5.3 Energy and ecosystems Flashcards
In any ecosystem, plants synthesise organic compounds from carbon dioxide. From what two sources?
In any ecosystem, plants synthesise organic compounds from atmospheric, or aquatic, carbon dioxide.
Most of the sugars synthesised by plants are used by the plant as _____________________. The rest are used to __________________ .
Most of the sugars synthesised by plants are used by the plant as respiratory substrates. The rest are used to make other groups of biological molecules.
Biomass is….
Some of the sugars synthesised by plants are used by the plant to make other groups of biological molecules. These biological molecules form the biomass of the plants.
Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area.
Biomass can be measured as…
mass of carbon or dry mass of tissue per given area
What does calorimetry do?
Gives you an estimate of the chemical energy store in dry biomass
GPP?
GPP=NPP+R
Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume.
NPP?
NPP=GPP-R
Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account.
This net primary production is available for plant growth and reproduction. It is also available to other trophic levels in the ecosystem, such as herbivores and decomposers.
The net production of consumers (N), such as animals, can be calculated as:
N=I-(F+R)
I represents the chemical energy store in ingested food.
F represents the chemical energy lost to the environment in faeces and urine.
R represents the respiratory losses to the environment.
N represents secondary production.
What is productivity?
Productivity is the rate of production.
Primary productivity is the rate of primary production (GPP or NPP).
Secondary productivity is the rate of secondary production (N).
What is the unit of productivity?
It is measured as biomass in a given area in a given time eg kJ ha–1 year–1
You should be able to appreciate the ways in which production is affected by farming practices designed to increase the efficiency of energy transfer by:
simplifying food webs to reduce energy losses to non-human food chains.
Humans eat livestock, making us secondary consumers.
Livestock has to be fed.
Farming produces the feed crops for the livestock.
NPP = GPP - R
N = I - (F + R)
The GPP from the producers (on the land farmed to produce the feed) loses R to become NPP. Not all of the NPP is grazed by the livestock (they may not pull up and eat the roots, for example), and of that which they do ingest (I) not all can be digested and so passes out as faeces (F). There are further energy losses from the livestock as R (which are considerable, given that all our livestock is endothermic, being mammals or birds). Added to which, we don’t ingest all of the body parts of the livestock. So this means that only a small proportion of the GPP is Ingested by us.
GPP is directly related to area of land (as the input is light, and we can’t increase the intensity of light, so if you want to increase your input of light you need more land). So as our meat sales go up, so does our land use.
However, if we just ate the producers ourselves, we could stop the losses from R and F that occur in our livestock. Then we could reduce the area of land required for farming, and begin to rewild it.
Another option is to eat more decomposers (ie fungi), or herbivorous insects (which have much lower losses from F and R).
You should be able to appreciate the ways in which production is affected by farming practices designed to increase the efficiency of energy transfer by:
reducing respiratory losses within a human food chain.
Humans eat livestock, making us secondary consumers.
Livestock has to be fed.
Farming produces the feed crops for the livestock.
Feed crops cost money.
Farmers want to maximise their returns on this investment, so use techniques which minimise losses from R in their livestock, for example by:
reducing movement by using pens and cages
reducing energy spend on thermal homeostasis by keeping livestock in heated buildings
reducing unnecessary protein synthesis (ie antibody formation) by giving antibiotics as standard (ie just as part of their feed, regardless of their health).
