Carbon Cycle — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Carbon Cycle MCQs with step-by-step solutions (13 questions). Part of Carbon & Its Compounds. Practise online on Prepizo — no login needed.
▶ Practise Carbon Cycle online (free)
Questions with solutions
Q1 — Carbon Cycle · medium · theory
The carbon cycle describes the continuous exchange of carbon among the atmosphere, plants, animals and:
A. the soil and oceans ✓ Correct
B. outer space
C. the Sun
D. the Moon
Solution: Carbon circulates among air, living things, soil and oceans in the carbon cycle.
Q2 — Carbon Cycle · medium · theory
The process by which green plants remove carbon dioxide from the atmosphere is:
A. combustion
B. photosynthesis ✓ Correct
C. decomposition
D. respiration
Solution: During photosynthesis, plants take in CO₂ to make food, removing it from the air.
Q3 — Carbon Cycle · hard · theory
Which processes ADD carbon dioxide to the atmosphere?
A. Respiration and combustion of fuels ✓ Correct
B. Photosynthesis only
C. Filtration
D. Condensation and melting
Solution: Respiration by living things and the burning of fuels both release CO₂.
Q4 — Carbon Cycle · hard · theory
The increasing concentration of carbon dioxide in the atmosphere due to burning of fossil fuels leads to:
A. more rainfall everywhere
B. a decrease in temperature
C. thicker ozone layer
D. global warming (enhanced greenhouse effect) ✓ Correct
Solution: Extra CO₂ traps more heat, raising global temperatures (global warming).
Q5 — Carbon Cycle · medium · theory
Fossil fuels such as coal and petroleum were formed from:
A. sea salt
B. melted rocks
C. the remains of dead plants and animals over millions of years ✓ Correct
D. volcanic lava
Solution: Fossil fuels formed from buried remains of ancient organisms under heat and pressure over ages.
Q6 — Carbon Cycle · medium · theory
The gas released back into the air by both plants and animals during respiration is:
A. carbon dioxide ✓ Correct
B. nitrogen
C. hydrogen
D. oxygen
Solution: Respiration uses oxygen and releases carbon dioxide.
Q7 — Carbon Cycle · hard · theory
The decomposition of dead plants and animals by microbes returns carbon to the environment mainly as:
A. oxygen
B. pure carbon
C. nitrogen gas
D. carbon dioxide ✓ Correct
Solution: Decomposers break down organic matter, releasing CO₂ back into the cycle.
Q8 — Carbon Cycle · medium · theory
Green plants play a key role in the carbon cycle because they:
A. produce fossil fuels directly
B. absorb nitrogen from air
C. fix atmospheric carbon dioxide into food ✓ Correct
D. release carbon dioxide only
Solution: Plants convert atmospheric CO₂ into carbohydrates through photosynthesis, fixing carbon.
Q9 — Carbon Cycle · easy · theory
Which process removes carbon dioxide from the atmosphere?
A. Combustion
B. Respiration
C. Photosynthesis ✓ Correct
D. Decomposition
Solution: During photosynthesis green plants take in carbon dioxide and convert it into food, removing CO2 from the air. Respiration, combustion and decomposition all release CO2.
Q10 — Carbon Cycle · medium · theory
Which of the following processes ADD carbon dioxide to the atmosphere?
A. Photosynthesis only
B. Evaporation
C. Photosynthesis and condensation
D. Respiration and combustion ✓ Correct
Solution: Both respiration (in living things) and combustion (burning of fuels) release carbon dioxide into the air. Photosynthesis does the opposite by removing CO2, and condensation and evaporation involve water, not carbon.
Q11 — Carbon Cycle · medium · theory
In bright sunlight a healthy leafy plant carries out both photosynthesis and respiration at the same time. Overall, such a plant acts as a net:
A. producer of oxygen that releases no carbon dioxide at all
B. absorber of carbon dioxide, because photosynthesis outpaces respiration in strong light ✓ Correct
C. producer of carbon dioxide, because respiration outpaces photosynthesis
D. neither absorber nor producer of carbon dioxide
Solution: In bright light the rate of photosynthesis is much greater than the rate of respiration, so the plant takes in more carbon dioxide than it gives out and is a net absorber of CO2.
Q12 — Carbon Cycle · hard · theory
Carbon locked inside dead organisms slowly turned into fossil fuels such as coal and petroleum over millions of years. Burning these fuels today upsets the carbon cycle mainly because it:
A. releases stored carbon back into the air far faster than natural processes can remove it ✓ Correct
B. stops photosynthesis from happening anywhere on Earth
C. permanently destroys all the oxygen in the atmosphere
D. creates brand-new carbon atoms that did not exist before
Solution: Fossil fuels stored carbon slowly over millions of years, but burning them returns that carbon to the atmosphere as CO2 in a very short time. Nature cannot reabsorb it fast enough, so CO2 builds up and the natural balance is disturbed. Carbon atoms are recycled, not newly created.
Q13 — Carbon Cycle · hard · theory
Assertion (A): The total amount of carbon on Earth stays almost constant. Reason (R): Carbon is continuously recycled between the atmosphere, living organisms, oceans and rocks. Choose the correct option.
A. Both A and R are true, but R does not explain A
B. A is false but R is true
C. Both A and R are true, and R correctly explains A ✓ Correct
D. A is true but R is false
Solution: The total carbon on Earth stays nearly constant (A is true) precisely because carbon keeps moving in a cycle between air, living things, oceans and rocks without being created or destroyed (R is true and explains A).