3.1.1 Water & Carbon Cycles

Question 1

Example of a system in the water cycle

Answer 1

In a drainage basin system, water enters as rain (input). The system’s watershed is the boundary. Some water is stored in the soil and in vegetation. Water travels from the drainage basin to the river and then down the river (flows). It leaves the system where the river meets the sea (output).

Question 2

Example of an open system in the water cycle

Answer 2

Both energy and matter can enter and leave an open system - there are inputs and outputs of both. E.G: drainage basins are open systems - energy from the sun enters and leaves the system. Water is input as precipitation, and output as river discharge into the sea.

Question 3

Example of a closed system in the carbon cycle

Answer 3

Energy can enter and leave a closed system, but matter cannot - it can only cycle between stores. E.G: the carbon cycle is a closed system - energy is input from the sun by photosynthesis and output by respiration, but the amount of carbon on earth stays the same because there are no inputs or outputs of matter.

Question 4

Example of positive feedback in the water cycle

Answer 4

Positive feedback mechanisms amplify the change in inputs or outputs. E.G: Temperatures rise > ice covering cold parts or the earth melts due to higher temperatures > less ice cover means less of the sun’s energy is reflected > less of the sun’s energy being reflected means more is being absorbed by the earth, thus causing temperatures to rise again.

Question 5

Example of negative feedback in the carbon cycle

Answer 5

Negative feedback mechanisms counteract the change in the inputs or outputs. E.G: Large amounts of CO2 are emitted > CO2 in the atmosphere increases > extra CO2 causes plants to increase growth > plants remove and store more CO2 from the atmosphere > amount of CO2 in the atmosphere reduces.

Question 6

Breakdown of Carbon in each of the earth’s systems

Answer 6

Lithosphere: Over 99.9% is stored in sedimentary rocks and 0.004% is stored in fossil fuels
Hydrosphere: 0.04% is stored in the ocean
Atmosphere: 0.001% stored in the atmosphere
Biosphere: 0.004% stored in the tissue of living organisms
Cryosphere: less than 0.01% stored in cryosphere, most of it is stored in permafrost

Question 7

Photosynthesis in the carbon cycle

Answer 7

• Photosynthesis transfers carbon stored in the atmosphere to biomass.
• Plants and phytoplankton use energy from the sun to change carbon dioxide and water into glucose and oxygen, enabling plants to grow.
• Carbon is passed through the food chain and released through respiration and decomposition.

Question 8

Combustion in the carbon cycle

Answer 8

• Combustion transfers carbon stored in living, dead or decomposed. biomass (including peaty soils) to the atmosphere by burning.
• Wildfires cause carbon flow.

Question 9

Ocean uptake and loss in the carbon cycle

Answer 9

• CO2 is directly dissolved from the atmosphere into the ocean. It is also transferred to the ocean when it is taken up by organisms that live in them (e.g. plankton).
• Carbon is also transferred from the ocean to the atmosphere when carbon rich water from deep in the oceans rises to the surface and released CO2.

Question 10

Sequestration in the carbon cycle

Answer 10

• Carbon from the atmosphere can be sequestered (captured and held) in sedimentary rocks or as fossil fuels. Rocks and fossil fuels form over millions of years when dead animal and plant material in the ocean falls to the floor and is compacted.
• Carbon in fossil fuels is sequestered until we burn them (combustion).

Question 11

Respiration in the carbon cycle

Answer 11

• Respiration transfers carbon from living organisms to the atmosphere.
• Plants and animals break down glucose for energy, releasing carbon dioxide and methane in the process.

Question 12

Decomposition in the carbon cycle

Answer 12

• Decomposition transfers carbon from dead biomass to the atmosphere and the soil.
• After death, bacteria and fungi break organisms down. CO2 and methane are released.
• Some carbon is transferred to the soil in the form of humus.

Question 13

Weathering in the carbon cycle

Answer 13

• Chemical weathering transfers carbon from the atmosphere to the hydrosphere and biosphere.
• Atmospheric carbon reacts with water vapour to form acid rain.
• When this acid rain falls onto rocks, a chemical reaction occurs which dissolves the rocks.
• The molecules resulting from this reaction may be washed into the sea. Here, they react with CO2 dissolved in the water to form calcium carbonate which is used by sea creatures, e.g. to make shells.

Question 14

Wildfires (natural process)

Answer 14

• Wildfires rapidly transfer large quantities of carbon from biomass (or soil) to the atmosphere. Loss of vegetation decreases photosynthesis, so less carbon is removed from the atmosphere.
• In the longer term, however, fires can encourage the growth of new plants, which take in carbon from the atmosphere for photosynthesis. Depending on the amount and type of regrowth, fires can have a neutral effect on the amount of atmospheric carbon.

Question 15

Volcanic Activity (natural process)

Answer 15

• Carbon stored within the earth in magma is released during volcanic eruptions. The majority enters the atmosphere as CO2
• Recent volcanic eruptions have released much less CO2 than human activities. However, there is a potential for a very large eruption to disrupt the carbon cycle significantly.

