Energy and ecosystems Flashcards
How do plants use the sugars from photosynthesis?
Primarily as respiratory substrates
To synthesise other biological molecules e.g cellulose
What is biomass?
Total dry mass of tissue or mass of carbon measured over a given time in a specific area
How can the chemical energy store in dry mass be estimated?
Using calorimetry
Energy released = specific heat capacity of water x volume of water x temperature increase of water
Define gross primary production
Total chemical energy in plant biomass within a given volume or area
Define net primary productivity
Total chemical energy available for plant growth, plant reproduction and energy transfer to other trophic levels after respiratory losses
Why is most of the suns energy not converted to organic matter?
Most solar energy is absorbed by the atmosphere or reflected by the clouds
Photosynthetic pigments cannot absorb some wavelengths of light
Not all light falls directly on a chlorophyll molecule
Energy is lost as heat during respiration/photosynthesis
How can the net production of consumers be calculated?
N = I - (F + R)
I: chemical energy from ingested food
F: energy lost as faeces and urine
R: respiratory losses
Why does biomass decrease along a food chain?
Energy lost in nitrogenous waster and faeces
Some of the organism is not consumed
Energy is lost as heat
Define primary and secondary productivity
Rate of primary and secondary production
Biomass in a specific area over a given time period
Outline some common farming practices used to increase the efficiency of energy transfer
Exclusion of predators: no energy lost to other organisms in food web
Artificial heating: reduce energy lost to maintain constant body temperature
Restriction of movement
Feeding is controlled at the optimum
Explain why the length of the food chain is limited
Energy is lost at each trophic level
So there is insufficient energy to support a higher trophic level
Name the general stages of the phosphorous cycle
Weathering Runoff Assimilation Decomposition Uplift
Why is the phosphorus cycle a slow process?
Phosphorus has no gas phase so there is no atmospheric cycle
Most phosphorus is stored in rocks
What happens during weathering and runoff?
Phosphate compounds from sedimentary rocks leach into surface water and soil
Explain the significance of phosphorus to living organisms
Plants convert inorganic phosphate into biological molecules e.g DNA, ATP
Phosphorus is passed to consumers via feeding
What happens during uplift?
Sedimentary layers from oceans are brought up to land over many years
How does mining affect the phosphorus cycle?
Speeds up uplift
Name the 44 main stages in the nitrogen cycle
Nitrogen fixation
Ammonification
Nitrification
Dentrification
Why can’t organisms use nitrogen directly from the atmosphere?
N2 is very stable due to strong covalent triple bond so can’t be broken down
What happens during atmospheric fixation of nitrogen?
- High energy of lightning breaks N2 into N
- N reacts with oxygen to form NO2-
- NO2- dissolves in water to form NO3-
Outline the role of bacteria in nitrogen fixation
Mutualistic nitrogen-fixing bacteria in nodules of legumes and free living bacteria in soil
Use the enzyme nitrogenase to reduce gaseous nitrogen into ammonia
How does ammonium change into nitrogen?
Ammonia - Nitrite - Nitrate
Outline the role of bacteria in ammonification
- Saprobionts feed on and decompose organic waste containing nitrogen
- NH3 released
- NH3 dissolves in water in soil to form NH4+
Outline the role of bacteria in nitrification
2 step process carried out by saprobionts in aerobic conditions:
2NH4+ + 3O2 = 2NO2- + 2H2O +4H+
2NO2- + O2 = 2NO3-
Outline the role of bacteria in dentrification
Anaerobic dentrifying bacteria convert soil nitrates back into gaseous nitrogen
Explain the significance of nitrogen to living organisms
Plant roots uptake nitrates via active transport and use them to make biological compounds e.g amino acids, NAD/NADP and nucleic acids
Outline the role of mycorrhizae
Mutualistic relationship between plant and fungus increases surface area of root system = increases uptake of water and mineral ions
Give 3 benefits of planting a different crop on the same field each year
Nitrogen fixing crops e.g legumes make soil more fertile by increasing soil nitrate content
Different crops have different pathogens
Different crops use different proportions of certain ions
Name the 2 categories of fertiliser and state the purpose of using fertiliser
Organic: decaying organic matter and animal waste
Inorganic: minerals from rocks, usually containing nitrogen, phosphorus, potassium
Increase gross productivity for higher yield
At a certain point, using fertiliser no longer increases crop yield. Why?
A factor unrelated to the concentration of mineral ions limits the rate of photosynthesis so rate of growth cannot increase any further
Outline 2 main environmental issues caused by the use of fertilisers
Leaching: nitrates dissolve in rainwater and runoff into water sources
Eutrophication: water source becomes putrid as a result of algal bloom
What happens during eutrophication?
- Aquatic plants grow exponentially since nitrate level is no longer a limiting factor
- Algal bloom on water surface prevents light from reaching the bottom and plants die
- Oxygen levels decrease as population of aerobic saprobionts increases to decay dead matter so fish die
- Anaerobic organisms reproduce exponentially and produce toxic waste which makes water putrid
How can the risk of eutrophication be reduced?
Sewage treatment marshes on farms
Pumping nutrient enriched sediment out of water
