Energy Transfers and Nutrient Cycles Flashcards
Biomass
mass of carbon or dry mass of tissue per unit area
Suggest how to determine the chemical energy store in dry biomass
- calorimetry
- burn in pure oxygen and heat water until no further change in mass
Suggest limitations of biomass measurements
- accurate measurement involves removes all water from an organism which kills it
- estimations based on samples can be unrepresentative
Give reasons why only 1% of light energy is captured by plants
- reflected by water vapour and particulates in atmosphere
- wrong wavelength of light so not absorbed
- light misses chloroplasts
Gross Primary Production
- chemical energy stored in plant biomass in a given AREA
- production = kJm^-2 and productivity kJm^-2year^-1
Suggest how sugars and other organic compounds synthesised by plants are used
- respiratory substrates
- stored as biomass
Net Primary Production
- chemical energy stored in plant biomass for a given AREA after respiratory losses to the environment have been taken
into account - NPP = GPP - R
Suggest what net primary production is available for
- plant growth
- plant reproduction
- available to consumers at other trophic levels
Net Primary Production of consumers
N = I - (F + R)
where I = chemical energy store in ingested food, F
= chemical energy lost to the environment in faeces and
urine and R = respiratory losses to the environment
Explain why most food chains only reach four or five trophic levels at most
- energy lost at each stage of food chain
- insufficient energy to support a large enough breeding population
How to increase GPP and NPP of plants
GPP
- high light intensity via open field/artificial light of correct wavelength
- warm temperature via warm climate/heaters
- plentiful water supply via rainfall/irrigation
- rich mineral supply via fertilisers
NPP
- selectively bred
Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer
- some light energy fails to strike chloroplast/is reflected/not of appropriate wavelength
- efficiency of photosynthesis in plants is low/approximately 2% efficient
- respiratory loss / excretion / faeces / not eaten
- loss as heat
- efficiency of transfer to consumers greater than transfer to producers/approximately 10%
- efficiency lower in older animals/herbivores/ primary consumers/warm blooded animals
- carnivores use more of their food than herbivores
Explain briefly how to improve efficiency of energy transfer in human food chains
- simplify food webs by removing competitors and pests
- reduce respiratory losses
- keep food chains short
Intensive Farming
- optimal conditions
- reduce respiratory losses
- high efficiency of energy transfer hence net production
- maximise profits
Explain how intensive rearing of livestock increases net productivity
- keep in enclosed spaces to limit movement/warm so more energy for growth
- controlled diet with high nutrient concentration
- protect from predators
- selectively breed
- slaughter before fully grown
Evaluate the use of chemical pesticides in intensive farming
- kills pests directly
- immediate response
- pest can develop resistance
- expensive/frequent treatment
- pollute water sources
Evaluate the use of biological agents
- little environmental impact in terms of pollution
- cheaper since predator species reproduces
- gradual process
- could become pests themselves
- could leave area
- may not eat pest
- may disrupt food chain
Suggest advantages of artificial fertilisers over natural
- select exact minerals and optimal concentrations
- inorganic ions so more soluble in water so higher rate of uptake of minerals (but eutrophication)
Saprobiotic Nutrition
- extracellular digestion
- secrete enzymes which digest waste and decaying organic matter
Nitrogen Fixation
- free-living nitrogen-fixing bacteria convert atmospheric nitrogen to ammonium
- mutualistic nitrogen fixing bacteria in root nodules of legume plants convert atmospheric nitrogen to nitrates
Nitrification
- two state oxidation
- NH4+ (ammonium) to NO2- (nitrites) by nitrifying bacteria
- NO2- (nitrites) to NO3- (nitrates) by nitrobacter (nitrifying bacteria)
Ammonification
- decomposer bacteria convert nitrogen rich waste products into ammonium
- waste = urea + ammonia
- dead matter = amino acids, DNA, RNA
Denitrification
- denitrifying bacteria convert nitrates to atmospheric nitrogen
Suggest why farmers must plough soil regularly to ensure maximum uptake of nitrates from soil
- denitrifying bacteria thrive in anaerobic, water-logged conditions
- denitrifying bacteria remove nitrates from soil
- ploughing aerates soil
Outline the phosphate cycle
- phosphate ions dissolved in oceans, lakes and soil
- actively transported into root hair cells of plants
- animals feed on plants containing phosphate
- excretion and decomposition removes phosphate in waste (i.e. guano, bones and shells)
- phosphate returned to soil
or - sedimentation occurs so phosphate found in rocks
- sedimentary rocks erode and return phosphate ions to ocean
Mycorrihizae
associations between plant roots and beneficial fungi (mutualistic relationship)
- plant provides glucose to fungi
- fungi increases surface area of root for higher water and mineral uptake (sponge)
Suggest why organisms require phosphorus
- ATP
- phospholipid bilayer (cell membrane)
- nucleic acids, e.g. DNA and RNA
Describe the process of eutrophication
- overuse of soluble inorganic fertilisers containing nitrates and phosphates
- minerals leach into ground water when it rains and run off into nearby rivers and lakes
- high nitrate and phosphate concentration results in algae bloom
- blocks out sunlight so plants cannot photosynthesise so die
- plants decomposed by saprobiotic, aerobic bacteria
- water becomes anoxic so aquatic organisms cannot respire so die
