5.15 Quiz: Carbon And Oxygen Cycles

13 – 25 Questions 10 min

This 5.15 Quiz: Carbon And Oxygen Cycles focuses on tracing carbon and oxygen through photosynthesis, respiration, combustion, and decomposition in ecosystems and the atmosphere. You will practice interpreting biogeochemical cycle diagrams and predicting human impacts, skills valuable for biology students, earth science learners, and future environmental or natural resource technicians.

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Part 1 — Questions

Answer each question on paper. Do not turn the page until you are ready to check your work.

Which process removes carbon dioxide from the atmosphere and stores it in glucose inside plant cells?

Photosynthesis
Combustion
Cellular respiration
Decomposition

Photosynthesis in green plants converts carbon dioxide and water into sugar and releases oxygen into the atmosphere.

True
False

A potted plant is moved into a completely dark closet for 24 hours. Which statement best describes the plant’s net gas exchange with the air during this time?

Cellular respiration continues, so there is a net release of carbon dioxide.
Photosynthesis continues, so there is a net uptake of carbon dioxide.
Net gas exchange stops because the plant shuts down all metabolism.
Both photosynthesis and respiration speed up, so net gas exchange is zero.

Which reservoir currently holds the largest amount of carbon in the Earth system among these choices?

The deep ocean
Terrestrial plants
The atmosphere
The surface layer of the ocean

Decomposer activity in soil consistently increases oxygen levels in the small air spaces between soil particles.

True
False

Which statement correctly describes a similarity between the carbon cycle and the water cycle that you studied in a 5.14 quiz on water and nitrogen cycles?

In the water cycle, matter can leave Earth, but in the carbon cycle it cannot.
Only the water cycle is powered by energy from the Sun.
In both cycles, the same matter is recycled through living and nonliving parts of Earth many times.
Only the carbon cycle includes living organisms.

In the context of carbon stored in carbonate rocks that you studied in a 5.03 quiz on mineral resources, which process returns some of this rock-bound carbon to the atmosphere as carbon dioxide?

Burial of shells and carbonate sediments on the seafloor
Subduction and heating of carbonate rocks, followed by volcanic eruptions
Formation of new coral reefs along continental margins
Physical weathering of limestone into smaller rock fragments

A coastal city wants to reduce its contribution to atmospheric carbon dioxide while still meeting its electricity needs. Which change would most directly lower the city’s carbon emissions from electricity generation?

Building more multi-level parking garages downtown
Installing additional gas-powered space heaters in homes
Replacing a coal-fired power plant with a wind farm
Converting a large city park into cropland

Select all that apply. Which processes move carbon from living things into the atmosphere as carbon dioxide?

A.Photosynthesis
B.Cellular respiration
C.Decomposition by bacteria
D.Combustion of wood
E.Fossilization of plant material

10.

During a warm, still summer night, a lake experiences a dense algal bloom. Just before sunrise, which change is most likely in the surface water compared with the previous afternoon?

Dissolved oxygen will drop to zero because oxygen is converted into ozone at the water surface.
Dissolved oxygen will stay the same because algae balance respiration and photosynthesis at night.
Dissolved oxygen will decrease because many organisms are still respiring.
Dissolved oxygen will increase because algae continue photosynthesis all night.

11.

Unlike the nitrogen cycle, the carbon cycle does not involve any gas phase in the atmosphere.

True
False

12.

Select all that apply. Which land-use changes are likely to increase the net flux of carbon from the land biosphere to the atmosphere?

A.Converting natural grassland to an urban area with concrete and buildings
B.Clearing a forest and converting it to cattle pasture
C.Restoring wetlands on former farmland
D.Planting long-lived trees on degraded land
E.Draining a peatland and burning the vegetation

13.

Arrange the following events in the correct order to show how a carbon atom in atmospheric carbon dioxide could move through a food chain and back into the air.

Put these in the correct order (write 1–4 beside each):

____An herbivore eats the plant and incorporates the carbon into its tissues.
____A predator eats the herbivore and uses the carbon in its own cells.
____The predator respires and releases CO2 back into the air.
____CO2 is taken into a leaf and fixed into an organic molecule.

