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Energy and Living Things. Outline. Energy Sources Solar-Powered Biosphere Photosynthetic Pathways Using Organic Molecules Chemical Composition and Nutrient Requirements Using Inorganic Molecules Energy Limitation Food Density and Animal Functional Response Optimal Foraging Theory.

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Energy and Living Things

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Energy and living things

Energy and Living Things



  • Energy Sources

  • Solar-Powered Biosphere

  • Photosynthetic Pathways

  • Using Organic Molecules

  • Chemical Composition and Nutrient Requirements

  • Using Inorganic Molecules

  • Energy Limitation

  • Food Density and Animal Functional Response

  • Optimal Foraging Theory

Energy and living things

Energy Flows Through Living Systems


Plants= Autotrophs

Energy and living things

  • Autotroph: ‘self feeder’ - an organism that can gather energy (usually from light) … to store in organic molecules

    • Photosynthesis

    • chemosynthesis

  • Heterotroph: An organism that must rely on other organisms to capture light energy … must rely on breakdown of organic molecules produced by an autotroph as an energy source

    • Classified by trophic level

Energy and living things


Capture and transfer light energy to chemical bonds

Occurs in:



Certain Bacteria

Not a perfect process – some energy is lost - entropy

Energy and living things

How Photosynthesis Works

  • Light strikes leaf

  • Energy absorbed by chemical pigments

  • Absorbed energy drives chemical processes to convert CO2 into larger molecules

    • First simple sugars – 6 carbon ring structures

    • Later many molecules of simple sugars joined together to form larger molecules or converted to other compounds

    • Energy absorbed in building larger molecules, released as they are broken down

Energy and living things

Only certain Wavelengths of Light are Used in Photosynthesis

  • Light Energy Used = ‘Photosynthetically Active Radiation’ or PAR

    • How Much is absorbed: determined as photon flux density.

      • Number of photons striking square meter surface each second.

  • Chlorophyll absorbs light as photons.

    • Landscapes, water, and organisms can all change the amount and quality of light reaching an area.

  • Light not absorbed is reflected

    • Some in PAR + all in green and yellow wavelengths

  • Energy and living things

    Wavelengths most useful in driving photosynthesis

    Absorption spectra of chlorophylls and carotenoids

    Wavelengths not used - reflected

    Fall color

    Fall color

    • In many plants production of chlorophyll ceases with cooler temperatures and decreasing light

    • other pigments become visible

    Energy and living things

    Modifications of Photosynthesis for Dry Climates

    • C3 Photosynthesis

      • Used by most plants and algae.

      • CO2 enters leaves BUT water vapor leaves

        • Poorly adapted to hot dry environments

    • C4/CAM photosynthesis: Modifications in biochemical processes

      • Increased efficiency in CO2 absorption

      • Fewer stomata required/stomata only open during night  decreased loss of water vapor

    C 3 photosynthesis

    C3 Photosynthesis

    CO2 enters passively so stomata have to be open for long periods of time

    Why c3 photosynthesis doesn t always work out co 2 must enter though stomata

    Why C3 Photosynthesis Doesn’t always work out - CO2 must enter though stomata

    • stomata (sing., stoma) are tiny holes on the undersides of leaves

    • CO2 enters and moisture is released

    • In hot, dry climates, this moisture loss is a problem

    Energy and living things

    C3 grasses (yellow) dominant in cool temperate – C4 plants don’t compete so well there

    C4 grasslands (orange) have evolved in the tropics and warm temperate regions

    C 4 photosynthesis

    C4 Photosynthesis

    Photosynthetic pathways

    Photosynthetic Pathways

    • CAM Photosynthesis

      • (Crassulacean Acid Metabolism)

      • Limited to succulent plants in arid and semi-arid environments.

        • Carbon fixation takes place at night.

          • Reduced water loss.

        • Low rates of photosynthesis.

        • Extremely high rates of water use efficiency.

    Cam photosynthesis

    CAM Photosynthesis

    Energy and living things


    • Herbivores

      • Animals that eat plants

      • The primary consumers of ecosystems

    • Green plants and algae

    • Use solar energy to build energy-rich carbohydrates

    • Carnivores

    • Animals that eat herbivores

    • The secondary consumers of ecosystems

    • Omnivores are animals that eat both plants and animals

    • Tertiary consumers are animals that eat other carnivores

    • Detritivores

    • Decomposers

      • Organisms that break down organic substances

    • Organisms that eat dead organisms

    Energy and living things

    Efficient Breakdown of Products of Photosynthesis Requires Oxygen

    • Complex series of reactions, oxygen serves as the terminal electron acceptor

    • May occur in some organisms w/o oxygen (anoxic conditions)

      • anaerobic respiration= fermentation

      • Inefficient

      • End products vary with organism involved

        • Ethanol, proprionic acid, lactic acid, etc.

