Chapter 2: The Physical Chapter 2: The Physical EnvironmentEnvironment

11

Constraints, Solutions, and Constraints, Solutions, and MoreMore

• Physical properties of the environment and of Physical properties of the environment and of biological materials constrain life, but also biological materials constrain life, but also provide solutions to many of its problems.provide solutions to many of its problems.

• Living things have a purposeful existence; their Living things have a purposeful existence; their structures, physiology, and behavior are directed structures, physiology, and behavior are directed toward procuring energy and resources and toward procuring energy and resources and producing offspring. They:producing offspring. They:• depend on the physical world for:depend on the physical world for:

• energy from sunlightenergy from sunlight• nutrients from the soil and waternutrients from the soil and water

• affect and alter the physical worldaffect and alter the physical world• function within limits set by physical lawsfunction within limits set by physical laws22

Water has many properties favorable for Water has many properties favorable for the maintenance of life.the maintenance of life.

• Water, an ideal life medium:Water, an ideal life medium:• is abundant over most of earth’s surfaceis abundant over most of earth’s surface• is an excellent solvent and medium for is an excellent solvent and medium for

chemical processeschemical processes• allows for high concentrations of molecules allows for high concentrations of molecules

necessary for rapid chemical reactionsnecessary for rapid chemical reactions• enables movements of organisms because of enables movements of organisms because of

its fluidityits fluidity

33

Thermal Properties of Thermal Properties of WaterWater

• liquid over broad range of temperaturesliquid over broad range of temperatures

• conducts heat rapidlyconducts heat rapidly

• resists temperature changes because of its resists temperature changes because of its heat capacityheat capacity

• resists changes in state:resists changes in state:• freezing requires heat removal of 80 cal/gfreezing requires heat removal of 80 cal/g• evaporation requires heat addition of over evaporation requires heat addition of over

500 cal/g500 cal/g• So? Helps to keep large bodies of water So? Helps to keep large bodies of water

from freezing solid during winterfrom freezing solid during winter44

Water has other remarkable Water has other remarkable thermal properties.thermal properties.

• Most substances become denser as they Most substances become denser as they cool.cool.

• Water also becomes denser, to a point, but:Water also becomes denser, to a point, but:• reaches maximum density at 4reaches maximum density at 4ooC, and expands C, and expands

as it cools below that pointas it cools below that point• expands even further upon freezingexpands even further upon freezing

• This property is of monumental importance This property is of monumental importance to life on earth:to life on earth:• bottoms of lakes and oceans prevented from bottoms of lakes and oceans prevented from

freezingfreezing• floating layer of ice with covering of snow forms floating layer of ice with covering of snow forms

protective, insulating surfaceprotective, insulating surface

55

Water: less dense as it freezes, so ice floats. Water: less dense as it freezes, so ice floats. More than 90% of the bulk of this Antarctic iceberg lies More than 90% of the bulk of this Antarctic iceberg lies

below the surfacebelow the surface

The Buoyancy and The Buoyancy and Viscosity of WaterViscosity of Water

• Density of water (800x that of air) means that Density of water (800x that of air) means that water is water is buoyantbuoyant..

• Aquatic organisms achieve neutral density through:Aquatic organisms achieve neutral density through:• reduction (bony fish) or elimination (sharks) of hard skeletal reduction (bony fish) or elimination (sharks) of hard skeletal

componentscomponents• use of gas-filled swim bladder (plants too!)use of gas-filled swim bladder (plants too!)• accumulation of lipidsaccumulation of lipids

• Water’s Water’s viscosityviscosity retards the movement of retards the movement of organisms (some organisms are streamlined, organisms (some organisms are streamlined, others deploy parachutes).others deploy parachutes).

77

The droplet of oil in this algal cell provides The droplet of oil in this algal cell provides buoyancybuoyancy

All natural waters contain All natural waters contain dissolved substances.dissolved substances.

• Water is a powerful Water is a powerful solventsolvent because of its because of its charge polarity.charge polarity.

