Download Describing Matter

Name: _______________________
Date: ________________________
Flynt - _____ Period
___th Grade Science
Connection: What
are the 5 main gases
that make up the
atmosphere?
Main Idea: What
are 4 examples of
how nitrogen is
important to living
things?
Vocab: What is a
nutrient?
Connection: Can
you think of any
other nutrients?
Review: The prefix
“di-” means
_______.
Review: What are
eukaryotes?
Vocab: What is a
compound?
Connection: Can
you list any other
examples of
compounds?
Vocab: What is
Nitrogen Fixation?
Summary:
As you already know, ____________________ is the most abundant gas
in Earth’s atmosphere. You also know that nitrogen is essential to all living
things. Nitrogen is found in nucleic acids like DNA and RNA, which are
molecules that carry the genetic code and allow inheritable traits to be passed
down from one generation to the next. Nucleic acids also serve as the blueprints
of life, as they carry instructions for building proteins and enzymes, as well as
the directions for numerous cell structures and processes. Proteins and
enzymes, in turn, are also made up of nitrogen. Protein and enzymes serve as
the workhorses and building blocks of many cell structures and processes.
Therefore, all organisms need nitrogen in order to build cell structures, carry
out cellular processes, repair worn out cell parts, and make new cells (growth
and reproduction). In plants, nitrogen is also part of chlorophyll (klor-oh-fill),
the green pigment of the plant that is responsible for photosynthesis!
Nitrogen is a great example of a nutrient (noo-tree-int). A nutrient is a
substance that an organism must have in order to survive, but cannot make on
its own. So if organisms cannot make their own nitrogen, how do they get it?
Every time you take a breath, you are breathing in nitrogen gas (N2). In
fact, _____% of each breath that you take is composed of nitrogen gas.
Nitrogen gas in the atmosphere is made of two nitrogen atoms joined together;
thus, it is sometimes called di-nitrogen gas. It is also sometimes called
molecular nitrogen, since molecules are substances made of two or more
atoms joined together (even if they are the same type of atom). Unfortunately,
our bodies cannot absorb and use the di-nitrogen gas from the atmosphere. The
reason why has to do with the chemical properties of di-nitrogen gas. Molecular
nitrogen is often said to be inert, or unreactive. This is because of the strong
triple bond between the two nitrogen atoms; the triple bond
makes N2 molecules very difficult to break apart, and the
process of splitting molecular nitrogen is very “expensive”
energetically. Thus, while nitrogen is all around us in the
atmosphere, most organisms can’t “afford” to spend energy breaking dinitrogen molecules apart, and therefore never evolved the ability to do so.
Instead, all single-celled and multi-cellular eukaryotic organisms depend on
other organisms and natural processes to supply nitrogen compounds that CAN
be easily broken and recombined to form nucleic acids and proteins!
In order for organisms to obtain the nitrogen they need, the molecular
nitrogen first must be split so that each nitrogen atom can be recombined with
other atoms to form a nitrogen compound. A compound is a molecule made of
two or more different kinds of atoms joined together. The act of breaking the
triple bond in molecular nitrogen (N2) apart so that its atoms can combine with
other atoms to form new, biologically available nitrogen compounds is called
nitrogen fixation. And as you can imagine, breaking that triple bond requires
the input of a lot of energy; thus nitrogen fixation is very “expensive” in terms
of energy.
Page 2 of 8
Main Idea: What
are the three
methods of nitrogen
fixation?
NITROGEN FIXATION: Nitrogen fixation is the building up or “synthesis” part of
the nitrogen cycle! There are three ways that nitrogen can get fixed:
1. Atmospheric fixation (lightning fixation).
2. Biological fixation:
a. By symbiotic bacteria living in the root nodules of
legumes (Rhizobia).
b. By free-living bacteria in the soil or water (Azotobacter and
Cyanobacteria).
3. Industrial/Anthropogenic Fixation (artificial fixation by humans).
Connection/Key
Concept: Which of
Earth’s “spheres”
interact in lightning
fixation?
Connection/Key
Concept: How is
the water cycle
connected to the
nitrogen cycle?
Micro =
Scopic =
Connect: What are
prokaryotic
organisms?
