Question

10 where is phosphorus stored?
11 how do people obtain phosphorus?
12 how does the release of large amounts of phosphorus by humans cause problems?
the nitrogen cycle
for questions 13–15, circle the letter of the correct answer.
13 most of the nitrogen on earth is located in the
a biosphere.
b geosphere.
c atmosphere.
d hydrosphere.
14 which of the following crops increases the amount of usable nitrogen in soil?
a corn
b wheat
c legumes
d tomatoes
15 the haber - bosch process enabled people to
a fix nitrogen artificially.
b clean up nitrogen pollution.
c create natural nitrogen.
d acquire nitrogen from plants.
16 name two ways nitrogen can be fixed naturally for plant use.
17 what happens to nitrogen during the process of denitrification?
skill builder organize information
18 fill in the compare/contrast table with information about the different biogeochemical cycles.

carbon cycle

phosphorus cycle

nitrogen cycle

Explanation:

1. Phosphorus is mainly stored in rocks and sediments.
2. People obtain phosphorus by consuming plants and animals that have absorbed phosphorus from the soil, or through fertilizers containing phosphorus.
3. The release of large - amounts of phosphorus by humans can cause water pollution, leading to eutrophication in water bodies which results in excessive growth of algae and depletion of oxygen levels harming aquatic life.
4. Most of the nitrogen on Earth is located in the atmosphere (about 78% of the atmosphere is nitrogen gas). So the answer is C.
5. Legumes have symbiotic relationships with nitrogen - fixing bacteria. These bacteria convert atmospheric nitrogen into a usable form for plants, increasing the amount of usable nitrogen in the soil. So the answer is C.
6. The Haber - Bosch process is an artificial method to fix nitrogen, converting atmospheric nitrogen into ammonia for use in fertilizers. So the answer is A.
7. Two natural ways nitrogen can be fixed for plant use are: lightning (the high energy of lightning causes nitrogen and oxygen in the atmosphere to react, forming nitrogen oxides which are then converted into nitrates in the soil) and nitrogen - fixing bacteria in the root nodules of legumes.
8. During the process of denitrification, nitrate (NO₃⁻) is converted into nitrogen gas (N₂) or nitrous oxide (N₂O) by denitrifying bacteria, returning nitrogen to the atmosphere.

18.

	Carbon Cycle	Phosphorus Cycle	Nitrogen Cycle
Main Processes	Photosynthesis, respiration, decomposition, combustion	Weathering of rocks, uptake by plants, consumption by animals, return to soil/sediments	Nitrogen fixation, nitrification, denitrification, assimilation
Human Impact	Burning of fossil fuels increases CO₂ in atmosphere, deforestation reduces carbon sequestration	Over - use of phosphorus fertilizers leads to water pollution, mining disrupts natural phosphorus cycle	Use of synthetic fertilizers, industrial processes increase nitrogen in environment causing pollution

Answer:

1. Phosphorus is mainly stored in rocks and sediments.
2. By consuming plants/animals or through fertilizers.
3. Causes water pollution and eutrophication.
4. C. atmosphere
5. C. legumes
6. A. fix nitrogen artificially
7. Lightning and nitrogen - fixing bacteria in legume root nodules.
8. Nitrate is converted into nitrogen gas or nitrous oxide and returned to the atmosphere.
9. See the above - constructed table.