4.2 Energy Flow

photosynthesis

conversion of light energy from the sun into chemical energy

trophic level

the position an organism occupies within a feeding sequence (food chain)
producers occupy the first level and from then on then primary consumers occupy level 2 as they feed on them, etc.

higher trophic levels

further down in the chain, the carnivores eating each other
less energy and biomass

lower trophic levels

the producers, the beginning of the food chain
more biomass here

food chain

a model that represents how nutrients and energy are passed from producer to primary consumer and so on in a community

food web

a diagram that shows how food chains are linked together into more complex feeding systems, representative of the feeding pathways in an ecosystem

food chain vs food web

chain is a simplified illustration of energy flow, while a food web is a more realistic depiction of an ecosystem. in a web, organisms can have more than one food source/predator, and can occupy more than one trophic level.

arrows in food chains/webs

the arrows always point in the direction of nutrient and energy flow (not in the direction of who eats who)

energy stored in organic molecules

sugars and lipids, released by cell respiration to produce ATP

thermal energy

heat

the chemical energy produced by an organism can be converted into a number of forms, including:

kinetic, electrical and light energy

kinetic energy

energy of motion

electrical energy

energy caused by the movement of electrons.

light energy

energy produced by the vibrations of electrically charged particles

exothermic

chemical reaction in which energy is primarily given off in the form of heat

biomass

the total mass of a group of living organisms
biomass diminishes along food chains as less energy is stored
expressed as dry weight per unit area

units of energy per area per time

kJ m^-2 year^-1, the measurement in a pyramid of energy

ecological productivity

the rate of generation of biomass in an ecosystem, expressed in units of mass per area per time

primary production

the production of light energy converted to chemical energy in organic compounds by autotrophs.

gross primary production (GPP)

the amount of chemical energy as biomass that a producer creates in a given length of time

net primary production (NPP)

the amount of chemical energy that is NOT consumed by respiration (NPP \= GPP-respiration)

energy source

sunlight is the initial form of energy in almost all communities (in some they use energy derived from chemical processes). light energy is converted into chemical energy via photosynthesis

energy flow

energy flows through the ecosystem through the different trophic levels in the food chains

energy loss

not all energy stored in organic molecules is transferred, but instead becomes lost by excretion, being unconsumed, respiration and heat energy (as it cannot be converted)

energy efficiency

energy transformations are only about 10% efficient as 90% is lost between the trophic levels

bioaccumulation

the increase of a substance in a particular organism (the zoomed in version of biomagnfication)

biomagnification

the increase of a concentration of a substance at a particular trophic level (the zoomed out version of bioaccumulation)

energy pyramid

a model of the amount of energy at each trophic level of a food chain and the flow of energy
each level is one tenth of the size of the preceding level

a numbers pyramid

a model that depicts the number of organisms at each trophic level in an ecosystem, similar to the energy pyramid

biomass pyramid

a model representing the dried mass of the living organisms at each trophic level of an ecosystem