Unit 1 Lesson 6 Part A - The Nitrogen Cycle

Cells require nitrogen to make….

Amino acids and Nucleotides

Amino acids are the building blocks of….

Proteins

What helps carry out biochemical reactions?

Enzymes

What are the building blocks of DNA?

Nucleotides

What is the biggest source/reservoir of nitrogen?

The Atmosphere

What does the term “fixing” mean?

It refers to converting a substance into a usable form, like nitrogen fixation, where bacteria convert nitrogen gas (N₂) into ammonia (NH₃) for plants.

Why can humans not fix nitrogen in their cells?

Humans do not have the enzymes required to fix nitrogen.

What is the 1st step of the Nitrogen Cycle?

Nitrogen Fixation

What is an abiotic factor that can cause nitrogen fixation?

Lighting

What is a biotic factor that can cause nitrogen fixation?

Bacteria

What occurs in nitrogen fixation?

Nitrogen gas (N2) is turned into solid ammonia (NH3)

What is the 2nd step of the Nitrogen Cycle?

Ammonification

What are two ways ammonification can occur?

Bacteria and Decomposition

How does ammonification by bacteria occur?

Ammonia (NH3) is turned into Ammonium (NH4+)

How does ammonification by decomposition occur?

Urine, feces, and death can add ammonia to the soil, allowing bacteria to convert it.

What is the 3rd step in the Nitrogen Cycle?

Nitrification

What occurs during Nitrification?

A two-step process occurs. Ammonium (NH4+) turns into Nitrite(NO2-) and then into Nitrate (NO3-)

What is the 4th step in the Nitrogen Cycle?

Assimilation

What occurs during assimilation?

Plants and other organisms use nitrates to create proteins and DNA

What is the last step of the Nitrogen Cycle?

Denitrification

What happens during nitrification?

Nitrates (NO3-) are converted back into a gas (N2) to be released into the atmosphere.

List ways humans have impacted the nitrogen cycle

Soil Erosion/Fertilizers/Burning of Fossil Fuels

How do humans cause soil erosion/degradation and impact the nitrogen cycle?

Overfarming depletes nitrates in the soil. Tilling disrupts the natural microbiomes of the soil, which can kill nitrogen-fixing bacteria over time.

True or False? Nitrogen is a limiting factor.

True (A very extreme limiting factor)

How does the use of artificial fertilizers negatively impact the nitrogen cycle?

They add excess nitrogen to soils, causing runoff, water pollution, algal blooms, and dead zones.

What is eutrophication?

The excessive enrichment of water with nutrients (like nitrogen and phosphorus), causing algal blooms, oxygen depletion, and harm to aquatic life.

Explain the process of eutrophication

• Extra nutrients (N & P) enter water.

• Algal bloom forms.

• Sunlight blocked → plants die.

• Bacteria decompose algae → use oxygen.

• Low oxygen (hypoxia) kills fish & aquatic life.

How does the burning of fossil fuels impact the nitrogen cycle?

Releases nitrogen oxides (NOₓ), leading to photochemical smog, acid rain, and excess nitrogen in ecosystems.