1E2 The Carbon & Nitrogen Cycles

Question 1

What is the carbon cycle?

Answer 1

The process through which carbon continuously moves between the atmosphere, hydrosphere, lithosphere, and biosphere, involving both living (biotic) and non-living (abiotic) components.

The carbon cycle is crucial for regulating Earth’s climate and involves various processes such as photosynthesis, respiration, decomposition, and fossil fuel combustion.

Question 2

Why is the carbon cycle important?

Answer 2

It regulates global climate, supports photosynthesis, and maintains ecological balance essential for sustaining life.

Question 3

How does carbon exist in the atmosphere?

Answer 3

Mainly as carbon dioxide (CO₂), which acts as a greenhouse gas and regulates Earth’s temperature.

Question 4

What happens when there is excessive CO₂ in the atmosphere?

Answer 4

It leads to global warming by trapping heat and raising Earth’s average temperature.

Question 5

How does increased atmospheric CO₂ affect water vapor?

Answer 5

It increases evaporation, leading to higher levels of water vapor, which is a potent greenhouse gas and amplifies warming.

Question 6

What comprises the hydrosphere in the carbon cycle?

Answer 6

• Oceans
• Lakes
• Rivers
• Water vapor

Question 7

How does the ocean interact with CO₂ ?

Answer 7

The ocean absorbs significant amounts of CO₂ from the atmosphere, which can lead to ocean acidification.

Question 8

What is ocean acidification?

Answer 8

Excess CO₂ dissolves in seawater to form carbonic acid, which releases hydrogen ions, lowering the pH and making the ocean more acidic.

Ocean acidification affects marine life, particularly organisms with calcium carbonate structures, which are vital for marine ecosystems.

Question 9

How does ocean acidification impact marine organisms?

Answer 9

It impairs the ability of marine organisms, like corals and shellfish, to build and maintain their calcium carbonate shells and skeletons.

Question 10

Where is carbon stored in the biosphere?

Answer 10

In living organisms as organic compounds, including carbohydrates, lipids, proteins, and nucleic acids (DNA and RNA).

Question 11

How do plants and phytoplankton use CO₂?

Answer 11

They convert atmospheric CO₂ into organic molecules through photosynthesis, which are then used by other organisms for energy and growth.

Question 12

How do non-photosynthetic organisms contribute to the carbon cycle?

Answer 12

They release CO₂ back into the atmosphere through respiration.

Question 13

Where is carbon stored in the lithosphere?

Answer 13

In rocks and sediments, including fossil fuels like coal, oil, and natural gas, as well as carbonate rocks like limestone.

Question 14

What are fossil fuels?

Answer 14

They are carbon-rich energy sources formed from ancient organic matter.

Burning them releases stored CO₂, disrupting the carbon cycle.

Question 15

What are carbon sinks?

Answer 15

Natural systems that absorb more CO₂ than they emit, aiding in regulating atmospheric CO₂ levels.

Question 16

Give examples of carbon sinks.

Answer 16

• Oceans
• Forests
• Soil

Question 17

What role do trees play in the carbon cycle?

Answer 17

Trees sequester CO₂ from the atmosphere during photosynthesis, storing it as biomass and helping to regulate atmospheric CO₂ levels.

Question 18

How does the water cycle support the carbon cycle?

Answer 18

It supplies water essential for plant photosynthesis, which is crucial for carbon fixation and the growth of carbon-storing biomass.

Question 19

What are carbon reservoirs?

Answer 19

Natural or artificial systems that store carbon, influencing its availability and affecting climate and ecosystems.

Examples include forests, oceans, soil, and fossil fuels.

Question 20

Give examples of carbon reservoirs.

Answer 20

• Forests
• Oceans
• Soil
• Fossil fuels

Question 21

What is the impact of fossil fuel extraction on the carbon cycle?

Answer 21

It releases large amounts of CO₂, disrupting the balance of the carbon cycle.

Question 22

How is carbon sequestered in marine environments?

Answer 22

Marine organisms incorporate CO₂ into their shells and skeletons; when they die, their carbon-rich remains settle into ocean sediments.

The sequestration of carbon in marine sediments plays a significant role in the long-term carbon cycle and climate regulation.

Question 23

How is carbon stored long-term in the ocean?

Answer 23

In ocean sediments, where it can eventually form sedimentary rocks like limestone over millions of years.

Question 24

What is the overall function of the carbon cycle?

Answer 24

It involves the continuous exchange of carbon between the sky, Earth, water, and living organisms, crucial for sustaining life.

Question 25

How is the carbon cycle similar to the water cycle?

