Question 18N.3.HL.TZ0.16
| Date | November 2018 | Marks available | [Maximum mark: 6] | Reference code | 18N.3.HL.TZ0.16 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Describe, Explain | Question number | 16 | Adapted from | N/A |
The pie chart shows the world demand for phosphorus in 2010. The fraction used as detergents and in industries has decreased in recent years in response to evidence that phosphate pollution of surface waters causes eutrophication.
Describe reasons that the availability of phosphates may become limiting to agriculture in the future.
[3]
a. phosphate-rich rocks/resource is limited ✔
b. demand exceeds availability of phosphorus
OR
there is greater consumption than P available ✔
c. cycling of phosphorus is slow ✔
d. as crops are removed, the phosphate levels within the soil is continually depleted ✔
e. there is no biological/industrial way to replenish the mineral «fast enough» OWTTE
OR
«phosphate» fertilizers need to be added «to replenish it in the soil»
OR
«lost phosphate» does not go back in the cycle ✔
Explain how eutrophication can occur from the excessive use of phosphates.
[3]
a. phosphates are leached to lakes/rivers ✔
b. induces incremental growth of plants/bloom/algae ✔
c. algae do not let light go through water so less photosynthesis ✔
d. plants/algae die/decay ✔
e. bacterial decomposition consumes the oxygen ✔
f. creating state of hypoxia
OR
greater biochemical oxygen demand ✔
g. causing death of «aerobic» organisms ✔
eg: fish