Main Idea: What is
the purpose of this
paragraph? (What
point is being
made?) 
Summary
Lightning fixation happens in the atmosphere and probably contributes
around 5– 8% of the total fixed nitrogen cycling in the biosphere. Lightning is
able to provide the enormous amounts of energy needed to break nitrogen (N2)
molecules apart, enabling their atoms to combine with oxygen (O2) molecules in
the air, forming nitrogen oxides. These nitrogen oxides dissolve in rain and
cloud droplets in the atmosphere, forming a new nitrogen compound called
nitrate (NO3-). The nitrate then gets carried by precipitation like rain and snow
to the ground, where it can infiltrate into and percolate through the soil.
Once it has soaked into the soil, the nitrate can be absorbed (soaked up) by the
roots of plants.
However, not all of the nitrate ends up in the soil. Nitrate can also be
carried by surface runoff into rivers, lakes, canals, and even back to the
ocean. The nitrogen can also become part of the groundwater and flow into
aquifers in a process called leaching.
Lightning fixation only produces a tiny bit of the fixed nitrogen that living
things need. Instead, most fixed nitrogen is produced by bacteria. Bacteria are
tiny, microscopic, prokaryotic organisms that are made up of only one cell.
They are so small that hundreds of thousands of bacteria would fit on a rounded
dot made by a pencil ().
Bacteria are some of the oldest
organisms on Earth. The earliest
bacteria probably lived about 3.5
billion years ago, long before humans
or other plants and animals! Today,
bacteria live all around us and within
us. Bacteria live in the deepest parts
of the ocean and deep within Earth.
They are in the soil, in our food, and
on plants and animals. Even our
bodies—inside and out—are home to many different kinds of bacteria. Our lives
are closely intertwined with theirs, and the health of our planet depends very
much on their activities. While it is true that a few types of bacteria can be
harmful to humans and other mammals, most bacteria are in no way harmful
and instead are extremely important to keeping our planet healthy!
Page 3 of 8
Bacteria play a key role in the nitrogen cycle and making soil fertile. They
convert molecular nitrogen gas (N2) in Earth’s atmosphere into compounds like
ammonium (NH4+) or nitrate (NO3-), both of which can be used by plants. For
a long time, microbiologists thought that bacteria were the only organisms that
were able to carry out nitrogen fixation. Today, there is growing evidence that
some types of Archaea can fix nitrogen as well! Still, most of the fixed nitrogen
Key Concept:
that cycles through the biosphere (and especially through land-based
Which types of
organisms CAN and ecosystems) is contributed by the activities of nitrogen-fixing bacteria.
CANNOT fix
Technically speaking, there are two distinct processes involved in turning
nitrogen?
molecular nitrogen into a form that is biologically available: the transformation
of unfixed molecular nitrogen into ammonium (nitrogen fixation) and the
transformation of ammonium into nitrate (nitrification). For our purposes, we
will refer to both processes as nitrogen fixation. Both of these processes are
carried out by certain types of bacteria living in the soil and/or water.
Key Concept: What
are the two main
types of “fixed”
nitrogen that plants
can use?
Sym =
Biotic =
Key Concept:
Legumes include
peas, soybeans,
peanuts, clover,
alfalfa, and lupine.
Connection: What
are the other types
of symbiotic
relationships?
Is corn a legume?
Can it fix it’s own
nitrogen?
Some of the bacteria that fix nitrogen live in a
mutually beneficial symbiotic (sim-by-ah-tik) relationship
with certain plants. Symbiotic literally means “living things
living together.” Plants in the legume (ley-goom) family—
which includes beans, peas, and clover—have special root
structures called nodules (nod-yewls). Nodules are
bumpy growths housing tens of thousands of symbiotic
bacteria called Rhizobia (rhy-zōh-bee-ya). The Rhizobia
bacteria in the nodules “fix” nitrogen for the legume,
turning nitrogen (N2) gas into ammonium (NH4+) that the
legume can use. In return, the legume makes glucose (and
other carbohydrates) using photosynthesis and shares its
food with the bacteria in the nodules.
