AP Environmental Science Gleason Notes 5
Ecosystems: Components, Energy Flow, and Matter Cycling
1. What tasks do insects perform for the ecosystems in which they live?
Insects are vital members of ecosystems. It is estimated that insects makeup 10% of the biomass
on the planet. Some of the tasks insects perform are:
1. Decomposition of dead and decaying plant and animal matter to return vital nutrients
to the soil.
2. Pollination of plants to assist in reproduction
3. Serving as a food source for predators
Each of these tasks are so vital to ecosystems, that without insects, the ecosystems would be
2. If all of Earth’s ecosystems disappeared today, how would the planet be affected?
If all of Earth’s ecosystems disappeared today, most of Earth’s animals would become extinct
because of the disappearance of so much plant life. Additionally, the earth would be covered
with rotting vegetation and animal carcasses being decomposed by unimaginably huge hordes of
bacteria and fungi.
3. What is ecology?
Ecology is the study of how organisms interact with one another and with their non-living
environment. Simply put, ecology is the study of the connections in nature and will be our focus
of this chapter. Ecologists focus on trying to understand the interactions between organisms,
populations, communities, ecosystems and the biosphere.
4. The following levels of biological organization fall under the realm of ecology. Please
define the following terms:
1. Organism: An organism is any form of life. All organisms are made up of cells which
are the basic unit of life.
2. Species: Species are groups of organisms that resemble one another in appearance,
behavior, chemistry, and genetic makeup. According to the biological definition, two
organisms are of the same species if they can interbreed and have viable fertile offspring.
Reproduction can be either sexual or asexual. A reasonable estimate of the number of
species that exist on earth is between 10 and 14 million.
3. Population: A population is a group of interacting individuals of the same species that
occupy a specific area at the same time. Examples of a population include all sunfish in a
pond, all white oak trees in a forest and all people in a country.
4. Community: A community of organisms consists of populations of different species
occupying the same area. Communities are a complex interacting network of plants,
animals and microorganisms.
5. Ecosystem: An ecosystem is a community of different species interacting with one
another and with their nonliving environment of matter and energy. Ecosystem can range
in size from a puddle of water to a stream, a patch of woods, an entire forest, or a desert.
Ecosystems can be natural or artificial (human-made). Examples of human-created
ecosystems include crop fields, farm ponds, and reservoirs.
6. Biosphere: The sum total of all of Earth’s ecosystems makes up the biosphere.
5. Populations of organisms are often described by ecologists in five main ways. What are
the five main ways that ecologists describe populations?
Populations are often described in terms of their:
B. Age Distribution: The number of individuals of each given age group
C. Density: The number of individuals in a given amount of space
D. Genetic Composition: The prevalence of key genes in the population’s gene pool
E. Habitat: The place where the population (or individual organism) lives
6. The Earth itself is made up of several spherical layers. What are the layers of the Earth?
1. Atmosphere: The thin envelope of air that exists around the planet. There are two layers
of the lower atmosphere:
a. Troposphere: Extends from sea level to approximately 17 kilometers (11 miles)
above sea level. It contains most of the planet’s air (most Nitrogen -78% and
b. Stratosphere: The stratosphere extends from 17-48 kilometers (11-30 miles)
above the Earth’s surface. The lower portion of the stratosphere consists of the
ozone layer which filters out most of the sun’s harmful ultraviolet radiation, thus
allowing life to exist on land and in surface layers of bodies of water.
2. Hydrosphere: Consists of Earth’s
a. Liquid water (Both surface and underground)
b. Ice (Polar ice, icebergs and ice in frozen soil layers (permafrost))
c. Water vapor in the atmosphere
3. Lithosphere: The lithosphere consists of the solid part of the Earth. The Earth’s crust
and upper mantle makeup the lithosphere. (The more liquid “plastic” lower mantle makes
up the asthenosphere. It is the asthenosphere that is responsible for plate tectonics.
4. Biosphere: The portion of the earth in which living (biotic) organisms exist and interact
with one another in their nonliving (abiotic) environment. The biosphere includes most of
the hydrosphere, and parts of the lower atmosphere and upper lithosphere reaching from
the deepest ocean floor below sea level to the tops of the highest mountains. If the earth
were an apple, the biosphere would be no thicker than the apple’s skin.
7. What is the goal of ecology?
The goal of ecology is to understand the interactions in the thin, life-supporting global “skin” of
air, water, soil, and organisms.
8. All life on Earth depends on three interconnected factors. What are the three
interconnected factors that are critical to sustaining life on earth?
1. One-way Flow of Solar Energy: Solar energy is of high quality (low entropy) and then
enters the biosphere and moves into materials and living things in their feeding
interactions. Energy then leaves these materials and organisms as low quality (high
entropy) energy. Energy than returns to space as heat.
