Big on Biology

The Nitrogen and Phosphorus

Cycled

9-12 Science Std: Bio 6d, Geo 7a,b,c

C. NITROGEN CYCLE• Nitrogen (N2) is basic building block

for life. It is a colorless, odorless, and nontoxic gas. Nitrogen is found mostly in:All DNAAnimal proteinAtmosphere (78%!)

• N2 is a very stable molecule, so is hard to take out of atmosphere. It has to be taken out and then used in another form called nitrate (NO3). Conversion of nitrogen (N2) to nitrate (NO3)

is called nitrogen fixation.o How does it get converted to nitrate?

¨ Lightning¨ Bacteria in soil

Nitrogen fixing bacterium

Azospirrillum found soils.

¨ Lightning- This method does not happen often,

since lightning doesn’t occur often.- Energy from lightning causes N2 gas

to react with O2 in the air, producing NO3

>Nitrates dissolve in rain, then fall to Earth, enter the soil, then move into plants through their roots.

>Plants use nitrates to make their own DNA, and to make amino acids which make proteins.

¨ Bacteria in Soil- Since there is a lot of bacteria around, this

is how most nitrates are produced- Bacteria are found in small lumps or nodules on the roots of most plant legumes like clover, soybeans, peas, and alfalfa.

nodules

clover

soybeans

peasalfalfa

LEGUMES

> These give the plant built-in supply of usable nitrogen to help plants grow, while plant gives bacteria sugar they need to make nitrates.~Farmers usually rotate crops – first crop

uses up nitrogen, next legume crop replenishes nitrogen, third crop uses up nitrogen again, over and over

Uses NO3 Uses NO3Makes NO3 Makes NO3

Crop Rotation

Uses nitrates

Makes nitrates

Uses nitrates

Makes nitrates

• Conversion of nitrate (NO3) back to nitrogen (N2) is called denitrification and takes a couple of steps by different bacteria:First NO3 has to be converted to nitrite

(NO2)

NO2 is converted to N2 and released back into atmosphere

• Gets recycled again and again in the nitrogen cycle

N2Nitrogen gas NITROGEN FIXATION

fertilizers

decomposers

Nitrogen in protein

bacteria

NO3 & NO2Nitrates & Nitrites

feeding

DENITRIFICATION

NITROGEN FIXATION

The Nitrogen Cycle

N2 In Air

Denitrification

Fertilizer Factory

Fixation(Lightning)

N Fixing Bacteria

NO3

Nitrate Bacteria

NO2

Nitrite BacteriaNH4

+

Decomposers

Decay and Waste

Plants Animals

Bacteria in Nodules

D. PHOSPHOROUS CYCLE• Phosphorus (P) is not found in the

atmosphere but is found in Earth-bound matterIn living things, its found in DNA, bones,

and shellso Short cycle since it doesn’t take long

(few months) for phosphorus to become a part of a living creature

In non-living rocks due to other fossils being trapped in sediment during the rock cycleoLonger cycle since it takes a long time

for rocks to form (millions of years)

• Phosphorus (P) tends to combine with oxygen (O2) to form phosphate (PO4) ions. Can be removed from dead organisms by

decomposing bacteria

Are soluble (dissolvable) in water, so they can be drawn (taken) out of rock by weathering and become part of the water cycleoNow can be absorbed by plants and

phytoplankton to enter food sources

PO4PO4

PO4 PO4

weathering

PO4

decomposers

P P

PHOSPHOROUSCYCLE

E. AGRICULTURE AND NITROGEN AND PHOSPHOROUS CYCLES

• Seeds, leaves, flowers, and fruits of plants contain valuable nutrients, which is why we eat them. But as crops are harvested, valuable nitrogen and phosphorous in these plant parts get removed and do not return to the soil they came from

This removal of nitrates and phosphates from the soil make it almost impossible to grow crops again since it has no nutrients for the seeds.

o This is why farmers use fertilizers that contain nitrates and phosphates in their soil.¨ Estimated that these can DOUBLE the

amount of cereal crops like wheat and barley.

+ fertilizer

- Hey, if a little fertilizer can produce double the amount, shouldn’t a lot produce more?> More is not necessarily better

• Spring rains on the farms make water run off into rivers, lakes, streams, or oceans. That water now contains nitrogen and phosphates from all that fertilizer.These extra nutrients in the water cause

algae and other aquatic plants like seaweed to grow like crazy – this is called algal bloom.

Algal Bloom

o Once these plants die, bacteria that decompose them need to use extra oxygen from the water to do so.¨ Use of too much oxygen from water will kill

fish and the animals that eat fish!- Dead fish means more bacteria to

decompose them, which use more oxygen, which means more dead fish!

oThe End???????