chap 11 organisms and their environment

• living organisms can be categorised as producers, consumers and decomposers
• producers are organisms that makes their own food and contain chlorophyll to absorb light to convert CO2 and water into glucose via photosynthesis
• consumers are organisms that are not able to make their own food, obtaining energy and nutrients by feeding on other organisms
• consumers can be classfied into primary, secondary and tertiary consumers
• primary consumers feed on producers only
• secondary consumers are organism that feed on primary consumers
• tertiary consumers feed on secondary consumers
• decomposers break down dead organisms, faeces and excretory products, returning nutrients like mineral salts to the environment
• food chain is a series of organisms, beginning with the producer, through which energy and nutrients are transferred
• producers tend to be on trophic level 1
• a food web consists of a network of interconnected food chains
• principal source of energy is the sun. during photosynthesis, energy from the sun is absorbed by chlorophyll in producers and transferred to chemical stored of energy in glucose molecules
• energy in the producers is passed from one trophic level to another by feeding. the amount of energy at each trophic level decreases as it flows through the ecosystem as only some of the energy from one trophic level gets transferred to the next level
• the rest of the energy that is not transferred to the next trophic level, is largely transferred to the environment as heat, through respiration. since this energy does not return to the same system as the organisms that produced it, it cannot be recycled in the ecosystem. hence, the flow of energy through the ecosystem is non- cylical
• egested and excreted materials, and dead organisms contain trapped chemical energy, which is released through the activity of decomposers. decomposers use some of this trapped chemical energy for their needs while the rest is transferred as heat to the environment
• shorter food chains are more efficient than longer food chains as greater amounts of energy is available to the final consumer because less energy is transferred to the environment
• As we move along the food chain, there is less and less energy available for the organisms at the next trophic level due to them being lost to the environment as heat or transferred to uneaten body parts, faeces and excretory products
• 90% of energy is lost to the environment
• how can energy be lost as it is transferred from one trophic level to the next ?

  transferred to the environment as heat during respiration

  transferred to uneaten body parts, faeces and excretory products
• why do food chains usually have < 5 trophic levels ?

  much of the energy is lost, causing there to be insufficient energy to support a long food chain
• predators and prey have a predator- prey relationship
• what can ecological pyramids represent ?

  numbers and biomass
• pyramid of numbers allows us to compare the number of organisms present in each trophic level at a particular time
• in a pyramid of biomass, producers tend to have the broadest base while tertiary consumers have the smallest base
• (-) of pyramid of nuumbers

  it does not consider the size and mass of organisms, and whether the organism is an adult or a juvenile
• pyramid of biomass allows us to compare the mass of organisms present in each trophic level
• biomass refers to the dry mass of the organism, where all water in an organism has been removed
• (+) of pyramid of biomass

  considers the size and mass of organisms, making it more of an accurate representation of energy flow through a food chain than pyramid of numbers
• (-) of pyramid of biomass

  organisms have to be killed to obtain biomass

  it has to be constructed at a particular point in time
• substances such as carbon, oxygen, nitrogen and water which are essential substances in nutrients, are released back into the soil when organisms die. decomposers break down dead organisms, allowing the locked up materials to be returned to the physical environment, to be used again by green plants. hence, in a balanced ecosystem, nutrients are never lost but are continuously recycled, brought about by physical, chemical and biological processes
• the processes by which carbon is removed from and released into the environment make up a carbon cycle
• during photosynthesis, plants absorb CO2 and use it to synthesise carbohydrates, some of which as convberted to proteins and fats. animals can obtains carbon compounds by feeding on these plants or other animals
• plants and animals respire, releasing CO2 into the atmosphere
• decomposers break down dead organic matter and release CO2
• eg of decomposers

  fungi and bacteria
• dead bodies of plants and animals may be buried deep into the earth, and are subjected to high pressures and temperatures, causing them to convert to fossil fuels such as coal, natural gas and oil. combustion of these fossil fuels release CO2 into the environment
• why is carbon cycle important ?

  ensures that there is a continuous supply of CO2 for plants to carry out photosynthesis, where they trap light during photosynthesis to synthesise glucose which acts as a store of chemical energy
• why is carbon cycle important ?

  enables energy to flow through the ecosystem as carbon compounds carry the stored energy from organism to organism in the food chains of an ecosystem
• why is carbon cycle important ?

  regulates the amount of CO2 in the atmosphere
• carbon sink

  it is an area that stores carbon from the atmosphere for a long period of time, storing more carbon than it releases