T10.2 - Energy Transfer Through Ecosystems Flashcards
Define gross primary productivity (GPP)
The rate at which producers (plants/producers) incorporate light energy into biomass (organic matter)
What units is gross primary productivity and net primary productvity measured in?
KJ m-2 year-1
or
g (of carbon) m-2 year-1
Explain why the value for GPP is lower than the light energy available to the ecosystem.
Not all of the light falls on the { leaves / plants / producers }
Some of the light is reflected from the surface of the leaf
Some of the light misses the chloroplasts and passes through leaf
Some of the light is { the wrong wavelength / not absorbed by the chlorophyll }
Define net primary productivity (NPP)
The rate at which producers (plants/autotrophs) incorporate light energy into biomass (organic matter), after losing energy in respiration, and made available to consumers.
How is net primary productivity calculated?
NPP = GPP – R (energy lost by plant respiration)
What abiotic factors limit the productivity of the least productive ecosystems?
Lack of water, lack of light, low temperatures
(not CO as likely to be same everywhere)
What biotic factors could limit the productivity of all ecosystems?
Disease
Grazing by herbivores
Competition e.g. for light
Decomposition (slower at higher latitudes, so less mineral ion availability)
Human factors e.g. deforestation / pesticide use / fertilizer use / crop planting
Explain why the primary productivity of oceans is lower overall than terrestrial (land-based) ecosystems.
Most light energy is reflected or absorbed by water before it reaches producers.
State how light intensity affects primary productivity
As light intensity increases, productivity increases.
Explain why increasing light intensity increases primary productivity
Light is required for the light dependent reactions of photosynthesis; light energy excites electrons, which release energy for chemiosmosis to produce ATP, and reduce NADP.
ATP and NADPH are used to reduce GP to GALP. Therefore more light produces more ATP/NADPH and therefore more GALP.
State how water availability affects primary productivity
Low water environments limit productivity
Explain why low water environments limits primary productivity
- Water is required for photolysis; less water results in less photolysis, so electrons are not replaced in PSII during the light dependent reactions, so less ATP/NADPH is produced.
- Water is also needed to transport mineral ions and sucrose around a plant; less water means less mineral ions are transported.
- If cells go flaccid chemical reactions may not cannot occur as they happen in solution.
Explain how temperature affects primary productivity
Warm temperate environments have higher productivity.
The Calvin Cycle is controlled by enzymes e.g. RUBISCO which carboxylates RuBP.
The higher the temperature, the higher the enzyme activity as they gain kinetic energy, but they denature at very high temps (e.g.
deserts).
Temperature also affects transpiration.
State why disease and grazing by herbivores limits primary productivity.
Damage leaves, which are the site of photosynthesis.
State how human factors affect primary productivity
Deforestation, construction, crop planting limit productivity
Pesticide/fertiliser use could increase productivity.
State what is meant by gross secondary productivity
The rate at which energy / biomass is assimilated by consumers
How do calculate gross secondary productivity?
Energy in food eaten - energy in faeces
State what is meant by net secondary productivity
The rate at which energy / biomass is assimilated by consumers
How is net secondary producitvity calculatd?
NSP = GSP - R
How is the efficiency of energy transfer from one trophic level to another (%) calculated?
(energy available afer transfer / energy available before the transfer) x 100
How is energy lost in the transfer of energy between and within organisms?
Heat energy is lost via respiration.
Toxic waste organic molecules (urea) are excreted.
Some ingested material is not absorbed and ends up being egested.
Some parts of an organism remain uneaten, e.g. woody fibres from plants and the bones of animals.
What type of energy is lost at every trophic level?
Heat (thernal) energy
Explain why ecosystem require a continuous supply of energy (e.g. sunlight) to persist
All energy is eventually lost from organisms as thermal energy, which dissipates into the ecosystem and is eventually lost from it.
Explain why energy transfer between producer and primary consumer is rarely greater than 10%
- Plants using most of the ATP they produce to maintain their own metabolism.
- Plants lose energy as heat via respiration.
- Some parts of the plant may be indigestible and the primary consumer therefore egests, in the form of faeces, non-utilisable energy.
- Any consumer does not eat all of any particular plant e.g. roots may be left in ground.
How are nutrients recycled within an ecosystem?
By microorganisms
What is a carbon sink?
A reservoir where carbon has been removed from the atmosphere and ‘locked up’ or stored in organic or inorganic compounds.
What is a carbon source?
Reservoirs that release CO into the atmosphere
What process releases carbon from fossil fuels into the atmosphere in CO ?
Combustion
What process fixes carbon in CO into glucose in plant cells?
Photosynthesis (C-fixation during Light Indpendent Reactions)
What process converts dead organic matter into fossil fuels?
Fossilisation
What process breaks down dead organic matter?
Decomposition
What type of microorganisms are decomposers?
Bacteria and fungi
By what process do decomposers release CO back into the atmosphere?
