Plant Biology - Biogeochemical Cycles - Quick Guides

Page 1 of 15

Plant Biology - Biogeochemical Cycles - Page 1 preview image

Study GuidePlant Biology–Biogeochemical Cycles1. The Carbon Cycle1.1Why Carbon MattersCarbon is the element that makes life possible. It forms the backbone of molecules likecarbohydrates, proteins, lipids, and DNA. Carbon enters living systems throughphotosynthesis, andthe oxygen released during this process allows most organisms to carry outaerobic respiration.Even though carbon is essential for life, only asmall fractionof Earth’s carbon is actively cyclingthrough living organisms. Most carbon is stored inabiotic reservoirssuch as sedimentary rocks,fossil fuels, and deep-sea sediments.1.2The Core of the Carbon CycleThe carbon cycle is driven mainly byphotosynthesisandrespiration.•Photosynthesis:Plants, algae, and some bacteria take in carbon dioxide (CO₂) from theatmosphere. Using energy from sunlight, they convert CO₂into carbohydrates and otherorganic molecules.

Page 2 of 15

Plant Biology - Biogeochemical Cycles - Page 2 preview image

Study Guide•Respiration:Plants, animals, decomposers, and microorganisms break down organicmolecules to release energy. During this process, carbon is returned to the atmosphere asCO₂.Because of this back-and-forth movement, carbon constantly cycles between living organisms and theatmosphere.1.3Carbon on Land and in the OceansOn land, plants remove CO₂from the air during photosynthesis. This removal is mostly balanced byCO₂released through respiration by plants and by decomposers in the soil.In the oceans,planktonplay a similar role. They absorb CO₂near the surface during photosynthesisand release it back through respiration. However, a small amount of carbon sinks into deeper watersand becomes buried in ocean sediments. Over long periods, this carbon can be locked away from theatmosphere.1.4The Atmosphere: The Connecting LinkTheatmosphere connects all partsof the carbon cycle—land, oceans, and living organisms.Because of this, changes in atmospheric CO₂levels give scientists an important clue about thehealthand balance of ecosystemsaround the world.1.5Human Impact on the Carbon CycleOne concerning trend today is thesteady increase in atmospheric CO₂. Over the last 50 years ofaccurate measurements, CO₂levels have risen by about0.4% per year (around 1.5 parts permillion). This shows that a carbon cycle that stayed balanced for roughly100,000 yearsis now out ofbalance.Since the start of theIndustrial Revolution, atmospheric CO₂has increased by as much as30%.This rise is strongly linked to:•Burning fossil fuels (coal, oil, and natural gas)•Large-scale changes to natural vegetation, such as deforestation

Page 3 of 15

Plant Biology - Biogeochemical Cycles - Page 3 preview image

Study Guide1.6The Greenhouse EffectHigher CO₂levels can trap more heat in the atmosphere. This trapped heat increases Earth’s surfacetemperature, a process known as thegreenhouse effect. As a result, changes in the carbon cycleare closely tied toglobal climate changeand have major consequences for ecosystems worldwide.2. The Nitrogen CycleNitrogen is essential for life. It is a key part ofproteins, DNA, and many important moleculesinliving organisms. Even though nitrogen is everywhere, using it is not as simple as it seems.2.1Nitrogen in the Atmosphere: Plenty but UnusableTheatmosphere contains the largest supply of nitrogen, mostly as nitrogen gas (N₂). However,this form of nitrogen ischemically inertbecause the two nitrogen atoms are held together by astrong triple bond.•Plantscannot use N₂directly.•Most other organisms also cannot use it.So even though nitrogen is abundant, it must first be changed into a usable form.2.2Nitrogen Fixation: Making Nitrogen UsableOnly a few special bacteria can use atmospheric nitrogen. These bacteria have an enzyme callednitrogenase, which allows them to convert nitrogen gas (N₂) intoammonium ions (NH₄⁺).

Page 4 of 15

Plant Biology - Biogeochemical Cycles - Page 4 preview image

Study GuideThis process is callednitrogen fixation.•Ammonium can be used by plants and other organisms.•Nitrogen fixation isas important to life as photosynthesis, because it makes nitrogenavailable to living systems.2.3From Death to Reuse: Recycling NitrogenWhen plants and animals die,decomposer bacteria and fungibreak down their bodies. During thisprocess:•Nitrogen from organic compounds is released back into the soil.•This nitrogen is reused by new organisms to build:oAmino acids and proteinsoNucleic acids (DNA and RNA)oNucleotides, coenzymes, and vitaminsThese molecules are essential for all life.2.4Returning Nitrogen to the Air: DenitrificationSome bacteria carry out a process calleddenitrification.•These bacteria convert nitrogen compounds back intonitrogen gas (N₂).•The nitrogen is then released into the atmosphere.•Denitrification occurs underanaerobic (low-oxygen) conditions.•It takes place inalmost all types of soil.Because bacteria carry out fixation, recycling, and denitrification,microorganisms control the majorsteps of the nitrogen cycle.

Page 5 of 15

Plant Biology - Biogeochemical Cycles - Page 5 preview image

Study Guide2.5Abiotic Nitrogen Fixation: Nature Without LifeNot all nitrogen fixation involves living organisms.A smaller amount of nitrogen is fixed throughabiotic (non-living) processes, such as:•Lightning•Volcanic emissionsThese processes create nitrogen compounds that are washed out of the atmosphere byrain, addingusable nitrogen to soil and water.2.6Human Impact on the Nitrogen CycleHuman activities have greatly changed the natural nitrogen balance. Major influences include:•Manufacturing and using nitrogen fertilizers•Burning fossil fuels•Growing nitrogen-fixing cropsThese activities disrupt the natural balance between nitrogen fixation and denitrification.In addition:•Burning fuels releases nitrogen oxides (NOₓ compounds) into the air.•These pollutants contribute toair pollutionand can combine with rain to formacid rain,especially in industrialized regions.2.7Nitrogen Cycle (At a Glance)The nitrogen cycle is easiest to understand when broken into five main processes:1.Nitrogen Fixation–Converting N₂into usable nitrogen forms2.Ammonification–Releasing ammonium from dead organisms3.Nitrification–Converting ammonium into nitrates4.Assimilation–Plants absorbing nitrogen to build organic molecules5.Denitrification–Returning nitrogen to the atmosphere as N₂

Preview Mode

This document has 15 pages. Sign in to access the full document!

Report

Learning Tools

Writing Tools

Browse Resources

Plant Biology - Biogeochemical Cycles - Page 1

Plant Biology - Biogeochemical Cycles

Study Now!

Document Details

Related Documents

Plant Biology - Tissues

Plant Biology - Themes of Plant Biology

Plant Biology - The Shoot System Stems

Plant Biology - The Shoot System Leaves

Plant Biology - The Shoot System Flowers, Fruits, Seeds

Plant Biology - Systematics

Plant Biology - Seedless Vascular Plants

Plant Biology - Seed Plants

Plant Biology - Roots

Plant Biology - Respiration

Company

Explore

Study Tools