• Almost all substances dissolve to some Almost all substances dissolve to some extent in water.extent in water.

• Nearly all water contains some dissolved Nearly all water contains some dissolved substances:substances:• rainwater acquires dissolved gasses and trace rainwater acquires dissolved gasses and trace

mineralsminerals• lakes and rivers contain 0.01-0.02% dissolved lakes and rivers contain 0.01-0.02% dissolved

mineralsminerals• oceans contain 3.4% dissolved mineralsoceans contain 3.4% dissolved minerals

99

Fresh Versus Salt WaterFresh Versus Salt Water

• Noteworthy differences in makeup of solutes:Noteworthy differences in makeup of solutes:• salt water is rich in (sodium) Nasalt water is rich in (sodium) Na++, (cholorine) Cl, (cholorine) Cl--

(magnesium) Mg(magnesium) Mg2+2+, (sulfate) SO, (sulfate) SO442-2-

• fresh water is rich in (calcium) Cafresh water is rich in (calcium) Ca2+2+, (bicarbonate) , (bicarbonate) HCOHCO33

--, and (sulfate ions) SO, and (sulfate ions) SO442-2-

• Solute loads of surface waters reflect bedrock Solute loads of surface waters reflect bedrock chemistry:chemistry:• water of limestone areas is “hard” with substantial water of limestone areas is “hard” with substantial

CaCa2+2+, HCO, HCO33--

• water of granitic areas contains few mineral elementswater of granitic areas contains few mineral elements

• Oceanic waters are saturated with respect to Oceanic waters are saturated with respect to CaCa2+2+, but continue to accumulate Na, but continue to accumulate Na++..

1010

Minerals have accumulated in the oceans for eonsMinerals have accumulated in the oceans for eons

Waters differ in contents of Waters differ in contents of essential nutrients.essential nutrients.

N and P are among most the important N and P are among most the important essential elements and are often essential elements and are often limiting:limiting:• typical typical fresh waterfresh water N is 0.40 mg/L, while P N is 0.40 mg/L, while P

is about 0.01 mg/L (is about 0.01 mg/L (N>PN>P).).• typical typical salt water salt water N is less than 0.01 mg/L, N is less than 0.01 mg/L,

while P is about 0.01-0.1 mg/L (while P is about 0.01-0.1 mg/L (P>NP>N).).

• So?So?1212

pH - the Concentration of pH - the Concentration of Hydrogen IonsHydrogen Ions

• Normal pH range of surface waters is 6-9.Normal pH range of surface waters is 6-9.

• Acid rain can lower pH to as low as 4 in Acid rain can lower pH to as low as 4 in some areas. some areas. ( [ ] of hydrogen ions in a solution ( [ ] of hydrogen ions in a solution = acidity)= acidity)

• Acidity dissolves mineralsAcidity dissolves minerals• water in limestone areas is “hard” with water in limestone areas is “hard” with

substantial Casubstantial Ca2+2+, HCO, HCO33--

• most organisms regulate pH around neutrality; most organisms regulate pH around neutrality; adaptations to life out of balance with external adaptations to life out of balance with external medium (high or low pH) are costly (it takes medium (high or low pH) are costly (it takes energy to be different!)energy to be different!)

1313

The pH scale of The pH scale of hydrogen ion hydrogen ion concentration concentration

extends from O extends from O (highly acidic) to 15 (highly acidic) to 15

(highly alkaline).(highly alkaline).

C and O are intimately involved in C and O are intimately involved in energy transformations.energy transformations.

• Compounds contain energy in their Compounds contain energy in their chemical bonds:chemical bonds:• energy is required to create bondsenergy is required to create bonds• energy is released when bonds are brokenenergy is released when bonds are broken

• Energy transformations proceed by Energy transformations proceed by oxidation and reduction, often involving oxidation and reduction, often involving C:C:• oxidationoxidation removes electrons, releases removes electrons, releases

energyenergy• reductionreduction adds electrons, requiring energy adds electrons, requiring energy

1515

Heterotrophs &AutotrophsHeterotrophs &Autotrophs

• HeterotrophsHeterotrophs obtain their energy by obtain their energy by consuming organic (biological) sources of consuming organic (biological) sources of carbon-rich food, which they oxidize.carbon-rich food, which they oxidize.

