Biogeochem - Phosphorus cycle

Question 1

Is phosphorus a macronutrient, micronutrient or both?

Answer 1

both

Question 1

what is the connection between water pollution and phosphorus?

Answer 1

increase in phosphorus levels increases the growth rate of phytoplankton and algae, causing algal blooms which removes the oxygen from the water system, causing water degradation

Question 2

phosphorus role in cells?

Answer 2

Backbone of all nucleic acids
DNA
- 2 strands
RNA
- single strand

Phospholipid bilayer
- Polar heads and hydrophobic tails

ATP and ADP

Question 3

how Adenosine triphosphate (ATP) converting to ADP release energy?

Answer 3

the breaking of the phosphate bond releases energy which is used for doing work

Question 4

What happens when phosphorus is discharged in large quantities into the environment ?

Answer 4

life becomes more productive… ie
- alae, phytoplankton, cyanobacteria use it to increase rates of photosynthesis

Question 5

Why does the environment degrade when phosphorus is released into the environment

Answer 5

lots of organic matter is produced which is then oxidised by organisms consuming the oxygen, leading to deoxygenation within the water body

Question 6

Why is phosphorus a biolimiting nutrient?

Answer 6

because its availability restricts the growth of organisms and the productivity in ecosystems

Question 7

What is the link between phosphorous and O2 levels in the atmosphere

Answer 7

volumes of phosphorus in the oceans in the early earth was low until volcanic activity and the movement of tectonic plates started occurring

this released phosphorus trapped in the rocks in to the seawater which photosynthetic organisms could consume and photosynthesise to produce oxygen and organic carbon

Question 8

what is the dominant form of phosphorus in the evnironment?

Answer 8

Phosphate (5+)

Question 9

phosphorus assimilation into biomass

Answer 9

• nucleic acids
• phospholipids in cell membrane
• energy (ATP)
• bones in vertebrates

Question 10

forms of phosphorus in the environment

Answer 10

• Phosphate (+5)
• Phosphite (+3, rare)
• Hypophosphite (+1, rare)

Question 11

What do high levels of phosphorus in the environment signify?

Answer 11

lots of DNA synthesis is occurring, meaning high levels of growth, reproduction

theres lots of recycling phosphorus into cells

Question 12

what do low levels of phosphorus in the environment signify?

Answer 12

there is more internal cycling of P in the environment.

Cells are trying to preserve the phosphorus by intracellular cycling. The cell adapts how it assimilates phosphorus depending on how much is available in the environment

Question 13

In acidic conditions, what form of P is commonly found?

Answer 13

P compounds which have formed with hydrogen

Phosphoric Acid

Question 14

what is the typical pH in marine systems

Answer 14

8

Question 15

What form is phosphorus present in at pH 8 in marine enviornments?

Answer 15

HPO42-

Hydrogen phosphate

Question 16

Why is phosphorus present as HPO42- in marine environments

Answer 16

The acidity of the environment impacts the form in which Phosphorus is present. This is due to the dissociation constant pKa and redox reactions.

In oxic environments, phosphorus gets bound to iron(III), making it not bioavailable to organisms to use. This leads to phosphate having the the potential to be buried in the sediment. In anoxic conditions, iron(III) is reduced to iron(II), releasing phosphate.

The form in which is it appears id dependent on the pH value. As marine environments are ~ pH 8, phosphorus is present as hydrogen phosphate HPO42-, whereas in acidic conditions, due to the increase in hydrogen ions, the compounds formed will obtain more hydrogen, hence H3PO4 is the common form in acidic conditions.

Question 17

Factors limiting phosphate uptake in cells

Answer 17

• bound to rock minerals
• bound to detrital minerals
• competition between arsenic or phosphate

Question 18

Methods in which P is taken up into cells

Answer 18

• taken up as PME (phosphate monoesters)
• taken up at PDE (phosphate diesters)
• mycorrhizal fungal association

Question 19

how is phosphate taken up into cells through phosphate transportation

(hint: affinity)

Answer 19

Low affinity phosphate transportation
- allows phosphate to migrate into cells at any time
- this only works when there is lots of P in the environment

High affinity phosphate transportation
- they can take small amounts of phosphorus into the cell
- is there is competition with arsenate, they can distinguish between P and As and just take up P.

Question 20

What is alkaline phosphatase?

Answer 20

An enzyme that the cell produces which gets released into the environment and binds to phosphorus which assimilates into it

Question 21

How do iron oxides act as a source and a sink of P in the environment?

Answer 21

In the water column (in oxic conditions) iron is found in its oxidised form, Fe(III) which has a high affinity to phosphate. This means that phosphate gets bound to Fe(III) which gets buried in sediments, providing a sink for P.

When the Fe(III) gets buried, in the sediment profile, oxygen is consumed which turns the conditions anoxic. When the iron reaches the iron reduction layer, due to the anoxic conditions, Fe(III) gets reduced by iron-reducing bacteria to Fe(II), aided by the spare electrons from organic matter degradation. This causes P to be released into the sediment column, indicating that iron oxides can also be a sink.

Question 22

What is formed when P levels become saturated in the sediment column?

Answer 22

Apatite can be formed in the sediments which is a carbonate form of phosphate.

Question 23

How did the snowball glaciation cause an increase in phosphate levels in marine sediments and thus marine life?

Answer 23

as the glaciers were melting, the ice ‘churned’ up the rocks, causing mechanical weathering to occur. This caused an increase in clay minerals which acted as surfaces which phosphorus could attach to and was transported into the seawater.

due to the pH of seawater, is dissociated and became bioavailable. This presence triggered of animals and photosynthetic cyanobacteria.

This started producing oxygen and food (organic matter), increasing the marine life numbers