cycles

Document Sample
cycles Powered By Docstoc
					                                             Cycles

•   Life is composed of cycles - cycles of energy, cycles of materials, cycles of information
    (reproduction)
•   Life is maintained by a constant flow of chemical energy

•   Energy means motion - kinetic energy is energy of motion
     > Light
     > Heat
     > Electricity
     > Moving objects

•   Energy can also be stored - potential energy
     > Water behind a dam
     > Batteries
     > Gasoline
     > Firewood
     > Stretched rubber bands

•   Gasoline has potential energy, stored in the chemical bonds between its component atoms
•   Burn it, releases kinetic energy - heat, light, motion - that was stored in the molecules
•   Some released energy powers engine, much escapes as heat energy, radiates away

•   First Law of Thermodynamics - energy can neither be created nor destroyed, but it can be
    changed from one form into another
•   Energy enters ecosystems as solar energy, (kinetic) transformed by photosynthesis into
    chemical energy (potential - chemical bonds in glucose)

•   Energy transformation never 100% efficient
•   Much energy lost as heat, radiates away
•   Conversion of auto gas (chemical energy) to moving car parts (mechanical energy) is about
    20-30% efficient
•   Cellular metabolism about 50% efficient

•   Second Law of Thermodynamics - universe tends to become more disordered - over time,
    energy becomes scattered or dispersed
•   Entropy - universal tendency towards disorder
•   Life is a highly ordered state, seems to defy entropy
•   Eventually the Second Law predicts less energy locked up in stable bonds in molecules and
    more scattered and dispersed
•   Heat death of the universe predicted by cosmologists

•   Sun pays the entropic price for all of us
•   Sun is exploding, consuming itself, generates tremendous amount of scattered energy

•   Earth intercepts a tiny piece of the energy released by the sun’s thermonuclear explosions -
    enough to cause local reversals in entropy
•   Life is a local reversal of entropy

•   Photosynthesis converts solar energy into chemical energy
•   How efficient is photosynthesis??
•   Only 2% efficiency

•   Photosynthesis combines carbon dioxide, water, sunlight, to form glucose (simple sugar)
•   Photosynthesis converts solar energy into the chemical bond energy that holds the glucose
    molecule together

•   What is a chemical bond?

•   Remember that atoms are made up of a nucleus with protons (+ charge) and neutrons (no
    charge), surrounded by cloud of electrons (- charge)
•   Atom as a whole is electrically neutral - no net + or - charge

•   Visualize a whirling cloud of atoms and molecules - atoms are always in motion
•   Constantly bumping into one another
•   Mostly just bounce away, bump into another molecule - but not always

•   Energy of motion is kinetic energy
•   Moving atoms have kinetic energy - temperature = average kinetic energy

•   Atoms or molecules bump into one another with sufficient speed, lots of kinetic energy
•   May overcome the natural repulsion of their electron clouds, cause them to bond together
•   Some of the energy of their collision is stored as potential energy in the chemical bond they
    form

•   When atoms bond together, one or more of the electrons in their outer shell is exchanged or
    becomes shared
     > One atom acquires net positive charge (loses one or more electron - oxidation)
    > Other atom acquires net negative charge (gains one or more electrons - reduction)

•   Electrically charged atoms (or groups of atoms) are called ions
•   Ions of opposite charge will stick together (opposite charges attract, like charges repel)

•   Chemical bonds are formed by exchanging or sharing of electrons between atoms
•   Chemical bonds are a type of potential energy
•   Can later release that stored energy by breaking the chemical bond

•   In photosynthesis, the captured chemical energy comes from sunlight
•   Light has kinetic energy
•   Light strikes the outer electrons of the chlorophyll molecule, “excites” its electrons

•   Electrons release the energy they absorbed as they go back to usual level of energy
•   Cells capture that tiny bit of released energy, use it to:
     > Break water into hydrogen and oxygen
     > Combine the hydrogen with carbon dioxide to form glucose (sugar)

•   Energy stored in glucose powers the cell
•   As glucose is burned, the energy released by the chemical bonds is transferred to ADP
    (adenosine diphosphate)

•   The released energy goes into forming a new high energy bond to add a third phosphate to
    ADP = ATP (triphosphate)
•   Cells can then break that bond at will, changing ATP back to ADP, and using the energy
    released by the broken bond to power the cell

•   When used for “fuel”, a single glucose molecule makes 36 ATP “power packs”
•   Glucose also used as a building block to make smaller molecules like amino acids and nucleic
    acids
•   These in turn form DNA, proteins

•   Ecosystems are composed of organisms that produce their own energy (autotrophs) and
    organisms that use the energy made by others (heterotrophs)

•   Autotroph = producers, “self-feeder” - autotrophic organisms produce their own energy
    (photosynthesis, chemosynthesis)

• 6CO2 + 12H2O + light => C6H12O6 + 6H2O + 6O2

•   Heterotrophs = consumers, fed by others, eat other organisms to survive
•   Heterotrophs burn (oxidize) glucose (and other compounds) to recover the energy stored in
    the chemical bonds (respiration)

• C6H12O6 + 6O2 + 6H2O => 6CO2 + 12H2O + energy

•   There are over 100 different kinds of atoms in nature, but only ~20 found in cells, and only a
    few of these are common
•   Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorous

