Nitrogen, which comprises 78 percent of Earth's atmosphere, is necessa

Question

Nitrogen, which comprises 78 percent of Earth's atmosphere, is necessary for plant nutrition. But agriculture and industry have doubled the rate at which nitrogen is "fixed" and in so doing may have raised a serious environmental threat. Despite the natural abundance of nitrogen, most of it is in the form of an inert gas, N2, which cannot be used by living things. To nourish plants, it must be fixed—bonded with hydrogen or oxygen. In nature, some of this fixing is done by lightning, but most of it is the work of certain algae and bacteria. Human activity has greatly increased the supply of usable nitrogen. The largest artificial source of fixed nitrogen is chemical fertilizer. The cultivation of plants such as legumes that carry nitrogen-fixing bacteria on root nodules is another major source. Automobiles, factories, and power plants release significant amounts of fixed nitrogen by bu ming fossil fuels such as oil and coal. Other sources include forest fires and sewage treatment.

It is uncertain what effect these changes have had so far, but the potential for harm is considerable. Burning forests and fossil fuel creates fixed-nitrogen gases that increase smog and acid rain, damage the ozone layer, and add to global warming by trapping heat in the atmosphere. Synthetic fertilizers, along with this airborne fixed nitrogen, cause plants that thrive on nitrogen to drive out other species, which may become extinct along with the animals that depend on them. Also, since many bacteria and fungi feed on nitrogen, these nitrogen-rich plants decompose faster than other plants. This prevents the plant community from storing larger amounts of carbon. The failure of plant communities to absorb more carbon dioxide and store it as carbon may become another contributor to global warming.

Finally, fixed nitrogen in the air settles and adds to the fixed nitrogen already in the soil from chemical fertilizers. This fixed nitrogen runs off, or seeps into rivers and streams, where, with fixed nitrogen from sewage treatment plants, it flows into lakes and oceans. Besides making drinking water unsafe, this can lead to algae blooms that kill fish. It can also spur the growth of small aquatic plants that cloud the water and deprive larger plants of sunlight. When these larger plants die, they are consumed by bacteria that multiply and deplete the water of oxygen, rendering it incapable of sustaining life.   1 
 1.According to the passage, which of the following may be an effect of artificial fertilizers?

I.  Increased acid rain
 II.  Extinction of some plant species
 III.  Algae blooms

A) I only 
B) II only 
C) I and II only 
D) II and III only 
E) I, II, and III

2 
 2. It can be inferred that the author would be most likely to agree with which of the following statements?

A) Most of the fixed nitrogen in the environment today is of human origin. 
B) Nitrogen in the form of N2 is relatively harmless. 
C) Excess fixed hydrogen has done irreversible harm to the environment. 
D) The plants that are grown for food are not the ones that do best in a high-nitrogen environment. 
E) Algae blooms are caused by a loss of oxygen in the water.

3 
 3. Which of the following areas would probably be hardest hit by the effects of fixed nitrogen?

A) a region where thunderstorms are frequent 
B) the part of a river upstream from a sewage treatment facility 
C) an area where legumes are grown 
D) a bay at the mouth of a major river that flows past farms that use chemical fertilizers
E) a region where fungi are grown commercially

4 
 4. Which of the following statements, if true, would most weaken the author's claim?

A) Forest fires generate more fixed oxygen than do automobiles. 
B) Fixed-nitrogen gasses are not the only gasses that trap heat in the atmosphere
C) The demand for food grown without chemical fertilizers has been increasing. 
D) Earth's forests have enormous untapped potential to absorb and store carbon dioxide. 
E) Most of the bacteria and fungi that consume nitrogen are harmless to humans.

anmit123 · Accepted Answer

Q1-
I is incorrect (acid rain is because of burning fossil fuels as per para 2),this eliminates A,C,E 
Now we are left with B and D
Both contain II, which means we actually need to check whether statement III is correct or not.
III is also mentioned in the passage.

Ans:D

Q2-
A is wrong, the author only says that human activities have increased the supply. This is different from what statement A is conveying.
B could be correct, keep it for now.
C is incorrect as in para 2 the author mentions-'It is uncertain what effect these changes have had so far, but the potential for harm is considerable'
D and E are irrelevant.

Ans:B

Q3-
D is the answer because it will carry nitrogen from all these farms

Q4-
Answer is D
As per para 2-'Synthetic fertilizers, along with this airborne fixed nitrogen, cause plants that thrive on nitrogen to drive out other species, which may become extinct along with the animals that depend on them. Also, since many bacteria and fungi feed on nitrogen, these nitrogen-rich plants decompose faster than other plants. This prevents the plant community from storing larger amounts of carbon. The failure of plant communities to absorb more carbon dioxide and store it as carbon may become another contributor to global warming. '
If Earth's forests have enormous untapped potential to absorb and store carbon dioxide, then it won't contribute to global warming as is claimed by the author.

apovit · Answer

Hello,
Please post the explanation for the last ques "Selected option B"-the wrong one.

anmit123 · Answer

This does not weaken the author's claim about global warming.

