producers and consumers?
Only consumers and decomposers? Only producers and decomposers? Explain the reasons for
your answers.
Ans: Ecosystems must contain a balanced representation of producers, consumers, and
decomposers, all of which have indispensable roles in ecosystems. Producers provide both food
and oxygen for the rest of the community. Consumers play an important role by maintaining a
balance between producers and decomposers. Detritus feeders and decomposers are necessary
for the long-term survival of any ecosystem because, without them, dead organisms and waste
products would accumulate indefinitely.
14. How have humans affected the Antarctic food web?
Ans: Humans have had an impact on the Antarctic food web, as they have on most other
ecosystems. Past whaling reduced the number of large baleen whales in Antarctic waters, as a
result of fewer whales eating krill, more krill became available for other krill-eating animals,
whose populations increased. The second major impact is the thinning of the ozone layer in the
stratospheric region of the atmosphere. Scientists are concerned that ozone thinning over
Antarctica may damage the algae that form the base of the food web in the Southern Ocean. The
third human-induced change that may be responsible for declines in certain Antarctic populations
is global warming. As the water has warmed in recent decades around Antarctica, less pack ice
has formed during winter months. Years with below-average pack ice cover means less algae,
which mean less krill spawning. Scientists are concerned that global warming may continue to
decrease the amount of pack ice, which will reverberate through the food web. Lastly,
commercial fisherman have directly harvested krill to make fishmeal for aquatic industries.
15. Suggest a food chain with an inverted pyramid of numbers—that is, greater numbers of
organisms at higher than at lower trophic levels.
Ans: Inverted pyramids of numbers, in which higher trophic levels have more organisms than
lower trophic levels, are often observed among decomposers, parasites, tree-dwelling
herbivorous insects, and similar organisms.
16. Is it possible to have an inverted pyramid of energy? Why or why not?
Ans: It is not possible to have an inverted pyramid of energy. Energy pyramids show that most
energy dissipates into the environment when going from one trophic level to the next. Less
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energy reaches each successive trophic level from the level beneath it because organisms at the
lower level use some energy to perform work, and some is lost.
17. Relate the pyramid of energy to the second law of thermodynamics.
Ans: According to the second law of thermodynamics, when energy is converted from one form
to another, some of it is degraded into heat. No biological process is ever 100% efficient so as
energy is transferred from one trophic level to the next there is less energy available to the higher
trophic level. Energy pyramids show that most energy dissipates into the environment when
going from one trophic level to the next.
18. Is this an example of an open system or a closed system? Explain your answer.
Ans: This is an example of an open system because an open system exhibits an exchange of
energy with its surroundings.
19. Is a rabbit an example of a closed system or an open system? Why?
Ans: A rabbit is an open system. An open system exhibits an exchange of energy with its
surroundings. The rabbit takes in food and water from its surroundings, and releases sewage and
solid waste back out to its surroundings.
20. Explain why a living system is more ordered than the abiotic environment.
Ans: Entropy is a measure of disorder or randomness; organized, usable energy has low entropy,
whereas disorganized energy such as heat has high entropy. A living system contains more
useable energy, such as chemical energy, so it has greater order than the abiotic environment
which contains more heat energy.
Answers to Review Questions
What is ecology? (p. 50)
1. What is ecology?
Ans: Ecology is the study of the interactions among organisms and between organisms and their
abiotic environment.
2. What is the difference between community and an ecosystem? Between an ecosystem and a
landscape?
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Ans: A community is a natural association that consists of all the populations of different species
that live and interact within an area at the same time. An ecosystem is a community and its
physical environment. A landscape is a region that includes several interacting ecosystems.
The Energy of Life (p. 53)
1. Is water stored behind a dam an example of potential or kinetic energy? What would cause the
water to convert to the other form of energy?
Ans: Water behind a dam is potential energy because it is stored energy. As water is release from
the dam via a spillway or break in the dam it is converted to kinetic energy-energy in motion.
2. When coal is burned in a power plant, only 3% of the energy in the coal is converted into light
in a light bulb. What happens to the other 97% of the energy? Explain your answer using the
laws of thermodynamics.
Ans: The majority of energy is released as heat. The first law of thermodynamics states that
energy cannot be created or destroyed. The burning of coal simply converts the potential energy
in coal to eclectic and heat energy. The second law of thermodynamics states that when energy is
converted from one form to another, some of it is degraded into heat. This explains why no
process requiring energy is 100% efficient.
3. Distinguish between photosynthesis and cellular respiration. Which organisms perform each
process?
Ans: Plants, algae, and some bacteria capture radiant energy during photosynthesis and
incorporate some of it into carbohydrate molecules. All organisms obtain the energy in
carbohydrates and other molecules by cellular respiration, in which molecules such as glucose
are broken down with release of energy.
The Flow of Energy Through Ecosystems (p. 62)
1. What are producers, consumers, and decomposers?
Ans: Producers are organisms that manufacture organic molecules from simple inorganic
substances using the energy of sunlight. In other words they perform photosynthesis and become
potential food for other organisms. Consumers, which feed on other organisms, are almost
exclusively animals. Decomposers feed on the components of dead organisms and organic waste
to provide themselves with energy and return simple inorganic molecules to the ecosystem.
2. How does energy flow through a food web consisting of producers, consumers, and
decomposers?
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Ans: Energy flow through an ecosystem is linear, from the sun to producer to consumer to
decomposer. Much of this energy is converted to less usable heat as the energy moves from one
organism to another, as stipulated in the second law of thermodynamics. Producers are the
photosynthetic organisms that are potential food resources for other organisms. Consumers,
which feed on other organisms, are almost exclusively animals. Primary consumers feed on
plants; secondary consumers feed on primary consumers; detritus feeders feed on detritus, dead
organic material. Microbial decomposers feed on the components of dead organisms and organic
wastes, degrading them into simple inorganic materials that producers can then use to
manufacture more organic material.
3. What is a pyramid of energy?
Ans: A pyramid of energy illustrates the energy content of the biomass of each trophic level.
4. What is gross primary production? net primary production?
Ans: Gross primary productivity (GPP) is the total amount of photosynthetic energy that plants
capture and assimilate in a given period. Net primary productivity (NPP) is productivity after
respiration losses are subtracted.
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