The symbiotic relationship between legumes and Rhizobium bacteria is
mutualistic (both organisms benefit). The legume receives nitrogen in a form
that can easily be converted into nucleic acids and proteins, and the Rhizobium
receives carbohydrates produced by the legume during photosynthesis.
However, the relationship is actually much more complex than what is
described here. Legumes and Rhizobia have coevolved for hundreds of
thousands of years; each type of legume hosts its own unique species of
Rhizobia, and therefore each type of legume has evolved unique nodule
structures that are specific to the needs of their own particular species of
Rhizobia.
Not all of the “fixed” nitrogen made by Rhizobia in the root nodules gets
used by the legume plant. When the legume plant dies, any extra ammonium in
the nodules enters the soil, making the soil more fertile (better for growing
Connect: What does other plants). Farmers often grow legumes like soybeans in order to build up
it mean when soil is the nitrate in their soil and make the soil more fertile. After harvesting the
said to be fertile?
soybeans, the farmers plow the remnants of the soybean plants into the soil
and then plant crops like corn that DO NOT have symbiotic bacteria living in
Summary
Page 4 of 8
Key Concept: How
do practices like
crop rotation and
companion planting
impact soil fertility?
Connection:
Cyanobacteria (syan-oh-bak-teer-eeah) play a
significant role in
what other cycle of
matter?
Synthesize: How
many types of
bacteria have been
mentioned so far?
What are their roles
in the Nitrogen
Cycle?
Key Concept: Why
is nitrate leached
more than
ammonium?
Connect: Do you
think that nitrate
leaching is a
problem in Florida?
Comprehension
Check: What is
nitrate enrichment?
Summary
their roots. Eventually the corn will use up all of the left over fixed nitrogen, and
the farmer will have to grow more legumes to replace the nitrogen. This is
called crop rotation. Small-scale organic gardeners often grow legumes
simultaneously in and around other crops to help add nitrogen to the soil
throughout the growing season; this method is an example of companion
planting.
While the symbiotic relationship between legumes and Rhizobia plays an
important part in the nitrogen cycle, most plants do NOT have symbiotic
bacteria in their roots. Luckily there are also free-living bacteria that can “fix”
nitrogen and turn it into a form that plants can use. Azotobacter (As-zōh-tōhbak-ter) is a type of nitrogen-fixing bacteria that lives freely in the soil. Like
Rhizobia, Azotobacter can carry out chemical reactions that transform molecular
nitrogen into ammonium, but Azotobacter adds this ammonium directly to the
soil where it is available to all plants, not just legumes. Cyanobacteria
(sometimes mistakenly called blue-green algae) are another type of free-living
nitrogen-fixing bacteria that can convert di-nitrogen to ammonium.
Cyanobacteria are arguably the most successful group of microorganisms on
earth. They occupy a broad range of habitats across all latitudes, and are
widespread in freshwater, marine and terrestrial (land-based) ecosystems.
Thus, cyanobacteria play a critical role in nitrogen fixation in a variety of
habitats all over the world.
Once ammonium has been added to the soil or water, other bacteria—
which we will refer to as nitrifying bacteria—can convert the ammonium to
nitrate (NO3-) in a process called nitrification. While both ammonium and
nitrate are considered “fixed” nitrogen, too much ammonium can actually be
toxic to many organisms. Thus, nitrifying bacteria and the process of
nitrification plays a critical role in transforming toxic ammonium into the lesstoxic nitrates preferred by more plants.
Unfortunately, excess nitrate made by nitrifying bacteria does not last
very long in the pedosphere, especially in ecosystems that experience periods
of heavy rainfall. This is due to the fact that negatively charged nitrate (NO3-)
compounds are much more easily leached from soils than positively charged
ammonium (NH4+) compounds. Leaching occurs when runoff or groundwater
percolating through soils washes away critical nutrients like fixed nitrogen.
The ammonium ions are positively charged and therefore stick to (are attracted
by) negatively charged clay particles and organic matter in soil. This attraction
between positively and negatively charged ions—known as the Law of
Attraction—prevents ammonium from being leached out of the soil by
groundwater flow. In contrast, the negatively charged nitrate ions are actually
repelled by negatively changed soil particles, and so nitrates can be washed out
of surface soils in ecosystems where there is heavy rainfall, leading to
decreased soil fertility. The leached nitrates don’t just disappear; they are
carried downstream by surface runoff, stream flow and groundwater flow,
leading to nitrate enrichment of ponds, lakes, aquifers and other downstream
bodies of water.