•   Where did these elements come from?
•   Atoms which make up living things were all formed from simpler atoms in the heart of a
    vanished star
•   Younger suns made of hydrogen - nuclear fusion creates the higher elements, from helium, on
    to carbon, oxygen etc…

•   When aging suns explode (nova), they disperse atoms of higher elements which go into the
    next generation of stars
•   We are all made of stardust

•   Lets look at the way these important elements cycle through natural systems
•   Start with the water cycle

•   Water is the essence of life
    > Living things made mainly of water
    > Water is an essential ingredient in photosynthesis
    > Chemical and physical properties of water make life possible

•   Water has a high specific heat - it requires a huge amount of energy to heat water, and it gives
    off much energy when it cools
•   Water expands just before the freezing point - so ice is lighter than water, floats to the top -
    makes aquatic life possible

•   Rain falls from the sky
•   Some rain enters surface water as runoff
•   Some percolates down through the soil, until it reaches a layer it can’t penetrate
•   Water under the ground is called groundwater

•   Top of this layer of groundwater is the water table
•   Porous layer of saturated rock in which water moves (or pools up) is an aquifer
•   Groundwater eventually finds its way towards the surface (springs, wells…)
•   Part of the rain that enters the soil is captured by plant roots
•   Pulled up through the plant by capillary action (wet paper towel)
•   Water exits the leaves as water vapor - transpiration

•   Some water held by capillary action in the soil evaporates directly from the soil
•   Combination of evaporation from the soil and transpiration from plants called
    evapotranspiration

•   Surface waters also evaporate, return water vapor to the atmosphere
•   Water vapor in the atmosphere condenses into clouds, falls back as rain

•   Carbon is another element with unusual properties that make it highly suitable for life
•   Bonds to itself very firmly, forms long chains that are the backbone of most biomolecules
    (C/H/O)

• Carbon enters living systems through photosynthesis
• Atmospheric CO2 fixed into glucose
• CO2 exhaled by plants and animals in respiration (break glucose down into CO2, oxygen and
  water)

•   Lots of carbon in plant bodies as glucose, or starch, or other biomolecules made from glucose
•   Some carbon locked up as dead tissue, finds its way into the soil when organisms decompose

•   Photosynthesis is also important in aquatic habitats
•   Atmospheric CO2 dissolves in water to make bicarbonate ions (HCO3-)
•   Carbon used by many sea creatures to make shells of calcium carbonate (Ca CO3 )

•   Deep part of the carbon cycle
     > Marine shells pool in bottom sediments
     > Form limestone and marble
     > Return to the surface over millions of years through volcanic eruptions (CO2 ) and
       weathering of rocks
•   Deep part of the carbon cycle
     > Organic sediments converted over millions of years into coal, oil, natural gas (fossil fuels)
     > Carbon returned to the atmosphere when these fuels are burned by autos, industry etc…
     > Renewable resource, but only on a geological time scale!!

•   Nitrogen cycle is more complex
•   Nitrogen and phosphorous are essential for all organisms, especially plants
•   Nitrogen is a limiting nutrient
•   But our atmosphere is 78% Nitrogen
•   ???

•   Nitrogen in the air is N2 - plants can’t use it directly in this form
•   Some bacteria can use N2 , convert to form plants can use = nitrogen fixation
•   Plants take up nitrogen as ammonium (NH4+) or nitrate (NO3-) ions

•   Some bacteria make N2 into ammonium (nitrogen fixing bacteria)
•   Some bacteria convert ammonium in soil to nitrate (nitrifying bacteria)
•   Lightning also causes nitrogen fixation

•   Humans also fix nitrogen (fertilizers)
•   Humans now dominate global cycling of nitrogen!!

•   Plants take up nitrogen as ammonium or nitrate, incorporate it into biomolecules
•   Nitrogen of plants consumed by herbivores, carnivores
•   Animals excrete large amounts of nitrogen as ammonia, urea, uric acid - recycled to the soil
    when they die

•   If soils become anaerobic, soil bacteria start using the oxygen locked up in nitrates, release N2
    back to the air
•   Farmers must plow ASAP in spring to aerate the soil before this happens, or soil loses some
    fertility

•   Phosphorous is another essential nutrient, commonly found in mineral form as phosphate
    (PO4-3)
•   Plants get phosphate from soil or water, goes into compounds like ATP

•   Some phosphate excreted by animals
•   Some phosphate returned to soil when organisms decompose
•   Unlike water, carbon, and nitrogen - phosphorous doesn’t exist as a gas
•   When nitrogen or carbon enter the air or water, they can be transported anywhere on Earth

•   When phosphorous is added, it stays put
•   When phosphorous is removed, it does not readily return (ex. tropical deforestation)

•   Phosphorous stays in or on the ground
•   Deep part of the phosphorous cycle
     > Finds its way into many rocks or minerals
     > Released millennia later via weathering or mining (Polk County, Fla.)

•   Energy and matter flow through ecosystems in many complex and interdependent ways
•   Cyclic processes regulated by feedback
•   Humans have altered these natural cycles in many ways - changing amount and timing of
    inputs or out puts, sources and sinks…

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:11
posted:11/10/2011
language:English
pages:7