Question 16

Hydrocarbon extraction and use (human cause)

Answer 16

• Extracting and burning (combustion) of fossil fuels releases CO2 into the atmosphere.
• Without human intervention, the carbon would remain sequestered in the lithosphere for thousands or millions of years to come.

Question 17

Deforestation (human cause)

Answer 17

• Forests may be cleared for agriculture, logging, or to make way for developments.
• Clearance reduces the size of the carbon store and, if the cleared forest is burned, there is a rapid flow of carbon from the biosphere to the atmosphere.

Question 18

Farming practices (human cause)

Answer 18

• Animals release CO2 and methane when they respire and digest food.
• Ploughing can release CO2 stored in soil.
• Growing rice in rice paddies releases a lot of methane.
• As the world’s population has risen, so has food production. As a result, carbon emissions from farming practices have increased. Mechanisation of farming has also increased CO2 emissions.

Question 19

Land use changes (human cause)

Answer 19

• Vegetation is removed to make way for buildings - this reduces carbon storage in the biosphere.
• Concrete production releases lots of CO2 and lots of concrete is used when urban areas expand.

Question 20

How does the carbon cycle affect the atmosphere and climate?

Answer 20

• Carbon cycle affects the amount of gases containing carbon in the atmosphere. These are greenhouse gases - they trap some of the Sun’s energy, keeping some of the heat in and keeping the planet warm.
• As the concentrations of greenhouse gases in the atmosphere increase, temperatures as expected to rise. This is global warming.
• Changes in temperatures across the globe will affect other aspects of the climate, e.g. more intense storms are predicted.

Question 21

How does the carbon cycle affect the land?

Answer 21

• The carbon cycle allows plants to grow - if there was no carbon in the atmosphere, plants could not photosynthesise. If there was no decomposition, dead plants would remain where they fell and their nutrients would never be recycled.
• Changes in the carbon cycle can reduce the amount of carbon stored in the land, e.g. warmer temperatures caused by global warming are causing permafrost to melt. This releases carbon previously stored in permafrost into the atmosphere.
• An increase in global temperatures could also increase the frequency of wildfires.

Question 22

How does the carbon cycle affect oceans?

Answer 22

• CO2 is dissolved directly into the oceans from the atmosphere.
• CO2 in oceans is used by phytoplankton and seaweed during photosynthesis and by other marine organisms to form calcium carbonate shells and skeletons.
• Increased levels of CO2 can increase the acidity of the oceans, this can have adverse effects on marine life.
• Global warming can also affect oceans. E.G: organisms that are sensitive to temperature (phytoplankton) may not be able to survive at higher temperatures, so their population decreases.
• Warmer water is also less able to absorb CO2, so as temperatures rise the amount of CO2 that could potentially be dissolved in the sea decreases.

Question 23

The relationship between the water and carbon cycles.

Answer 23

1) Plant form the base of most food chains - when photosynthesis occurs, they use energy from the sunlight to convert CO2 and water into biomass that gets passed up the food chain.
2) Water is present in the atmosphere as water vapour (and water droplets), and carbon exists as CO2 and methane. These are greenhouse gases - they cause a natural greenhouse effect that prevents some energy escaping into space and reflects it back to earth. This causes temperatures on Earth to be higher than they would otherwise be - without the natural greenhouse effect the earth would be frozen and uninhabitable.

Question 24

How does climate change affect life on earth>

Answer 24

• The pattern of precipitation is expected to change - wet areas expected to get wetter and dry areas expected to get drier.
• Extreme weather events (storms, floods and droughts) expected to get more frequent.
• Agricultural productivity may decrease in some areas, leading to food shortages.
• Sea levels expected to rise further.
• The geographical range of some species will change as climate changes.
• Plankton number may decline as a result of temperature increase, which will have a knock-on effect on marine food chains.

Question 25

Human intervention in the carbon cycle - Individual

Answer 25

• People can choose to use their cars less and buy more fuel efficient cars.
• They could also make their homes more energy efficient with double glazing, insulation and more efficient appliances.

Question 26

Human intervention in the carbon cycle - Regional & National

Answer 26

• Governments can reduce reliance on fossil fuels for heating and powering homes by increasing the availability of renewable energy sources (e.g. solar panels).
• Afforestation and restoring degraded forests can increase carbon uptake by the biosphere.
• Planners can increase the sustainability of developments by improving public transport and creating more green spaces.
• Governments can invest in carbon capture and storage.

Question 27

Human intervention in the carbon cycle - Global

Answer 27

• Countries can work together to reduce emissions. E.G: the Kyoto Protocol in 1997 and the Paris Agreement (2015) are international treaties to control the total amount of greenhouse gases released. Participating countries agree to keep their emissions within set limits.
• There are also international carbon trading schemes. Countries and businesses are given a limit on the emissions they can produce - if they produce less, they can sell extra credits, if they produce more they need to buy more credits.