2. The Cycling of Matter: (The atoms, ions, or molecules needed for survival by living
organisms) through parts of the biosphere. The Earth is closed to significant inputs of
matter from space. Thus, essentially all nutrients used by organisms are already present
on earth and must be recycled again and again for life to continue.
3. Gravity: Which allows the planet to hold onto its atmosphere and causes the downward
movement of chemicals in the matter cycles.
9. The sun is a middle-aged star whose energy is important in sustaining life on Earth. How
does the sun sustain life on Earth?
The sun sustains life on Earth by:
Lighting and warming the planet
Powering the cycling of matter
Driving the climate and weather systems that distribute heat and fresh water over the
10. Please list three important facts about the sun:
The sun is made up of 72% hydrogen and 28% helium gases. Temperatures and pressures
in the inner core of the sun are so high that the hydrogen nuclei fuse to form helium
nuclei releasing enormous amounts of energy. The sun is really a gigantic nuclear reactor
that runs on hydrogen fuel.
The sun releases electromagnetic radiation as a result of this nuclear reaction in all
directions. This radiation makes the trip from the sun to the earth in approximately 8
The distance between the sun and the earth is 93 million miles.
11. What fraction of the sun’s total energy output is received by the Earth?
Because the earth is a tiny sphere in the vastness of space, it receives only 1 billionth of the solar
output of energy. Much of this energy is either reflected away or absorbed by chemicals in the
atmosphere. Most of what reaches the troposphere is visible light, infrared radiation (heat) and
that small amount of ultraviolet radiation that is not absorbed by ozone in the stratosphere.
12. Please describe how the solar energy that reaches the Earth is allocated:
34% of the solar energy that reaches the troposphere is reflected back into space by
clouds, chemicals, dust and the earth’s surface land and water.
66% or solar energy:
o Warms the troposphere and land
o Evaporates water and cycles it through the biosphere
o Generates winds
0.023% is captured by green plants, algae and bacteria to fuel photosynthesis and make
the organic compounds most forms of life need to survive.
13. What is the greenhouse effect?
Most unreflected solar radiation is degraded into infrared radiation (which we experience as
heat) as it interacts with the earth. Greenhouse gases such as water vapor, carbon dioxide,
methane, nitrous oxide and ozone reduce this flow of heat back into space. This helps warm the
earth by acting somewhat like the glass in a greenhouse or the windows in a closed car, which
allow for the buildup of heat. Without the greenhouse effect, the earth would be nearly as cold as
Mars, and life as we know it could not exist.
14. What is an ecotone?
Natural ecosystems rarely have distinct boundaries and are not truly self-contained, self-
sustaining systems. Instead, one ecosystem tends to merge with the next in a transitional zone
called an ecotone. Ecotones are a region containing a mixture of species from adjacent
ecosystems and often species not found in either of the bordering ecosystems.
15. How is a marsh an example of an ecotone?
A marsh is a transitional life zone between dry land and an aquatic ecosystem. In a marsh you
will find organisms from each of the bordering ecosystems in addition to organisms that are
unique to the transitional ecosystem.
16. The biosphere and its ecosystem can be separated into two main parts. What are these?
The biosphere and its ecosystems can be separated into two components:
1. The biotic component
2. The abiotic component
17. What is the biotic component of an ecosystem?
The biotic component of an ecosystem is the living component, which consists of all of the
plants, animals and microorganisms (sometimes called the biota)
18. What is the abiotic component of an ecosystem?
The abiotic component of an ecosystem is the non-living component, which consists of the
water, air, nutrients and solar energy. The abiotic components of an ecosystem are the physical
and chemical factors that influence living organisms in terrestrial ecosystems and aquatic life
19. What is the range of tolerance for a population of organisms?
The range of tolerance for a population of organisms is the range of variations in the physical
and chemical environment that can be tolerated by a population of organisms. For example, a
species of trout has a range of tolerance of temperatures, pH levels, etc. that they can survive in.
If the temperature or aquatic pH falls outside of this range, the trout will not be able to survive.
All organisms have an optimum level or optimum range at which they can survive.
20. What is the law of tolerance for a population of organisms?
The law of tolerance states that the existence, abundance and distribution of a species in an
ecosystem are determined by whether the levels of one or more physical or chemical factors fall
within the range tolerated by that species. In other words, there are minimum and maximum
limits for physical conditions (such as temperature) and concentrations of substances called
tolerance limits beyond which no members of a particular species can survive. Highly tolerant
species can live in a variety of habitats with different conditions.
21. What is a limiting factor?
A limiting factor is something that limits the number of organisms in a population.
