8.2 Energy Flow Through Ecosystems

Describe the strategies organisms use to acquire and use energy.

• Organisms use energy to organize, grow, reproduce, and maintain homeostasis.
  • i. Organisms use different strategies to r egulate body temperature and metabolism. Endotherms use thermal energy generated by metabolism to maintain homeostatic body temperatures. Ectotherms lack efficient internal mechanisms for maintaining body temperature, although they may regulate their temperature behaviorally by moving into the sun or shade or by aggregating with other individuals.
  • ii. A net gain in energy results in energy stor age, the growth of an organism, and increased reproductive output.
  • iii. A net loss of energy results in loss of mass, a decreas e in reproductive output, and, eventually, the death of an organism.
• Different organisms use various reproductive strategies in response to energy availability. Some organisms alternate between asexual and sexual reproduction in response to energy availability.

Explain how energy flows and matter cycles through trophic levels.

• Ecological levels of organization include populations, communities, ecosystems, and biomes.
• Energy flows through ecosystems, while matter and nutrients cycle between the environment and organisms via biogeochemical cycles. The cycles are essential for life, and each cycle demonstrates the conservation of matter. The cycles are interdependent.
• Biogeochemical cycles include abiotic and biotic reservoirs, as well as processes that cycle matter between reservoirs.
• The hydrologic (water) cycle involves water movement and storage within the hydrosphere. Reservoirs include oceans, surface water, the atmosphere, and living organisms. Processes include evaporation, condensation, precipitation, and transpiration.
• The carbon cycle involves recycling carbon atoms through Earth’s biosphere into organisms as carbohydrates and back into the atmosphere as carbon dioxide ()CO At the highest levels of organization, 2 . the carbon cycle can be simplified into four parts: photosynthesis, cellular respiration, decomposition, and combustion.
• The nitrogen cycle involves several steps, including nitrogen fixation, assimilation, ammonification, nitrification, and denitrification. These steps are performed by microorganisms in the soil. The largest reservoir of nitrogen is the atmosphere. In nitrogen fixation, nitrogen gas ()N2 is fixed into ammonia ()NH3 , which ionizes to ammonium (NH + 4 ) by acquiring hydrogen ions from the soil solution.
• The phosphorus cycle involves weathering rocks releasing phosphate ()PO 3− 4 into soil and groundwater. Producers take in phosphate, which is incorporated into biological molecules; consumers eat producers, transferring phosphate to animals. Phosphorus returns to the soil via decomposition of biomass, or excretion. Phosphate can also be incorporated back into the environment via decomposition of decaying organic matter.

Explain how changes in energy availability affect populations, communities, and ecosystems.

• Changes in energy availability can result in changes in population size.
• Changes in energy availability can result in disruptions to an ecosystem.
  • i. A change in energy resources such as sunlight can affect the number and size of the trophic levels. Trophic levels include producers; primary, secondary, tertiary, and quaternary consumers; and decomposers.
  • ii. A change in the biomass or number of producers in a given geographic area can affect the number and size of other trophic levels.

Explain how the activities of autotrophs and heterotrophs enable the flow of energy within an ecosystem.

• Autotrophs capture energy from physical or chemical sources in the environment.
  • i. Photosynthetic organisms capture energy present in sunlight contributing to primary productivity.
  • ii. Chemosynthetic organisms capture energy from small inorganic molecules present in their environment, which can occur in the absence of oxygen.
• Heterotrophs, which include carnivores, herbivores, omnivores, decomposers, and scavengers, metabolize carbohydrates, lipids, and proteins as sources of energy. Heterotrophs capture the energy present in carbon compounds by consuming organic matter derived from autotrophs incorporating matter into their tissues. 156AP Biology Course and Exam Description Ecology UNIT 8