Cycles in NatureCycles in Nature

Chapter 25, Section 2Chapter 25, Section 2

Cycles of MatterCycles of Matter

The biosphere contains a fixed amount of The biosphere contains a fixed amount of water, carbon, nitrogen, oxygen, and other water, carbon, nitrogen, oxygen, and other materials required for life.materials required for life.

These materials are cycled through the These materials are cycled through the biosphere and used by many different biosphere and used by many different organisms.organisms.

Water CycleWater Cycle

A model that describes how water moves from A model that describes how water moves from the surface of the earth to the atmosphere and the surface of the earth to the atmosphere and back to the surface again.back to the surface again.

Water CycleWater Cycle

Processes that “add” water to the air:Processes that “add” water to the air: EvaporationEvaporation

Occurs when liquid water turns into water vapor (gas).Occurs when liquid water turns into water vapor (gas). TranspirationTranspiration

Occurs when plants release water into the air.Occurs when plants release water into the air. RespirationRespiration

Releases water vapor to the air.Releases water vapor to the air. Animal WastesAnimal Wastes

Returns water to the environment.Returns water to the environment.

Water CycleWater Cycle

Processes that “subtract” water from the air.Processes that “subtract” water from the air. CondensationCondensation

Occurs when water vapor changes to a liquid.Occurs when water vapor changes to a liquid. CloudsClouds

When water vapor cools, it condenses on tiny particles When water vapor cools, it condenses on tiny particles of matter (like dust) in the air and forms tiny droplets.of matter (like dust) in the air and forms tiny droplets.

Precipitation Precipitation Eventually the “cloud” droplets become so heavy that Eventually the “cloud” droplets become so heavy that

they fall to the earth as precipitation.they fall to the earth as precipitation.

Water CycleWater Cycle

Affects on the cycle by humans:Affects on the cycle by humans: Water use by humans (households, factories, Water use by humans (households, factories,

agriculture, etc) can reduce the amount of water agriculture, etc) can reduce the amount of water that evaporates into the atmosphere and limits the that evaporates into the atmosphere and limits the amount of water available to plants and animals.amount of water available to plants and animals.

Nitrogen CycleNitrogen Cycle

Nitrogen CycleNitrogen Cycle A model that describes how nitrogen A model that describes how nitrogen moves from the atmosphere to the moves from the atmosphere to the soil to living organisms and back soil to living organisms and back again.again.

Nitrogen CycleNitrogen Cycle

Importance of Importance of nitrogennitrogen

Needed to build proteins (building Needed to build proteins (building blocks of cells).blocks of cells).

Essential part of DNA.Essential part of DNA.

Nitrogen CycleNitrogen Cycle

Processes that Processes that remove nitrogen remove nitrogen from the from the atmosphere:atmosphere:

Nitrogen fixation:Nitrogen fixation: Plants cannot use nitrogen directly from Plants cannot use nitrogen directly from

the air.the air. So, bacteria in soil convert the nitrogen So, bacteria in soil convert the nitrogen

from the air into compounds that plants from the air into compounds that plants can use.can use.

Animals get the nitrogen they need by Animals get the nitrogen they need by eating plants.eating plants.

Nitrogen CycleNitrogen Cycle

Processes that Processes that return nitrogen return nitrogen to the soil:to the soil:

Animal wastes.Animal wastes. Dead and decaying organisms.Dead and decaying organisms.

Nitrogen CycleNitrogen Cycle

Affects on the Affects on the cycle by cycle by humans:humans:

Removing crops from the land Removing crops from the land removes any nitrogen that would be removes any nitrogen that would be added to the soil through the decay of added to the soil through the decay of the plants.the plants.

Adding fertilizer, compost, or animal Adding fertilizer, compost, or animal manure returns nitrogen to the soil.manure returns nitrogen to the soil.

Planting nitrogen-fixing crops (such Planting nitrogen-fixing crops (such as peas, clover, and beans) adds as peas, clover, and beans) adds nitrogen to the soil.nitrogen to the soil. Nitrogen-fixing crops have roots with Nitrogen-fixing crops have roots with

nodules that contain nitrogen-fixing nodules that contain nitrogen-fixing bacteria. bacteria.

Carbon CycleCarbon Cycle

Carbon CycleCarbon Cycle A model that describes how carbon A model that describes how carbon moves from living to non-living moves from living to non-living things.things.

Carbon CycleCarbon Cycle

Carbon CycleCarbon Cycle Carbon is located in humus in the Carbon is located in humus in the soil and as part of carbon dioxide in soil and as part of carbon dioxide in the atmosphere.the atmosphere.

Carbon CycleCarbon Cycle

Processes that Processes that remove carbon remove carbon from the from the atmosphere:atmosphere:

PhotosynthesisPhotosynthesis Uses carbon dioxide, water, and Uses carbon dioxide, water, and

sunlight to produce sugars.sunlight to produce sugars.

Carbon CycleCarbon Cycle

Processes that Processes that add carbon to add carbon to the atmosphere:the atmosphere:

RespirationRespiration Uses oxygen and releases carbon Uses oxygen and releases carbon

dioxide.dioxide.

Carbon CycleCarbon Cycle

Affects on the Affects on the cycle by cycle by humans:humans:

Carbon dioxide is released into the Carbon dioxide is released into the air when humans burn fossil fuels air when humans burn fossil fuels (gas, coal, oil, etc), which are the (gas, coal, oil, etc), which are the remains of once-living organisms.remains of once-living organisms.

Use of trees for fuel or for building Use of trees for fuel or for building reduces the number of plants that reduces the number of plants that remove carbon dioxide from the air.remove carbon dioxide from the air.