• AutotrophsAutotrophs obtain their energy from obtain their energy from inorganic sources, and use this energy to inorganic sources, and use this energy to reduce carbon, which they store for later reduce carbon, which they store for later use:use:• photoautotrophsphotoautotrophs obtain energy from light obtain energy from light• chemoautotrophschemoautotrophs obtain energy from oxidation obtain energy from oxidation

of inorganic compounds such as Hof inorganic compounds such as H22S, NHS, NH44++

1616

Photosynthesis and Photosynthesis and RespirationRespiration

•Think of photosynthesis and respiration Think of photosynthesis and respiration as complementary reactions which:as complementary reactions which:• reduce carbon (reduce carbon (photosynthesisphotosynthesis):):

• energy + 6COenergy + 6CO22 + 6H + 6H22O O C C66HH1212OO66 + 6O + 6O22

• water is an electron donor (reducing agent)water is an electron donor (reducing agent)• oxidize carbon (oxidize carbon (respirationrespiration):):

• CC66HH1212OO66 + 6O + 6O22 energy + 6CO energy + 6CO22 + 6H + 6H22OO

• oxygen is an electron acceptor (oxidizing oxygen is an electron acceptor (oxidizing agent)agent)

1717

The Limited Availability of The Limited Availability of Inorganic Carbon Inorganic Carbon

•Terrestrial plants have a difficult time Terrestrial plants have a difficult time acquiring inorganic carbon:acquiring inorganic carbon:• carbon (as COcarbon (as CO22) diffuses into leaf from ) diffuses into leaf from

atmosphere:atmosphere:• rate of diffusion of a gas is proportional to rate of diffusion of a gas is proportional to

concentration difference between external and internal concentration difference between external and internal mediamedia

• atmosphere-to-plant difference in [COatmosphere-to-plant difference in [CO22] is small] is small

• plant-to-atmosphere difference in [Hplant-to-atmosphere difference in [H22O] is greatO] is great

• bottom line: plants lose enormous amounts of water to bottom line: plants lose enormous amounts of water to the atmosphere relative to carbon gained, at a rate of the atmosphere relative to carbon gained, at a rate of 500 g water for each g of carbon500 g water for each g of carbon

1818

Tendency of water Tendency of water to leave the leaf to leave the leaf far exceeds the far exceeds the

tendency of tendency of carbon dioxide to carbon dioxide to

enter the leafenter the leaf..

Gas exchange occurs across the surface of a leaf.

Carbon dioxide diffuses slowly Carbon dioxide diffuses slowly through water.through water.

• Both COBoth CO22 and HCO and HCO33-- (bicarbonate ions) diffuse slowly (bicarbonate ions) diffuse slowly

through water.through water.

• A thin boundary layer (10-500 um) adjacent to the plant A thin boundary layer (10-500 um) adjacent to the plant surface becomes carbon-depleted, and it forms a surface becomes carbon-depleted, and it forms a diffusion barrier between the plant and C-rich water diffusion barrier between the plant and C-rich water beyond.beyond.

• Thus – photosynthesis may still be limited by a diffusion Thus – photosynthesis may still be limited by a diffusion barrier of still water at the surface of the organismbarrier of still water at the surface of the organism

2020

Oxygen is scarce in Oxygen is scarce in water.water.

