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level: 13.2 Energy transfer and productivity

Questions and Answers List

level questions: 13.2 Energy transfer and productivity

QuestionAnswer
Chemical energy stores- GPP (Gross primary production) - NPP (Net primary production)
GPP (Gross primary production)- The amount of light energy converted into chemical energy, per unit area
NPP (Net primary production)- The amount of energy converted into chemical energy that is available to consumers
How primary production is expressed as rate- Typical units might be kJ ha-1 year-1 (kilojoules per hectare per year)
NPP equationnet primary production = gross primary production - respiratory loss
Net production of consumers- Consumers also store chemical energy in their biomass - Get energy by ingesting other organisms - However not all chemical energy stored in the consumers food is transferred to the next trophic level - Around 90% of the total available energy is lost is various ways
Where the energy is lost to- Egested as faeces + urine - Respiration - The energy that's left after all this is stored in the consumers biomass, is available to the next trophic level
Net production equationN = I - (F + R) N = Net production F = Chemical energy lost in faeces and urine I = Chemical energy in ingested food R = Energy lost through respiration
Two ways in which farming increases the amount of energy available for human consumption- The energy lost to other organisms e.g. pests, can be reduced - The energy lost through respiration can be reduced
The energy lost to other organisms e.g. pests- Farmers can reduce pest numbers using chemical pesticides + biological agents, so crops lose less energy + biomass - Increasing efficiency of energy transfer to humans - Combined effect of using both can reduced pest no. even more than either method alone, so NPP is increased even more
The energy lost through respiration can be reduced- Controlling the conditions that they live on - So that more of the energy is used for growth + less is lost through respiration - This means that more biomass is produced + more chemical energy can be stored - Increasing NP + efficiency of energy transfer to humans
Productivity in animal farming- High protein diet, decreases faeces, increase absorption - Kill animals are 1 year, when productivity is highest - Antibiotics in feed, prevent loss of biomass due to disease - Movement restricted, less muscle contractions, less respiratory losses - Kept at 25c, less energy used for thermoregulation