Chemical CyclesChemical Cycles

What is a cycle?What is a cycle?

cy·clecy·cle  n.n. A A periodically periodically repeated repeated sequence of sequence of events.events.

Why are chemical cycles necessary Why are chemical cycles necessary for life to exist?for life to exist?

1.1. Nutrients such as carbon, oxygen, and Nutrients such as carbon, oxygen, and nitrogen are needed for organisms to live nitrogen are needed for organisms to live and grow.and grow.

2.2. These elements, along with all others, These elements, along with all others, are not constantly replenished from an are not constantly replenished from an outside source.outside source.

Remember that the energy cycle has a constant Remember that the energy cycle has a constant input of energy from the sun.input of energy from the sun.

The three cyclesThe three cycles

1.1. The carbon cycle—the movement of The carbon cycle—the movement of carbon through the environment.carbon through the environment.

2.2. The nitrogen cycle—the pathway by The nitrogen cycle—the pathway by which nitrogen moves through the which nitrogen moves through the environment.environment.

3.3. The water cycle—the continual The water cycle—the continual movement of water from the Earth’s movement of water from the Earth’s surface to the atmosphere and back to surface to the atmosphere and back to the surface again.the surface again.

The Carbon CycleThe Carbon Cycle

Carbon is the building block Carbon is the building block atom of all organic compounds.atom of all organic compounds.

Carbon-based compounds Carbon-based compounds move through air or water, move through air or water, through living things, and back through living things, and back to air or water again.to air or water again.

The driving forces behind the The driving forces behind the carbon cycle are:carbon cycle are:

1.1. photosynthesisphotosynthesis2.2. andand cellular respirationcellular respiration

PhotosynthesisPhotosynthesisCOCO22 + H + H220 + energy 0 + energy →→ C C66HH12120066 + O + O22

The process by which The process by which autotrophs convert autotrophs convert sunlight into a sunlight into a useable form of useable form of energy (glucose).energy (glucose).

Occurs in the Occurs in the chloroplastschloroplasts of plant of plant cells (an organelle).cells (an organelle).

Cellular RespirationCellular RespirationCC66HH1212OO66 + O + O22 →→ CO CO22 + H + H220 + energy0 + energy

res·pi·ra·tionres·pi·ra·tion n.n. The act The act or process of inhaling and or process of inhaling and exhaling; breathing. exhaling; breathing.

Cellular respiration is the Cellular respiration is the process by which glucose process by which glucose is broken down to release is broken down to release energy.energy.

Occurs in in the Occurs in in the mitochondriamitochondria of ALL cells of ALL cells (another organelle).(another organelle).

Photosynthesis—the construction of Photosynthesis—the construction of glucose to store energy.glucose to store energy.COCO22 + H + H220 + energy 0 + energy →→ C C66HH12120066 + O + O22

Cellular Respiration—the breakage of Cellular Respiration—the breakage of glucose to release energyglucose to release energy

CC66HH1212OO66 + O + O22 →→ CO CO22 + H + H220 + energy0 + energy

Humans and the carbon cycleHumans and the carbon cycle

Humans have begun to interfere with the Humans have begun to interfere with the carbon cycle by:carbon cycle by:

1.1. Cutting down forestsCutting down forests

2.2. Burning fossil fuels (energy-rich organic Burning fossil fuels (energy-rich organic materials that are formed from geological materials that are formed from geological processes: coal, gasoline, oil, etc.)processes: coal, gasoline, oil, etc.)

The Nitrogen CycleThe Nitrogen Cycle

Nitrogen is needed to make amino acids, Nitrogen is needed to make amino acids, proteins, and other necessary proteins, and other necessary substances.substances.

It moves through atmosphere and soil, It moves through atmosphere and soil, through living things, and back to the through living things, and back to the atmosphere and soil again.atmosphere and soil again.

Composition of the atmosphereComposition of the atmosphere

Nitrogen makes up Nitrogen makes up almost 80% of the air almost 80% of the air you breathe every you breathe every day!day!

The rest is made up The rest is made up of Oof O22, Ar, CO, Ar, CO22, and , and

other traces of gases.other traces of gases.

