Set 8 - Part 5 - Biogeochemical cycles - Khan Academy

celine's version from 2018-02-22 23:03

Section 1

Question Answer
Energy flows through an ecosystem and is dissipated as ____________, but chemical elements are recycled.heat
The ways in which an element—or compound such as water—moves between its various living and nonliving forms and locations in the biosphere is called a ____________ biogeochemical cycle
Biogeochemical cycles important to living organisms include thewater, carbon, nitrogen, phosphorous, and sulfur cycles.
The vast majority of Earth's water is ____________ found in oceans. Only a tiny fraction is readily accessible freshwater, which is what humans need.saltwater
Water found at the Earth's surface can cycle rapidly, but much of Earth's water lies in ____________, ____________, and ____________; this is why water cycles, oceans, and underground reservoirs
____________ is found underground between soil particles and in cracks of rocks.Groundwater
____________are groundwater reservoirs often tapped by wells.Aquifers
Where does the energy that powers the water cycle come from?the sun
What is evaporation?Water gets warm and changes from liquid water to water vapor.
What is the correct term for moisture that falls to the ground from clouds?precipitation
From where does most water evaporate?oceans
What is the correct term for rising water vapor meeting colder air and turning back into water droplets?condensation
What is the only thing in nature that can be a solid, a liquid, or a gas?water
What are the three stages of the water cycle?evaporation, condensation, precipitation
What is the correct term for plants releasing water from their leaves, which then evaporates?transpiration
Where does some water from the water cycle collect underground?aquifers

Section 2

Question Answer
Carbon is an essential element in the bodies of living organisms. It is also economically important to modern humans, in the form of ____________.fossil fuels
Carbon dioxide from the atmosphere is taken up by ____________ organisms and used to make organic molecules, which travel through food chains. In the end, the carbon atoms are released CO2 in respiration.photosynthetic
The carbon cycle begins with photosynthesis in plants. True or False?False
Plants are primary consumers of carbon dioxide. True or False?True
Animals are primary consumers of carbon dioxide. True or False?False
Humans are producers of carbon dioxide. True or False?True
Carbon dioxide is easily dissolved in water. True or False?True
All of the carbon in existence is continually recycled in the carbon cycle.True
Where does the carbon come from that the plants use?Air
Are humans primary consumers of carbon dioxide or secondary consumers?Neither. Humans produce carbon dioxide.

Section 3

Question Answer
What is nitrogen used for in a plant?Making proteins
How do plants take in nitrogen?Through the roots
In what form is nitrogen taken into a plant?Nitrates
What word describes the relationship between the plant and nitrogen-fixing bacteria?Mutualistic
Which microorganism turns nitrogen gas into ammonia?Nitrogen fixing bacteria
Which microorganisms convert nitrates to nitrites?Denitrifying bacteria
Which microorganism turns ammonia into nitrates?Nitrifying bacteria
Another method for fixing nitrogen?Lightning converts nitrogen gas into soluble nitrates.
What is the name of the soil bacteria that convert proteins and urea into ammonia?Decomposers
Nitrogen exists in the atmosphere as ____________ gas.N2
In ____________, bacteria convert N2 into ammonia, a form of nitrogen usable by plants. When animals eat the plants, they acquire usable nitrogen compounds.nitrogen fixation
The nutrient that's in shortest supply and limits growth.limiting nutrient
Nitrogen is a common ____________ in nature, and agriculture.limiting nutrient
When fertilizers containing nitrogen and phosphorous are carried in runoff to lakes and rivers, they can result in blooms of algae—this is called eutrophication.
What is the most common way that nitrogen fixation occurs?nitrogen fixing bacteria
Organic nitrogen is coverted back to inorganic nitrogen like ammonium through the process ofdecay (After nitrogen is incorporated into organic matter, it is often converted back into inorganic nitrogen by decay. When organisms die, bacteria and fungi consume the organic matter. During decomposition, a significant amount of the nitrogen contained within the dead organism is converted to ammonium)
Ammonium (NH4) stays in soil, while nitrate (NO3) is easily leached out. Why do they behave so differently?NH4 has a positive charge and sticks to soil particles. (In nitrification, some positively charged ammonium ions are converted to negatively charged nitrate. The positive charge prevents ammonium nitrogen from being leached out of the soil by rainfall. In contrast, the negatively charged nitrate ion is not held by soil particles and so can be washed out of the soil and into surface and groundwater)
Which process releases dinitrogen gas (N2) back into the atmosphere?denitrification (In the process of denitrification, bacteria convert nitrate to dinitrogen (N2), a gas which is rapidly lost to the atmosphere)
Once bacteria have fixed nitrogen, it can be taken up by plants and animals, where it is used in the production ofproteins (Nitrogen (N) is an essential component of DNA, RNA, and proteins. In the process of nitrogen fixation, bacteria convert N2 from the atmosphere into ammonium, a form that plants and animals can use. The ammonia produced by nitrogen fixing bacteria is used to make protein)
Synthetic fertilizers add _____________ to the soil.fixed nitrogen (ammonium) (Using synthetic nitrogen fertilizers fixes nitrogen in the soil. Through the use of synthetic fertilizers, humans have more than doubled the amount of fixed nitrogen that is pumped into the biosphere every year)

Section 4

Question Answer
The phosphorous cycle is ____________ compared to other biogeochemical cycles such as the water, carbon, and nitrogen cycles.^1 ​slow
In nature, phosphorous is found mostly in the form of ____________phosphate ions
Over land, most of the water in the atmosphere results from ___________, whereas over the oceans, most of the water in the atmosphere results from ____________.transpiration/evaporation
The largest store of carbon molecules on earth is inmarine sediments
Some bacteria have the ability to "fix" nitrogen. This meansthey convert atmospheric nitrogen gas into biologically useful forms of nitrogen.
The phosphorous cycle differs from the water, carbon, and nitrogen cycles in thatthe reservoir for phosphorous exists in mineral form in rocks rather than in the atmosphere.
What percentage of the energy that hits a plant's leaves is converted into chemical (food) energy?1%
Phosphorus is difficult for plants and animals to access in nature becausemost phosphorus in the environment is stored in reservoirs.
Phosphorus does NOT travel through which sphere?atmosphere (Since phosphorous does not involve a gas stage, it does not become part of the atmosphere in any significant way)
In urban areas, water can contain high levels of phosphorous due to use of agents such as fertilizers. What is a possible negative effect of excess phosphorus in the water?Development of "dead zones" (High levels of phosphorus that is carried into the water via runoff can cause an excessive growth of algae known as eutrophication. The algae may deplete oxygen from the water and create a dead zone)

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