chapter 4 the abiotic environment (ecology)

8/11/2019 Chapter 4 the Abiotic Environment (Ecology)

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THE ABIOTIC

ENVIRONMENT


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The interaction between organisms and theirenvironment includes both biotic (living) andabiotic (nonliving), often referred to as thebiological and physical environment respectively.The physical environments of organisms arecharacterized by light, temperature, moistureand nutrients.Solar radiation involves both light energy andthermal energy, the visible portion of solarradiation is the energy source of photosynthesis,the basic process supporting life on earth.The infrared portion of solar radiation, theprimary source of Earths heat budget,influences the thermal environment in whichorganisms live.


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Solar Radiation

Includes VisibleLight


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Light has major effect on almost all livingorganisms. Visible light, that part of theelectromagnetic spectrum between thewavelengths of 400-700 nm, is known asphotosynthetically active radiation (PAR).

Short wavelengths between 280-380nmare ultraviolet light wavelengths longerthan 740 nm are infrared.

In addition to its spectral qualities, lightalso possesses intensity, duration, anddirectionality, all of which vary daily and

seasonally.


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Light impinging on an object may bereflected, absorbed or transmitted throughit.Plants reflect green light most strongly andabsorb violet, blue and red wavelengthused in photosynthesis.Plants transmit the wavelengths they donot reflect o absorb.Light passing through a canopy ofvegetation or through water becomesattenuated. Certain wavelength drop out

before others.


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On a clear day in a forest, green and far-red wavelengths pass through relativelyunaltered.In pure water, red and infrared light areabsorbed first, followed by yellow, greenand violet; blur penetrates the deepest.


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Plant Cover

Intercepts Light


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The density and orientation of leaves in aplant canopy influence the amount of light

reaching the ground. Foliage density isexpressed as leaf area index (LAI), the areaof leaves per unit of ground area.

The amount of light reaching the ground interrestrial vegetation varies with the season.In forest only about 1-5 percent of lightstriking the canopy reaches the ground. Sunflecks on the forest floor enable plants toendure shaded conditions. The amount oflight reaching a plant influences its

photosynthetic rate.


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Daily and Seasonal

Patterns of LightGovern Lifes Activities


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Light influences the daily and seasonalactivities of living organisms. Livingorganisms, except bacteria, have aninnate rhythm of activity and activity. Thisrhythm is free-running under constantconditions, with an oscillation that deviatesslightly from 24 hours. For that reason it iscalled a circadian rhythm.Under natural conditions, external timecues, notably light and dark (day andnight), set or entrain the circadian rhythmto the 24-hour day.


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This setting synchronizes the activity ofplants and animals with the environment.The onset and cessation of activity dependupon whether the organisms are light-active or dark-active.


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The Structure ofWater Is Based onHydrogen bonds


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Water has a unique molecular structure.One large oxygen atom and two smallerhydrogen atoms are bonded covalently. Thetwo hydrogen atoms are separated by an105 degree angle, which results in a V-

shaped molecule.Because of this arrangement, the hydrogenatom side has a positive charge, and the

oxygen side has a negative charge,polarizing the water molecule. Because oftheir polarity, water molecules becomecoupled with neighboring water moleculesto produce a lattice like structure with


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Water HasImportant

PhysicalProperties


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Considerable quantities of heat with asmall rise or fall in temperature.Water has a high viscosity that affectsits flow. It exhibits high surface

tension, caused by a strongerattraction of water molecules for eachother than for the air above the

surface. These properties areimportant ecologically andbiologically.


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Transfer of WaterBetween the

Environment andOrganisms involves

Osmosis


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Osmosis and Osmosis Pressure

Water moves from the environment intoorganisms through permeable cellmembranes or conductive tissues.

Molecules move from areas of highconcentration to areas of lowconcentration until both sides are inequilibrium. This movement of moleculesacross membranes, called osmosis,generates pressure that slows themovement .


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The amount of pressure needed tocounteract the movement is osmosispressure. The tendency of a solution toattract water molecules from areas of highconcentration to areas of lowconcentration is osmosis potential.


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Water Cycles

Between Earth andthe Atmosphere


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Water Movements Shape

Freshwater and marineEnvironment


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Water movementCurrents in streams and rivers and wavesin open sea and breaking on ocean shoresdetermine the nature of many aquatic andmarine environments. Velocity of currentsshape the environment of flowing water.Waves pound rocky shores and rear awayand build up sandy beaches. Rising and

falling tides shape the environment andinfluence the rhythm of the life of thecoastal intertidal zones

chapter 4 the abiotic environment (ecology)

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