23.2 Biomass Tranfer Through An Ecosystem Flashcards
What is the source of energy for almost all the ecosystems on earth?
The sun
How is energy from the sun used?
Photosynthetic organisms like plants convert the sun’s light energy into chemical energy, which is then transferred to other non photosynthetic organisms
Trophic level
Each stage in a food chain
Producer
Organism that converts light energy into chemical energy by the process of photosynthesis
Consumer
Organisms that obtain their energy by feeding on other organisms
Why is there a limit on the number of trophic levels in a food chain?
There is not sufficient biomass and stored energy left to support any further organisms
Decomposers
Feed on dead and decaying matter to release nutrients back into the ecosystem
Biomass
Dry mass of living material present in a particular place or in particular organisms
How is biomass at each trophic level calculated?
Biomass in each organism x total number of organisms in that trophic level
Why is dry mass taken for pyramid of biomass?
Water content must be discounted
Different organisms have different amounts of water
Why is it difficult to find dry mass of organisms?
Organisms have to be killed in order to be dried
Organisms have to be put in an oven at 80oC until all water is evaporated
Units for biomass
g/m2 (areas of land)
g/m3 (areas of water)
Why is biomass in each trophic level nearly always less than the trophic level below?
Biomass consists of all the cells and tissues of the organism present, including carbohydrates and carbon compounds
As carbon compounds are a store of energy, biomass can be equated to energy content
Only a small proportion of food eaten by animals can be converted into new tissue (biomass)
What is biomass at each trophic level measured in?
Kilojoules per metre squared per year
Allows for changes in photosynthetic production and consumer feeding patterns throughout the year
Ecological efficiency
Efficiency with which biomass or energy is transferred from one trophic level to the next
Why can producers only convert 1-3% of sunlight into chemical energy?
Not all the solar energy available is used for photosynthesis
- 90% is reflected
- some is transmitted through the leaf
- some is unusable wavelength
Other factors may limit photosynthesis, such as water availability
Proportion of energy is lost - used for photosynthetic reactions
Gross production
Total solar energy that plants convert to organic matter
Formula for energy available to the next trophic level
Net production = gross production - respiratory losses
Why do consumers at each trophic level convert only around 10% of biomass in their food into their own organic tissue?
Not all of the biomass of an organism is eaten
Some energy is transferred to the environment as metabolic heat, due to movement and respiration
Some parts are eaten but not digested, egested as faeces
Some energy is lost from animals via excretory products such as urine
Ecological efficiency formula
Energy or biomass available after transfer / energy or biomass available before the transfer x 100
How do we ensure that maximum energy is transferred into biomass that can be eaten by humans?
Agriculture creates very simple food chains
There are just two trophic levels - producers (crops) and humans (consumers)
Minimum energy is lost - fewer trophic levels