22. What is the limiting factor principle?
The limiting factor principle states that: Too much or too little of any abiotic factor can limit or
prevent growth of a population, even if all other factors are at or near the optimum range of
23. Please explain how water can act as a limiting factor for organisms and how water falls in
line with the limiting factor principle.
Water is a factor that affects the growth of many agricultural crops. Different crops (plants) have
different ranges of tolerance for the amount of water they can handle. If a plant doesn’t receive
enough water, it will die, thus water is a limiting factor. Conversely, if a plant receives too much
water, the plant’s root system will suffocate and the plant will die. This illustrates the limiting
factor principle that too much or too little of an abiotic factor can prevent growth.
24. Please explain how soil nutrients act as a limiting factor for plant growth and how soil
nutrients fall in line with the limiting factor principle.
If a plant doesn’t have enough nutrients available in the soil (nitrogen, phosphorus, etc., than the
plant cannot grow and runs the risk of dying. For this reason, soil nutrient levels act as a limiting
factor for growth. Conversely, if you “over-fertilize” a plant, the pH of the soil can be
compromised and the dissolved salts in the soil water will cause for the root cells to plasmolyse.
It is important to mention that the limiting factor for a population can change. For example,
at the beginning of a plant’s growing season, temperature may be the limiting factor; later on,
the supply of a nutrient may limit growth; if a drought occurs, water may be a limiting factor.
25. What are the important limiting factors in terrestrial (land) ecosystems?
F. Fire Frequency
26. What are the important limiting factors in aquatic ecosystems?
C. Dissolved Oxygen Content (The amount of oxygen gas dissolved in a given
volume of water at a particular pressure and temperature)
D. Nutrient Availability
E. Salinity (The amount of salts dissolved in the water) (Sea water is about 3.4% salt
by weight and it has been less than 4% for recorded history. If the salinity of the
ocean (or any body of water for that matter) rose above 6%, all life in the sea
except maybe halophilic archaebacteria would perish!)
27. What is metabolism?
Metabolism refers to the ability of an organism to release or consume energy. Living organisms
capture and transform matter ad energy from their environment to supply their needs for
survival, growth, and reproduction.
28. All living organisms can be classified as either autotrophs or heterotrophs. What is an
An autotroph is a “self feeder” and serves as the producer for a community of living organisms.
Autotrophs construct their own food from compounds obtained from their environment. All other
organism are consumers, which depend directly or indirectly on food provided by producers. On
land, plants are the main autotroph and in water algae are the main autotroph (although
chemoautotrophs are found in both locations).
29. What is a photoautotroph?
A photoautotroph is an organism that uses solar energy to construct food for a community of
living organisms. All green plants and algae are considered to be photoautotrophs because they
use the sun’s energy to construct “food”.
30. What is photosynthesis? What is the overall chemical equation to describe the process?
Photosynthesis is a process in which photoautotrophs convert water and carbon dioxide into
organic sugars with the assistance of energy harnessed from the sun. The overall chemical
equation to describe photosynthesis is:
6CO2 + 6H2O C6H12O6 + 6O2
31. What is a chemoautotroph?
Chemoautotrophs are autotrophic organisms that can construct food using an energy source that
is not sunlight. For example, there are chemoautotrophs found in deep sea vents that convert
hydrogen sulfide gas and dissolved carbon dioxide into organic molecules by harnessing the
thermal energy of the vent. Whereas photoautotrophs participate in photosynthesis,
chemoautotrophs participate in chemosynthesis.
32. What is a heterotroph (consumer)?
Heterotrophs (which literally means “other feeder”) obtain their energy and nutrients by feeding
on other organisms and their remains.
33. Based on their primary source of food, all consumers fall into one of six categories. What
are the six different types of heterotrophs?
Herbivores: Herbivores are the “plant eaters” of the community. They are the primary
consumers that feed directly on the producers.
Carnivores: Carnivores are the “meat eaters” of the population. The feed on consumers, with
those feeding only on primary consumers called secondary consumers and those ffeding on
other carnivores call tertiary (high level) consumers..
Omnivores: Omnivores (such as pigs, rats, foxes, bears, cockroaches and humans) eat both plans
and animals. Its hard to place an omnivore in food web because they consume food at multiple
different trophic levels.
Scavengers: Scavengers (such as vultures, flies, hyenas, and some species of sharks and ants)
feed on dead organisms.
Detritovores: Detritovores (crabs, carpenter ants, termites and earthworms) are also known as
detritus feeders or decomposers. They feed on detritus, or parts of dead organisms and cast off
fragments and wastes of living organisms.