Two important NTwo important N22-cycle processes-cycle processes

1. Nitrogen fixation—1. Nitrogen fixation—bacteria in the soil bacteria in the soil or the root nodules or the root nodules of legumes convert of legumes convert NN22 that is present in that is present in

the atmosphere to the atmosphere to ammonium ions that ammonium ions that plants can take up plants can take up and use.and use.

Two important NTwo important N22-cycle processes-cycle processes

2. Denitrification—2. Denitrification—another group of another group of bacteria convert some bacteria convert some of the ammonium and of the ammonium and nitrates in the soil into nitrates in the soil into free nitrogen gas.free nitrogen gas.

Humans and the NHumans and the N22 cycle cycle Nitrogen compounds dissolve Nitrogen compounds dissolve

easily in water, so are lost with easily in water, so are lost with erosion (the result of erosion (the result of deforestation).deforestation).

Crop plants like corn and cotton Crop plants like corn and cotton absorb nitrogen excessively—absorb nitrogen excessively—causing farmers to use nitrogen causing farmers to use nitrogen fertilizers, which are very fertilizers, which are very expensive to make (and pollute expensive to make (and pollute the environment during the the environment during the process).process).

The Water CycleThe Water Cycle

Water is necessary for all life processes.Water is necessary for all life processes. Water cycles from the atmosphere, to the Water cycles from the atmosphere, to the

Earth, through organisms, and back to Earth, through organisms, and back to the atmosphere.the atmosphere.

The two driving forces of the water cycle The two driving forces of the water cycle are:are:

1.1. Solar energySolar energy

2.2. GravityGravity

Definitions (write down what you Definitions (write down what you don’t know)don’t know)

Evaporation—liquid changing to a gas.Evaporation—liquid changing to a gas.Transpiration—evaporation from the Transpiration—evaporation from the

leaves of trees.leaves of trees.Condensation—gas changing to a Condensation—gas changing to a

liquid.liquid.Precipitation—rain, snow, sleet, and Precipitation—rain, snow, sleet, and

hail.hail.

The steps of the water cycleThe steps of the water cycle

1.1. Water evaporates or transpires and rises in the Water evaporates or transpires and rises in the atmosphere (this requires energy from the atmosphere (this requires energy from the sun).sun).

2.2. As it rises, it cools and condenses to form As it rises, it cools and condenses to form clouds.clouds.

3.3. The droplets of the clouds eventually get big The droplets of the clouds eventually get big enough and fall back to the surface of Earth by enough and fall back to the surface of Earth by gravity.gravity.

4.4. The water is absorbed and collected in lakes, The water is absorbed and collected in lakes, streams, ponds, and oceans—the cycle begins streams, ponds, and oceans—the cycle begins all over again. all over again.

Humans and the water cycleHumans and the water cycle Chemicals, sewage, trash, Chemicals, sewage, trash,

and toxic wastes find their and toxic wastes find their way into rivers, ponds, and way into rivers, ponds, and lakes all over the world.lakes all over the world.

These eventually travel These eventually travel underground and underground and contaminate our contaminate our groundwater—the source of groundwater—the source of all our fresh drinking water.all our fresh drinking water.

Deforestation also prevents Deforestation also prevents absorption of rainfall making absorption of rainfall making land susceptible to flooding land susceptible to flooding and erosion.and erosion.

To ReviewTo Review Nutrients such as carbon, oxygen, and Nutrients such as carbon, oxygen, and

nitrogen are needed for organisms to live and nitrogen are needed for organisms to live and grow.grow.

These elements, along with all others, are not These elements, along with all others, are not constantly replenished from an outside source.constantly replenished from an outside source.

1.1. The carbon cycle—the movement of carbon through The carbon cycle—the movement of carbon through the environment.the environment.

2.2. The nitrogen cycle—the pathway by which nitrogen The nitrogen cycle—the pathway by which nitrogen moves through the environment.moves through the environment.

3.3. The water cycle—the continual movement of water The water cycle—the continual movement of water from the Earth’s surface to the atmosphere and from the Earth’s surface to the atmosphere and back to the surface again.back to the surface again.