Topic 4.2 - Energy Flow
SUNLIGHT, ECOSYSTEMS AND ENERGY CONVERSION
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Sunlight = initial source of energy for most ecosystems
Autotrophs/producers harvest light by photosynthesis
Producers absorb sunlight using chlorophyll + accessory pigments, convert to chemical
energy used to make carbs,lipids & other carbon compounds
compounds used in cellular respiration release energy/used in cell activities
In Cellular respiration heat is lost to surrounding
Heterotroph indirectly dependent, use carbon compounds in food as source of energy
ENERGY IN FOOD CHAINS
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Food chain starts with producer
PRIMARY CONSUMERS feed on PRODUCERS
SECONDARY CONSUMERS feed on PRIMARY CONSUMERS
TERTIARY CONSUMERS FEED ON SECONDARY CONSUMERS
I.e Grassland food chain
grass ——- grasshopper —— toad ——— hog nose snake ——— hawk
TROPHIC LEVELS
T1 - PRODUCERS
T2 - PRIMARY CONSUMERS
T3 - SECONDARY CONSUMERS
T4 - TERTIARY CONSUMERS
T5 - QUATERNARY CONSUMERS
RESPIRATION AND ENERGY RELEASE
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Energy released through cellular respiration used on living organisms/cell activities
ATP from CR supplies energy needed for cellular activities ( i.e synthesizing large
molecules like RNA, DNA & proteins, or active transport)
Cellular respiration = chemical energy ———- glucose/carbon compounds ——— ATP
Not all energy transferred, remainder converted to heat, heat also produced when ATP
used in cell activities
HEAT ENERGY IN ECOSYSTEMS
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Living organisms can only light energy to chemical energy or chemical energy into KE,
electrical energy, or heat energy
Cannot convert heat energy to other form of energy ∴ heat lost in ecosystems
ENERGY LOSS
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BIOMASS = total mass of a group of organisms
Energy loss between trophic levels restrict food chain length/biomass of higher lvls
Small proportion of energy in biomass of organisms in 1 trophic level will transfer to
biomass of organisms in next lvl ( approx. 10% - 20%)
Reasons for energy loss:
● Some animals cannot fully digest food ( not all of organism swallowed as food source )
● Not all of swallowed food can be absorbed/used in body
● Some organisms die before being eaten by next trophic lvl organism
● Considerable heat loss due to cellular respiration in all trophic lvls
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Moving up food chain = energy available becomes less & less, most food chain have 5
lvls ( no more energy left for other consumers)
SKILL: PYRAMID OF ENERGY
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Illustrates energy loss/transfer between trophic levels
*Remember to label trophic levels, know
correct units
(kJ m^-2 yr^1)start with producers as
lowest bar, bar should be proportional to
energy lost
Starts at 10000 to approx 10
UNITS = energy per unit area per unit per
time: kilojoules per square meter per year,
kJ m^-2 yr^1
ENERGY AND NUTRIENT
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ENERGY ENTERS/LEAVES ECOSYSTEMS (NOT RECYCLABLE) BUT NUTRIENTS
MUST BE RECYCLED
Energy enters as light & exits as heat ( Sun rise brings light energy, organisms can use
up/lose heat energy)
Organisms must recycle nutrients (i.e carbon,nitrogen & other compounds necessary for
life)
Organisms absorb valuable organic molecules/organisms molecules, resource no longer
available to others (only through eating or decomposition)
DECOMPOSERS
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break down/recycle bodies of dead organisms ( frees up nutrient stored in cells of plants
& animals)
Digestive enzymes convert organic matter to more usable form for themselves/others
Play vital role in formation of soil