Question 1

Which of the following best describes the primary source of phosphorus in the phosphorus cycle?

Accepted Answer

Weathering of rocks releasing phosphate ions ($PO_4^{3-}$)

Question 2

Why is phosphorus considered a limiting factor in many ecosystems?

Accepted Answer

It is not found in the atmosphere and its availability depends on slow geological processes

Question 3

Which process in the phosphorus cycle is most directly affected by human activities such as agriculture?

Accepted Answer

Loss of phosphorus from soil due to fertilizer runoff

Question 4

What is the role of decomposers in the phosphorus cycle?

Accepted Answer

They release phosphate ions ($PO_4^{3-}$) back into the soil from dead organic matter

Question 5

Which of the following is NOT a step in the phosphorus cycle?

Accepted Answer

Nitrogen fixation by bacteria

Question 6

A farmer applies excess phosphate fertilizer to a field. Which environmental consequence is most likely to occur?

Accepted Answer

Eutrophication of nearby aquatic ecosystems due to runoff

Question 7

Which equation best represents the chemical form of phosphate ions found in soil?

Accepted Answer

$PO_4^{3-}$

Question 8

How does geological uplift contribute to the phosphorus cycle?

Accepted Answer

It exposes new rock surfaces, allowing weathering to release more phosphate ions ($PO_4^{3-}$)

Question 9

Which of the following best explains why phosphorus does not cycle through the atmosphere?

Accepted Answer

Phosphorus compounds are not volatile and remain in solid or dissolved forms

Question 10

A scientist observes that a lake has high levels of algae growth. Which step in the phosphorus cycle is most likely responsible for this phenomenon?

Accepted Answer

Runoff of phosphate ions ($PO_4^{3-}$) from surrounding agricultural land

Question 11

Which of the following is a direct consequence of low phosphorus availability in soil?

Accepted Answer

Limited plant growth and productivity

Question 12

Which process returns phosphorus from dead organisms back to the soil?

Accepted Answer

Decomposition by bacteria and fungi

Question 13

Which of the following best describes the movement of phosphorus from land to aquatic systems?

Accepted Answer

Runoff carrying phosphate ions ($PO_4^{3-}$) into rivers and lakes

Question 14

Which human activity most directly alters the natural phosphorus cycle?

Accepted Answer

Application of phosphate fertilizers

Question 15

Which of the following is a multi-step process involving both biotic and abiotic components in the phosphorus cycle?

Accepted Answer

Phosphate ions ($PO_4^{3-}$) are released from rocks, taken up by plants, consumed by animals, and returned to soil by decomposers

Question 16

Which of the following would most likely increase the rate of phosphorus cycling in an ecosystem?

Accepted Answer

Higher rates of decomposition and mineralization by soil microbes

Question 17

If a region experiences rapid soil erosion, what is the most likely impact on the phosphorus cycle?

Accepted Answer

Phosphorus will be lost from the soil and transported to aquatic systems

Question 18

Which of the following is true about the role of animals in the phosphorus cycle?

Accepted Answer

Animals obtain phosphorus by consuming plants and return it to the soil through waste and decomposition

Question 19

Which of the following best explains the effect of geological processes on the long-term availability of phosphorus in ecosystems?

Accepted Answer

Geological uplift exposes new rocks, slowly increasing phosphorus availability over millions of years

Question 20

A community experiences a decline in plant productivity. Soil tests reveal low levels of $PO_4^{3-}$. Which intervention would most directly address this issue?

Accepted Answer

Apply phosphate fertilizers to the soil

Phosphorus Cycle

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