The Nitrogen Cycle Flashcards
Is nitrogen gas reactive or unreactive?
Nitrogen gas is very unreactive.
What percentage of the Earth’s atmosphere is nitrogen gas?
About 79%.
Why is nitrogen important for living organisms?
It is a key part of proteins and DNA, which are essential for growth and functioning of cells.
How do plants obtain nitrogen?
They absorb nitrate ions from the soil.
How do animals obtain nitrogen?
From the proteins in the plants and animals they eat.
What is nitrogen fixation?
The process by which nitrogen gas is converted into nitrates by nitrogen-fixing bacteria.
Which bacteria are involved in nitrogen fixation in the soil?
Azotobacter and Clostridium.
What is the role of Rhizobium bacteria?
They live in the root nodules of legumes and fix nitrogen gas directly into nitrates for the plant.
Why can’t plants absorb nitrogen gas directly?
Because it is unreactive; plants can only absorb nitrogen in the form of nitrates.
What is decay in the nitrogen cycle?
The breakdown of dead plants, animals, faeces and urine by decomposers into ammonium compounds.
What is nitrification?
The process of converting ammonium compounds into nitrites, then nitrates by nitrifying bacteria.
Which bacteria carry out nitrification?
Nitrosomonas (ammonium → nitrites) and Nitrobacter (nitrites → nitrates).
What is denitrification?
The conversion of nitrates back into nitrogen gas by denitrifying bacteria.
What effect does denitrification have on soil fertility?
It reduces soil fertility because it removes nitrates that plants need to grow.
How does lightning help in the nitrogen cycle?
It provides energy to convert nitrogen gas into nitrogen oxides, which dissolve in rain and form nitrates.
Why are fertilisers used in agriculture?
To add nitrates to the soil and help crops grow better.
What is leaching?
The process by which rainwater washes nitrates and nutrients out of the soil into rivers, lakes or the sea.
Why is the nitrogen cycle important to life?
It recycles nitrogen, a vital element needed by all living organisms for proteins and DNA.
Can nitrogen atoms be created or destroyed in nature?
No, they are reused over and over through the nitrogen cycle.
Why are bacteria crucial in the nitrogen cycle?
They perform nitrogen fixation, nitrification, and denitrification, making nitrogen available and cycling it through ecosystems.
What is the relationship between nitrogen-fixing bacteria and plants called?
Mutualism – both organisms benefit.
