NITROGEN CYCLE: A level biology AQA. Saprobionts, nitrogen-fixing, ammonification & nitrification

Summary

In this video, Miss Esther explains the nitrogen cycle, highlighting its importance for both plants and animals. She covers key processes including nitrogen fixation, ammonification, nitrification, and denitrification. The nitrogen cycle is crucial because plants and animals cannot directly utilize atmospheric nitrogen. Instead, microorganisms convert it into usable forms like ammonium, nitrites, and nitrates. These compounds are absorbed by plants, then passed through the food chain. The video also discusses how nitrogen is recycled through decomposers, and emphasizes the role of bacteria in the cycle. Tips for understanding and applying this knowledge in exams are also provided.

Takeaways

• 😀 The nitrogen cycle is essential because nitrogen makes up 30% of the atmosphere but cannot be directly absorbed by plants and animals due to its inert gas properties.
• 😀 Nitrogen fixation is the first step, where nitrogen gas is converted into nitrogen-containing compounds that plants can absorb.
• 😀 Leguminous plants like beans and clover have root nodules containing bacteria that directly convert nitrogen gas into ammonium or nitrates.
• 😀 Ammonification occurs when decomposers break down dead plants and animals, releasing nitrogen-containing compounds like ammonium into the soil.
• 😀 Nitrification is a two-step process where nitrifying bacteria convert ammonium into nitrites, and then nitrites into nitrates, which plants can absorb.
• 😀 Assimilation is the process by which plants absorb nitrates from the soil, using them to produce amino acids, proteins, ATP, and DNA.
• 😀 Animals obtain nitrogen by eating plants, and through digestion, they incorporate nitrogen into their own biological molecules.
• 😀 Denitrification is the conversion of nitrates back into nitrogen gas by anaerobic bacteria in oxygen-poor environments, completing the nitrogen cycle.
• 😀 Denitrification can be detrimental in agriculture as it reduces the amount of nitrogen available in the soil, which is essential for plant growth.
• 😀 Proper soil aeration is important in farming to prevent waterlogging, which can lead to denitrification and loss of nitrogen from the soil.

Q & A

Why is the nitrogen cycle important?

The nitrogen cycle is crucial because although 30% of the atmosphere is made up of nitrogen gas, plants and animals cannot directly use nitrogen from the air due to its inert nature. The nitrogen cycle allows nitrogen to be converted into forms that plants can absorb and animals can use.

Why can't plants and animals obtain nitrogen directly from the atmosphere?

Plants and animals cannot obtain nitrogen directly from the atmosphere because nitrogen gas (N2) has a triple bond, making it very stable and chemically inert, so it cannot be readily used by organisms.

What role do microorganisms play in the nitrogen cycle?

Microorganisms are essential in the nitrogen cycle as they break the triple bond in nitrogen gas, converting it into nitrogen-containing compounds like ammonia, nitrites, and nitrates, which plants can absorb and use.

What is nitrogen fixation, and how does it occur?

Nitrogen fixation is the process of converting nitrogen gas into nitrogen-containing compounds that plants can use. This can occur either through symbiotic bacteria in root nodules of leguminous plants or through free-living nitrogen-fixing bacteria in the soil.

What are leguminous plants, and how do they contribute to nitrogen fixation?

Leguminous plants, such as beans and clover, have root nodules that contain nitrogen-fixing bacteria. These bacteria convert atmospheric nitrogen into ammonia or nitrates, which the plant can then absorb for growth.

What is ammonification, and why is it necessary?

Ammonification is the process by which decomposers break down organic matter from dead plants and animals into ammonia. This step is necessary because ammonia can be further processed in the nitrogen cycle to become usable nitrogen for plants.

What is nitrification, and how does it occur?

Nitrification is the two-step process where ammonia is first converted into nitrites by nitrifying bacteria, and then nitrites are further converted into nitrates. These nitrates are then available for absorption by plants.

How do animals contribute to the nitrogen cycle?

Animals contribute to the nitrogen cycle by consuming plants that contain nitrogen. When animals excrete waste or die, their nitrogen-rich proteins, DNA, and RNA are broken down by decomposers, returning nitrogen to the soil in the form of ammonia.

What is denitrification, and why is it problematic in agriculture?

Denitrification is the process by which nitrates are converted back into nitrogen gas by denitrifying bacteria, usually in anaerobic conditions. In agriculture, denitrification is problematic because it leads to the loss of nitrogen from the soil, reducing the availability of nitrogen for plants.

Why is oxygen important in the nitrogen cycle, particularly in nitrification?

Oxygen is essential for nitrification because nitrifying bacteria require oxygen to convert ammonia into nitrites and nitrites into nitrates. Without sufficient oxygen, this process cannot occur efficiently, impacting the nitrogen cycle.