• Oxygen is rather limited in water:Oxygen is rather limited in water:• low solubilitylow solubility• limited diffusionlimited diffusion• below limit of light penetration and in sediments below limit of light penetration and in sediments

rich in organic matter, conditions become rich in organic matter, conditions become anaerobicanaerobic or or anoxicanoxic

2121

The ‘knees’ of bald cypress trees conduct air from the The ‘knees’ of bald cypress trees conduct air from the atmosphere to roots when a swamp is flooded and oxygen is atmosphere to roots when a swamp is flooded and oxygen is

limitedlimited

Availability of Inorganic Availability of Inorganic NutrientsNutrients

• After H, C, and O, elements required in After H, C, and O, elements required in greatest quantity are N, P, S, K, Ca, Mg, greatest quantity are N, P, S, K, Ca, Mg, and Fe.and Fe.

• Certain organisms require other elements:Certain organisms require other elements:• diatoms require Si for their glassy casesdiatoms require Si for their glassy cases• nitrogen-fixing bacteria require Molybdenum as nitrogen-fixing bacteria require Molybdenum as

part of the key enzyme in N assimilationpart of the key enzyme in N assimilation

• Terrestrial plants acquire most elements Terrestrial plants acquire most elements from water in soil around roots:from water in soil around roots:• availability varies with temperature, pH, availability varies with temperature, pH,

presence of other ionspresence of other ions• P is particularly limiting in soilsP is particularly limiting in soils

2323

Light is the primary source of Light is the primary source of energy for the biosphere.energy for the biosphere.

•A quick primer on light:A quick primer on light:• energy reaching earth from the sun covers a energy reaching earth from the sun covers a

broad spectrum of wavelengths:broad spectrum of wavelengths:• visible lightvisible light ranges from 400 nm (violet) to 700 nm ranges from 400 nm (violet) to 700 nm

(red)(red)• shorter wavelength energy (<400 nm) is shorter wavelength energy (<400 nm) is ultravioletultraviolet

(UV)(UV)• longer wavelength energy (>700 nm) is longer wavelength energy (>700 nm) is infraredinfrared (IR) (IR)

• energy content of light varies inversely with its energy content of light varies inversely with its wavelengthwavelength• the shorter the wavelength, the more energetic the the shorter the wavelength, the more energetic the

lightlight

2424

Ozone and Ultraviolet Ozone and Ultraviolet RadiationRadiation

• UV “light” has a high energy level and can UV “light” has a high energy level and can damage exposed cells and tissues.damage exposed cells and tissues.

• Ozone in upper atmosphere absorbs strongly Ozone in upper atmosphere absorbs strongly in ultraviolet portion of electromagnetic in ultraviolet portion of electromagnetic spectrum.spectrum.

• Chlorofluorocarbons (formerly used as Chlorofluorocarbons (formerly used as propellants and refrigerants) react with and propellants and refrigerants) react with and chemically destroy ozone:chemically destroy ozone:• ozone “holes” appeared in the atmosphereozone “holes” appeared in the atmosphere• concern over this phenomenon led to strict controls concern over this phenomenon led to strict controls

on CFCs and other substances depleting ozoneon CFCs and other substances depleting ozone

2525

Infrared Light and the Infrared Light and the Greenhouse Effect Greenhouse Effect

• All objects, including the earth’s surface, emit All objects, including the earth’s surface, emit longwave (infrared) radiation (IR).longwave (infrared) radiation (IR).

• Atmosphere is transparent to visible light, which Atmosphere is transparent to visible light, which warms the earth’s surface.warms the earth’s surface.

• Infrared light (IR) emitted by earth is absorbed in Infrared light (IR) emitted by earth is absorbed in part by atmosphere, which is only partially part by atmosphere, which is only partially transparent to IR.transparent to IR.

• Substances like carbon dioxide and methane Substances like carbon dioxide and methane increase the absorptive capacity of the increase the absorptive capacity of the atmosphere to IR, resulting in atmospheric atmosphere to IR, resulting in atmospheric warming.warming.

