The Phosphorous Cycle

Question 1

Erosion and weathering of rocks?

Answer 1

Phosphate ions are released from phosphate containing rocks by EROSION and WEATHERING
These phosphate ions dissolve in soil and water
Phosphate ions from fertilisers also leach into bodies of water

Question 2

Absorption by plants?

Answer 2

Plants absorb phosphate ions from the soil through active transport
They incorporate these into organic compounds like DNA,RNA,ATP and phospholipids

Question 3

Feeding and digestion?

Answer 3

Animals obtain phosphorous by feeding on plants (or other animals)
They incorporate these into their organic compounds like DNA,RNA,ATP and phospholipids

Question 4

Excretion and decomposition?

Answer 4

Excretion e.g. urine and faeces and death return organic phosphate compounds to the soil
Saprobionts decompose organic material, releasing phosphate ions back into the soil by extracellular digestion

Question 5

Deposition and sedimentation?

Answer 5

Phosphate ions can be deposited in sediments and form rocks again over time
This process is very slow

Question 6

What are mycorrhizae?

Answer 6

Mutualistic associations between certain types of fungi and the roots of plants

Question 7

Mutualistic relationship between mycorrhizae and plant?

Answer 7

The fungus grows around and into the plants root cells
The fungal hyphae increase the surface area of the plants roots
The plant can absorb water and mineral ions more efficiently
In return, the plant provides the fungus with carbohydrates e.g. sugars from photosynthesis

Question 8

Key stages of phosphorous cycle?

Answer 8

Erosion and weathering of rocks
Absorption of plants
Feeding of animals
Excretion and decomposition
Deposition and sedimentation