energy and ecosystems

Question 1

what are the principles of an ecosystem

Answer 1

producers (autotrophs)
- photosutotrophs use light energy , chemoautothropes use inorganic molecules
- through photosynthesis plant’s synthesis organic compounds from atmospheric or aquatic carbon dioxide
- most sugars synthesised are used as respiratory substrates
- rest used to make other biological molecules : biomass

heterotrophs cannot synthesise own energy but obtain from autotrophs or other heterotrophs as they act as consumers

biomass and it’s stored energy are transferred through trophic levels in a food web

Question 2

how can you measure biomass

Answer 2

mass of carbon or dry mass of tissue per given area

1. sample if organism dried in oven at low temp to avoid combustion
2. sample reweighed at regular intervals
3. all water removed when mass remains constant
4. mass of carbon taken to be 50% of dry mass

dry mass more representative because water content of samples varies

the chemical energy stored in dry biomass can be estimated using calorimetry
- sample of dry biomass burnt
- energy released is used to heat known volume of water
- change in temp of water used to calculate chemical energy

Question 3

what is gross primary production

Answer 3

chemical energy store in plant biomass in a given area in a given time
eg. total energy resulting from photosynthesis

Question 4

what is net primary production and how to work it out

Answer 4

chemical energy store in plant biomass after respiratory losses
GPP-R
NPP is available for plant growth and reproduction and also to other trophic levels in the ecosystem

Question 5

how to work out the net production of consumers

Answer 5

N= I-(F+R)
I - the chemical energy stored in ingested food
F- chemical energy lost through farces and urine
R - respiratory losses

Question 6

what are the rates of productivity units

Answer 6

kJ ha^-1 year^-1
year takes into account seasonal variation
per unit area takes into account environments vary in size

Question 7

why is energy transfer between the sun and producer inefficient

Answer 7

wrong wavelength of light
light strikes no photosynthetic region eg. barn
light is reflected
lost as heat

Question 8

why is the energy transfer between producers and primary consumers inefficient

Answer 8

respiration loss
lost as heat
not all plant/ animal eaten eg. bones
some food not digested

Question 9

what farming practices in crops can be used to increase energy transfer efficiency

Answer 9

herbicides kill weeds-> less competition -> more energy to create biomass
fungicides reduce fungal infections-> more energy to create biomass
pesticides - reduce loss of biomass from crops

fertilisers prevent poor growth from lack of nutrients

Question 10

what farming practices in livestock can be used to increase energy transfer efficiency

Answer 10

reducing respiratory losses
- restrict movement
- keep warm
slaughter animal while still growing when most of their energy is used for growth
selective breeding to produce breeds with higher growth rates
tested with antibiotics to prevent loss of energy to die to pathogens