Topic 3 Day 3 Carbon and Water Cycle

This diagram shows the flow of carbon in a terrestrial ecosystem. What will most likely happen if the decomposers are removed from the carbon cycle?

• The amount of carbon dioxide in the atmosphere will decrease.

• The amount of carbon dioxide in the atmosphere will increase.

• The amount of carbon dioxide used by producers will increase.

• The amount of carbon dioxide needed by consumers will decrease.

Answer explanation

In a terrestrial ecosystem, decomposers play a crucial role in the carbon cycle. They break down dead organic matter and release carbon dioxide back into the atmosphere. If they are removed, the process of decomposition will slow down, reducing the amount of carbon dioxide returned to the atmosphere, hence the amount of carbon dioxide in the atmosphere will decrease.

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The framework of organic molecules essential to all organisms is composed mainly of carbon atoms. Which processes are involved in the cycling of carbon within an environment?

• photosynthesis and respiration

• evaporation and condensation

• transcription and translation

• diffusion and transpiration

Answer explanation

Photosynthesis is the process by which plants use sunlight to convert carbon dioxide and water into glucose, a type of sugar. Respiration is the process by which organisms convert glucose and oxygen back into carbon dioxide and water, releasing energy. Together, these two processes form the primary pathway for carbon cycling in the environment.

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All organisms contain carbon and oxygen. Both of these elements are also found in Earth’s atmosphere. Which of the following processes does not return carbon to the atmosphere?

• Combustion

• Decomposition

• Photosynthesis

• Cellular respiration

Answer explanation

Photosynthesis is a process by which green plants use sunlight to synthesize foods with the help of carbon dioxide and water. In this process, instead of releasing carbon to the atmosphere, it actually absorbs carbon dioxide and converts it into glucose, hence it does not return carbon to the atmosphere. Combustion, decomposition, and cellular respiration are all carbon sources, so they add carbon dioxide to the atmosphere.

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Over the past two centuries, people’s use of coal and oil has increased dramatically. The graph above shows the amount of carbon dioxide in the atmosphere and changes in Earth’s average temperature from the middle 1800s to the early 2000s.

Which of the following is the best explanation for the data shown in the graph?

• Carbon dioxide increases naturally over time and causes temperatures to rise.

• The use of fossil fuels puts carbon dioxide into the air and causes temperatures to rise.

• Increases in temperature are not related to increases in carbon dioxide.

• Increases in carbon dioxide are not related to human activities.

Answer explanation

The best explanation for the data shown in the graph is that the use of fossil fuels puts carbon dioxide into the air and causes temperatures to rise. Over the past two centuries, human activities, specifically the increased use of coal and oil, have dramatically increased CO2 levels in the atmosphere, leading to a rise in Earth's average temperature.

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Tropical rain forests receive as much as 450 cm of rain per year. They are the richest biome in terms of number of species.

Which statement best explains how destruction of tropical rain forests could affect the carbon cycle?

• Destroying rain forest trees would cause carbon dioxide levels in the atmosphere to drop dangerously low.

• A loss of rain forest trees would have only a small effect on the carbon cycle, because they are green all year long.

• Rain forest destruction would cause only a small increase in carbon dioxide levels if the roots were left to remove carbon dioxide from the air.

• Cutting down rain forests could increase atmospheric carbon dioxide levels, because trees that could take up carbon dioxide would be removed.

Answer explanation

The destruction of tropical rainforests results in an increase in atmospheric carbon dioxide levels. This is because trees, which absorb carbon dioxide, are being removed during deforestation. As such, the process disrupts the carbon cycle by reducing the amount of carbon dioxide that can be absorbed from the atmosphere.

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The diagram shows a simplified carbon cycle.

Which of the following major storage reservoirs of carbon, stored in the form of carbon dioxide, is not represented in this diagram?

• Algae

• Soil bacteria

• Ocean

• Decay

Answer explanation

The question asks about the major storage reservoirs of carbon, stored in the form of carbon dioxide, not represented in the given diagram. The correct answer is 'Ocean'. This indicates that in the provided diagram, the ocean, which is a significant reservoir of carbon dioxide, is not depicted.

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NGSS.MS-LS2-3