The nitrogen cycle | Energy and matter in biological systems | High school biology | Khan Academy

Summary

This video highlights the critical role of nitrogen in our biosphere, accounting for 78% of the Earth's atmosphere. Unlike carbon, which plants can directly fix, nitrogen requires prokaryotic bacteria to convert atmospheric N2 into ammonia, a vital nutrient for plants and other organisms. The process involves nitrogen recycling through decomposition, where dead organisms are broken down by bacteria, returning nitrogen to the soil and atmosphere. The video emphasizes the importance of nitrogen in fertilizers, which can enhance plant growth, and discusses its essentiality alongside phosphorus in supporting life.

Takeaways

• 🌍 Nitrogen makes up 78% of our atmosphere in the form of molecular nitrogen (N2).
• 🔄 Unlike carbon, nitrogen cannot be directly fixed by plants; it requires specific prokaryotes like bacteria.
• 🦠 Certain bacteria in soil play a crucial role in converting nitrogen (N2) into ammonia (NH3), which is usable by plants.
• 🌱 Ammonia produced by nitrogen-fixing bacteria is essential for the synthesis of important organic molecules in plants.
• ⚗️ Nitrogen is a key component of amino acids, ATP (adenosine triphosphate), and DNA (deoxyribonucleic acid).
• 👥 When organisms die, decomposing bacteria break down their nitrogen-containing compounds back into nitrites and nitrates.
• 🔄 The nitrogen cycle is a continuous process where nitrogen is recycled through the biosphere, involving both living and dead organisms.
• 🌱 Fertilizers often contain nitrogen, which is vital for plant growth and can enhance the rate of growth when added to soil.
• ⏳ The availability of nitrogen and phosphorus in soil can limit plant growth, making them essential nutrients in agriculture.
• 🔄 Nitrogen plays a critical role in life and is essential for biological systems, despite receiving less attention than carbon or oxygen.

Q & A

What percentage of the atmosphere is composed of molecular nitrogen (N2)?

Molecular nitrogen (N2) makes up 78% of our atmosphere.

Why is nitrogen often overlooked compared to carbon and oxygen?

Nitrogen gets less attention because it is less directly involved in processes like photosynthesis, where carbon and oxygen play more prominent roles.

How do plants obtain nitrogen from the atmosphere?

Plants cannot directly fix nitrogen from the atmosphere; instead, they rely on bacteria that convert molecular nitrogen (N2) into ammonia (NH3), which is usable by plants.

What role do prokaryotes, such as bacteria, play in the nitrogen cycle?

Prokaryotes, particularly certain types of bacteria, are essential for fixing nitrogen from the atmosphere and converting it into ammonia, which plants can absorb and utilize.

What are some organic molecules that contain nitrogen?

Nitrogen is found in several important organic molecules, including amino acids, adenosine triphosphate (ATP), and DNA.

What happens to nitrogen when organisms die?

When organisms die, bacteria decompose their nitrogen-containing compounds, breaking them down into nitrites and nitrates, which can be converted back into ammonia or returned to molecular nitrogen (N2).

How does nitrogen contribute to plant growth?

Nitrogen is a key component of fertilizers, and its availability in the soil often determines the rate of plant growth. Adding nitrogen to the soil can enhance plant growth significantly.

What is the significance of ammonia (NH3) in the nitrogen cycle?

Ammonia (NH3) is a critical form of nitrogen that plants can use to synthesize organic molecules necessary for their growth and development.

Can nitrogen be stored in the soil in forms other than ammonia?

Yes, nitrogen can be stored in the soil as nitrites and nitrates before being converted back to ammonia or released as molecular nitrogen (N2) into the atmosphere.

What are the implications of nitrogen being a limiting factor for plant growth?

Since nitrogen availability often limits how fast plants can grow, understanding and managing nitrogen levels in the soil is crucial for effective agriculture and ecosystem management.