Energy transfer and productivity (BIOL4) Flashcards
Describe food chains and food webs
Food chains - feeding relationships between organisms, each stage of the chain called trophic level
Food web - overlapping of food chains
How is energy transferred through ecosystems?
Energy enter ecosystem by photosynthesis - convert light into energy to be used by producers
Energy transferred through living organisms eating other organisms
Producers eaten by primary consumers Primary eaten by secondary
Secondary eaten by tertiary
Energy in uneatable organisms recycled by decomposers (saprobiotic nutrition)
Why doesn’t plants absorb all the sun’s energy available?
90% sun energy reflected back into space by the atmosphere
Not all wavelengths of light can be absorbed by plants
Light not actually fall onto chlorophyll
Limiting factors may slow down photosynthesis
Why isn’t all energy transferred between trophic levels?
Some of organism not eaten Some parts eaten, but not digested
Energy lost in excretion
Some energy lost via respiration used to maintain high body temp
Why is energy transfer in food chains insufficient?
Only have 4-5 trophic levels as there isn’t enough energy to support a large breeding population at trophic levels h. than these
Total biomass less at h. trophic levels
Total amount of energy stored is less at each stage of the food chain
How much energy is lost is lost during energy transfer?
100% available
60% never taken in initially
40% absorbed - gross productivity: 30% respiratory loss, 10% net productivity
Define gross productivity
Total amount of energy absorbed
Define respiratory loss
Amount of energy loss by respiration
Define net productivity
The amount of energy available for the next trophic level
How do you calculate net productivity?
Net productivity (kJm/yr) = gross productivity - respiratory loss
How do you calculate energy transfer efficiency from one trophic level to another?
(Net productivity / gross productivity) x 100
Features of pyramid of numbers
No. of organisms at each trophic level
No account for size e.g 1 tree equal to 1grass blade, obviously that a tree can sustain more life than a blade of grass
No. of individuals can be so great it can be almost impossible to count them
Features of pyramids of biomass
Biomass is the total mass of plants/animals of species in area
Biomass can be unreliable - various different amount of water can be stored in an organism
Dry mass is measured, but organism must be killed - thus large sample can’t be taken
Disadvantage of pyramid of numbers and biomass
Unreliable as they don’t account for seasonal differences in amount of organisms present
Features of pyramids of energy
Shows amount of energy available at each trophic level
Always pyramid shaped
Collecting data is complex
