Name _______________________
Word
Nutrient Cycles Review Packet
Definition
Water cycle
Explains how water molecules cycle through the 4 spheres
(hydrosphere, biosphere, atmosphere, lithosphere – not so
much in the last one)
Evaporation
The process where water changes from a liquid to a gas and
enters the atmosphere
Condensation
The process where water changes from a gas to a liquid and
enters the hydrosphere (and from there to the biosphere)
Precipitation
The process where water falls (in liquid or solid form) from
the atmosphere to the lithosphere/hydrosphere/biosphere
Groundwater
Runoff
The water stored underground
Water that flows from land into bodies of water
Carbon cycle
Explains how carbon atoms cycle through the 4 spheres
Nitrogen cycle
Explains how nitrogen atoms cycle through the 4 sphere
Nitrogen fixation
The process in which nitrogen in the atmosphere or
lithosphere is brought into the biosphere (generally by
bacteria or fungi)
Reading – Annotate 6 times.
Water Cycle
Water on Earth is billions of years old. However, individual water molecules keep moving
through the water cycle. The water cycle is a global cycle. It takes place on, above, and below
Earth’s surface.
During the water cycle, water occurs in three different states: gas (water vapor), liquid (water),
and solid (ice). Many processes are involved as water changes state in the water cycle.
Evaporation occurs when water on the surface changes to water vapor. The sun heats the water
and gives water molecules enough energy to escape into the atmosphere.
Condensation and Precipitation
Rising air currents carry water vapor from all these sources into the atmosphere. As the water
vapor rises in the atmosphere, it cools and condenses. Condensation is the process in which
water vapor changes to tiny droplets of liquid water. The water droplets may form clouds. If
the droplets get big enough, they fall as precipitation—rain, snow, sleet, hail, or freezing rain.
Most precipitation falls into the ocean. Eventually, this water evaporates again and repeats the
water cycle. Some frozen precipitation becomes part of ice caps and glaciers. These masses of
ice can store frozen water for hundreds of years.
Groundwater and Runoff
Precipitation that falls on land as rain may flow over the surface of the ground. This water is
called runoff. It may eventually flow into a body of water. Some precipitation that falls on
land may soak into the ground, becoming groundwater. Groundwater may seep out of the
ground at a spring or into a body of water such as the ocean. Some groundwater may be taken
up by plant roots. Some may flow deeper underground to an aquifer. This is an underground
layer of rock that stores water, sometimes for thousands of years.
Carbon Cycle
Molecules are considered organic molecules if they contain the element carbon. Carbon is
important to the structure of living organisms because it is used to create all the biomolecules:
carbohydrates, lipids, proteins, and nucleic acids. The carbon cycle, shown in Figure 1.1,
moves carbon back and forth between the environment and the living organisms. In other
words, the carbon cycle is the movement of carbon through the abiotic and biotic factors of the
ecosystem.
Carbon cycles quickly between organisms and the atmosphere. Photosynthesis removes carbon
dioxide from the atmosphere and uses it to make food. Have you heard the saying “you are
what you eat”? The food made helps the producer grow by contributing to the structure of its
cells. When a producer is consumed, the carbon moves into the consumer and again the carbon
can be used for the growth of the consumer. The matter in the food you consume is literally
used as the building blocks for creating you!
For all organisms, producers and consumers, food also provides the organism with energy. As
organisms convert food into energy they can use through the process of cellular respiration,
carbon is released back into the atmosphere as carbon dioxide. When organisms die,
decomposition releases the carbon within the organism back into the atmosphere.
Carbon cycles far more slowly through geological processes such as sedimentation. Carbon
may be stored in sedimentary rock for millions of years. Flowing water can slowly dissolve
carbon in sedimentary rock. Most of this carbon ends up in the ocean. The deep ocean can store
carbon for thousands of years. Sedimentary rock and the ocean are major reservoirs of stored
carbon.
Another reservoir of stored carbon is fossil fuel deposits. If dead organisms are covered before
they can decompose and are not exposed to oxygen, over millions of years they can form fossil
fuels. When we burn fossil fuels such as coal and oil, we release carbon back into the
atmosphere.
Nitrogen Cycle
Nitrogen makes up 78 percent of Earth’s atmosphere. It’s also an important part of living
things. Nitrogen is found in proteins, nucleic acids, and chlorophyll. The nitrogen cycle moves
nitrogen through the abiotic and biotic parts of ecosystems. Figure 1.12 shows how nitrogen
cycles through a terrestrial ecosystem. Nitrogen passes through a similar cycle in aquatic
ecosystems.
Although nitrogen gas is abundant in the atmosphere, plants cannot use nitrogen gas from the
air to make organic compounds for themselves and other organisms. The nitrogen gas (N2)
must be changed to a form called nitrates (NO3), which plants can absorb through their roots.
The process of changing nitrogen gas to nitrates is called nitrogen fixation, which is carried
out by nitrogen-fixing bacteria. The bacteria live in soil and roots of legumes such as peas or
beans. The nitrates can then be used by plants to create proteins, nucleic acids, and chlorophyll.
When consumers eat these plants the nitrogen gets reused to make new proteins.
When plants and other organisms die, decomposers break down their remains. In the process,
they release nitrogen in the form of ammonium ions (NH4+). Nitrifying bacteria change the
ammonium ions into nitrates. Some of the nitrates are used by plants. Some nitrates are
changed back to nitrogen gas by denitrifying bacteria.
Lesson Review Questions
Recall
1.
Identify and define two processes in the water cycle.
Evaporation, condensation (see vocab above for definitions)
2.
State three ways that carbon dioxide enters Earth’s atmosphere.
Carbon dioxide gas enters the atmosphere by diffusion from water, release from animals (in
cellular respiration) and through burning of fossil fuels
3.
List all the ways that a single tree may be involved in the carbon cycle.
A tree can absorb carbon dioxide from the atmosphere and use it for photosynthesis. When it
dies, it can be decomposed and release carbon dioxide. It may also become a fossil fuel,
and then the carbon stored in its remains would be converted to carbon dioxide through a
combustion reaction when it is burned. It’s mitochondria also use oxygen to produce
carbon dioxide when it does cellular respiration (in order to make ATP from sugars).
Apply Concepts
4.
Assume you are a molecule of water. Describe one way you could go through the water
cycle, starting as water vapor in the atmosphere.
Water vapor condenses and precipitates as rain into the ocean. The water molecule is
swallowed by a fish, which is then eaten by a human. The human sweats it out during
exercise and the water molecule percolates through the lithosphere into ground water.
The groundwater flows back to the ocean, and the water molecule evaporates back into
the atmosphere.
Think Critically
5.
Compare and contrast biological (life) and geological (rock/lithosphere) pathways of the
carbon cycle.
Biological – gas exchange through respiration and photosynthesis, also used in all organic
molecules (lipids, carbohydrates, nucleic acids, and proteins)
Geological – stored in fossilized organic matter (fossils or fossil fuels like coal and oil),
released naturally through volcanism (volcanic eruptions)
6.
Explain why bacteria are essential parts of the nitrogen cycle.
Bacteria fix nitrogen by bonding nitrogen atoms to oxygen or hydrogen atoms. This process
bring the nitrogen out of the atmosphere or lithosphere and makes it available for use in the
biosphere.