Nutrient cycles

Percentage of oxygen in the atmosphere

• 78%

• 42%

• 21%

• 18%

Coal oil and gas are examples of ... ?

Rain, hail, snow are examples of

• Evaporation

• Precipitation

• Condensation

• Transpiration

Forms the basis of all organic compounds

• Carbon

• Nitrogen

• Oxygen

• Hydrogen

Living organisms return CO2 to the atmosphere through this process

Which of the following processes does not return CO2 into the atmosphere?

• Cellular respiration

• Photosynthesis

• Burning fossil fuels

• Decomposition

Nitrogen is required to make which important organic compounds?

Nitrogen-fixing bacteria can be found

• On the leaves of legume plants

• In the fruits of most plants

• In the roots of legume plants

• In the stems of legume plants

What role does lightning play in the nitrogen cycle?

Organisms can only take in nitrogen in the form of

• N2

• NO3-

• NO2-

• NH3