Answer 25

Both are global biogeochemical cycles essential for life, involving the movement of elements through the Earth’s systems and supporting various biological processes. They are interdependent.

Both cycles are driven by energy from the sun and involve the movement of their respective elements through different Earth systems, maintaining ecological balance.

Question 26

What is nitrogen fixation?

Answer 26

The conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by bacteria, making nitrogen available for use by plants and other organisms.

The Earth’s atmosphere is almost 80% nitrogen, however in its pure gas form it cannot be used by living organisms.

Question 27

Why is atmospheric nitrogen unusable for most organisms?

Answer 27

Because it is in a stable N₂ form that cannot be directly utilized by plants or animals.

Question 28

Which organisms are primarily responsible for nitrogen fixation?

Answer 28

Nitrogen-fixing bacteria

This includes free-living soil bacteria, symbiotic bacteria in plant roots, and cyanobacteria in oceans.

Question 29

What is the role of ammonia in the nitrogen cycle?

Answer 29

It is a usable form of nitrogen that can be incorporated into organic molecules like amino acids by producers.

Some bacteria have evolved the ability to add hydrogen atoms to nitrogen and create ammonia, which can be easily incorporated into organic molecules like amino acids.

Question 30

What is nitrification?

Answer 30

The biological oxidation of ammonia to nitrite (NO₂⁻) and then to nitrate (NO₃⁻) by nitrifying bacteria.

Question 31

Why is nitrification important?

Answer 31

It converts ammonia into nitrate, making nitrogen available to plants in a form they can absorb and use for growth.

Question 32

What is denitrification?

Answer 32

The process by which bacteria convert nitrate (NO₃⁻) back into atmospheric nitrogen (N₂), completing the nitrogen cycle.

Question 33

How does nitrogen return to the atmosphere?

Answer 33

Through denitrification, where bacteria convert nitrate (NO₃⁻) back into nitrogen gas (N₂).

Question 34

What are the primary steps of the nitrogen cycle in a terrestrial ecosystem?

Answer 34

1. Nitrogen fixation
2. Nitrification
3. Assimilation by plants
4. Consumption by herbivores
5. Excretion
6. Denitrification

Question 35

What is eutrophication?

Answer 35

The process by which excessive nutrients, particularly nitrogen and phosphorus, lead to the rapid growth of algae and plants in aquatic environments.

Eutrophication can lead to significant ecological disruptions, including loss of biodiversity and changes in water quality.

Question 36

What can cause eutrophication?

Answer 36

Excessive use of fertilizers on farmland and the discharge of untreated sewage into water bodies.

Question 37

What are the consequences of eutrophication?

Answer 37

• Algal blooms.
• Oxygen depletion.
• The death of aquatic organisms due to hypoxia.

Question 38

What happens to aquatic ecosystems during an algal bloom?

Answer 38

Algae produce oxygen during the day but consume it at night, leading to oxygen depletion and potential suffocation of aquatic life.

Question 39

What is acid rain?

Answer 39

Rain that has been made more acidic due to the presence of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) in the atmosphere.

Question 40

How are sulfur dioxide and nitrogen oxides produced?

Answer 40

By burning fossil fuels such as coal, petroleum, and natural gas.

Question 41

What are the effects of acid rain on the environment?

Answer 41

It lowers the pH of water and soil, harming aquatic life, damaging forests, and eroding buildings and monuments.

Acid rain can have widespread impacts, including soil nutrient depletion, forest damage, and acidification of water bodies.

Question 42

What is the chemical equation for the formation of nitric acid in the atmosphere?

Answer 42

NO₂ + H₂O → HNO₃ (nitric acid)

Question 43

What is the main source of nitrogen for plants and producers?

Answer 43

• Ammonia
• Nitrite
• Nitrate

These nitrogen sources are produced by nitrogen-fixing and nitrifying bacteria.

Question 44

Why are synthetic fertilizers used in agriculture?

Answer 44

To replenish the soil with usable nitrogen compounds when crops are removed after harvest.

Question 45

What is the role of animal waste in the nitrogen cycle?

Answer 45

It supplies ammonia and compounds like urea, which plants can use.

Question 46

What happens to nitrate in the soil if there is an abundance?

Answer 46

It can be converted back to atmospheric nitrogen by denitrifying bacteria.

Question 47

What are cyanobacteria also known as?

Answer 47

Blue-green algae.

Question 48

Why is coal considered the ‘dirtiest’ fossil fuel?

Answer 48

It releases the most pollutants, including sulfur dioxide and nitrogen oxides, when burned, compared to natural gas and petroleum.