III. Cycles of Matter *While energy is crucial to an ecosystem,all organisms need water, minerals, andother life-sustaining compounds to survive.

In most organisms, more than 95% of thebody is made up of oxygen, carbon, hydrogen,and nitrogen that must be broken down into a chemical form that the cells can take up. 

A. Recycling in the Biosphere 

*Energy and matter move through thebiosphere very differently. Matter is recycledwithin and between ecosystems.

Elements, compounds, and other formsof matter are passed through biogeochemicalcycles that connect the biological, ecological,and chemical aspects of the biosphere. 

Cycles of Matter

-Matter cycles over and overagain through the biospherebecause biological systems don’tuse up matter but transform it.

It is assembled into living tissueor passed out of the body aswaste products.

B. The Water Cycle 

-The water that living thingsneed to survive moves between the ocean, atmosphere, and land.  

The Water CycleEntering the atmosphere –

watermolecules enter the atmosphereas water vapor (a gas) when

theyevaporate from the ocean, otherbodies of water, or when theyevaporate from the leaves ofplants. 

Evaporation – the process bywhich water changes from

liquidform to an atmospheric gas. 

Transpiration – loss of waterfrom a plant through its leaves of plants.

The Water CycleLeaving the atmosphere – the sun heatsthe atmosphere throughout the day,causing warm, moist air to rise and cool. The water vapor condenses into tinydroplets that form clouds. Once largeenough, the water droplets fall to thesurface in the form of precipitation : rain, snow, sleet, hail, etc. 

Traveling on the surface – most precipitationruns along the surface of the ground until itenters a river or stream that carries the

runoffback to an ocean or lake. Some rain willseep into the soil and become ground water. Water in the soil enters plants through theroots, restarting the cycle. 

C. Nutrient Cycles

 Nutrients – all the chemicalsubstances that an organismneeds to sustain life (chemical“building blocks” that come

fromfood). 

-Every living organism needsnutrients to build tissues andcarry out essential life

functions. Like water, nutrients are passedbetween organisms and theenvironment throughbiogeochemical cycles. 

 

3 Major biogeochemical cycles 1. Carbon cycle – cycle

that moves carbon through the biosphere. Carbon is found in several large reservoirs in the biosphere : in the atmosphere as CO2 gas, in the oceans as dissolved carbon dioxide, on land in organisms, rocks, and soil, & underground as coal, petroleum, and calcium carbonate rock.

The Carbon Cycle

Carbon’s role in the biosphere : Makes up living tissue & animal skeletons

Makes up rock

It forms CO2 gas in the atmosphere

Carbon dioxide is taken in by plants during photosynthesis and is given off by both plants and animals during respiration.

Four main types of processes move carbon through its cycle :

 Biological processes, such as photosynthesis, respiration, and decomposition, take up and release carbon and oxygen.

Geochemical processes, such as erosion and volcanic activity, release carbon dioxide to the atmosphere and oceans.

Mixed biogeochemical processes, such as the burial and decomposition of dead organisms and their conversion under pressure into coal and petroleum (fossil fuels), store carbon underground.

Human activities, such as mining, cutting and burning forests, and burning fossil fuels, release carbon dioxide into the atmosphere.

The Nitrogen Cycle

2. Nitrogen Cycle – cycle that moves nitrogen through the biosphere. The atmosphere is the main reservoir of nitrogen in the biosphere (78% of the atmosphere). It also cycles through the soil and through the tissues of living organisms.

 Nitrogen’s role in the

biosphere : 

All organisms need nitrogen tomake amino acids, which areused to build proteins. 

How nitrogen moves through the biosphere :

Nitrogen gas from the atmosphere is taken in by bacteria in the soil/on the

roots of plants and converted into ammonia.

 

Nitrogen fixation – process ofconverting nitrogen gas intoammonia. 

Other bacteria in the soil convert ammonia into

nitrates and nitrites. 

How nitrogen moves through the biosphere :

Producers use nitrates and nitrites to make proteins. 

Consumers eat the producers and reuse the nitrogen to make

their own proteins. 

When organisms die, decomposers

return nitrogen to the soil as ammonia for producers to use.

 

-Some soil bacteria release nitrogeninto the atmosphere bydenitrification converting nitratesinto nitrogen gas.

The Phosphorous Cycle

3. Phosphorous Cycle – cycle that moves phosphorous through the biosphere. Phosphorous in the biosphere cycles among the land, ocean sediments, and living organisms. Although important, it is not common because it doesn’t enter the atmosphere. It is mostly within rock and soil minerals on land, and in ocean sediments.

 

Phosphorous’ role in the biosphere : 

Phosphorous is essential to livingorganisms because it forms part ofimportant life-sustaining moleculessuch as DNA and RNA.  

How phosphorous moves through the biosphere :

Rocks and sediments wear down, releasing phosphate – some phosphate stays on land and cycles between organisms and the soil.

 

-When plants absorb phosphate

from the soil or from water, the

plants bind the phosphate intoorganic compounds, which

movethrough the food web fromproducers to consumers to therest of the ecosystem. 

 

How phosphorous moves through the biosphere :

Phosphate washes into rivers & streams & dissolves. 

Phosphate makes its way to the ocean, where it is used by marine organisms.

D. Nutrient Limitation

*One key point of interest toecologists is primary productivity –the rate at which organic matter iscreated by producers. 

-One factor that controls the primary

productivity of an ecosystemis the amount of available nutrients.

If a nutrient is in short supply,it will limit an organism’s growth.

When an ecosystem is limitedby a single nutrient that is scarce orcycles very slowly it is referredto as a limiting nutrient. 

D. Nutrient Limitation

*The ocean is nutrient-poorcompared to the land andwhen aquatic ecosystemsreceive large amounts of alimiting nutrient (ex : runoff from heavily fertilized fields)algae &other producers increase quickly and can lead to algal blooms which can disrupt ecosystem equilibrium.