Decomposers: Decomposers (mostly bacteria fungi) recycle organic matter in ecosystems. They
do this by breaking down (biodegrading) dead organic material (detritus) to get nutrients and
releasing the resulting simpler inorganic compounds into the soil and water where they can be
taken up as nutrients by the producers.
34. All living organisms (both autotrophs and heterotrophs) use the chemical energy stored in
glucose and other chemical compounds to fuel their life processes. What are the two
ways in which chemical energy can be broken down?
1. Aerobic Respiration: Occurs in the mitochondria of eukaryotic organisms. In aerobic
respiration, oxygen is used to break down glucose into ATP, CO2 and H2O. Aerobic
respiration can be represented by the following equation:
C6H12O6 + 6O2 6CO2 + 6H2O
2. Anaerobic Respiration: Occurs in the cytoplasm of cells. Anaerobic respiration is also
called fermentation and instead of the end products being carbon dioxide and water, the
end products are compounds such as methane gas, ethyl alcohol (C2H5OH), acetic acid
(HC2H3O2) and hydrogen sulfide gases.
35. If the world had lost all of its decomposers, what would happen to life on the planet?
If the world lost all of its decomposers, the entire world would soon be knee-deep in plant litter,
dead animal bodies, animal wastes and garbage. Decomposers are incredibly important in the
cycling of nutrients throughout organisms.
36. The survival of an ecosystem is dependent on what two main factors?
In order for an ecosystem to survive:
1. Energy must flow one way through the organisms in the ecosystem (most often from
the sun to the producers and later to the higher-level consumers.
2. Nutrients must cycle so that the nutrients from dead and decaying matter can serve as
building blocks for new life.
37. Please create a model that shows how an ecosystem’s main structural components
(energy, chemicals and organisms) are linked by matter recycling by decomposers and
the flow of high quality energy from the sun through organisms and back to the
environment as low quality heat.
Please Miller APES Book Page 82
38. What is a food chain?
A food chain is a map that shows the feeding habits of different organisms in an ecosystem. Food
chains give us the ability to determine how energy and nutrients move from one organism to
another through the ecosystem.
39. All organisms in a food chain belong to a trophic level. What is a trophic level?
A trophic level represents an organism’s place in the food chain. There are several trophic levels:
A. Producers (The autotrophs and primary source of energy for all organisms in the
B. Primary Consumers (The organisms that consume the producers)
C. Secondary Consumers (Organisms that consume the primary consumers)
D. Tertiary Consumers (Organisms that consume the secondary consumers)
40. To what trophic level do decomposers and detritovores belong?
Decomposers and detritovores process detritus at all trophic levels, and therefore do not belong
to a unique individual trophic level.
41. Please identify the trophic level each organism belongs to in the simple food web below.
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42. What is biomass?
Biomass is a measure of the dry weight of all organic matter contained within the organisms
within a food chain. In a food chain or a food web, chemical energy stored in the biomass is
transferred from one trophic level to another, with some usable energy degraded and lost to the
environment as low quality heat in the transfer.
43. What is ecological efficiency a measure of?
Ecological efficiency is a measure of the percentage of usable energy transferred as biomass
from one trophic level to the next.
44. What is the typical ecological efficiency range from one trophic level to the next?
Typical ecological efficiency ranges are approximately 5-20% from one trophic level to the next.
This means that 80-95% of the energy is lost from one trophic level to the next as low quality
heat or through lost energy to wastes. Ecologists approximate the average ecological efficiency
to be approximately 10% (this is referred to as the 10% Rule).
45. If green plants in an area capture 10,000 units of energy from the sun, how much of that
energy will be passed onto the herbivores (primary consumers) in the area?
According to the 10% rule, if green plants capture 10,000 units of energy, only 1,000 units of
energy will be passed onto the primary consumer trophic level. The rest of that energy will be
lost as low quality heat energy from the plant’s metabolism.
46. Of the amount of energy, captured by the primary consumers, how much of that energy
will be passed onto the secondary consumers?
Again, the 10% rule applies. Only 10% of the 1,000 units passed to the primary consumers will
be available for the secondary consumers. (100 units).
47. How much of this energy will be passed onto the tertiary consumers?
10% of the energy is always passed from one trophic level to the next. The rest is lost as low
quality heat. Therefore, only 10 units will be passed to the third trophic level. In summary, if the
plants of a community capture 10,000 units of energy, only 10 units will reach the tertiary
consumer trophic level! This shows why there are always more producers than tertiary
consumers in community of living organisms.
48. What is a pyramid of energy flow?
In a community of living organisms, 90% of all energy is lost as heat as energy is passed from
one trophic level to the next. Because of this, the number of organisms at each trophic level is
less than the number of organisms at the trophic level below it. Because of this, a “pyramid or
organism abundance” can be formed with the producers on bottom and the tertiary consumers on
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49. Why are there so few top-level carnivores in a community of living organisms?
