AP Environmental Science 1.4: Carbon Cycle

Practice AP Environmental Science questions on photosynthesis, respiration, decomposition, combustion, carbon sinks, and human carbon emissions.

[Maximum number: 7]

Biogeochemical cycles describe the movement of certain elements (typically bound with other elements in compounds) through Earth's atmosphere, hydrosphere, biosphere, and lithosphere. These elements and their compounds are necessary components of all life, and because they cycle, they can be used repeatedly by new generations of organisms. Each biogeochemical cycle has different pathways with various reservoirs (sources and sinks) where elements may reside for days or millions of years.

(a)

The atmosphere is one important carbon reservoir.

[ 2 ]

(i)

Describe a biological process by which carbon is removed from the atmosphere and converted to organic molecules.

[ 1 ]

(ii)

Describe a biological process by which carbon is converted from organic molecules to a gas and returned to the atmosphere.

[ 1 ]

Describe a biological process by which carbon is converted from organic molecules to a gas and returned to the atmosphere.
(1 point for a correct description: A student can earn the point even without explicitly identifying the process if an accurate description is provided. No point is earned for listing a word as an answer; the answer must identify the form of carbon being released into the atmosphere as part of the description)

- Respiration breaks down food/glucose/sugar/complex carbohydrates and releases $\mathrm{CO}_{2}$ into the atmosphere

- Animals digest food and produce gases such as methane that can be emitted either through belching or flatulence

- Decomposition of organic material by bacteria or fungi converts organic carbon into gases such as methane

(b)

Oceans and terrestrial systems are also important carbon reservoirs.

[ 3 ]

(i)

Explain how atmospheric carbon is incorporated into two oceanic sinks.

[ 2 ]

(2 points: 1 point for each correct description of carbon incorporation into an oceanic sink. Only the first two descriptions can earn points)

- Carbon $\left(\mathrm{CO}_{2}\right)$ can be taken up by organisms like phytoplankton for photosynthesis

- Carbon can be taken up by marine organisms and used for shells, skeletons, coral, etc.

- Biological pump (organisms in the upper ocean sink to the bottom of the ocean)

- Atmospheric $\mathrm{CO}_{2}$ can dissolve directly into ocean water OR atmospheric $\mathrm{CO}_{2}$ can dissolve into precipitation and ultimately reach the ocean

- Carbon can react with other elements/compounds and form carbonates/limestone/sedimentary rocks (just "rocks" is too vague to earn a point)

(ii)

Identify one terrestrial sink, other than fossil fuels, that stores carbon for thousands to millions of years.

[ 1 ]

(c)

The burning of fossil fuels has been shown to increase the concentration of carbon in the atmosphere. Discuss TWO other human activities that increase the concentration of carbon in the atmosphere.

[ 2 ]

(2 points: 1 point for each accurate discussion of a human activity that increases atmospheric carbon compounds NOT related to burning fossil fuels)

- Deforestation-cutting down trees reduces the reservoirs for carbon OR cutting down trees can result in carbon being released back into the atmosphere through the process of decay/decomposition

- Biomass burning releases carbon (CO, CO2, carbon particulates)

- Trash/waste incineration can release carbon ( $\mathrm{CO}_{2}, \mathrm{CO}$ , carbon particulates)

- Slash and burn agricultural practices-burning organic matter releases carbon ( $\mathrm{CO}_{2}, \mathrm{CO}$ , carbon particulates)

- Deep plowing or strip mining disrupts soil and releases carbon $\left(\mathrm{CO}_{2}\right)$

- Humans make landfills that can produce carbon-containing carbon-based gases (mainly methane)

- Raising cows and/or other ruminant animals releases carbon-containing gases (methane)

- Manufacture and use of CFCs/HCFCs/other carbon-containing compounds releases carbon

- Destruction of wetlands (releases $\mathrm{CO}_{2}$ /removes sink for $\mathrm{CO}_{2}$ )

- Production of cement releases $\mathrm{CO}_{2}$

All question bank results loaded

Covered syllabus points

1.4 The Carbon Cycle question 1

Question (a)

Question (i)

Question (ii)

Question (b)

Question (i)

Question (ii)

Question (c)