14.

A sealed terrarium contains green plants and small snails and is kept under a regular day–night light cycle. Over a full 24-hour period, which statement best describes the overall relationship between carbon dioxide and oxygen inside the terrarium?

Over 24 hours, oxygen will gradually increase because plants photosynthesize more than they respire.
Over 24 hours, carbon dioxide will gradually increase because animals respire more than plants photosynthesize.
Over 24 hours, total amounts of carbon dioxide and oxygen will stay nearly constant because photosynthesis and respiration balance each other.
At night, both photosynthesis and respiration stop, so gas levels remain fixed until daylight returns.

15.

A student is comparing fast and slow components of the carbon cycle. Which example best represents a slow-carbon process?

Carbonate shells settling on the seafloor and forming limestone rock
A person exhaling during exercise
Burning gasoline in a car engine
A forest fire releasing carbon dioxide

16.

Select all that apply. Which processes directly produce free molecular oxygen (O2) as a product?

A.Photosynthesis by phytoplankton in the surface ocean
B.Aerobic respiration in plant roots
C.Denitrification by certain bacteria
D.Ultraviolet splitting of water vapor in the upper atmosphere
E.Combustion of methane in air

17.

A student reviews both the 5.14 quiz on water and nitrogen cycles and the 5.15 quiz on carbon and oxygen cycles. Which statement describes a fundamental similarity among all these biogeochemical cycles?

Each is driven only by slow geological processes.
Each has its largest reservoir outside the Earth system.
Each involves matter being recycled between reservoirs instead of being used up.
Each can occur without any involvement of living organisms.

18.

Industrial cement production releases carbon dioxide both from burning fuels for heat and from chemically converting limestone into clinker.

True
False

19.

A scientist observes that atmospheric carbon dioxide concentrations are rising while the average carbon isotope ratio is becoming lighter, showing more carbon-12 relative to carbon-13. Which source best explains both changes?

Enhanced weathering of silicate rocks on continents
Increased release of carbon dioxide from volcanic eruptions
Expanded burning of fossil fuels by humans
Stronger upwelling of deep ocean water

20.

In a deep, stratified lake during summer, the bottom water is cut off from surface mixing and receives a steady rain of organic matter from above. Select all that apply. Which processes are most responsible for declining oxygen levels in the deep water over the season?

A.Respiration by fish and invertebrates living near the bottom
B.Mixing of oxygen-rich surface water into the deep layer
C.Aerobic decomposition of sinking organic particles
D.Diffusion of oxygen from the atmosphere directly into bottom sediments
E.Photosynthesis by phytoplankton in the deep water

Part 2 — Answer key

Compare your answers after you have finished Part 1.