    Energy and living things

    • Three Feeding Methods of Heterotrophs:

      • Herbivores: Feed on plants.

      • Carnivores: Feed on animal flesh.

      • Detritivores: Feed on non-living organic matter.

    Energy and living things

    Classes of Herbivores

    • Grazers – leafy material

    • Browsers – woody material

    • Granivores – seed

    • Frugivores – fruit

    • Others – nectar and sap feeders

      • Humming birds, moths, aphids, sap suckers …

    Energy and living things


    • Substantial nutritional chemistry problems.

      • Low nitrogen concentrations – difficulty extracting needed protein/amino acids from source.

      • Require 20 amino acids to make proteins ~ 14 are must come from diet

    Energy and living things

    How do plants respond to feeding pressures by herbivores?

    • Mechanical defenses – spines

    • Chemical defenses

      • Digestion disrupting chemicals – tannins, silica, oxalic acid

      • Toxins – alkaloids

        • More common in tropical species

          How do animals respond?

      • Detoxify

      • Excrete

      • Chemical conversions – use as nutrient

    Energy and living things

    • Digestion Schemes of Herbivores

    • Require extensive digestive processing

    • Rumnants – 4 part stomach

      • Rapid feeding, coarse material is re-milled (regurgitated bolus) after initial fermentation

        • ‘Chewing their cud’

    Energy and living things

    • Coprophagy: expel moist fecal material, re-ingest

      • 50-80% of fecal material recycled

        • acts as external rumen

        • bacterial activity produces B vitamin

    Cecum is site of much bacterial activity, moist fecal pellets enclosed in protein produced

    Energy and living things


    • Predators must catch and subdue prey - size selection.

      • Usually eliminate more conspicuous members of a population (less adaptive).

      • act as selective agents for prey species.

    Energy and living things

    European River Otter:

    Lutra lutra

    Widest ranging of otters

    Diet varies with abundance of prey

    Optimal foraging theory

    Optimal Foraging Theory

    • Assures if energy supplies are limited, organisms cannot simultaneously maximize all life functions.

      • Must compromise between competing demands for resources.

        • Principle of Allocation

    • Fittest individuals survive based on ability to meet requirements principle of allocation

    Optimal foraging theory1

    Optimal Foraging Theory

    • All other things being equal,more abundant prey yields larger energy return. Must consider energy expended during:

      • Search for prey

      • Handling time

  • Tend to maximize rate of energy intake.

  • What would a starving man do at an all you can eat buffet?

  • Optimal foraging in bluegill sunfish

    Optimal Foraging in Bluegill Sunfish

    Energy and living things

    Adaptations of Prey to being preyed upon

    • Predator and prey species are engaged in a co-evolutionary race.

    • Avoid being eaten – avoid starving/becoming extinct

    • Defenses:

      • Run fast

      • Be toxic – and make it known

      • Pretend to be toxic

    • Predators learn to avoid



    • Consume nutritionally-rich prey.

      • Cannot choose prey at will.

        • Prey Defenses:

          • Aposomatic Coloring - Warning colors.

          • Mullerian mimicry: Comimicry among several species of noxious organisms.

          • Batesian mimicry: Harmless species mimic noxious species.

    Energy and living things

    Mullerian mimicry: Comimicry

    Energy and living things

    Batesian mimicry: Harmless species mimic noxious species

    Energy and living things

    Aposomatic Coloring - Warning colors



    • Consume food rich in carbon and energy, but poor in nitrogen.

      • Dead leaves may have half nitrogen content of living leaves.

    • Fresh detritus may still have considerable chemical defenses present.

    Detritivores and decomposers

    Detritivores and decomposers



    • Energy Sources

    • Solar-Powered Biosphere

    • Photosynthetic Pathways

    • Using Organic Molecules

    • Chemical Composition and Nutrient Requirements

    • Using Inorganic Molecules

    • Energy Limitation

    • Food Density and Animal Functional Response

    • Optimal Foraging Theory

    • Adaptations

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