In order for there to be enough energy to support top-level consumers, there must be a larger
number of lower-level organisms, because only 10% of the energy is passed from one trophic
level to the next. In order for there to be a great deal of top-level carnivores, there must be a
significant amount of biomass in the lower trophic levels.
50. Looking at the pyramid of energy flow, why can the Earth support more people if we all
eat at lower trophic levels?
If we eat at higher trophic levels, a great deal of high-quality energy is lost as heat. If we eat at
lower trophic levels, we avoid this waste of energy and thus the planet can sustain more
51. What is gross primary productivity (GPP)?
Gross primary productivity is the rate at which an ecosystem’s producers convert solar energy
into chemical energy as biomass. In other words, GPP is the rate at which plants or other
producers use photosynthesis to make more plant material (biomass). Worldwide, GPP is highest
in terrestrial regions that receive adequate amounts of precipitation and have reasonable
temperatures. In aquatic regions, GPP is highest near coastal areas and near reefs where nutrient
levels are high to stimulate algae growth. Additionally areas of the open ocean where upwelling
currents bring nutrients to the surface have a high GPP.
52. What is net primary productivity (NPP)?
In order to stay alive, grow and reproduce, an ecosystem’s producers must use some of the total
biomass they produce for their own respiration. The chemical energy that remains in the biomass
is called the net primary productivity.
NPP= Rate at which producers store chemical energy as biomass (produced by photosynthesis)
Rate at which producers use chemical energy stored as biomass (through aerobic respiration)
It’s important to note that NPP is the rate at which energy for use by consumers is stored in new
biomass. It is typically measured in kcal/m2/year.
53. According to the table below, which type of ecosystem has the greatest NPP? Which type
has the lowest NPP?
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According to the diagram above, the extreme desert has the lowest NPP and estuaries, swamps,
marshes and tropical rain forests have the highest NPP.
54. Which of the above life zones contributes the greatest amount to the whole plant’s gross
primary productivity (GPP)?
Despite its low net primary productivity, the open ocean produces more of the earth’s net
primary productivity per year than any other ecosystem or life zone. This fact is strictly true
because of the vast size of the ocean.
55. If the open ocean has such a high gross primary productivity, why don’t we harvest its
tiny producers such as floating and drifting phytoplankton to help feed the growing
There are two main reasons why it wouldn’t be wise to harvest the phytoplankton out of the open
ocean. The first reason is that it would take much more fossil fuel and other types of energy than
the energy that we would get. The second reason is that it would disrupt the food webs of the
open ocean that provide us and other consumer organisms with important sources of energy and
protein from fish and shellfish.
56. According to the graph above, it appears that estuaries, swamps and marshes have the
highest net primary productivity. Given this, why don’t we harvest more plants from
estuaries swamps and marshes to feed the world’s hungry?
There are two reasons for this. The first is that most plants in estuaries, swamps and marshes
cannot be eaten by people. The second is that most of the plants in these life zones are vital food
sources (and spawning areas) for fish, shrimp, and other aquatic life forms that provide us and
other consumers with protein.
57. What is a nutrient?
A nutrient is any atom, ion or molecule and organisms needs to live, grow, or reproduce. Some
elements such as carbon, hydrogen, nitrogen, phosphorus, sulfur and calcium are needed in fairly
large amounts whereas others (such as sodium, zinc, copper and iodine) are needed in small or
even trace amounts.
58. What is a biogeochemical cycle?
A biogeochemical cycle is one in which a nutrient is cycled between the non-living environment
(air, water, soil and rock) and the living environment (the organisms that inhabit the ecosystem).
The earth’s chemical cycles connect past, present and future forms of life. Some of the carbon
atoms in your skin may once have been part of a leaf, a dinosaur’s skin, or a layer of limestone
rock. Some of the oxygen atoms that you just inhaled may have been inhaled by your
grandmother, Plato, or a hunter-gatherer who lived 25,000 years ago.
59. What are the three main types of nutrient cycles?
The three main types of nutrient cycles are:
60. What is the hydrologic (water) cycle?
The hydrologic cycle involves the movement of water in the form of ice, liquid water and water
vapor as it cycles through the biosphere.
61. What is an atmospheric cycle?
In an atmospheric cycle, a large portion of a given element exists in its gaseous form in the
atmosphere. Examples include nitrogen (N2) gas and carbon dioxide (CO2) gas which cycle fairly
rapidly from the atmosphere, through soil organism and back into the atmosphere. Because they
involve the atmosphere, such cycles operate at local, regional and global levels.
