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How Ecosystems Work. Honors Biology PFHS Chapter 5. Energy Flow in an open system. Life depends on the sun (energy source) Energy captured by photosynthesis This energy is used by organisms to move, grow, and reproduce Energy is constantly coming in and going out of the earth system.

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How ecosystems work

How Ecosystems Work

Honors Biology


Chapter 5

Energy flow in an open system
Energy Flow in an open system

  • Life depends on the sun (energy source)

  • Energy captured by photosynthesis

  • This energy is used by organisms to move, grow, and reproduce

  • Energy is constantly coming in and going out of the earth system



Jobs, occupations, or roles in the ecosystem

Examples: producer (autotroph), consumer (heterotroph), decomposer


  • Producer (autotroph) makes nutrient molecules from photo-/chemosynthesis


  • Consumer – obtains nutrient molecules by eating another organism

  • 1st order – herbivore; eats photosynthetic plants

  • 2nd order – carnivore; eats flesh of herbivore

  • Tertiary – carnivore/omnivore; eats flesh of carnivore/omnivore

  • Omnivore – eats both plant and animal material


  • Saprovore – eats dead/decaying material

  • Scavenger – roadkill specialist

  • Decomposer – breaks down dead material to energy and recycles matter to the environment

Burning the fuel
Burning the Fuel

  • Cellular respiration – 90% of energy obtained is used for daily activity; 10% available for next trophic level

  • C6H12O6 + 6O2 -----> 6CO2 + 6H20 + energy (heat and ATP)

Recycling of matter in a closed system
Recycling of Matter in a Closed System

  • Closed system means a finite supply of matter; unlike infinite supply of energy

  • Material must be used over and over

  • Earth system has many biogeochemical cycles

How ecosystems work

Succession Defined:

  • The sequential change in the relative abundances of the dominant species in a biological community following a disturbance.

  • Primary succession: beginning from a abiotic environment following a cataclysmic disturbance.

  • Secondary succession: beginning from a major disturbance, but all forms of life are not destroyed.

Primary succession
Primary Succession

  • No soil

  • Pioneer species take hold, break down rock and contribute organic material = soil

  • Grasses, shrubs, then trees after soils

  • Climax community

    • May vary

    • Depends on environment

How ecosystems work

Stages of Succession

  • Early: plants typically small with short lifecycles (annuals…), rapid seed dispersal, environmental stabilizers.

  • Middle: plants typically longer lived, slower seed dispersal, and in woodland systems: larger.

  • Late: plants and animal species are those associated with older, more mature ecosystem.

  • “Climax”?

Marine succession 1
Marine Succession 1

  • Whale dies and sinks to floor

  • Scavengers/decomposers

Marine succession 2
Marine Succession 2

  • Smaller # of organisms

  • Sediment dwellers with enrichment of sediments from decomposition

Marine succession 3
Marine Succession 3

  • Skeleton remains

  • Heterotrophic bacteria decompose oils in bones

  • Release chemicals for chemosynthetic bacteria

  • Bacteria support mussels, limpets, snails, worms, crabs, clams, sediment dwellers around remaining bones

Greenhouse effect
“Greenhouse Effect” with succession.

  • Solar energy passes mostly unimpeded through the atmosphere and is absorbed at the surface

  • Outgoing long-wave radiation off the surface is absorbed by the atmosphere

  • A portion of the absorbed long-wave radiation is sent back down to the surface

  • The surface has a temperature 30˚ C warmer than it normally would have

  • This process is termed the “greenhouse effect”

“Greenhouse”?! with succession.

  • Greenhouses are certainly warm places on sunny days

  • However, greenhouses are not warm because of the trapping of infrared radiation

  • A greenhouse is warm because convection is inhibited by the glass (the warm air is stuck inside the greenhouse)

  • Therefore, the term “greenhouse effect” is a misnomer and does not apply to the atmosphere

Greenhouse effect vs global warming
Greenhouse Effect vs. Global Warming with succession.

  • The “greenhouse effect” is a good thing, otherwise we would be an ice planet

  • The terms “greenhouse effect” and “global warming” do not mean the same thing

  • Global warming is the concern that, by increasing the gases that trap infrared radiation in our atmosphere, we will increase the average surface temperature of the Earth