Question
(a) State two causes of the decrease of biomass along food chains in terrestrial ecosystems. [2]
(b) The table shows the global carbon budget over two decades; the years 1990 to 1999 and 2000 to 2009.
Carbon | Global carbon budget / ×1012 kg | |
1990 to 1999 | 2000 to 2009 | |
Atmospheric carbon dioxide | 3.0 | 4.0 |
Fossil fuel and cement | 6.5 | 8.0 |
Land use change | 1.5 | 1.0 |
Carbon storage in land | 2.5 | 2.0 |
Carbon storage in oceans | 2.0 | 2.5 |
Using the table, explain causes of the changes in carbon flux over the two decades. [3]
▶️Answer/Explanation
Ans:
a
a. «cell» respiration/loss of CO2/biomass consumed to provide/as a source of energy
b. loss of energy «as heat» between trophic levels means less energy available for building biomass
c. waste products «other than CO2»/loss of urea/feces/egesta
d. material used/CO2 released by saprotrophs
e. undigested/uneaten material «teeth, bones, etc»/detritus buried/not consumed OR formation of peat/fossils/limestone
b.
a. increased CO2 flux to the atmosphere due to increased burning of fossil fuels by industry/transportation / cement production
b. «land use change leading to» decreased rate of forest burning OR better fire suppression leading to decrease in CO2 release OR example of land use changes that uses less fossil fuel OR increase in land covered by forests/plants / forests recovering from historical forestry OR any other reasonable explanation of land use change that would lead to decreased rate of carbon flow to atmosphere
c. carbon storage in land decreased as less photosynthesis due to fewer forests/more construction OR release of methane due to «drying of» wetlands/sealing of land with concrete/buildings/roads
d. carbon storage in ocean increased due to more photosynthesis/algae/greater concentration of CO2 in the atmosphere OR increased diffusion/rate of dissolving of CO2 into ocean from the atmosphere OR limestone/carbonate accumulation «more snails»
Question
The diagram below shows the carbon cycle.
State the process occurring at X and Y.
X: …………………………………………………………
Y: …………………………………………………………
Suggest one type of organism that can be involved in process Z.
Explain the relationship between the rise in concentration of atmospheric carbon dioxide and the enhanced greenhouse effect.
▶️Answer/Explanation
Markscheme
X: combustion / burning;
Y: photosynthesis;
(saprotrophic) bacteria/fungi / saprotrophs
Award [0] for decomposers
carbon dioxide is a greenhouse gas (naturally produced by organisms);
human activity has increased the normal level of CO2/caused enhanced greenhouse effect;
short-wave radiation from the Sun is re-radiated as longer wave radiation/ infrared/heat;
infrared/heat captured by greenhouse gases/CO2;
Accept any of the above points shown in a clearly annotated diagram.