62. What is a sedimentary cycle?
A sedimentary cycle is a cycle in which an element does not have a gaseous phase, or its gaseous
compounds do not make up a significant portion of its supply. In this case, the earth’s crust is its
main storehouse. Phosphorus and non-renewable solid minerals are circulated in such cycles.
63. Below are key terms describing the hydrologic (water) cycle. Please define these key
Evaporation: The conversion of liquid water into water vapor. Evaporation takes place from the
surface of a body of water (either large or small).
Transpiration: Evaporation from leaves of water extracted from soil by roots and transported
throughout the plant.
Condensation: Conversion of water vapor into liquid water (usually occurs in the upper
atmosphere and forms clouds).
Precipitation: Rain, sleet, hail or snow that falls from the upper atmosphere to the surface of the
Infiltration: Movement of water into the soil.
Percolation: The downward flow of water through soil and permeable rock formations to
groundwater storage areas called aquifers.
Runoff: Downslope surface movement of water back into the sea to continue the cycle.
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64. What powers the hydrologic cycle?
The hydrologic cycle is powered by the sun and by gravity. Incoming solar energy evaporates
water from oceans, streams, lakes, soil and vegetation. About 84% of the water vapor in the
atmosphere comes from the ocean and the rest comes from land.
65. What determines the amount of water vapor air can hold?
The temperature of the air determines the amount of water it can hold. Warm air can hold more
water than cold air.
66. What is absolute humidity?
Absolute humidity is the amount of water vapor found in a certain mass of air and is usually
expressed as grams of water per kg of air.
67. What is relative humidity?
Relative humidity is the amount of water vapor in a certain mass of air, expressed as a
percentage of the maximum amount it could hold at this temperature. For example, a relative
humidity of 60% at 27 degrees C (80 degrees F) means that each kg of air contains 60% of the
maximum amount of water vapor it could hold at that temperature.
68. What is the dew point?
The dew point is the temperature at which condensation occurs. In order for condensation to
occur in the upper atmosphere, the air must contain condensation nuclei which are tiny particles
on which drops of water can collect. Volcanic ash, soil dust, smoke, sea salts, and particulate
matter emitted by factories, coal-burning power plants, and vehicles are sources of such particles.
69. What are three ways in which humans are affecting the hydrologic cycle?
1. Humans are withdrawing large quantities of fresh water from streams, lakes, and
underground sources. In heavily populated or heavily irrigated areas, withdrawals have
led to groundwater depletion or intrusion of ocean salt water into underground water
2. Clearing vegetation from land for agriculture, mining, road and building construction and
other activities has increased runoff, reduced infiltration that recharges groundwater
supplies, increases the risk of flooding, and accelerates soil erosion and landslides.
3. Modifying water quality by adding nutrients (such as phosphates) and other pollutants
and by changing ecological processes that purify water naturally.
70. How is carbon useful to living organisms?
Carbon is essential to life as we know it. It serves as the basic building block of the organic
compounds necessary for life such as carbohydrates, fats, proteins and nucleic acids.
71. Carbon exists in the atmosphere in the form of carbon dioxide (CO2). What processes
remove carbon dioxide from the atmosphere?
1. Photosynthesis: Both aquatic and terrestrial photosynthesis remove carbon dioxide from
the atmosphere to synthesize organic compounds.
2. Sedimentation: In marine ecosystems, some organisms take up dissolved CO2
molecules, carbonate ions, and bicarbonate ions from ocean water. These ions react with
dissolved calcium ions to form Calcium Carbonate (CaCO3) to build the shells and
skeletons of marine organisms. When these organisms die, tiny particles of their shells
and bone drift slowly to the ocean depths and are buried for eons (as long as 400 million
years) in deep bottom sediments where under immense pressure they are converted to
3. Death, Burial and Compaction: As terrestrial and marine organisms die, the carbon in
their bodies is decomposed and compacted over geologic time, and converted into fossil
fuel in the form of oil or coal.
72. How is carbon returned to the atmosphere?
1. Aerobic Respiration: The metabolism of organisms as they break down glucose and
other macromolecules yields carbon dioxide.
2. Fossil Fuel Consumption and Burning: Over millions of years, buried deposits of dead
plant matter and bacteria are compressed between layers of sediment, where they form
carbon-containing fossil fuels such as coal and oil. This carbon is not released to the
atmosphere until it is brought to the earth’s surface and exposed to air.
3. Dissolving of Limestone: As limestone is exposed to oxygen and dissolved by water, the
calcium carbonate is decomposed and CO2 is released.
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73. What are two main ways in which humans have altered the carbon cycle?
