4. Air page 2

Which gas is primarily taken from the air by bacteria to convert into a form that plants can use?

• Oxygen
• Carbon dioxide
• Nitrogen
• Hydrogen

What process do green plants use to convert carbon dioxide into food and release oxygen?

• Respiration
• Photosynthesis
• Combustion
• Evaporation

What role do bacteria in the soil and plant roots play in the nitrogen cycle?

• They convert nitrogen into oxygen
• They absorb nitrogen from water
• They take nitrogen from the air and change its form
• They release nitrogen into the air

How do humans and animals contribute to the balance of oxygen and carbon dioxide in the atmosphere?

• They release oxygen during photosynthesis
• They release carbon dioxide during respiration
• They release carbon dioxide during photosynthesis
• They release oxygen during respiration

What effect does cutting down trees have on the balance of gases in the atmosphere?

• It increases the oxygen content
• It decreases the oxygen content
• It increases the carbon dioxide content
• It has no impact on the balance

What gas is released into the atmosphere by burning fuels like coal and oil?

• Oxygen
• Nitrogen
• Carbon dioxide
• Hydrogen

How does air circulation take place in the atmosphere?

• Cold air rises, hot air sinks
• Hot air rises, cold air sinks
• Both hot and cold air rise
• Both hot and cold air sink

What happens to air when it is heated?

• It becomes denser
• It contracts
• It becomes heavier
• It expands and becomes lighter

Which gas is the second most plentiful in the atmosphere and is taken in by humans and animals as they breathe?

• Nitrogen
• Carbon dioxide
• Oxygen
• Hydrogen

What is the primary function of bacteria living in the soil and plant roots with regard to nitrogen?

• Converting nitrogen into oxygen
• Absorbing nitrogen from water
• Changing nitrogen's form for plant use
• Releasing nitrogen into the air