C4.2 - nutrient cycling in ecosystems (4g)

Question 1

what is the recycling of chemical elements in ecosystems like, including the roles of organisms?

Answer 1

• all elements used by living organisms, not just carbon, are recycled in ecosystems
• producers obtain inorganic nutrients for the abiotic environment
• decomposers play a key role in this recycling by breaking down organic matter, releasing the nutrients trapped in the biomass of dead organisms, and returning the nutrients to the soil
• nutrients are not lost but transformed into different compounds

Question 2

what are carbon sources?

Answer 2

there is a net release of carbon dioxide, when the rate of respiration exceeds that of photosynthesis

Question 3

what are carbon sinks?

Answer 3

there is a net uptake of carbon dioxide, when the rate of photosynthesis exceeds that of respiration

Question 4

what is the relationship between photosynthesis and carbon sink size?

Answer 4

the higher the relative rate of photosynthesis, the larger the carbon sink that is formed

Question 5

what are examples of carbon sinks?

Answer 5

carbon sinks include: limestone, oceans, permafrost in frozen tundra, and trees

Question 6

what is the role of combustion?

Answer 6

combustion of fuels release carbon dioxide into the atmosphere

Question 7

what are examples of combustible carbon sinks?

Answer 7

biomass, peat and fossil fuels are combustible carbon sinks

Question 8

how can combustion occur naturally?

Answer 8

combustion can occur naturally from lightning strikes and lava flows

Question 9

what is primary production?

Answer 9

primary production is the accumulation of carbon compounds in biomass by autotrophs

Question 10

how is biomass accumulated in primary production?

Answer 10

this occurs through fixation of carbon through photosynthesis

Question 11

what can be observed when biomass accumulates?

Answer 11

biomass accumulates when autotrophs and heterotrophs grow or reproduce

Question 12

what is biomass?
what are the units?

Answer 12

biomass is the mass of all living organisms
- measured in mass of carbon, per unit area, per unit time (g m-2 yr-1)

Question 13

what is a biome?

Answer 13

a large community of plants and animals
- biomes vary in their capacity to accumulate biomass

Question 14

what is the relationship between photosynthesis and biomass production?

Answer 14

factors increasing the rate of photosynthesis relative to respiration should increase biomass production

Question 15

what is secondary production?

Answer 15

secondary production is the accumulation of carbon compounds in biomass by heterotrophs
- carbon compounds (eg, proteins and lipids) are ingested during feeding, the large molecules are digested to form small soluble molecules that are absorbed
- the heterotroph then assimilates these small molecules to form its own carbon compounds

Question 16

why is secondary production lower than primary production?

Answer 16

secondary production is lower than primary production in an ecosystem because biomass is lost when:
- carbon compounds are converted to carbon dioxide and water in cell respiration
- waste products (eg, urea) are excreted

Question 17

how are respiration and photosynthesis dependent on each other?

Answer 17

aerobic respiration requires atmospheric oxygen produced by photosynthesis, whilst photosynthesis requires atmospheric carbon dioxide produced by respiration

Question 18

what interaction is there between autotrophs and heterotrophs?

Answer 18

the fluxes involved per year are huge, in the region of 200 gigatonnes of carbon per year, so this is a major interaction between autotrophs and heterotrophs

Question 19

what are carbon fluxes?

Answer 19

carbon fluxes are movement of carbon between stores

Question 20

why is photosynthesis a negative flux?

Answer 20

photosynthesis is a negative flux because it removes carbon dioxide from the atmosphere

Question 21

why is respiration a positive flux?

Answer 21

respiration is a positive flux because it adds carbon dioxide to the atmosphere

Question 22

what is the keeling curve?

Answer 22

a daily record of global atmospheric carbon dioxide concentration from the Mauna Loa Observatory, in Hawaii, started in 1958 by Keeling

Question 23

what is the annual fluctuation analysis of the keeling curve?

Answer 23

• during the summer and autumn, when greater day lengths and light intensity plus a larger biomass of plant increases the rate of photosynthesis, the rate of photosynthesis exceeds the rate of carbon dioxide production (eg, from respiration and combustion) there is a decrease in the carbon dioxide concentration
• during winter and spring, when there is a relatively low rate of photosynthesis, the carbon dioxide fixation by photosynthesis is slower than its production so there is an increase in carbon dioxide concentration

Question 24

what is the long-term analysis of the keeling curve?

Answer 24

there is an increase in carbon dioxide concentration over time because over the course of each year more carbon dioxide is released into the atmosphere by respiration, combustion and weathering, than is fixed from the atmosphere by photosynthesis

Question 25

what is the carbon cycle, including the roles of photosynthesis, feeding and respiration?

Answer 25

photosynthesis: absorption of carbon dioxide from the atmosphere or water by autotrophs, which use photosynthesis to fix carbon dioxide and form carbohydrates
- thus plants act as carbon sinks
- humans use plant products for making cloth/household items/building/arts creating a reservoir for carbon

feeding: plants are eaten by consumers (moving carbon in the food chain)
- carbon compounds are transferred through food chains, for example as protein

respiration: in plants and animals converts carbohydrates to carbon dioxide and releases it into the atmosphere/water

respiration: saprotrophs and detritivores digest dead plants releasing carbon dioxide, in the process of decomposition

peat forms when decomposition of dead plant matter is incomplete, storing carbon in a carbon sink
- peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils

fossilization of carbon stores it as coal, oil, or natural gas, as a carbon sink

carbon dioxide dissolves in aquatic ecosystems, forming carbonic acid
- reef-building corals and molluscs use calcium carbonate to build shells and exoskeletons
- hard parts, shells and exoskeletons precipitation of calcium carbonate to form limestone and creating a carbon sink

methane is produced from organic matter in anaerobic conditions (by methanogenic archea)
- some methane diffuses into the atmosphere and some accumulates in the ground
- methane is oxidized to carbon dioxide (and water) in the atmosphere