Understanding the Nitrogen Cycle

Nitrogen is crucial for life, cycling through the biosphere like carbon and oxygen. It makes up 78% of our atmosphere as N2, but unlike carbon, it cannot be directly fixed by plants. Bacteria in the soil convert N2 into ammonia, which plants can use. Nitrogen is vital in organic molecules like amino acids, ATP, and DNA. The nitrogen cycle involves recycling nitrogen through decomposition and conversion back to atmospheric N2. Fertilizers rich in nitrogen enhance plant growth, highlighting its importance in agriculture.

What percentage of the Earth's atmosphere is composed of molecular nitrogen?

• 21%

• 78%

• 50%

• 33%

Which organisms are primarily responsible for fixing atmospheric nitrogen?

• Plants

• Fungi

• Bacteria

• Animals

What is the form of nitrogen that plants can directly use?

• NO3

• NO2

• NH3

• N2

Which of the following is NOT an example of an organic molecule containing nitrogen?

• Glucose

• Amino acids

• ATP

• DNA

What is the role of bacteria in the nitrogen cycle?

• They convert nitrogen into carbon.

• They decompose dead organisms.

• They produce oxygen.

• They fix nitrogen and decompose organic matter.

What happens to nitrogen when an organism dies?

• It is converted into carbon.

• It is broken down into nitrites and nitrates.

• It is released as oxygen.

• It disappears.

How is nitrogen returned to the atmosphere in the nitrogen cycle?

• Through photosynthesis

• By plants absorbing it

• Through animal respiration

• By bacteria converting it back to N2

Why is nitrogen a key component in fertilizers?

• It is a rate-limiting factor for plant growth.

• It is not essential for plants.

• It limits plant growth.

• It helps in photosynthesis.

What other element, along with nitrogen, is often a rate-limiting factor for plant growth?

• Carbon

• Oxygen

• Phosphorus

• Hydrogen

What is the effect of adding more nitrogen to the soil?

• No effect on plant growth.

• Plants stop growing.

• Plants grow faster.

• Plants grow slower.