Part 10 – Nutrient Cycles
Part 10 – Nutrient Cycles (Carbon, Nitrogen, Phosphorus) (25 MCQs)
Q1.
Which cycle is a gaseous cycle?
a) Nitrogen cycle
b) Carbon cycle
c) Phosphorus cycle
d) Both a and b
Answer: d) Both a and b
Explanation:
Carbon & nitrogen → gaseous; phosphorus → sedimentary.
Q2.
Phosphorus cycle is:
a) Gaseous
b) Sedimentary
c) Both
d) Neither
Answer: b) Sedimentary
Explanation:
Phosphorus cycle does not have a gaseous phase.
Q3.
Which process releases CO₂ into atmosphere?
a) Photosynthesis
b) Respiration
c) Combustion
d) Both b and c
Answer: d) Both b and c
Explanation:
Respiration + burning fossil fuels release CO₂.
Q4.
Major reservoir of carbon is:
a) Soil
b) Ocean
c) Atmosphere
d) Plants
Answer: b) Ocean
Explanation:
Oceans hold maximum carbon (carbonates).
Q5.
Nitrogen fixation converts:
a) N₂ → NH₃
b) NH₃ → N₂
c) NO₂⁻ → N₂
d) NO₃⁻ → NH₄⁺
Answer: a) N₂ → NH₃
Explanation:
Atmospheric nitrogen fixed into ammonia.
Q6.
Which organisms fix atmospheric nitrogen?
a) Rhizobium
b) Azotobacter
c) Nostoc
d) All of the above
Answer: d) All of the above
Explanation:
Both symbiotic (Rhizobium) & free-living (Azotobacter, Nostoc).
Q7.
Which step of nitrogen cycle is carried out by Nitrosomonas?
a) Ammonification
b) Nitrification (NH₄⁺ → NO₂⁻)
c) Nitrification (NO₂⁻ → NO₃⁻)
d) Denitrification
Answer: b) Nitrification (NH₄⁺ → NO₂⁻)
Explanation:
Nitrosomonas oxidizes ammonium to nitrite.
Q8.
Which step is carried out by Nitrobacter?
a) Ammonification
b) Nitrification (NO₂⁻ → NO₃⁻)
c) Nitrogen fixation
d) Denitrification
Answer: b) Nitrification (NO₂⁻ → NO₃⁻)
Explanation:
Nitrobacter converts nitrite into nitrate.
Q9.
Denitrification releases:
a) NH₄⁺
b) NO₂⁻
c) N₂ gas
d) NO₃⁻
Answer: c) N₂ gas
Explanation:
Denitrifying bacteria (Pseudomonas) release N₂ back to atmosphere.
Q10.
Ammonification produces:
a) NH₄⁺
b) NO₂⁻
c) NO₃⁻
d) N₂
Answer: a) NH₄⁺
Explanation:
Decomposition of organic nitrogen → ammonium.
Q11.
Phosphorus is mostly found in:
a) Rocks
b) Atmosphere
c) Oceans
d) Soil microbes
Answer: a) Rocks
Explanation:
Main reservoir = phosphate rocks.
Q12.
Phosphorus cycle lacks a:
a) Sedimentary phase
b) Gaseous phase
c) Aquatic phase
d) Decomposition phase
Answer: b) Gaseous phase
Explanation:
No atmospheric reservoir in phosphorus cycle.
Q13.
Excessive nitrogen and phosphorus in water bodies leads to:
a) Desertification
b) Eutrophication
c) Deforestation
d) Acid rain
Answer: b) Eutrophication
Explanation:
Algal bloom depletes oxygen → aquatic death.
Q14.
Which process removes CO₂ from atmosphere?
a) Respiration
b) Photosynthesis
c) Combustion
d) Volcanic activity
Answer: b) Photosynthesis
Explanation:
Plants fix CO₂ → organic carbon.
Q15.
The largest reservoir of nitrogen is:
a) Ocean water
b) Atmosphere
c) Soil organic matter
d) Plants
Answer: b) Atmosphere
Explanation:
78% nitrogen in atmosphere.
Q16.
The process converting NO₃⁻ → N₂ is called:
a) Ammonification
b) Nitrification
c) Denitrification
d) Assimilation
Answer: c) Denitrification
Explanation:
Denitrifying bacteria release N₂ gas.
Q17.
Which of the following is NOT a nitrogen-fixing organism?
a) Azotobacter
b) Nostoc
c) Pseudomonas
d) Rhizobium
Answer: c) Pseudomonas
Explanation:
Pseudomonas = denitrifying bacteria.
Q18.
Which cycle is considered a perfect cycle?
a) Carbon
b) Nitrogen
c) Phosphorus
d) Sulphur
Answer: b) Nitrogen
Explanation:
Lost nitrogen is returned completely → perfect cycle.
Q19.
Which cycle is considered an imperfect cycle?
a) Carbon
b) Nitrogen
c) Phosphorus
d) Oxygen
Answer: c) Phosphorus
Explanation:
Lost phosphorus is trapped in sediments, not readily available.
Q20.
Carbon dioxide concentration in atmosphere is approximately:
a) 0.03%
b) 0.3%
c) 3%
d) 30%
Answer: a) 0.03%
Explanation:
Atmospheric CO₂ ~0.03–0.04%.
Q21.
Which human activity disturbs carbon cycle most?
a) Agriculture
b) Combustion of fossil fuels
c) Deforestation
d) Both b and c
Answer: d) Both b and c
Explanation:
Burning fossil fuels + deforestation increases CO₂ levels.
Q22.
Assimilation of nitrogen by plants occurs in the form of:
a) N₂ gas
b) NH₃, NO₃⁻, NO₂⁻
c) Proteins directly
d) Organic matter
Answer: b) NH₃, NO₃⁻, NO₂⁻
Explanation:
Plants absorb nitrogen in inorganic forms.
Q23.
Which bacteria convert ammonium into nitrites?
a) Nitrosomonas
b) Nitrobacter
c) Rhizobium
d) Pseudomonas
Answer: a) Nitrosomonas
Explanation:
First step of nitrification.
Q24.
Excessive use of phosphate fertilizers may cause:
a) Eutrophication
b) Desertification
c) Global warming
d) Ozone depletion
Answer: a) Eutrophication
Explanation:
Excess phosphate → algal blooms in water bodies.
Q25.
Which step of nitrogen cycle is carried out by decomposers?
a) Ammonification
b) Nitrification
c) Denitrification
d) Fixation
Answer: a) Ammonification
Explanation:
Decomposers convert organic nitrogen → ammonium.
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