Biogeochemical Cycles — Homi Bhabha Class 9 Biology MCQs with Solutions
Free Homi Bhabha Class 9 Biology Biogeochemical Cycles MCQs with step-by-step solutions (10 questions). Part of Ecosystem & Environmental Management. Practise online on Prepizo — no login needed.
▶ Practise Biogeochemical Cycles online (free)
Questions with solutions
Q1 — Biogeochemical Cycles · medium · theory
The continuous circulation of water between the Earth and the atmosphere is called the:
A. nitrogen cycle
B. water cycle ✓ Correct
C. carbon cycle
D. rock cycle
Solution: The water cycle involves evaporation, condensation and precipitation.
Q2 — Biogeochemical Cycles · hard · theory
The conversion of atmospheric nitrogen into compounds usable by plants is called:
A. nitrogen fixation ✓ Correct
B. denitrification
C. respiration
D. nitrification only
Solution: Nitrogen fixation converts inert N₂ into usable nitrogen compounds, often by bacteria.
Q3 — Biogeochemical Cycles · medium · theory
The process that adds oxygen to the atmosphere in the oxygen cycle is:
A. decomposition
B. combustion
C. photosynthesis ✓ Correct
D. respiration
Solution: Photosynthesis by green plants releases oxygen into the air.
Q4 — Biogeochemical Cycles · hard · theory
Bacteria that live in the root nodules of leguminous plants and fix nitrogen are:
A. Plasmodium
B. yeast
C. Lactobacillus
D. Rhizobium ✓ Correct
Solution: Rhizobium bacteria in legume root nodules fix atmospheric nitrogen.
Q5 — Biogeochemical Cycles · medium · theory
In the carbon cycle, carbon dioxide is removed from the air mainly by:
A. photosynthesis ✓ Correct
B. burning of fuels
C. respiration
D. volcanic eruption
Solution: Plants remove CO₂ from the atmosphere during photosynthesis.
Q6 — Biogeochemical Cycles · hard · theory
Biogeochemical cycles are important because they:
A. recycle essential nutrients so that life can continue ✓ Correct
B. only occur in oceans
C. destroy nutrients permanently
D. stop energy flow
Solution: These cycles continuously recycle nutrients (carbon, nitrogen, water) between living things and the environment.
Q7 — Biogeochemical Cycles · easy · theory
The conversion of atmospheric nitrogen gas into usable nitrogen compounds by bacteria in the root nodules of legumes is called:
A. Transpiration
B. Denitrification
C. Nitrogen fixation ✓ Correct
D. Condensation
Solution: Nitrogen fixation is the process by which nitrogen-fixing bacteria (such as Rhizobium in root nodules) convert inert atmospheric N2 into nitrogen compounds that plants can use.
Q8 — Biogeochemical Cycles · easy · theory
In the water cycle, the process by which plants release water vapour into the atmosphere from their leaves is called:
A. Evaporation
B. Precipitation
C. Transpiration ✓ Correct
D. Infiltration
Solution: Transpiration is the loss of water vapour from plant leaves through tiny pores called stomata. Evaporation refers to water lost from open surfaces like oceans and lakes.
Q9 — Biogeochemical Cycles · medium · theory
Burning of fossil fuels and respiration by living organisms both ___ atmospheric carbon dioxide, whereas photosynthesis ___ it. Choose the correct pair:
A. add; adds
B. add; removes ✓ Correct
C. remove; adds
D. remove; removes
Solution: Combustion and respiration release CO2 into the air, adding to it. Photosynthesis takes CO2 out of the air to build food, removing it. Together they keep the carbon cycle balanced.
Q10 — Biogeochemical Cycles · hard · theory
Assertion (A): The total amount of carbon on Earth stays roughly constant. Reason (R): Carbon continuously cycles between the atmosphere, living organisms, oceans, and rocks.
A. A is false but R is true
B. A is true but R is false
C. Both A and R are true but R is not the correct explanation of A
D. Both A and R are true and R is the correct explanation of A ✓ Correct
Solution: Carbon is neither created nor destroyed; it merely moves through different reservoirs in the carbon cycle. Because it is recycled rather than lost, the total remains constant, so R correctly explains A.