Which process removes carbon dioxide from the atmosphere and stores it in glucose inside plant cells?
Photosynthesis
Photosynthesis in green plants converts carbon dioxide and water into sugar and releases oxygen into the atmosphere.
True
A potted plant is moved into a completely dark closet for 24 hours. Which statement best describes the plant’s net gas exchange with the air during this time?
Cellular respiration continues, so there is a net release of carbon dioxide.
Which reservoir currently holds the largest amount of carbon in the Earth system among these choices?
The deep ocean
Decomposer activity in soil consistently increases oxygen levels in the small air spaces between soil particles.
False
Which statement correctly describes a similarity between the carbon cycle and the water cycle that you studied in a 5.14 quiz on water and nitrogen cycles?
In both cycles, the same matter is recycled through living and nonliving parts of Earth many times.
In the context of carbon stored in carbonate rocks that you studied in a 5.03 quiz on mineral resources, which process returns some of this rock-bound carbon to the atmosphere as carbon dioxide?
Subduction and heating of carbonate rocks, followed by volcanic eruptions
A coastal city wants to reduce its contribution to atmospheric carbon dioxide while still meeting its electricity needs. Which change would most directly lower the city’s carbon emissions from electricity generation?
Replacing a coal-fired power plant with a wind farm
Select all that apply. Which processes move carbon from living things into the atmosphere as carbon dioxide?
Cellular respiration; Decomposition by bacteria; Combustion of wood
During a warm, still summer night, a lake experiences a dense algal bloom. Just before sunrise, which change is most likely in the surface water compared with the previous afternoon?
Dissolved oxygen will decrease because many organisms are still respiring.
Unlike the nitrogen cycle, the carbon cycle does not involve any gas phase in the atmosphere.
False
Select all that apply. Which land-use changes are likely to increase the net flux of carbon from the land biosphere to the atmosphere?
Converting natural grassland to an urban area with concrete and buildings; Clearing a forest and converting it to cattle pasture; Draining a peatland and burning the vegetation
Arrange the following events in the correct order to show how a carbon atom in atmospheric carbon dioxide could move through a food chain and back into the air.
Correct order: CO2 is taken into a leaf and fixed into an organic molecule. → An herbivore eats the plant and incorporates the carbon into its tissues. → A predator eats the herbivore and uses the carbon in its own cells. → The predator respires and releases CO2 back into the air.
A sealed terrarium contains green plants and small snails and is kept under a regular day–night light cycle. Over a full 24-hour period, which statement best describes the overall relationship between carbon dioxide and oxygen inside the terrarium?
Over 24 hours, total amounts of carbon dioxide and oxygen will stay nearly constant because photosynthesis and respiration balance each other.
A student is comparing fast and slow components of the carbon cycle. Which example best represents a slow-carbon process?
Carbonate shells settling on the seafloor and forming limestone rock
Select all that apply. Which processes directly produce free molecular oxygen (O2) as a product?
Photosynthesis by phytoplankton in the surface ocean; Ultraviolet splitting of water vapor in the upper atmosphere
A student reviews both the 5.14 quiz on water and nitrogen cycles and the 5.15 quiz on carbon and oxygen cycles. Which statement describes a fundamental similarity among all these biogeochemical cycles?
Each involves matter being recycled between reservoirs instead of being used up.
Industrial cement production releases carbon dioxide both from burning fuels for heat and from chemically converting limestone into clinker.
True
A scientist observes that atmospheric carbon dioxide concentrations are rising while the average carbon isotope ratio is becoming lighter, showing more carbon-12 relative to carbon-13. Which source best explains both changes?
Expanded burning of fossil fuels by humans
In a deep, stratified lake during summer, the bottom water is cut off from surface mixing and receives a steady rain of organic matter from above. Select all that apply. Which processes are most responsible for declining oxygen levels in the deep water over the season?
Respiration by fish and invertebrates living near the bottom; Aerobic decomposition of sinking organic particles

1Which process removes carbon dioxide from the atmosphere and stores it in glucose inside plant cells?

2Photosynthesis in green plants converts carbon dioxide and water into sugar and releases oxygen into the atmosphere.

True / False

3A potted plant is moved into a completely dark closet for 24 hours. Which statement best describes the plant’s net gas exchange with the air during this time?

4Which reservoir currently holds the largest amount of carbon in the Earth system among these choices?

5Decomposer activity in soil consistently increases oxygen levels in the small air spaces between soil particles.

True / False

6Which statement correctly describes a similarity between the carbon cycle and the water cycle that you studied in a 5.14 quiz on water and nitrogen cycles?

7In the context of carbon stored in carbonate rocks that you studied in a 5.03 quiz on mineral resources, which process returns some of this rock-bound carbon to the atmosphere as carbon dioxide?

8A coastal city wants to reduce its contribution to atmospheric carbon dioxide while still meeting its electricity needs. Which change would most directly lower the city’s carbon emissions from electricity generation?

9Select all that apply. Which processes move carbon from living things into the atmosphere as carbon dioxide?

Select all that apply

10During a warm, still summer night, a lake experiences a dense algal bloom. Just before sunrise, which change is most likely in the surface water compared with the previous afternoon?

11Unlike the nitrogen cycle, the carbon cycle does not involve any gas phase in the atmosphere.

True / False

12Select all that apply. Which land-use changes are likely to increase the net flux of carbon from the land biosphere to the atmosphere?

Select all that apply

13Arrange the following events in the correct order to show how a carbon atom in atmospheric carbon dioxide could move through a food chain and back into the air.

Put in order

1An herbivore eats the plant and incorporates the carbon into its tissues.

