4.2 energy flow

Question 1

what is the initial source of energy for almost all communities? and what is the exception?

Answer 1

• sunlight: to sustain life within ecosystem, it is not sufficient to allow energy to cycle within the ecosystem
• biological and chemical reactions inefficient; losses mainly in the form of heat energy to environment
• photosynthesis is main form by which energy from the sun is used to synthesise high energy compounds that can be transferred down trophic levels in ecosystem
• light is the initial source of energy for almost all communities
• exception: ecosystems built around deep sea volcanic vents (chemoautotrophs [use energy derived from chemical processes] as producers)

Question 2

what do food chains show?

Answer 2

linear feeding relationship

Question 3

what happens to energy from respiration?

Answer 3

• organic molecules consumed as food digested into simpler molecules
• carbohydrates –> glucose, glucose / amino acids / lipids metabolised to produce atp
• atp used as energy source for cellular activities / metabolic reactions needed for growth and homeostasis
• chemical reactions innately inefficient; at every stage energy is lost to environment as heat
• given that all living organisms will lose energy as heat due to metabolic processes, implies that energy is lost from ecosystems in the form of heat
• not all energy stored in organic molecules is transferred via heterotrophic feeding; only about 10% gets passed on
• 90% lost via: faeces; used in respiration; lost as heat due to inefficiencies in respiration; waste materials and urine; not the entire organism may be consumed
• shorter food chains are more efficient as limited by energy losses between trophic levels
• living organisms cannot convert heat to other forms of energy

Question 4

explain the flow of nutrients and energy through the ecosystem (8 marks)

Answer 4

energy: (flows linearly)
- energy enters from sunlight
- autotrophs capture sunlight
- energy flows through trophic levels / stages in food chain
- energy transfer approximately 10% from one level to next
- energy loss due to material not fully consumed / assimilated / egested / excreted
- energy passes to decomposers / detritivores / saprotrophs in dead organic matter
- heat energy lost through cell respiration

nutrients: (cycled)
- nutrients are recycled / cycles within ecosystem
- nutrients from weathering of rocks enter ecosystem
- nutrients recycled from decomposition of dead organisms
- nutrients move through food chain by digestion of other organisms
- nutrients absorbed by producers / plants / roots
- nutrients lost by leaching / sedimentation