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
