13 - Energy and ecosystems Flashcards
(33 cards)
Define biomass (2)
Dry mass of tissue per given area OR
Mass of carbon per given area
What are most sugars synthesised by plants used as? What is the remainder used for?
Respiratory substrates, other biological molecules (biomass)
How can the chemical energy store of biomass be estimated?
Calorimetry
Give two examples of saprobionts.
Bacteria
Fungi
What is a trophic level?
A stage in a food chain.
Approximately how much of the Sun’s energy can a plant convert to organic substances?
1-3%
Suggest 4 reasons not all the Sun’s energy is converted to organic substances. (4)
> 90% reflected back into space by clouds/or is absorbed in atmosphere
Not all wavelengths can be absorbed and used for photosynthesis
Light may not fall on chlorophyll molecule
A factor may limit rate of photosynthesis
What is Gross Primary Production (GPP)?
The total quantity of chemical energy store in plant biomass, in a given area, in a given time.
Approximately how much of their chemical energy store do plants use in respiration?
20-50%
What is Net Primary Productivity (NPP)?
Gross Primary Production - respiratory losses
Approximately how much of a plant’s net primary production can be used by primary consumers for growth?
5-10%
Approximately how efficient are secondary and tertiary consumers at converting prey energy for growth?
15-20%
Why is there a low percentage transfer of energy between trophic levels?
Some of organism not consumed
Some parts cannot be digested so are lost as faeces
Some lost in excretory material ie urine
Some lost in respiration to heat organism to environment.
How can the net production of a consumer be calculated?
N = ingested (I) - faeces and urine (F) - respiratory losses (R)
What can the low energy transfer efficiency between trophic levels explain? (3)
Only 4-5 trophic levels as energy is too limited
Total biomass is less at higher trophic levels
Total energy available is less up the food chain
Give a basic summary of a nutrient cycle.
Nutrient taken up by producer
Converted to organic molecules
Passed into consumers
When producers/consumers die, saprobionts break down organic molecules into nutrients’ original form.
Give two nutrient cycles.
Phosphorus cycle
Nitrogen cycle
How is productivity defined?
Rate of production of biomass
What are the four main stages of the nitrogen cycle?
Ammonification
Nitrfication
Nitrogen fixation
Denitrification
What is the process of changing ammonium ions to nitrite ions, then nitrate ions?
Nitrification
What change does denitrification cause?
Nitrate ions go to nitrogen
What causes denitrification?
Conditions and type of bacteria
Low oxygen
Anaerobic denitrifying bacteria
What is the process of changing nitrogen in the atmosphere to ammonium ions?
Nitrogen fixing
What two kinds of nitrogen fixing bacteria exist?
Free-living
Mutualistic