Page 5 of 8
NITROGEN AND THE FOOD CHAIN
Herbivore =
Carnivore =
Omnivore =
Once nitrogen enters a plant, it becomes part of the food chain. The fixed
nitrogen absorbed by the plant is used to make proteins, amino acids and DNA
(nitrogen-containing organic macromolecules). If the plant gets eaten by an
herbivore (or other primary consumer), the herbivore will digest the nitrogencontaining organic macromolecules stored in the plant and use that nitrogen to
make new nitrogen-containing organic macromolecules. Through predation,
herbivores pass on the nitrogen in their bodies to carnivores (secondary
consumers). Omnivores can get the nitrogen they need from both the plants and
the animals that they eat. Thus, the only organisms that actually absorb fixed
nitrogen from the surrounding environment and allow it to enter the food chain are
producers like photosynthetic plants and algae.
Decomposers, the final step in the food chain, also play a vital role in the
nitrogen cycle. Decomposers are often called “Nature’s recycling system” because
of the role they play in the cycling of nutrients like fixed nitrogen back into the
abiotic (non-living) environment. Decomposers—which include some types of fungi,
mold, mushrooms, earthworms, and even our old friends bacteria—can break down
the nitrogen-containing organic compounds stored in the bodies of dead organisms
and release that nitrogen back into the soil. The process by which these organic
compounds (like proteins, amino acids, and DNA) are chemically changed back into
ammonium is called ammonification. Usually, the nitrogen released (produced) by
decomposers is ammonium (NH4+). This fixed nitrogen then can be re-absorbed by
plants and enter the food chain again. In other words, ammonification returns
valuable fixed nitrogen back to the soil (abiotic environment) where it can re-enter
to food chain (biotic environment) through uptake by plants.
Organic farmers sometimes use decomposers to help create natural soil
fertilizer for their crops. Autumn leaves, grass clippings, weeds, fruit and vegetable
trimmings, egg shells, coffee grounds, and manure from horses, chickens and cows
can be mixed with special decomposing bacteria in a compost bin or compost pile.
The decomposing bacteria break down the proteins and other organic nitrogen
compounds and turn them back into ammonia. After a certain amount of time, the
“mature” compost can then be applied to gardens and fields to enrich the soil, thus
turning “garbage” and “waste” into a valuable resource for growing crops.
The inert (unreactive) nature of the N2 molecule (remember that triple bond?)
means that biologically available (fixed) nitrogen is often in short supply in natural
ecosystems. Thus, the availability of fixed nitrogen in an ecosystem can be an
important limiting factor. A limiting factor is an environmental factor that is
essential for life that is absent or depleted below the critical minimum, or that
exceeds the maximum tolerable level for the species. When fixed nitrogen is in
short supply, the growth of plants and other producers is restricted, and this
cascades up through the entire food chain, limiting biomass growth throughout the
entire ecosystem. However, population sizes of organisms in natural ecosystems
have evolved in balance with the limited availability of fixed nitrogen sources in
each ecosystem. Disrupting the balance of nitrogen, either through addition or
removal, therefore can have significant negative consequences on the health of an
ecosystem.
Summary
Page 6 of 8
HUMAN IMPACTS
Sometimes plants and animals die and their
bodies do not get decomposed. Instead, their bodies
may quickly become
buried along with
other plants and
animals. Over millions
of years, the remains
of these organisms can
be turned into fossil
fuels like oil, coal, and
natural gas. If humans
extract (dig up) these
fossil fuels and burn
them, the combustion
reactions produce harmful nitrogen compounds like NO (nitric oxide), N2O (nitrous
oxide), and NO2 (nitrogen dioxide) that enter the atmosphere where they are
considered pollutants.
The nitrogen/oxygen compounds produced by the burning of fossil fuels can
cause serious environmental and health-related hazards, including acid rain,
photochemical smog, and high levels of ozone tropospheric (remember good up
high, bad nearby). Acid rain is rain or
any other form of precipitation that is
unusually acidic, meaning that it low pH.