1. Humans have cleared trees and other plants that absorb CO2 through photosynthesis.
2. Humans have removed large amounts of fossil fuels (coal, oil and natural gas) from
underground reservoirs and have returned them to the atmosphere.
3. As the temperature of the planet rises because of increased human release of fossil fuels
into the atmosphere, less CO2 can be dissolved in the ocean and even more will be
released into the atmosphere.
74. How is nitrogen useful to living organisms?
Organisms use nitrogen to make vital organic compounds such as amino acids, proteins, DNA
and RNA. Nitrogen makes up 78% of the volume of the troposphere, but atmospheric nitrogen
(N2) is useless to living organisms. Because of this, the nitrogen must be fixed (combined with
hydrogen or oxygen) to provide for useful compounds that plants can use.
75. What are the processes that remove nitrogen from the atmosphere?
1. Natural Nitrogen Fixation: Bacteria convert N2 to ammonia through the process N2 +
3H2 2NH3. This process is done by cyanobacteria (blue-green algae) and Rhizobium
bacteria which livie in the root systems of a variety of leguminous plant species. During
the nitrification process in the soil, ammonia molecules are converted to nitrate and
2. Industrial Nitrogen Fixation: Through the industrial Haber Process, atmospheric
nitrogen is converted into ammonia and then converted into ammonium and nitrate which
are placed into irorganic chemical fertilizers.
76. What is nitrogen assimilation?
Assimilation is a process in which plant roots absorb inorganic ammonia, ammonium ions, and
nitrate ions and use these ions to from nitrogen-containing organic molecules such as DNA,
amino acids, and proteins.
77. What is ammonification?
Ammonification is a process in which nitrogen-rich organic compounds and wastes are
converted into simpler nitrogen containing compounds such as ammonia and ammonium.
78. What is the main way in which nitrogen is returned to the atmosphere?
1. Denitrification: A process in which specialized bacteria (mostly anaerobic ones found in
waterlogged soil or in the bottom sediments of lakes, oceans, swamps and bogs) convert
ammonia and ammonium to nitrate and nitrite and ions and then into nitrogen and
nitrogen dioxide gas. These are then released into the atmosphere to continue the cycle.
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79. What are humans doing to alter the nitrogen cycle?
1. Over the last 100 years, human activities have more than doubled the amount of fixed
nitrogen entering the nitrogen cycle. Almost 60% of this human input of nitrogen comes
from commercial inorganic fertilizer. These fertilizers end up in aquatic ecosystems
through rainfall runoff and can cause for suffocating algal blooms in aquatic bodies of
2. The burning of any fuel releases NO (nitric oxide) gas into the atmosphere. In the
atmosphere, NO reacts with oxygen to form NO2 which reacts with water to form Nictric
acid (HNO3). These drops of acid dissolve in rain and snow water and have been known
Upset Aquatic Ecosystems through a disruption in the water pH
Corrosion of Metals
Damage of Marble, Stone and other Building Materials
3. Action of anaerobic bacteria on chemical fertilizes on livestock waste creates N2O
(nitrogen dioxide gas) which serves as a greenhouse gas and destroys the Earth’s ozone
80. How is phosphorus useful to biological organisms?
Phosphorus is a key component of nucleic acids (and thus DNA and RNA).
81. What type of biogeochemical cycle is phosphorus involved in?
Unlike carbon and nitrogen, phosphorus is involved in a sedimentary cycle. Earth’s temperature
and pressure conditions inhibit phosphorus from entering the gaseous state. Phosphorus is
typically found in phosphate salts containing phosphate (PO43-) ions in terrestrial rock formations
and ocean bottom sediments. Because most soils contain little phosphate, phosphorus often
serves as a limiting factor for plant growth unless it is applied through a chemical fertilizer.
82. What processes remove phosphorus from solid rock?
1. Mining: For the creation of inorganic chemical fertilizers.
2. Leaching and Runoff: Rainwater and weather conditions cause for phosphate to be
removed from rocks and enter the soil water and ocean water.
83. How is phosphorus cycled through terrestrial and aquatic ecosystems?
Phosphorus is cycled through marine and terrestrial ecosystems through uptake by autotrophs.
These autotrophs are then consumed by heterotrophs which take in the phosphorus. In death, the
phosphorus is returned to the soil and/or ocean water to be absorbed by other autotrophs and the
84. What processes return phosphorus to solid rock?
1. Sedimentation, Settling and Time cause for phosphorus to return to solid rock. The
rock-forming process takes a great deal of time.
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85. How are humans affecting the phosphorus cycle?
1. Humans are mining large quantities of phosphorus for use in inorganic chemical
fertilizers and detergents.
