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

Energy Flows Through Living Systems

Plants= Autotrophs

Heterotrophs

• 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

Photosynthesis • Capture and transfer light energy to chemical

bonds• Occurs in:

– Plants– Algae– Certain Bacteria

• Not a perfect process – some energy is lost - entropy

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

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

Absorption spectra of chlorophylls and carotenoids

Wavelengths most useful in driving photosynthesis

Wavelengths not used - reflected

Fall color• In many

plants production of chlorophyll ceases with cooler temperatures and decreasing light

• other pigments become visible

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

C3 PhotosynthesisCO2 enters passively so stomata have to be open for long periods

of time

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

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

C4 Photosynthesis

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

• Producers • Herbivores– Animals that eat plants– The primary consumers

of ecosystems

– Green plants and algae– Use solar energy to build

energy-rich carbohydrates

• Carnivores

– Organisms that eat dead organisms

• Decomposers– Organisms that

break down organic substances

– 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

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.

• Three Feeding Methods of Heterotrophs:– Herbivores: Feed on plants.– Carnivores: Feed on animal flesh.– Detritivores: Feed on non-living organic matter.

Classes of Herbivores

• Grazers – leafy material

• Browsers – woody material

• Granivores – seed

• Frugivores – fruit

• Others – nectar and sap feeders– Humming birds, moths, aphids, sap suckers

…

Herbivores

• 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

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

• 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’

• 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

Carnivores

• 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.

• European River Otter:• Lutra lutra• Widest ranging of

otters• Diet varies with

abundance of prey

• http://itech.pjc.edu/sctag/E_OTTER/Index.htm

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 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

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

Carnivores• 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.

Mullerian mimicry: Comimicry

Batesian mimicry: Harmless species mimic noxious species

Aposomatic Coloring - Warning colors

Detritivores

• 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

Review• 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