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Energy and Energetics

BIO 4730/5730 Environmental Biology Topic 3

Energy and Energy Metabolism■  Energy is required for:

●  Resisting entropy and maintaining !homeostasis Most of energy intake!(about 90%) is needed for this!maintenance metabolism (supporting !existing biological material)

■  Most adaptations are directly or !indirectly associated with maintaining !homeostasis while increasing energy !gain or decreasing energy wastage

■  Organisms must also produce new!biological material (biomass). Any !energy that is assimilated but not!needed for maintenance is available!for:●  Somatic (body) growth●  Reproduction

■  This increase in biomass by growth and!reproduction is known as production

Energy Availability on Earth ■  Energy is measured in joules (J)

●  1 J = 0.239 calories (actually, a gram-calorie, 1 g-cal = 4.186 J)●  1 kiloJoule (kJ) = 1000 Joules●  1 megaJoule (MJ) = 1,000,000 J

■  A calorie is the amount of energy required to increase the temperature of 1 g water 1 °C at 15 °C●  A kilocalorie (kcal) or Calorie = 1000 calories

■ Energy transfer requires the movement or flow of energy from one point to the other (energy flux = power)●  Unit of power (energy/time) is the watt (W) = 1 J s-1

●  Earth receives and average of about 1 W m-2 on its sunlit side (ultimate limit to global energy input)

●  Humans supplement solar energy using stored energy reserves (fossil fuels) deposited over 100s of millions of years

Earth Area Available to Support Humans

Productive sea and land area needed to produce the products consumed by each U.S. citizen:"

9.71 ha (the CSU campus is 64.75 ha: enough to sustain 12.3 U.S. citizens)

Productive sea and land area available to support each person in Africa:

1.36 ha

Each W. European/U.S. citizen:!5.06/5.26 ha World

Wildlife Fund,!

Living Planet Report 2002.

…on Earth: 1.90 ha

Energetics and ThermodynamicsEnergy is the ability to do work, and is the ultimate limiting resource for all living thingsFirst law of thermodynamics (Law of Conservation of Energy): energy can be neither created or destroyed, only converted from one form to another (energy input = energy output)

None of these ‘devourings’ creates any new energy, they just pass along energy that came from somewhere else. Where do you think the energy used by the organisms above comes from?

Energetics and ThermodynamicsSecond law of thermodynamics (‘Law of Entropy’): energy transformations are not completely efficient

■  Whenever energy is used to do !work, some energy is lost as heat

■  Result is that all complex systems!tend toward increasing disorder !(entropy)

■  Thus, all levels of life (organisms to ecosystems) require energy inputs to maintain their structure and function

Less than 15% of the original chemical energy contained in gasoline actually moves the car

Eating is also inefficient: only a fraction of the chemical energy in food is used by the consumer

Sunlight is generally considered to be the major !energy source powering ecosystems

■  Only a small proportion of incoming solar !energy is captured by living organisms during !photosynthesis

■  In cells of photosynthetic organisms,!a series of enzymes converts CO2 and!H2O into a sugar (glucose), which can!be stored

1% powers!photosynthesis

19% powers!water cycle

Energy Sources for Ecosystems

30% !reflected

50% !converted!

to heat

Energy to break and form the necessary chemical bonds comes from light photons at certain specific wavelengths of sunlight. Molecular oxygen is released as a byproduct

CO2 + H2O →���CH2O + O2

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Energy and Energetics

BIO 4730/5730 Environmental Biology Topic 3

Primary Production:■  Production of autotroph (producer)!

biomass■  Autotrophs capture and store their own!

energy and synthesize their own!structural materials

■  Limited by photosynthetic rates

Secondary Production:■  Production of heterotroph!

(consumer) biomass■  Heterotrophs’ structural!

materials (and energy) must be!obtained from their food

■  Limited by primary !productivity, number and efficiency of energy transfers, and other factors. Many chemical elements (e.g., Ca and P) must be provided in specific chemical forms or combinations

Ecological (Biomass) Production Energy-bearing Nutrients and RespirationCells use many organic molecules as fuel for respiration:

Energy-bearing Nutrients and BiosynthesisFood molecules are raw materials for biomass production "Energy in the form of ATP used to assemble macromolecules:

Energy-bearing Nutrient TypesCarbohydrates (CH2O)■  Manufactured by autotrophs from CO2 and H2O■  Easiest of nutrients to respire■  Form the bulk of the diet of many heterotrophs, yet are not

essential nutrients for heterotrophs!● Many carnivores exist on a carbohydrate-free diet, relying either

on lipids or on deaminated amino acids for energy (e.g., vampire bats and other blood parasites, Inuit humans)

■  Two categories of carbohydrates:● Highly digestible (e.g., starches and sugars) taken up by

assimilative digestion● Difficult to digest crude fiber (mostly cellulose): requires digestive

symbionts (prokaryotes) to convert cellulose into bacterial biomass (fermentative digestion) before energy-bearing nutrients can be assimilated

Trophic LevelsFirst tropic level: primary producers"

(autotrophs)

■  Photosynthetic Chemo- "prokaryotes synthetic"

prokaryotes■  Photosynthetic"

microalgae:!chlorophytes, diatoms,!dinoflagellates, etc.!

■  Macroalgae: large green, brown, and red algae!

■  Plants: mosses, ferns, and other vascular plants!!