2626

The greenhouse effectThe greenhouse effect

Carbon dioxide concentrations in the Carbon dioxide concentrations in the atmosphere – measured at Hawaiiatmosphere – measured at Hawaii

The Absorption Spectra The Absorption Spectra of Plantsof Plants

• Various substances (pigments) in plants have Various substances (pigments) in plants have different different absorption spectraabsorption spectra::• chlorophyll in plants absorbs red and violet light, chlorophyll in plants absorbs red and violet light,

reflects green and bluereflects green and blue• water absorbs strongly in red and IR, scatters water absorbs strongly in red and IR, scatters

violet and blue, leaving green at depthviolet and blue, leaving green at depth

• Absorption of light by water limits depth at Absorption of light by water limits depth at which aquatic photosynthetic organisms can which aquatic photosynthetic organisms can exist. exist. Euphotic zoneEuphotic zone……

2929

Algae and Light QualityAlgae and Light Quality

• The quality of light is related to The quality of light is related to photosynthetic adaptations in the ocean:photosynthetic adaptations in the ocean:• algae growing near the surface have pigments algae growing near the surface have pigments

like those in terrestrial plants (absorb blue and like those in terrestrial plants (absorb blue and red, reflect green)red, reflect green)

• algae growing at depth have specialized algae growing at depth have specialized pigments that enable them to use green light pigments that enable them to use green light more effectivelymore effectively

3030

Light IntensityLight Intensity

• Ecologists measure PAR Ecologists measure PAR (photosynthetically active radiation).(photosynthetically active radiation).

• Total radiation is measured as radiant Total radiation is measured as radiant flux = 1,400 W/mflux = 1,400 W/m22 above the above the atmosphere (solar constant).atmosphere (solar constant).

• Radiant flux at earth’s surface is Radiant flux at earth’s surface is reduced by:reduced by:• nighttime periodsnighttime periods• low angle of incidencelow angle of incidence• atmospheric absorption and scatteringatmospheric absorption and scattering• reflection from the surfaces of cloudsreflection from the surfaces of clouds

3131

The Thermal The Thermal EnvironmentEnvironment

• Energy is gained and lost through various Energy is gained and lost through various pathways:pathways:• radiationradiation - all objects emit electromagnetic radiation - all objects emit electromagnetic radiation

and receive this from sunlight and from other objects in and receive this from sunlight and from other objects in the environmentthe environment

• conductionconduction - direct transfer of kinetic energy of heat - direct transfer of kinetic energy of heat to/from objects in direct contact with one anotherto/from objects in direct contact with one another

• convectionconvection - direct transfer of kinetic energy of heat - direct transfer of kinetic energy of heat to/from moving air and waterto/from moving air and water

• evaporationevaporation - heat loss as water is evaporated from - heat loss as water is evaporated from organism’s surface (2.43 kJ/g at 30organism’s surface (2.43 kJ/g at 30ooC)C)

change in heat content = metabolism - evaporation change in heat content = metabolism - evaporation ++ radiationradiation

++ conduction conduction ++ convection convection

3232

Pathways of heat exchange Pathways of heat exchange

Staying coolStaying cool

• ?: Tern Island nests on the bare sand on small ?: Tern Island nests on the bare sand on small coral atolls in the Tropics – face high sunlight. coral atolls in the Tropics – face high sunlight. They nest on the surface of the sand in full They nest on the surface of the sand in full sunlightsunlight

• Wedge-tailed shearwater – similar size and Wedge-tailed shearwater – similar size and coloration – builds its nests in deep burrows coloration – builds its nests in deep burrows beneath the surface of the sand.beneath the surface of the sand.

• Why?Why?

3434

Hatching success of wedge-tailed shearwaters is Hatching success of wedge-tailed shearwaters is highly dependent on the thermal environmenthighly dependent on the thermal environment

3636

Why?Why?

• Diets and feeding regimesDiets and feeding regimes

• -- sooty terns feed on fish and squid – close -- sooty terns feed on fish and squid – close to the nesting sites; male and female to the nesting sites; male and female cooperationcooperation

• Shearwaters feed hundreds of km from ther Shearwaters feed hundreds of km from ther nesting sitesnesting sites

• So:So:

• Sooty terns have stomach full of water-laden food Sooty terns have stomach full of water-laden food water for evaporative heat loss water for evaporative heat loss

• Shearwaters Shearwaters plenty of fat for fast but little water plenty of fat for fast but little water

3737

Organisms must cope with Organisms must cope with temperature extremes.temperature extremes.