2. Humans are reducing available phosphate in tropical rainforests by removing trees. When
such forests are cut and burned, most remaining phosphorus and other soil nutrients are
washed away by heavy rains and the land becomes unproductive.
3. Adding excess phosphate to aquatic ecosystems from:
Runoff from animal wastes in livestock feedlots
Runoff of commercial phosphate fertilizers from cropland
Discharge of municipal sewage
All of the above process lead to eutrophication and algal blooms which suffocate aquatic
86. How is sulfur useful to biological organisms?
Sulfur is a key component of a few amino acids and thus is a critical component of many
87. What type of biogeochemical cycle is the sulfur cycle?
The sulfur cycle is a gaseous or atmospheric cycle. However, most of the earth’s sulfur is stored
underground in rocks and minerals including sulfate (SO42-) salts buried deep under ocean
88. Through what processes does sulfur enter the atmosphere?
1. Naturally: Swamps, bogs, and some marine algae release SO2 or SO3.
2. Industry: The burning of fuels releases SO2 and SO3 in addition to H2S
3. Volcanoes: Release H2S, SO3 and SO2
89. How does sulfur leave the atmosphere and return to land?
SO3 gas reacts with water vapor in the air to form sulfuric acid (H2SO4). The sulfuric acid returns
to the land in the form of precipitation. This sulfur is then cycled between hetrotrophic and
autotrophic organisms. Eventually, this sulfur can become deposited in rocks.
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90. What are some ways that humans have altered the sulfur cycle?
1. Through the burning of sulfur-containing coal and oil to produce electric power,
producing 2/3 of the human inputs of sulfur dioxide.
2. Using smelting to convert sulfur compounds of metallic minerals into free metals such as
copper, lead and zinc.
3. Refining petroleum (The process removes sulfur from petroleum and puts it into the
AP Environmental Science Class Notes 5 Problem Set A
Ecosystems: Components, Energy Flow, and Matter Cycling Review Questions
1. Why are insects important for many forms of life and for you and your lifestyle?
2. Please distinguish between the atmosphere, troposphere, stratosphere, hydrosphere, and
biosphere. Please give a brief definition of each.
3. What three processes are required to sustain life on earth? Please explain how each helps
life remain on earth.
4. How does the sun help sustain life on earth? How is this related to the earth’s natural
5. Please distinguish between the abiotic and biotic components of ecosystems and please
give three examples of each.
6. Please distinguish between the range of tolerance for a population in an ecosystem and
the law of tolerance.
7. What is a limiting factor and how do such factors affect the composition of ecosystems?
8. What are two important limiting factors for terrestrial ecosystems and for aquatic
9. Please distinguish between producers and consumers in ecosystems and please give three
examples of each type.
10. How does photosynthesis differ from chemosymthesis?
11. Why are decomposers important in a community of living organisms? What would
happen without them?
12. To what trophic level do all herbivores belong?
13. What is biomass?
14. What is the pyramid of energy flow in an ecosystem? How much usable energy is passed
from one trophic level to the next?
15. Please distinguish between gross primary productivity and net primary productivity.
Please explain how net primary productivity affects the number of consumers in an
ecosystem and on the earth.
16. Please list the two most productive ecosystems and the two least productive ecosytems in
terms of net primary productivity.
17. What is a biogeochemical cycle? How do such cycles connect past, present and future
forms of life?
18. Please give one example of an atmospheric and sedimentary biogeochemical cycle.
19. What is the difference between relative humidity and absolute humidity?
20. In what ways are humans affecting the hydrologic cycle?
21. In what ways are humans affecting the carbon cycle?
22. In what ways are humans affecting the nitrogen cycle?
23. In what ways are humans affecting the phosphorus cycle?
24. In what ways are humans affecting the sulfur cycle?
AP Environmental Science Gleason Notes 5 Problem Set B
Ecosystems: Components, Energy Flow, and Matter Cycling Critical Thinking Questions
1. A bumper sticker asks, “Have you thanked a green plant today?” Please give two reasons
for appreciating a green plant.
2. Please explain how decomposers help keep you alive.
3. Suppose you have a balanced aquarium that is sealed with a clear glass top. Can life
continue in the aquarium indefinitely as long as the sun shines regularly on it? If a friend
cleans out your aquarium and removes all the soil and plants, leaving only fish and water,
what will happen to the aquarium?
4. Why is it that most people in countries with limited resources live on a mostly vegetarian
5. Is it fair to say that the total amount of animal flash on earth would never exceed the total
amount of plant flesh, even if all animal were vegetarians?
6. Why are there more mice than lions in Africa- an environment equipped to support both
types of animals?
7. What would happen to an ecosystem if all its decomposers and detritus feeders were
eliminated? What would happen if all of its producers were eliminated?