Acid rain can have harmful effects on
plants, aquatic animals, and
infrastructure.
According to the American Lung
Association, your lungs and heart can be
permanently affected by ozone pollution
and smog. While the young and the
elderly are particularly susceptible to the
effects of smog, anyone with both short
and long term exposure can suffer ill
health effects. Problems include
Spruce forest killed by acid rain.
shortness of breath, coughing, wheezing, bronchitis, pneumonia, inflammation of
pulmonary tissues, heart attacks, lung cancer, increased asthma-related symptoms,
fatigue, heart palpitations, and even premature aging of the lungs and death.
N2O is also a dangerous greenhouse gas, with 310 times the ability per
molecule of gas to trap heat in the atmosphere. Thus, increased levels of N2O in the
atmosphere are exacerbating global warming.
The application of nitrogen-based fertilizers for agricultural purposes is
significant environmental issue here in Florida. In agricultural systems, fertilizers
are used extensively to increase plant production, but unused nitrogen, usually in
the form of nitrate, can leach out of the soil, enter streams and rivers, and
ultimately make its way into larger bodies of water, like lakes and oceans. Nitrates
Summary
Page 7 of 8
even end up in our drinking water, which comes from underground aquifers fed by
contaminated surface waters that infiltrate and percolate through the groundwater
flow.
The nitrogen-based fertilizers used in agriculture are man-made in a process
generally referred to as industrial fixation (anthropogenic fixation). The
production of synthetic fertilizers for use in agriculture by causing N2 to react with
H2 (technically known as the Haber-Bosch process) has increased significantly over
the past several decades. In fact, today, nearly 80% of the nitrogen found in
human tissues originated from the Haber-Bosch process (Howarth 2008).
Industrial nitrogen fixation has increased exponentially since the 1940s, and
human activity has doubled the amount of global nitrogen fixation (Vitousek et al.
1997).
And because nitrogen availability often limits the primary productivity (the
amount of usable energy that enters the food chain through the activities of
producers like plants and algae) of many ecosystems, large changes in the
availability of nitrogen can lead to drastic changes in the amount of biologically
available nitrogen in both aquatic and terrestrial ecosystems.
In terrestrial (land-based) ecosystems, the addition of nitrogen can lead to
nutrient imbalance in trees, changes in forest health, and declines in biodiversity.
With increased nitrogen availability there is often a change in carbon storage in the
carbon cycle, thus impacting more processes than just the nitrogen cycle.
Much of the nitrogen applied to agricultural and urban areas ultimately enters
rivers and near-shore coastal systems. In near-shore marine systems, increases in
nitrogen often lead to anoxia (no oxygen) or hypoxia (low oxygen)—conditions that
can lead to “dead zones” where the majority of oxygen-dependent organisms die or
migrate elsewhere due to lack of oxygen. As the size and frequency of dead zones
increase in near-shore environments, the end results include altered biodiversity,
changes in food-web structure, and general habitat degradation.
One common consequence of increased nitrogen is an increase in harmful
algal blooms (Howarth 2008). Toxic blooms of certain types of dinoflagellates have
been associated with high fish and shellfish mortality in some areas. Even without
such economically catastrophic effects, the addition of nitrogen can lead to changes
in biodiversity and species composition that may lead to changes in overall
ecosystem function. Some have even suggested that alterations to the nitrogen
cycle may lead to an increased risk of parasitic and infectious diseases among
humans and wildlife (Johnson et al. 2010). Additionally, increases in nitrogen in
aquatic systems can lead to increased acidification in freshwater ecosystems.
Many human activities have a significant impact on the nitrogen cycle.
Burning fossil fuels, application of nitrogen-based fertilizers, and other human
activities can dramatically increase the amount of biologically available nitrogen in
an ecosystem. Since fixed nitrogen is often a limiting factor, you might think that
increasing the amount of fixed nitrogen in an ecosystem might be a good thing.
However, the communities in an ecosystem co-evolve over millions of years based
on a fine balance of available resources as they move through the various cycles of
matter. A change in any one component in any part of the cycle can ripple
throughout an ecosystem and cause disruptions in other cycles of matter as well.
Summary
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Summary