4.3 Carbon cycling – Sciences for IGCSE & IB

1.The diagram shows the carbon cycle.

[Source: © International Baccalaureate Organization 2017] Which two processes correspond to the labelled arrows?

K is combustion and L is catabolism
J is anabolism and K is respiration
J is combustion and K is respiration
J is anabolism and L is catabolism

2. The diagram shows a version of the carbon cycle. What is indicated by the numbers?

A
B
C
D

3. Cladograms can be created by comparing DNA or protein sequences. The cladogram on the left is based on DNA sequences and the cladogram on the right is based on comparing protein sequences.

What is the reason that cladograms based on DNA sequences are more reliable predictors of the phylogenetic relationship of species than cladograms based on protein sequences?

Amino acids are not as chemically stable as DNA nucleotides
DNA mutates but amino acids do not
Several different triplets of bases can code for the same amino acid
There are 20 different amino acids but only 4 nucleotides

4. What favours the production of peat? I. Presence of organic matter II. Anaerobic conditions III. Acidic conditions

I and II only
I and III only
II and III only
I, II and III

5. The bacterium Neisseria gonorrhoeae causes infections related to the human reproductive system. The graph shows the percentage of samples in which this bacterium showed resistance to six antibiotics over a period of ten years.

What is a possible explanation for the total percentage resistance being larger than 100% in 2010?

People do not take the antibiotics as prescribed
More people have been sampled in that year
There was an epidemic of Neisseria gonorrhoeae in that year
Some bacteria are resistant to more than one antibiotic

6. Methanogens produce methane gas. What is this gas converted to in the atmosphere?

Carbon dioxide and oxygen
Ethanol and carbon dioxide
Carbon monoxide and ozone
Carbon dioxide and water

7. What favours the production of peat? I. Presence of organic matter II. Anaerobic conditions III. Acidic conditions

I and II only
I and III only
II and III only
I, II and III

8. How is peat formed?

From methanogenic archaeans under anaerobic and acidic conditions in deep sea vents
From partially decomposed organic matter under anaerobic and acidic conditions in waterlogged soils
From porous limestone under high pressure, aerobic and alkaline conditions in ocean beds
From bituminous coal under high pressure, anaerobic and acidic conditions below ground

9. The diagram represents the carbon cycle.

Which process has the greatest relative role in transferring carbon?

Decomposition
Combustion
Photosynthesis
Cell respiration

10. Which hypothesis is supported by evidence from ecological research?

Decomposers are the final stage in the food chain
Producers depend upon consumers more than on decomposers
Decomposers help to recycle energy from food chains
Producers use nutrients that decomposers help to recycle

11. What are examples of greenhouse gases?

Ethane and ozone
Methane and nitrogen
Methane and carbon dioxide
Ethane and oxygen

12. The diagram is a representation of a carbon cycle. Which arrow will reduce the greenhouse effect?

A
B
C
D

13. The diagram shows the carbon cycle. Which letter indicates respiration?

A
B
C
D

14. Which group of organisms in the carbon cycle converts carbon into a form that is available to primary consumers?

Decomposers
Saprotrophs
Detritus feeders
Producers

15. The diagram below shows some of the links in the carbon cycle.

What processes are taking place at I, II and III?

A
B
C
D

16. The graph below shows variation in the concentration of CO2 in the atmosphere as measured at Mauna Loa in Hawai’i. The small inset graph shows the variations in CO2 during a one year period.

Why does the amount of CO2 fall between April and August?

Seasonal increase in the rate of photosynthesis in northern hemisphere forests
Seasonal decrease in the rate of photosynthesis in northern hemisphere forests
Seasonal decrease in the rate of fossil fuel consumption
Seasonal increase in the amount of CO2 taken up by the oceans

17. The following graph refers to questions 19 and 20. It shows variation in the concentration of CO2 in the atmosphere as measured at Mauna Loa in Hawai’i. The small inset graph shows the variations in CO2 during a one year period.

Why does the amount of CO2 fall between April and August?

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