2A predator eats the herbivore and uses the carbon in its own cells.

3The predator respires and releases CO2 back into the air.

4CO2 is taken into a leaf and fixed into an organic molecule.

14A sealed terrarium contains green plants and small snails and is kept under a regular day–night light cycle. Over a full 24-hour period, which statement best describes the overall relationship between carbon dioxide and oxygen inside the terrarium?

15A student is comparing fast and slow components of the carbon cycle. Which example best represents a slow-carbon process?

16Select all that apply. Which processes directly produce free molecular oxygen (O2) as a product?

Select all that apply

17A student reviews both the 5.14 quiz on water and nitrogen cycles and the 5.15 quiz on carbon and oxygen cycles. Which statement describes a fundamental similarity among all these biogeochemical cycles?

18Industrial cement production releases carbon dioxide both from burning fuels for heat and from chemically converting limestone into clinker.

True / False

19A scientist observes that atmospheric carbon dioxide concentrations are rising while the average carbon isotope ratio is becoming lighter, showing more carbon-12 relative to carbon-13. Which source best explains both changes?

20In a deep, stratified lake during summer, the bottom water is cut off from surface mixing and receives a steady rain of organic matter from above. Select all that apply. Which processes are most responsible for declining oxygen levels in the deep water over the season?

Select all that apply

Frequent Errors on 5.15 Carbon and Oxygen Cycle Questions

Confusing photosynthesis and cellular respiration

Students often claim that photosynthesis releases carbon dioxide and that respiration produces oxygen. Photosynthesis uses carbon dioxide and water to form glucose and oxygen. Cellular respiration uses oxygen to break down glucose and releases carbon dioxide and water. Mixing these directions leads to wrong arrows on cycle diagrams.

Ignoring major carbon reservoirs

Many answers focus only on the atmosphere and living organisms. Large amounts of carbon are stored in oceans, fossil fuels, soils, and rocks. Forgetting these reservoirs leads to incomplete explanations of long term carbon storage and slow parts of the cycle, such as sedimentation and fossil fuel formation.

Overlooking decomposition and detritivores

Learners sometimes show dead organisms disappearing from the cycle. Decomposers break down dead matter and waste, returning carbon to the atmosphere as carbon dioxide and to soils as organic matter. Skipping decomposers gives an incorrect picture of how nutrients and elements recycle.

Missing combustion and human impacts

Combustion of fossil fuels, biomass burning, and industrial processes are often left off diagrams. These processes rapidly transfer carbon from long term reservoirs to the atmosphere as carbon dioxide. On quiz questions, missing these arrows usually leads to wrong predictions about climate change and greenhouse gas levels.

Separating carbon and oxygen cycles completely

Some students treat carbon and oxygen cycles as unrelated. In reality, they are tightly linked through water, nitrogen, and mineral use in photosynthesis and respiration. Misunderstanding this connection makes it harder to track how a single atom moves among carbon dioxide, water, glucose, and oxygen gas.

Carbon and Oxygen Cycles Quick Reference Sheet

How to use this sheet

Use this as a quick review before or after the 5.15 quiz on carbon and oxygen cycles. You can print it or save it as a PDF for offline study.

Core processes

Photosynthesis: CO2 + H2O + light → C6H12O6 + O2. Removes carbon dioxide from air or water. Releases oxygen gas.
Cellular respiration: C6H12O6 + O2 → CO2 + H2O + energy. Releases carbon dioxide. Uses oxygen.
Decomposition: Decomposers break down dead organisms and waste. Carbon returns to atmosphere as CO2 and to soil as organic matter.
Combustion: Burning fossil fuels or biomass releases CO2 quickly. Often linked to human activities such as driving or power generation.
Dissolution and outgassing: CO2 dissolves into ocean water and can later be released back to the atmosphere.

Major carbon and oxygen reservoirs

Atmosphere: CO2 and O2 gases.
Biosphere: Carbon in plant and animal biomass, oxygen in organic molecules and dissolved in fluids.
Hydrosphere: Dissolved CO2, bicarbonate, and carbonate ions in oceans, lakes, and rivers. Dissolved oxygen that supports aquatic life.
Lithosphere: Carbonates in rocks and sediments, fossil fuels such as coal, oil, and natural gas.

