BIOCHEMICAL CYCLES

Earth

cycles

Fig. 3-7, p. 55

Nitrogencycle

Biosphere

Heat in the environment

Heat Heat Heat

Phosphoruscycle

Carboncycle

Oxygencycle

Watercycle

CARBON CYCLE 1. CO2 is taken in by plants

and photosynthetic aquatic organisms.

2. Plants are eaten by animals

3a. Animals respire and release CO2 into the atmosphere or water.

or3b. Organism dies and CO2 is decomposed and transformed into rock, coal, gas or oil.

EFFECTS OF HUMAN ACTIVITIES ON CARBON CYCLE

• We alter the carbon cycle by adding excess CO2 to the atmosphere through:– Burning fossil

fuels.– Clearing

vegetation faster than it is replaced.

Figure 3-28

Phosphorous Cycle

FYI: PHOSPHORUS

• Bacteria are not as important in the phosphorus cycle as in the nitrogen cycle.

• Phosphorus is not usually found in the atmosphere or in a gas state only as dust.

• The phosphorus cycle is slow and phosphorus is usually found in rock formations and ocean sediments.

• Phosphorus is found in fertilizers because most soil is deficient in it and plants need it.

• Phosphorus is usually insoluble in water and is not found in most aquatic environments.

EFFECTS OF HUMAN ACTIVITIES ON THE PHOSPHOROUS CYCLE

• We remove large amounts of phosphate from the earth to make fertilizer.

• We reduce phosphorous in tropical soils by clearing forests.

• We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers.

Nitrogen Cycle

STEP 1:NITROGEN FIXATION

• This is the first step of the nitrogen cycle where specialized bacteria convert gaseous nitrogen to ammonia(NH4

+ ) that can be used by plants. This is done by cyanobacteria or bacteria (Rhizobium) living in the nodules on the root of various plants.

STEP 2: NITRIFICATION

• Ammonia is converted to – Nitrite– then to Nitrate

• Plant roots absorb ammonium ions and nitrate ions for use in making molecules such as DNA, amino acids and proteins.

Step 3: Assimilation

STEP 4: AMMONIFICATION

• After nitrogen has served its purpose in living organisms, decomposing bacteria convert the nitrogen-rich compounds, wastes, and dead bodies into simpler compounds such as ammonia.

• Nitrate ions and nitrite ions are converted into nitrous oxide gas and nitrogen gas.

• This happens when a soil nutrient is reduced and released into the atmosphere as a gas.

STEP 5: DENITRIFICATION

EFFECTS OF HUMAN ACTIVITIES ON THE NITROGEN CYCLE

• Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined.

Figure 3-30

EFFECTS OF HUMAN ACTIVITIES ON THE NITROGEN CYCLE

• We alter the nitrogen cycle by:– Adding gases that contribute to acid

rain.– Adding nitrous oxide to the

atmosphere through farming practices which can warm the atmosphere and deplete ozone.

– Contaminating ground water from nitrate ions in inorganic fertilizers.

– Releasing nitrogen into the troposphere through deforestation.

THE SULFUR CYCLE

Figure 3-32

EFFECTS OF HUMAN ACTIVITIES ON THE SULFUR CYCLE

• We add sulfur dioxide to the atmosphere by:– Burning coal and oil– Refining sulfur containing petroleum.– Convert sulfur-containing metallic

ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.