Ilanchezhiyan · Answer

For qn. 4, why cant the option be C?
The author says the that Chemical fertilizers are the greatest contributors for increase in fixed nitrogen.
Option C says that the demand for food grown without chemical fertilizers is increasing. = Meaning that the need for chemical fertilizers which are the greatest contributors to fixed nitrogen in the environment, are decreasing .

Rongoing · Answer

Hi, Ilanchezhiyan

The demand decrease doesn't necessarily mean it can not be the largest artificial source anymore

ready01 · Answer

For Q2-
Why E is irrelevant. Can some explain?

arushi118 · Answer

Because it is the algae blooms which indirectly deplete the oxygen and not the other way round.

Can you please explain that for Q3 why can it not be C.
And for Q4 why can it not be C?

guddo · Answer

3. Which of the following areas would probably be hardest hit by the effects of fixed nitrogen?

Most nitrogen is inert N2, so it must be “fixed” to be usable. Human activity has greatly increased fixed nitrogen through fertilizers, nitrogen fixing crops like legumes, and fossil fuel burning. A major harm is that fixed nitrogen accumulates in waterways through runoff and sewage, causing algae blooms, oxygen depletion, and die offs in lakes and oceans.

The passage says the worst aquatic impacts happen when fixed nitrogen from fertilizers and sewage enters rivers, then flows into lakes and oceans, leading to algae blooms and oxygen loss. So the hardest hit area would be where a lot of river borne nitrogen ends up and concentrates.

(A) a region where thunderstorms are frequent

Frequent thunderstorms increase natural fixing, but the passage’s hardest hit examples are about human added nitrogen and water pollution, not lightning.

(B) the part of a river upstream from a sewage treatment facility

Upstream from sewage treatment means it has not received that sewage nitrogen yet.

(C) an area where legumes are grown

Legumes add fixed nitrogen, but the most severe described damage is in downstream water bodies receiving runoff, not just the farm area.

(D) a bay at the mouth of a major river that flows past farms that use chemical fertilizers

A bay at a river mouth downstream of farms is exactly where fertilizer runoff (and other river carried nitrogen) would collect and trigger the algae and oxygen problems described.

(E) a region where fungi are grown commercially

Commercial fungi growing is not identified as a major source or a hardest hit area in the passage.

Answer: (D)

guddo · Answer

4. Which of the following statements, if true, would most weaken the author's claim?

(A) Forest fires generate more fixed oxygen than do automobiles.

This is about forest fires versus automobiles and even says “fixed oxygen,” which does not address the author’s argument about fixed nitrogen harms.

(B) Fixed-nitrogen gasses are not the only gasses that trap heat in the atmosphere

This does not weaken anything, since the author never claims fixed nitrogen gases are the only heat trapping gases.

(C) The demand for food grown without chemical fertilizers has been increasing.

This is only a consumer trend and does not show that fertilizer use or fixed nitrogen inputs are actually decreasing.

(D) Earth's forests have enormous untapped potential to absorb and store carbon dioxide.

This directly undercuts the author’s specific link between nitrogen driven faster decomposition and reduced carbon storage as a contributor to global warming by saying forests can absorb and store far more carbon dioxide.

(E) Most of the bacteria and fungi that consume nitrogen are harmless to humans.

This is irrelevant because the passage’s concern is ecological damage and unsafe water, not whether nitrogen eating microbes harm humans.

Answer: (D)

guddo · Answer

2. It can be inferred that the author would be most likely to agree with which of the following statements?

Most nitrogen is inert N2 and must be fixed to be usable. Human activity has greatly increased fixed nitrogen through fertilizers, legumes, and fossil fuel burning, and this extra fixed nitrogen can cause serious environmental harm, especially through air effects and water runoff that triggers algae blooms and oxygen depletion.

(A) Most of the fixed nitrogen in the environment today is of human origin.

The passage says humans have greatly increased fixed nitrogen and lists major human sources, but it does not say most fixed nitrogen today is human made, so this is too strong.

(B) Nitrogen in the form of N2 is relatively harmless.

The passage treats N2 as inert and unusable by living things, and the harms discussed come from fixed nitrogen, not N2. So the author would likely agree N2 is relatively harmless compared with fixed nitrogen.

(C) Excess fixed hydrogen has done irreversible harm to the environment.

“Fixed hydrogen” is not the topic, and “irreversible” is not supported.

(D) The plants that are grown for food are not the ones that do best in a high-nitrogen environment.

The passage says nitrogen loving plants drive out other species, but it does not claim food crops are not among the nitrogen loving plants.

(E) Algae blooms are caused by a loss of oxygen in the water.

The passage says fixed nitrogen leads to algae blooms, then later oxygen gets depleted due to decomposition. So algae blooms are not caused by oxygen loss, oxygen loss is a later effect.

Answer: (B)

Nitrogen, which comprises 78 percent of Earth's atmosphere, is necessa

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Nitrogen, which comprises 78 percent of Earth's atmosphere, is necessa

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