■  Some fungi (e.g., lichens) and animals (e.g., corals) with algal endosymbionts serve as ‘primary producers’ in some systems

Trophic LevelsSecond tropic level:!

primary (1°) consumers■ Heterotrophs that feed!

directly on autotrophs●  Sometimes referred to as!

grazers, these are the first!level of predators

●  In predation, one organism (predator) obtains its energy and/or nutrients from another living organism (prey)

■ Many are herbivores (technically, herbivory refers to leaf predators)

■ Important to humans because they convert cellulose in plants, which is not digestible by humans, into animal products (meat, milk, and blood), which are digestible by humans

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Energy and Energetics

BIO 4730/5730 Environmental Biology Topic 3

Trophic LevelsThird tropic level: secondary (2°)"

consumers● Heterotrophs that prey !exclusively on primary !consumers

● These are predators in the!commonly-accepted sense!(that predator and prey are!both heterotrophic, and the!prey is alive until preyed upon

■ Fourth tropic level:!tertiary (3°) consumers

■ Fifth tropic level:!quaternary (4°) consumers

Humans are Primarily Omnivorous■ Omnivores prey on both autotrophs and heterotrophs■ Humans obtain a highly variable percentage of their

calories from animal sources● In Inuit societies, nearly 100% of calories were from animal

protein and fat● In modern societies, 80% or more of calories comes from plants (in

U.S., about 38% of calories come from livestock calories and 62% from plants)

■ Some fishes we consume occupy !very high trophic levels

baked potato, squash, salad!(1° producers)

swordfish!(6° consumer)

butter !(1° consumer)

4° (quaternary) consumersred-tailed hawk killer whales!

3° (tertiary) consumersprairie rattlesnakes mackerel!

2° (secondary) consumersgrasshopper mice sardines!

1° (primary) consumers (‘herbivores’)grasshopper zooplankton!

Terrestrial and Marine ‘Food Chains’

1° (primary) producersgreen plants phytoplankton!

Detrivory (‘Saprophagy’)Detritivores and decomposers!are organisms that obtain!their energy and nutrients!from dead organisms,!organism wastes, or lost!body parts!

Generally, detritivores are macroconsumers that feed on as-yet undigested material (e.g., hyenas, vultures, earthworms)

■  A portion of the dead material is digested and a large portion of ecosystem energy is lost by respiration of these organisms

■  In many terrestrial systems, over 90% of 1° producer energy goes directly through decomposition pathways

■  Remaining undigested portion and/or simpler molecules present in detritivores’ feces, excretions, and other exudates is further processed during…

Decomposition■  Decomposers are microconsumers (heterotrophic bacteria,

protists, and fungi)■  Obtain energy by converting chemical energy in monomers of

once-living macromolecular material back into their original inorganic forms, e.g., Nitrogen/sulfur in amino acids into N2 gas/sulfates, etc.

■  Like detritivores, many decomposers!(e.g., fungi) convert macro molecules!back into monomers and use them !for life processes, but their food!source is more ‘biodegraded’

■  Important! All organisms can convert carbon compounds back into inorganic form (CO2) during respiration, but!final decomposition of other elements (e.g., N and S) in organic material back into inorganic forms requires bacteria

Energy Transfers and Trophic Levels■ If each trophic level receives all of its energy from the level

below (i.e., if energy transfers are linear), then the resulting trophic structure is known as a food chain

■ Energy loss due to respiration from each level is about 90%. Produces ecological pyramids–as trophic level increases, there are decreasing amounts of:● Stored energy in both:

❖  living matter (biomass)❖  Nonliving organic matter !

(detritus)● Numbers of organisms● Production

❖ Less total energy !available

❖ Greater respiratory !losses by foraging !(possibly endothermic)!predators

● Turnover (‘recycling rates’ of biomass)

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Energy and Energetics

BIO 4730/5730 Environmental Biology Topic 3

Livestock and Human Food Chains■  Often very short and linear: forage → livestock → human■  Livestock are generally ruminants (mammals with specially-adapted

fermentative digestion: cattle, sheep, goats, deer, and camels)●  Less energy efficient,!

but can be fed a poor-!quality plant diet,!converting it into food!(meat, milk, blood)!that contains all!human dietary needs

■  Availability of ruminants with suitable characteristics for domestication has been a major influence on civilization●  Most herding species originated in!

N. Hemisphere, e.g., sheep, goats,!cattle, camels, reindeer

●  S. Hemisphere ruminants (e.g.,!antelopes, gazelles, llamas) are!solitary (or have many predators)!and are too fast, agile, nervous, or !aggressive to be easily domesticated

But Man is a carnivorous production,And must have meals, at least one meal a day;He cannot live, like woodcocks, upon suction,But, like the shark and tiger, must have prey;Although his anatomical constructionBears vegetables, in a grumbling way,Your laboring people think beyond all question,Beef, veal, and mutton, better for digestion.

-George Gordon (Lord Byron), Don Juan

Food WebsIn most communities and ecosystems, trophic structure is not linear

■  Feeding only from trophic level immediately below is not!energetically advantageous

■  Number of linear transfers is limited by the amount of energy at the 1° producer base (i.e., more 1° producer energy = longer food chain)

■  Numbers and biomass of predatory consumers often low compared with detritivores and decomposers

■  Often very complicated trophic interconnections between species: many organisms feed from multiple trophic levels

■  These produce more elaborate trophic structures (food webs)

Tertiary (3°),!Quaternary !

(4°), etc.Consumers

Heat

Decomposers

Heat

General Structure of Food Webs

Primary (1°)!Producers

Primary (1°)Consumers

Secondary !(2°)

Consumers

DetritivoresNutrientPool

Energy andNutrient Sink

Nutrient Flow

Heat HeatHeat

Heat

Energy Flow

Detritus