• Unlike birds and mammals, most Unlike birds and mammals, most organisms do not regulate their body organisms do not regulate their body temperatures.temperatures.

• All organisms, regardless of ability to All organisms, regardless of ability to thermoregulate, are subject to thermal thermoregulate, are subject to thermal constraints:constraints:• most life processes occur within the most life processes occur within the

temperature range of liquid water, 0temperature range of liquid water, 0oo-100-100ooCC• few living things survive temperatures in excess few living things survive temperatures in excess

of 45of 45ooCC• freezing is generally harmful to cells and tissuesfreezing is generally harmful to cells and tissues

3838

Tolerance of HeatTolerance of Heat

• Most life processes are dependent on water Most life processes are dependent on water in its liquid state (0-100in its liquid state (0-100ooC).C).

• Typical upper limit for plants and animals is Typical upper limit for plants and animals is 4545ooC (some cyanobacteria survive to 75C (some cyanobacteria survive to 75ooC C and some archaebacteria survive to 110and some archaebacteria survive to 110ooC).C).

• Good: high temp -> organisms develop Good: high temp -> organisms develop quickerquicker

• The bad: High temperatures:The bad: High temperatures:• denature proteinsdenature proteins• accelerate chemical processesaccelerate chemical processes• affect properties of lipids (including membranes)affect properties of lipids (including membranes)

3939

Oxygen consumption increases as a Oxygen consumption increases as a function of temperaturefunction of temperature

Tolerance of FreezingTolerance of Freezing

• Freezing disrupts life processes and ice Freezing disrupts life processes and ice crystals can damage delicate cell crystals can damage delicate cell structures.structures.

• Adaptations among organisms vary:Adaptations among organisms vary:• maintain internal temperature well above maintain internal temperature well above

freezingfreezing• activate mechanisms that resist freezingactivate mechanisms that resist freezing

• glycerol or glycoproteins lower freezing point glycerol or glycoproteins lower freezing point effectively (the “antifreeze” solution)effectively (the “antifreeze” solution)

• glycoproteins can also impede the development of ice glycoproteins can also impede the development of ice crystals, permitting “supercooling”crystals, permitting “supercooling”

• activate mechanisms that tolerate freezingactivate mechanisms that tolerate freezing

4141

Glycoproteins Glycoproteins act as a act as a

biological biological antifreeze in the antifreeze in the

antarctic codantarctic cod

Start hereStart here

4343

Organisms use physical stimuli to Organisms use physical stimuli to sense the environment.sense the environment.

•To function in complex and changing To function in complex and changing environments, organisms must:environments, organisms must:• sense and detect environmental change sense and detect environmental change

(plants must sense changing seasons)(plants must sense changing seasons)• detect and locate objects (predators detect and locate objects (predators

must find food)must find food)• navigate the landscape (salmon must navigate the landscape (salmon must

recognize their home river to spawn)recognize their home river to spawn)

4444

Sensing Electromagnetic Sensing Electromagnetic RadiationRadiation

• Many organisms rely on vision (detection of Many organisms rely on vision (detection of visible light and other wavelengths):visible light and other wavelengths):• light has high energylight has high energy• light permits accurate location and resolution of light permits accurate location and resolution of

targetstargets

• Many variations in capabilities exist:Many variations in capabilities exist:• hawks have extreme visual acuityhawks have extreme visual acuity• insects and birds can perceive UVinsects and birds can perceive UV• insects can detect rapid movementsinsects can detect rapid movements

• Animals operating in dark surroundings may Animals operating in dark surroundings may sense IR (e.g., pit vipers utilize pit organs to sense IR (e.g., pit vipers utilize pit organs to sense prey).sense prey).

