APES Unit Two Test
Study Guide
1. Know all of the following about the nitrogen cycle:

Nitrates: form of nitrogen useable by plants

Chemical formula for nitrate: NO3
Formula for ammonium ion: NH4+

Formula for nitrite: NO2
Formula for ammonia: NH3

Nitrification: when ammonium ions are converted to nitrite ions and nitrate ions

Nitrogen fixation: when nitrogen gas (N2) is converted to ammonia or nitrate by lightning or bacteria

Denitrification: The process which ultimately returns diatomic nitrogen (N2) to the atmosphere

Assimilation: when organisms are able to take up the nitrogen that has been made useable by the plants, and
incorporate it into their body structure in the form of amino acids and proteins.

Ammonification: when dead organisms, through the process of decomposition, return nitrogen compounds,
such as ammonia back to the Earth.

Nitrogen gas (N2) is the largest portion of our atmosphere at 78%
2. Know all of the following about the carbon cycle:

Photosynthesis uses carbon dioxide, sunlight and water to manufacture carbohydrates and oxygen.

The major processes in the carbon cycle are photosynthesis and cellular respiration

One of Earth’s largest carbon sinks (place where carbon is stored) is the ocean. The carbon is stored as
dissolved CO2, calcium carbonate in the shells of sea creatures, in the living phytoplankton, and at the bottom in
the sediment.

Processes that increase carbon dioxide include: cellular respiration; biomass combustion; fossil fuel
combustion; decomposition; volcanism; deforestation (which removes the carbon absorbing trees)

Processes that remove carbon dioxide from the atmosphere include: photosynthesis; formation of sedimentary
rocks, including limestone (calcium carbonate)

Changes in the carbon cycle may indeed result in climate shifts and global warming or cooling, depending upon
the amount of CO2 in the atmosphere

Of all the global giants, the United States is the largest producer of carbon dioxide
3. Know the following about the sulfur cycle:

The largest sulfur sink is found in the rocks
4. Know the following about the hydrologic cycle:

Evaporation: liquid to a gas; condensation: gas to a liquid; precipitation: from atmosphere to surface; run-off:
over the surface; infiltration and percolation: movement of water down through the surface; transpiration
(evapotranspiration): plant participation in hydrologic cycle, whereby they pull water up through their bodies,
and allow it to evaporate out through their stomata

The only process in the water cycle that works to oppose the force of gravity is transpiration. This occurs when
water is ‘pulled’ up through a plant due to evaporation from the surface of the leaf through the stomata.

Currently, oceans cover nearly 70% of Earth’s surface.

Small droplets of water are able to condense into a liquid with the help of condensation nuclei. These are TINY
microscopic particles of dust, dirt, particulate matter, volcanic ash…even sea salt that is airborne.

Humans have disrupted the hydrologic cycle in the recent past through making large withdrawals in the
freshwater resources for drinking, agriculture, and hygienic reasons

We have changed land-use patterns, cutting down forests and fields and replaced them with pavement and
buildings, where run-off patterns are completely different. This diverts streams and rivers, and affects
infiltration rates, as well as encourages erosion and flooding.

The hydrosphere contains all the water in, on and around the Earth, including the cryosphere (which is the
frozen portion of the hydrosphere), and the atmosphere (which includes water vapor).

This will be your free response topic: It has often been said that the hydrologic cycle links all other
biogeochemical cycles. Think about ways that this might be true. Think of each cycle, and how the water cycle
contributes to it:
 Example: hydrologic cycle contributes to the phosphorus cycle, because it runs off over
the soil and rocks, carrying phosphates from these areas into the aquatic ecosystem,
where they become dissolved and absorbed by aquatic plants and animals.
 Example: hydrologic cycle contributes to the rock cycle by carrying sediments from one
place to another, and redepositing them. Then these layered deposits, if left undisturbed
for long enough, may form sedimentary rocks through the process of lithification
 Example: Nitrogen (nitrates) may be absorbed into plants in conjunction with water in the
root systems of legumes and other plants. Nutrients such as phosphorus and sulfur can
become dissolved in water and absorbed by plants in their root systems. Once there,
herbivores may consume them.
You get the idea…now go find some on your own!
5. The phosphorus cycle is one of the few cycles (besides sulfur) that does not contain a gaseous state, so it is rarely found in the
atmosphere.
6. Know all of the following about the rock cycle:

Sedimentary rocks are found at Earth’s surface and are layered materials that have become “lithified” over the
eons. Sandy beaches become sandstone over time. Sedimentary rocks are those that contain fossils, and as such,
remain of great value to scientists who use them to help determine early environments.

Coals (all but anthracite) are sedimentary rocks and are large storage areas of carbon. When they are burned
they release the stored carbon to the atmosphere.

Igneous rocks are associated with volcanoes, and are formed when molten rock beneath the surface (magma)
bubbles up and out, hardening on or just beneath the surface. Where they form and how slowly or quickly the
cool will determine the size of the crystals in these rocks. The longer they take to cool, the larger the crystal.

Metamorphic rocks are formed deep beneath the surface, where both heat and tremendous pressure act to form
the rocks. Sedimentary and igneous rocks forced beneath the surface, perhaps in a convergent area where
tectonic plates are colliding, may become “morphed” into metamorphic rocks. Just remember…heat and
pressure.
7. Know the diagram of the Earth on the next page well. Know all of the following:

The main reason for the seasons is the angle of
incoming solar radiation caused by the 23 ½
degree tilt of Earth’s axis…NOT proximity to the
sun! You should recognize it from the pre-lab
background information in the angle of insolation
lab.

The most direct rays of the Sun are striking the
Tropic of Capricorn in the southern hemisphere,
where it is Summer Solstice at this point.

Because it is Summer Solstice in the southern
hemisphere in this position, the Earth is at or
close to perihelion. In this position, even though
the Earth is closer to the sun by a few million
miles, the northen hemisphere is experiencing
winter solstice. This helps illustrate the fact that
proximity to the Sun has little or nothing to do
with the seasons on Earth.

The poles on Earth experience colder extremes because the Sun’s rays are most oblique there. Observe the
diagram!