2.3 - energy, flows, trophic levels, productivity

1st law of thermodynamics

energy cannot be created or destroyed, only transformed from one form to another.

autotrophs

organisms that produce their own food through

• photo-autotrophs

  • photosynthesis

• chemo-autotrophs

  • chemosynthesis

using energy from sunlight or chemical sources.

photosynthesis

photo-autotrophs convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

2nd law of thermodynamic

energy transformations in ecosystems are inefficient due to energy being dispersed to the environment

respiration formula

• biggest loss of energy

C₆H₁₂O₆ + O₂ → CO₂ +H₂O + energy

trophic level

a position that and organism occupies in a food chain

producers (autotrophs) position

• first trophic level in a food chain

consumers (heterotrophs)

organisms that feed on producers or other organisms

• gain chemical energy from carbon (organic) containing compounds obtain from other organisms

• occupy the second or higher trophic levels in a food chain.

decomposers/ scavengers

organisms that feed on producers or other organisms

• break down dead organic matter, recycling nutrients back into the ecosystem.

energy flow between the trophic levels

food chain

a linear sequence of organisms through which energy and nutrients pass as one organism eats another.

• shows feeding relationships between species

• shows energy flow

*usually up to 4 levels as lots of energy and organic matter is lost as matter is transferred along

• efficiency of each transfer is typically around 10%.

ecological efficiency formula

ecological efficiency (%) = (Energy at trophic level n) / (Energy at trophic level n-1) x 100

food web

complex network of feeding relationships among various organisms in an ecosystem

• illustrates how energy flows between multiple trophic levels.

biomass

the dry mass or weight of the living or once-living organisms in the environment

productivity

measure of biomass over a period of time

• helps scientists to understand the energy stored at each trophic level

• difficult to measure because the organism must be killed and dried to remove all water

primary productivity

the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances, typically measured in biomass.

gross primary productivity GGP

the total amount of organic matter produced by autotrophs in a given area and time.

net primary productivity NPP

the rate of energy storage by photosynthetic plants after accounting for respiration losses.

• reflects biomass available for consumption

• crucial for sustaining food chains

NPP = GPP - respiration

consumer and secondary productivity

gain in biomass by consumers using carbon compounds absorbed and assimilated from ingested food

gross secondary productivity GSP

total biomass that consumers obtain through ingestion of organisms

• energy assimilated from the food before accounting for losses due to excretion/ undigestion

GSP = ingested food energy - energy lost through waste

net secondary productivity NSP

amount of biomass remaining after respiration and wast losses have been subtracted

• energy available for growth and reproduction

NSP = GSP - respiration

role of glucose

• growth

• maintenance

• reproduction

• deposition in/around cells as new biomass