4545

Many organisms use signals that Many organisms use signals that are ‘visible’ only in UV lightare ‘visible’ only in UV light

The human eye sees this Yellow Daily in reflected light in the range of 400-700 nm

Bees see a different pattern in the same flower in the range of 300-400 nm. The light flecks are pollen grains

Pit organs of the rattlesnake detect Pit organs of the rattlesnake detect infrared radiationinfrared radiation

Sensing SoundSensing Sound• Sounds are pressure waves created by Sounds are pressure waves created by

movements, impacts, vibrations.movements, impacts, vibrations.

• Directional sensitivity possible by comparing Directional sensitivity possible by comparing signals received at two ears:signals received at two ears:• sensitivity is greatest when the distance between ears sensitivity is greatest when the distance between ears

matches wavelength (high-pitched sounds more useful to matches wavelength (high-pitched sounds more useful to smaller animals)smaller animals)

• asymmetrical shapes of owls’ ears enable accurate asymmetrical shapes of owls’ ears enable accurate pinpointing of sourcepinpointing of source

• Other examples:Other examples:• bats echolocate using sound pulses they generatebats echolocate using sound pulses they generate• whales communicate over long distances using low-whales communicate over long distances using low-

frequency soundsfrequency sounds

4848

Whales, U.S. Navy Whales, U.S. Navy clash at high court - clash at high court -

todaytoday

Sonar transmitters have been shown to cause hearing Sonar transmitters have been shown to cause hearing loss, disorientation, hemorrhaging, and even the loss, disorientation, hemorrhaging, and even the beaching of whales, beaching of whales, porpoises, and dolphins.porpoises, and dolphins.

4949

The head of a The head of a leaf-nose bat leaf-nose bat

is adapted is adapted for for

production production and and

detection of detection of sonar signalssonar signals

Sensing OdorsSensing Odors

• Smell is the detection of molecules diffusing Smell is the detection of molecules diffusing through air or water.through air or water.

• Odors differ from light and sound:Odors differ from light and sound:• odors are difficult to localizeodors are difficult to localize• odors persist long after source has disappearedodors persist long after source has disappeared

• Moving “upstream” along a concentration Moving “upstream” along a concentration gradient can help localize the source of odor.gradient can help localize the source of odor.

• Odors are the basis of much chemical Odors are the basis of much chemical communication:communication:• animals use odors to attract matesanimals use odors to attract mates• plants use odors to attract pollinatorsplants use odors to attract pollinators

5151

Sensing Electrical Sensing Electrical FieldsFields

• Some aquatic animals specialize in Some aquatic animals specialize in using and detecting electrical fields:using and detecting electrical fields:• some fish create electric fields and sense some fish create electric fields and sense

distortions caused by preydistortions caused by prey• paddlefish sense distortions caused by preypaddlefish sense distortions caused by prey• other species use electrical signals to other species use electrical signals to

communicatecommunicate• electric ray uses powerful currents to electric ray uses powerful currents to

defend itself and stun preydefend itself and stun prey

5252

Long rostrum of the paddlefish Long rostrum of the paddlefish is packed with sensory organsis packed with sensory organs

Sensing Physical Sensing Physical ContactContact

• Under conditions of poor visibility, catfish use Under conditions of poor visibility, catfish use fins and barbels as sensitive touch and taste fins and barbels as sensitive touch and taste receptors.receptors.

• Physical contact is limited in its range, but Physical contact is limited in its range, but useful under many circumstances.useful under many circumstances.

• Touch can provide tremendous amount of Touch can provide tremendous amount of information regarding texture and structure.information regarding texture and structure.

5454

Before you leave todayBefore you leave today

Take a small piece of paperTake a small piece of paper

Write your name, class, and dateWrite your name, class, and date

And tell me:And tell me:

- One interesting thing you learned today One interesting thing you learned today in classin class

- One boring item todayOne boring item today

(in other words: the good and the bad)(in other words: the good and the bad)

And give it to me on your way out of classAnd give it to me on your way out of class

5555