Ecosystems, Nutrient Cycles & Succession Flashcards
How can carbon be added to the atmosphere?
- Combustion
- Respiration
- From the sea
How can carbon be removed from the atmosphere?
- Photosynthesis
- Dissolve into the sea
Where is carbon found?
- The atmosphere
- Plants
- Animals
- Fossil fuels
- Decomposers
- The sea
How does atmospheric carbon dioxide vary during the day?
Lowest in the day
Highest at night
How does atmospheric carbon dioxide vary during the year?
Lowest in the summer
Highest in the winter
What is global warming?
Increase in the average global temperature
Caused by the greenhouse effect
How could global warming impact on crop yield?
Increase in carbon dioxide/temperature
⇒ Increase in rate of photosynthesis
⇒ Increased crop yield
How might global warming affect pest species?
Might affect the life cycle of the pest species (e.g. shorter larval stage)
Could affect abundance/distribution of species
How might global warming affect wild plants/animals?
Could affect the distribution/abundance of species
What are the stages of the nitrogen cycle?
Nitrification
Denitrification
Nitrogen fixation
Ammonification
Absorption
Consumption
Death/excretion
What is nitrogen fixing?
Nitrogen fixing bacteria convert nitrogen in the air into ammonium
Bacteria found in root nodules of leguminous plants and form mutualistic relationships

What is nitrification?
Ammonium compounds are oxidised by nitrifying bacteria to nitrate ions

What is ammonification?
Saprobiotic microorganisms convert dead organic matter and animal waste into ammonium compounds
What is denitrification?
Occurs in anaerobic conditions, denitrifying bacteria use nitrate ions for respiration and release nitrogen

What is the cause of eutrophication?
Nitrates in the soil leech into rivers
Why are organic fertilisers less likely to cause eutrophication than artificial fertilisers?
Insoluble so less likely to leech
Needs to be broken down
What is process of eutrophication?
- Nitrates cause an algal bloom
- This blocks out the light, plants can’t photosynthesise
- Plants die and are broken down by saprobiotic bacteria
- These bacteria respire aerobically, using oxygen
- Aquatic animals die due to lack of oxygen
- Anaerobic bacteria decompose the dead organisms making the water putrid
What do fertilisers do?
Increase productivity
How do fertilisers increase productivity?
Contain nitrogen in the form of nitrates:
- Nitrogen present in DNA & proteins
- Nitrogen increase height and leaf height
Why is energy lost within a food chain/web?
Producers:
- Some of the Sun’s energy is absorbed/reflected by the atmosphere
- Not all wavelengths of light can be used in photosynthesis
- Not all the light falls on the chlorophyll/photosynthesising cells
Consumers:
- Some parts of the organism aren’t eaten
- Some parts cannot be digested
- Energy is lost by excretion (e.g. in urine/faeces)
Both:
- Energy is lost as heat due to respiration




What are the three types of ecological pyramid and what are the associated units?
- Pyramids of number: no units
- Pyramids of biomass: kgm-2 or kgm-3
- Pyramids of energy: kJm-2year-1 or kJm-3year-1
What are the drawbacks of pyramids of number?
- Size not taken into account
- 1 large organism = 1 small organism
- Impossible to represent accurately when there are large differences in numbers
- Only considers one point in time