16. The nitrogen cycle

16. The nitrogen cycle

The synthesis of proteins and other compounds

What do plants need nitrogen for?

80%

How much of the Earth’s atmosphere does nitrogen gas make up?

Nitrate

What do plants absorb nitrogen as?

They don’t have the enzymes needed to use nitrogen directly

Why must plants absorb nitrogen as nitrate?

Nitrogen fixation and nitrification

Which two processes result in nitrate?

Microorganisms

What carries out nitrogen fixation and nitrification?

Nitrogen fixation

A process where nitrogen and hydrogen are combined to form ammonium ions and then nitrate

nitrogen-fixing bacteria

Nitrogen fixation is carried out by:

Nodules on the roots of leguminous plants

Where do nitrogen-fixing bacteria live?

Oxygen

What is required for nitrogen fixation:

When energy from lightning combines nitrogen directly with oxygen

How does nitrogen fixation occur naturally?

To avoid the use of so much nitrogen-containing fertilizer

Why do farmers plant legumes?

Save money (don’t have to buy nitrogen-containing fertilizer), and limits pollution of water

What are the advantages of planting legumes:

Nitrification

The process where ammonium ions produced by the decomposition of amino acids and proteins are oxidized, first to nitrite and then to nitrate

Nitrifying bacteria

What carries out nitrification?

Soil

Where do nitrifying bacteria live?

Oxygen

Requirement for nitrification:

The process is reversed and denitrifying bacteria obtain energy by converting nitrate to nitrogen gas

What happens to the process of nitrification when there is no oxygen?

Without oxygen, denitrifying bacteria can convert nitrate into nitrogen gas

Why do waterlogged soils lose nitrate as nitrogen gas?

Through roots in the process of diffusion and active transport

How do plants absorb nitrate?

They break down the nitrogen compounds in wastes and remains

How do decomposers play a role in the nitrogen cycle?

Denitrification and harvest of crops

What processes cause the loss of nitrate from the environment?

Nitrogen fixation and adding nitrate in the form of fertilizers

How do the processes of denitrification and harvest of crops be made up to increase nitrogen?

nitrification, absorption, feeding, death, excretion, decay

What processes make up the nitrogen cycle:

Proteins

Organic compounds in plants:

Proteins, amino acids, and urea

Organic compounds in animals:

Provides raw material for the action of decomposers

Why do farmers plough roots and stalks of harvested crops back into the soil?

Enzymes digest organic molecules to simpler forms

What happens during decay in the nitrogen cycle?