Topic 4 : Ecology
4.2 Energy flow
Energy Cycle:
- In food webs and communities all interactions between the organisms requires energy.
- Sunlight provides the initial energy source for almost all communities.
- Sunlight energy is converted to useable chemical energy through photosynthesis.
- Autotrophs that harvest the light energy and produce chemical energy through photosynthesis are called producers. These include plants, eukaryotic algae, and cyanobacteria.
- Heterotrophs feed on other organisms in order to obtain their energy
- Producers release energy using cellular respiration and use it for cellular activities; some energy lost as heat. The energy remaining in the cells and tissues is available for consumers
Energy Flow
- 1º consumers feed on the producers. Only around 10% of the energy from the
producer is passed on to the 1º consumers. The rest of the energy is lost as heat through cell respiration, death and waste. - 2º consumers feed on the 1º consumers. Again only 10% of the energy is passed on
to the next level, with the rest lost as heat through respiration, death, and waste. - 3º consumers feed on 2º consumers. 10% is passed on to the tertiary consumer and
the rest is lost as heat, death and waste. - Most ecosystem rely on a supply of energy from sunlight and the energy flows through the food chain, bing lost at each stage due to respiration (heat).
- Organisms can perform a variety of energy conversions, such as light to chemical energy during photosynthesis, chemical energy to KE during muscle contractions, chemical energy to electrical energy in nerve impulses and chemical energy to heat energy in heat-generating adipose tissue
- Organisms cannot turn heat energy into any other forms of energy
- Eventually though, since heat passes from warmer to colder bodies (thermodynamics), all heat is lost from the ecosystem
Pyramid of energy
- Only 10% of energy can be passed on to the next trophic level due to
energy loss as heat. - Energy is lost because:
- At each level, when an organism is consumed some parts might not
be eaten or consumed - Not all food is digested or absorbed fully. Indigestible food is egested in feces.
- Some energy can be trapped as fossil fuels or peat.
- Energy is also lost due to respiration (heat)
The length of food chain
- Biomass is the total dry mass of a group of organisms, consisting of the cells and tissues of the organisms and the carbohydrates and other carbon compounds they contain
- Since carbon compounds have chemical energy, scientists can measure the amount of energy added per year by groups of organisms to their biomass.
Results are calculated per square metre of the ecosystem and the trophic levels can be compared. The energy added to the biomass by each successive trophic level is always less - Food chain length is limited by the amount of energy available as we move up the different trophic levels.
- Most energy in food that is consumed, digested and absorbed by organisms for a certain trophic level is released by them during cellular
respiration used in cellular activities and is therefore lost as heat - As we go up the food chain, less energy will be available; thus, the limitation of energy will reduce the length of food chain.
- The unit of energy in biology is \(KJm^{-2}y^{-1}\) (energy per square meter per year)