This set of Class 12 Biology Chapter 14 Multiple Choice Questions & Answers (MCQs) focuses on “Ecosystem – Carbon Cycle”.
1. What percent of dry weight does carbon constitute in the living organisms?
a) 55 percent
b) 49 percent
c) 20 percent
d) 90 percent
View Answer
Explanation: The carbon constitutes approximately 49 percent of the total dry weight of living things. It is the second most abundant thing found in nature next to the water. It is the fourth most abundant element of the universe.
2. Which is the most abundant constituent found in living organisms?
a) Water
b) Oxygen
c) Ammonia
d) Hydrogen bicarbonate
View Answer
Explanation: The most abundant compound found in living organisms is water. It is the most important compound for the survival of living organisms. A human body consists of 60% water.
3. Out of the total quantity of global carbon, what percent of carbon is found dissolved in oceans?
a) 50 %
b) 71 %
c) 90 %
d) 25 %
View Answer
Explanation: Almost 71 percent of carbon is found dissolved in oceans out of the total quantity of global carbon. Out of this 71 percent, almost 90 percent is found in oceans. The oceans consist of 38,000- 40,000 gigatons (Gt) of carbon.
4. Which reservoir regulates the amount of carbon dioxide in the atmosphere?
a) Gaseous reservoir
b) Sedimentary reservoir
c) Atmospheric reservoir
d) Oceanic reservoir
View Answer
Explanation: Almost 71 percent of carbon is found dissolved in oceans out of the total quantity of global carbon. Out of this 71 percent, almost 90 percent is found in oceans. The regulation of carbon dioxide in the atmosphere is done by this oceanic reservoir
5. What percent of total global carbon does the atmosphere contain?
a) 5 %
b) 50 %
c) 1%
d) 20 %
View Answer
Explanation: Almost 49 percent of the total dry weight of living things is constituted by carbon. The atmosphere consists of only 1 % of the total global carbon. It is the fourth most abundant element of the universe.
6. Whose reservoir does fossil fuel represent?
a) Oxygen
b) Carbon
c) Helium
d) Argon
View Answer
Explanation: The fossil fuel represents the reservoir of carbon. Almost 21.3 gigatons of carbon dioxide are released per year due to the burning of fossil fuels.
7. From which stages does the carbon cycling occur?
a) Dead organisms → Living organisms → Oceans
b) Atmosphere → Living organisms → Dead organisms
c) Oceans → Atmosphere → Dead organisms
d) Atmosphere → Oceans → Living organisms → Dead organisms
View Answer
Explanation: The carbon from the atmosphere in the form of carbon dioxide gets into oceans. Through this, the carbon enters into living organisms and then to dead organisms. This carbon from dead organisms enters the Earth’s crust.
8. What amount of carbon is fixed in the biosphere through photosynthesis annually?
a) 1013 kg
b) 20 × 1020 kg
c) 4 × 1013 kg
d) 80 × 1035 kg
View Answer
Explanation: Photosynthesis is a process in which producers (green plants) in the presence of CO2, water, sunlight, and chlorophyll yield energy and oxygen is released in the form of gas. The amount of carbon fixed in the biosphere through photosynthesis annually is approximately 4 × 1013 kg.
9. By which process does the carbon return to the atmosphere as CO2?
a) Decayed organisms
b) Calcareous sediments
c) Photosynthesis
d) Respiration
View Answer
Explanation: The respiration is the process in which the organisms exchange gases with the environment. In this, the organisms take in the atmospheric oxygen for various cellular activities and release carbon dioxide. Thus the carbon returns to the atmosphere as CO2 with the help of respiration.
10. Which of the following organism contributes to the CO2 pool by the processing of waste materials and dead organic matter?
a) Carnivores
b) Herbivores
c) Decomposers
d) Producers
View Answer
Explanation: The organisms that are responsible for the break down complex organic matter (dead or decaying organisms) into inorganic substances are called decomposers (detritivores). They process the dead matter present on land and oceans. The decomposers or detritivores may include invertebrates, fungus or bacteria.
11. Which human activities have significantly influenced the carbon cycle?
a) Afforestation
b) Deforestation only
c) Burning of fossil fuel only
d) Both deforestation and burning of fossil fuel
View Answer
Explanation: The human activities like excessive deforestation and burning of fossil fuel has greatly influenced the carbon cycle. These activities have increased the rate of release of carbon dioxide into the atmosphere.
12. In which form does the carbon dioxide precipitate after dissolving in water?
a) Calcium oxide
b) Carbon mono-oxide
c) Calcium carbonate
d) Calcium phosphate
View Answer
Explanation: The CO2 in gaseous form is quite soluble in water. When carbon dioxide dissolves in water, it precipitates and leads to the formation of calcium carbonate.
13. What product does the plants from by photosynthesis using carbon dioxide?
a) Lipids
b) Carbohydrates
c) Proteins
d) Salts
View Answer
Explanation: The plants form carbohydrates using carbon dioxide through photosynthesis. Photosynthesis is a process in which producers (green plants) in the presence of CO2, water, sunlight, and chlorophyll yield energy and oxygen is released in the form of gas.
14. Which one of the following plants use as a source for carbon dioxide?
a) Carbonate rocks
b) Calcium rocks
c) Fossils
d) Atmospheric CO2
View Answer
Explanation: The plants use atmospheric CO2 as a source of carbon dioxide for food production. They produce food using photosynthesis. Photosynthesis is a process in which producers (green plants) in the presence of CO2, water, sunlight, and chlorophyll yield energy and oxygen is released in the form of gas.
15. For releasing CO2 in the atmosphere, how are fossil fuels exploited?
a) Mined and burned
b) Fragmented and leached
c) Leached and burned
d) Mined and fragmented
View Answer
Explanation: A fuel formed by anaerobic decomposition of buried dead organisms, containing energy is known as a fossil fuel. These are fossil fuels Mined and burned contributing to the atmospheric CO2.
Sanfoundry Global Education & Learning Series – Biology – Class 12.
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