What is the Nitrogen Cycle?

What is Nitrogen?

• N for Nitrogen on the Periodic Table

• Necessary building block in living things

• Air = 78% Nitrogen gas

• “Free Nitrogen” – not combined with any other element

Why do we need Nitrogen?

• All living organisms need nitrogen in order to build proteins and build DNA

• Most animals get the nitrogen they need by eating plants.

Available Nitrogen

• Nitrogen must be combined with something else in order for it to be used

• Most organisms can NOT use the nitrogen in the air

• Nitrogen must be “fixed” – needs to be combined with other elements

Nitrogen Cycle

• The process by which nitrogen is removed from the atmosphere, fixed in the soil by bacteria, incorporated in other living things, and then released back into the atmosphere.

Nitrogen Fixation• The process of changing

free nitrogen gas (from the air) into a usable form of nitrogen

• Performed by bacteria

Bacteria• Some of these

bacteria live in bumps called nodules on the roots of certain plants.

What kind of plants?

• Bacteria live in the roots of plants called legumes

• Example: Clover, beans, peas, alfalfa, and peanuts

Mutualism

• Both species benefit

• The bacteria feed on the plant’s sugar

• The plant is supplied with nitrogen in the useable form

Farmers

• Farmers will often plant alfalfa in their fields so that their soil will be rich in nitrogen

• Bacteria in the roots “fix” the nitrogen so it can be used.

Now What?

• Once bacteria in the roots of plants have “fixed” the nitrogen, the nitrogen can be used by organisms to build proteins and other complex substances.

• Plants absorb the nitrogen

• Animals eat the plants

Recycling

• Decomposers break down these complex compounds in animal wastes and in the bodies of dead organisms.

• Nitrogen is now returned to the soil

• Nitrogen can be recycled over and over again

• Bacteria can also return “free” nitrogen back to the air.

Human Influence

• Nitrogen enhanced fertilizer

• Chemical fertilizers– Is this considered organic?

• Cow manure has lots of nitrogen! – What do cows eat?

• Pollution

Nitrogen fertilizer is often added to soil to increase the growth of crops. Which of these ecosystems would most likely be harmed by the use of nitrogen fertilizer?

• Forest

• Pond

• Park

• Meadow

Question…

Answer

In this example, water ecosystems would be harmed the most from fertilizer runoff, making Choice B, a pond, the correct answer.

Fertilizer would increase the growth of water plants and algae, thus reducing the resources for some living organisms in the pond.

Journal Activity

1. Fold your notes in half and glue 2. Trim around the nitrogen cycle

3. Color the n.cycle and glue

Homework: