APES 1.5 Notes - Nitrogen Cycle

Summary

This video covers the nitrogen cycle, highlighting its steps, reservoirs, and key differences from the carbon cycle. It explains nitrogen fixation as the conversion of atmospheric nitrogen into forms usable by plants, which is essential for life. The video explores processes like assimilation, ammonification, nitrification, and denitrification, emphasizing the role of bacteria. Human impacts on the nitrogen cycle, such as greenhouse gas emissions, ammonia volatilization, and eutrophication, are also discussed. The video concludes by posing a question about the chemical transformations in the nitrogen cycle and their ecological importance.

Takeaways

• 🌿 The nitrogen cycle involves the movement of nitrogen between sources, sinks, and reservoirs.
• 🔄 Nitrogen reservoirs hold nitrogen for a shorter time than carbon reservoirs, with the atmosphere being the largest nitrogen reservoir (78%).
• ⚡ Most atmospheric nitrogen is in the unusable form of N2 gas, and nitrogen fixation is necessary to convert it into usable forms like ammonia (NH3) or nitrate (NO3).
• 🌩️ Nitrogen fixation can occur naturally through bacteria in the soil and in symbiotic relationships with legumes, as well as through lightning storms.
• 🏭 Synthetic nitrogen fixation, which requires energy, allows humans to produce fertilizers by fixing nitrogen into nitrates (NO3) for agricultural use.
• 🌱 Assimilation is when plants absorb nitrates or ammonia from the soil, while animals get their nitrogen by consuming plants or other animals.
• 🦠 Ammonification is the process where decomposers and bacteria convert dead biomass and waste back into ammonia, returning nitrogen to the soil.
• 🔄 Nitrification converts ammonium (NH4) into nitrite (NO2) and then nitrate (NO3), both processes driven by soil bacteria.
• 💨 Denitrification occurs when bacteria convert nitrate (NO3) back into gaseous forms like nitrous oxide (N2O), completing the nitrogen cycle.
• 🌍 Human activities, like agriculture, contribute to greenhouse gases (N2O), ammonia volatilization, acid rain, and eutrophication due to excess nitrogen from fertilizers.

Q & A

What is the main focus of the nitrogen cycle as discussed in the video?

The main focus of the nitrogen cycle in the video is on the movement of nitrogen molecules between sources, sinks, and reservoirs, as well as explaining the steps and reservoir interactions in the nitrogen cycle.

How does the nitrogen cycle differ from the carbon cycle?

The nitrogen cycle differs from the carbon cycle in that nitrogen reservoirs generally hold nitrogen for a much shorter period of time compared to carbon reservoirs, such as fossil fuels and sedimentary rocks, which can hold carbon for millions of years.

What is the biggest nitrogen reservoir, and why is it not directly usable by plants and animals?

The biggest nitrogen reservoir is the atmosphere, where about 78% of it is made up of nitrogen. However, most of this nitrogen exists in the form of N2 gas, which is not usable by plants or animals.

What is nitrogen fixation and why is it important?

Nitrogen fixation is the process of converting nitrogen gas (N2) from the atmosphere into biologically usable nitrogen forms such as ammonia (NH3) or nitrate (NO3). It is critical because it allows plants to absorb nitrogen, which is essential for their growth and for making DNA and proteins.

What are the two main natural ways nitrogen fixation occurs?

Natural nitrogen fixation primarily occurs through nitrogen-fixing bacteria in the soil or in symbiotic relationships with plants (like legumes). It can also occur through lightning storms, which can convert atmospheric nitrogen into ammonia.

How do humans contribute to nitrogen fixation, and what are the effects?

Humans contribute to nitrogen fixation synthetically by using fossil fuels to convert atmospheric nitrogen into nitrates (NO3) for fertilizers. This process is energy-intensive and is primarily used to increase agricultural yields.

What is assimilation in the nitrogen cycle?

Assimilation is the process in which plants take in nitrogen from the soil (as ammonia or nitrates) and incorporate it into their bodies, while animals obtain nitrogen by consuming plants or other animals.

What is ammonification and how does it relate to the nitrogen cycle?

Ammonification is the process in which soil bacteria and decomposers convert waste and dead biomass back into ammonia, which returns nitrogen to the soil, making it available for plants to use again.

What is nitrification, and how does it occur?

Nitrification is the process where ammonium (NH4) is converted into nitrite (NO2) and then into nitrate (NO3) by soil bacteria. This process makes nitrogen available in a form that plants can assimilate.

What is denitrification and what role does it play in the nitrogen cycle?

Denitrification is the process by which soil bacteria convert nitrate (NO3) back into nitrogen gas (N2) or nitrous oxide (N2O), releasing it back into the atmosphere. This completes the nitrogen cycle.