Respiration
What processes take the carbon in CO out of the atmosphere and store it in the oceans?
Dissolving / photosynthesis of algae/aquatic plants e.g. seaweed
What gases are produced by combustion?
Carbon dioxide and water vapour
Why is nitrogen gas (N ) unable to be used by plants and animals?
It is inert / too unreactive
Why is nitrogen essential for living organisms?
to make amino acids/proteins for growth and repair, and to make nucleic acids/DNA
What is the formula for nitrogen gas?
N2
What is the formula for ammonia?
NH3
What is the formula for an ammonium ion?
NH4+
What is the formula for nitrite ions?
NO2-
What is the formula for nitrate ions?
NO3-
What is the formula for nitrogen oxide?
NO2
Name the process in the nitrogen cycle that converts inert nitrogen gas into ammonia?
Nitrogen fixation
Describe what is meant by nitrogen fixation
The conversion of inert nitrogen gas into ammonia by nitrogen-fixing bacteria
Describe the role of nitrogen fixing bacteria in the nitrogen cycle
Nitrogen-fixing bacteria contain the enzyme nitrogenase, which catalyses the conversion of nitrogen into ammonia in a process
called nitrogen fixation.
Ammonia (NH ) becomes ammonium (NH +) when mixed with water in the soil, and this can be taken up and used by plants.
Name two types of nitrogen fixing bacteria and where they are found
Azotobacter which is found living freely in the soil
Rhizobium which is found in root nodules of legumes, and supplies ammonia to the plant in exchange for carbohydrates in a mutualistic relationship.
Name the processes that break down dead organic matter and urea to ammonium ions.
Decompostion and ammonification
Describe what is meant by ammonification
The conversion of amino acids/urea in dead organic matter to ammonium ions (NH +) by saprotrophs
Name the microorganisms responsible for ammonification
Saprotrophs - bacteria and fungi
Name the proces that converts ammonium ions into nitrites and nitrates.
Nitrification
Describe what is meant by nitrification
Nitrification is the conversion of ammonium ions into nitrites and nitrates by nitrifying bacteria in the soil
Name the bacteria that convert ammonium ions into nitrites
Nitrosomonas
Name the bacteria that convert nitrites into nitrates
nitrobacter
Name two types of nitrifying bacteria and state their role in the nitrogen cycle
Nitrosomonas oxidise ammonium ions into nitrites
Nitrobacter oxidises nitrites into nitrates
Explain why soil must be well aerated to ensure a rich supply of nitrites and nitrates
Oxidation of ammonium and nitrites requires good supply of oxygen
Nitrosomonas and nitrobacter derive their energy from oxidation of inorganic compounds (ammonium/nitrites) so are called….?
Aerobic chemoautotrophs
Why can nitrifying bacteria not live in waterlogged soils?
Nitrifying bacteria are aerobic, so require oxygen for respiration, oxygen is in short supply in waterlogged soil.
Name the process that converts nitrates into nitrogen gas
Denitrification
Describe what is meant by denitrification
Chemical reduction process that converts nitrates (NO –) into nitrogen gas (N ) by denitrifying bacteria.
Name the bacteria that convert nitrates into nitrogen gas
Pseudomonas bacteria
What type of conditions are required for denitrification?
Anoxic/anaerobic e.g. waterlogged soil
Explain how nitrates are converted into nitrogen gas by denitrifying bacteria
Denitrification- in anoxic (anaerobic) conditions, denitrifying bacteria e.g. use nitrates instead of oxygen as an electron acceptor during cellular respiration, producing nitrogen gas.
How does nitrogen get transferred from plants to animals?
Feeding
How do farmers increase the nitrate content of the soil?
Crop rotation, using fertilisers (ammonium nitrate
made by Haber process)
Plants require a source of nitrogen to produce what compounds?
ATP, DNA, RNA, Chlorophyll
Name a genus of bacteria which is responsible for each of the reactions
1 - Nitrogen gas -> ammonia
2 - Ammonia ->nitrite
3 - nitrite -> nitrate
4 - Nitrate -> nitrogen gas in atmosphere
1: Rhizobium (legumes) / Azobacter (soil)
2: Nitrosomonas
3: Nitrobacter
4: Pseudomonas
Explain why animals are not essential to the nitrogen cycle.
Nitrogen fixing bacteria fix nitrogen gas into ammonia in soil and legumes.
Denitrifying bacteria return nitrogen gas to the atmosphere.
Plants obtain their nitrogen from the soil or via fixation, so nitrogen can be cycled solely by plants.
Outline the roles of microorganisms in the nitrogen cycle
Nitrogen-fixing bacteria in root nodules of legumes / soil convert nitrogen gas into ammonia.
Saprotrophs convert dead organic matter / urea into ammonium.
Nitrifying bacteria convert ammonia into nitrites and nitrates.
Denitrifying bacteria convert nitrates back into nitrogen gas.