Human impacts and fast vs slow cycles

Fast cycle: Photosynthesis, respiration, and decomposition move carbon and oxygen over days to years.
Slow cycle: Weathering, sedimentation, rock formation, and fossil fuel formation operate over thousands to millions of years.
Burning fossil fuels moves carbon from the slow cycle into the fast atmospheric pool.
Deforestation reduces photosynthesis, so less CO2 is removed from the atmosphere.

Connections to water, nitrogen, and minerals

Water cycle supplies H2O for photosynthesis and transports dissolved CO2 and oxygen.
Nitrogen cycle supports plant growth, which affects how much carbon plants can store.
Mineral resources in soil, such as phosphorus and trace elements, influence primary productivity and therefore carbon uptake.

Worked Example: Tracing Carbon and Oxygen Through an Ecosystem

Scenario

A forest contains oak trees, deer, fungi, and nearby cars on a highway. The question asks: "Describe one path a single carbon atom could take from atmospheric CO2 into a deer and then back to the atmosphere. Name each process involved and identify which processes also change the form of oxygen."

Step 1: Entry into a producer

The carbon atom starts as CO2 in the atmosphere. A leaf on an oak tree absorbs CO2 through stomata. In photosynthesis, the tree uses CO2 and water, plus light, to form glucose. The carbon atom now sits in a glucose molecule inside a leaf cell.

Step 2: Movement through the food chain

A deer eats the oak leaf. During digestion, the leaf tissue is broken down into smaller molecules. The glucose, which contains the carbon atom, is absorbed into the deer’s bloodstream. The atom is now part of dissolved glucose in the deer.

Step 3: Cellular respiration in the deer

In a muscle cell, mitochondria carry out cellular respiration. The deer uses oxygen gas inhaled from the atmosphere to break down glucose. The carbon atom leaves glucose and becomes part of a new CO2 molecule. The deer exhales this CO2, returning the carbon atom to the atmosphere.

Step 4: Linking oxygen changes

During photosynthesis, oxygen atoms from water are rearranged to form O2 that enters the atmosphere. During respiration, that O2 is used and converted into water. The example shows both carbon and oxygen cycling through producers, consumers, and the atmosphere using the paired processes of photosynthesis and respiration.

5.15 Carbon and Oxygen Cycles Quiz FAQ

What should I focus on to succeed on the 5.15 carbon and oxygen cycles quiz?

Focus on the main processes that move carbon and oxygen, especially photosynthesis, respiration, decomposition, and combustion. Know the major reservoirs such as atmosphere, biosphere, hydrosphere, and fossil fuels. Practice reading and labeling arrows and boxes on cycle diagrams, including human impact pathways.

How are the carbon and oxygen cycles connected to water and nitrogen cycles?

The water cycle supplies liquid water for photosynthesis and transports dissolved CO2 and oxygen in rivers and oceans. The nitrogen cycle supports plant growth, which affects how much carbon ecosystems can store. Many quiz questions link these cycles by asking how changes in one cycle influence plant biomass and atmospheric gases.

Do I need to memorize full chemical equations for this standard?

You should recognize and interpret simplified equations for photosynthesis and cellular respiration. Understand reactants, products, and the direction of matter flow. Exact balancing of every coefficient is less important than knowing that photosynthesis removes CO2 and releases O2, while respiration uses O2 and releases CO2.

How do human activities appear in carbon and oxygen cycle questions?

Common examples include burning fossil fuels, deforestation, cement production, and large scale agriculture. These activities increase atmospheric CO2, reduce plant uptake of carbon, or change soil carbon storage. Quiz items often ask you to predict how such changes affect greenhouse gases, ocean chemistry, or ecosystem productivity.

How can I connect this quiz with topics like water, nitrogen, and mineral resources?

Think of carbon and oxygen cycles as part of a larger biogeochemical system. Water moves gases and dissolved minerals. Nitrogen and other soil nutrients control plant growth and carbon storage. Understanding these links helps with related quizzes on standards such as water and nitrogen cycles and mineral resources.