CBSE Class 12 Biology Ecosystem MCQs Set C

Question: In an ecosystem, bacteria are considered as–
a) Microconsumers
b) Macroconsumers
c) Primary consumers
d) Secondary consumers
Answer: a

Question: Which of these processes is incorrectly paired with its description?
a) Nitrification — oxidation of ammonium in the soil to nitrite and nitrate
b) Nitrogen fixation — reduction of atmospheric nitrogen into ammonia
c) Denitrification — removal of nitrogen from organic compounds
d) Ammonification — decomposition of organic compounds into ammonia
Answer: c

Question: Which of the following biogeochemical cycles is characterized by a form that is a major greenhouse gas?
a) Carbon cycle
b) Nitrogen cycle
c) Phosphorus cycle
d) Sulfur cycle
Answer: a

Question: Which of the following always has a “pyramidal” shape, i.e., decreasing values at higher trophic levels?
a) Pyramids of numbers only
b) Pyramids of biomass only
c) Pyramids of energy only
d) Both pyramids of biomass and pyramids of energy
Answer: c

Question: Black soil is due to the presence in it of–
a) Air
b) Minerals
c) More moisture
d) Organic matter
Answer: d

Question: Which of the following biogeochemical cycles has a gaseous phase released by volcanoes and fumaroles?
a) Carbon cycle
b) Nitrogen cycle
c) Phosphorus cycle
d) Sulfur cycle
Answer: d

Question: An inverted pyramid of ______ may occasionally be observed in ______ communities.
a) Energy, grassland
b) Energy, forest
c) Biomass, marine
d) Biomass, grassland
Answer: c

Question: Which of the following environments is richest in free oxygen?
a) Salt water
b) Atmosphere
c) Warm fresh water
d) Cold fresh water
Answer: b

Question: On average, how much of the energy assimilated at one trophic level is converted to production at the next (excluding the conversion of sunlight into chemical energy by plants)?
a) 5 – 20%
b) Less than 1%
c) 20 – 30%
d) 30 – 50%
Answer: a

Question: The large carnivores such as lion, tiger, which cannot be preyed upon further are called–
a) Predator
b) Organolithotroph
c) Top carnivore
d) Omnivore
Answer: c

Question: Which of the following is NOT a part of either gross or net primary production in plants?
a) Light reflected from the leaf
b) Energy fixed into glucose
c) Energy expended in moving material through membranes
d) None of the above
Answer: a

Question: A rat feeding on potato tuber is–
a) Carnivore
b) Decomposer
c) Producer
d) Primary consumer
Answer: d

Question: Stratification is more common in–
a) Deciduous forest
b) Tropical rain forest
c) Temperate forest
d) Tropical savannah
Answer: b

Question: Photosynthesis and respiration are central to which cycle?
a) The nitrogen cycle
b) The carbon cycle
c) The phosphorus cycle
d) The sulfur cycle
Answer: b

Question: Frog that feeds on an insect is–
a) Primary consumer
b) Secondary consumer
c) Tertiary consumer
d) Decomposer
Answer: b

Question: Productivity in terrestrial ecosystems is affected by–
a) Temperature
b) Light intensity
c) Availability of nutrients and water
d) All of the above
Answer: d

Question: Which of the following trophic levels would have the largest numbers of individuals?
a) Primary producers
b) Omnivores
c) Primary consumers
d) Opportunistic feeders
Answer: a

Question: The phosphorus cycle differs from the carbon cycle in that–
a) Phosphorus does not enter living organisms, whereas carbon does
b) The phosphorus cycle does not include a gaseous phase, whereas the carbon cycle does
c) The phosphorus cycle includes a solid phase, whereas the carbon cycle does not
d) The primary reservoir of the phosphorus cycle is the atmosphere, whereas for carbon it is rock
Answer: b

Question: Which of the following biogeochemical cycles lacks a gaseous phase?
a) Carbon cycle
b) Nitrogen cycle
c) Phosphorus cycle
d) Sulfur cycle
Answer: c

Question: In the past 150 years, there has been a major new input to the carbon cycle. What is it?
a) More humans releasing CO₂ through respiration
b) Increased animal farming releasing CO₂
c) Industrialization burning fossil fuels releasing CO₂
d) Changes in ocean currents releasing CO₂
Answer: c

Question: Nitrogen is often in short supply in terrestrial ecosystems because–
a) There is very little free nitrogen in the air
b) Atmospheric nitrogen is primarily in the stratosphere
c) Most organisms cannot use atmospheric nitrogen; it must be converted by bacteria and cyanobacteria
d) Nitrogen solubility in water is very low
Answer: c

Question: Carbon cycles relatively rapidly except when it is–
a) Dissolved in freshwater ecosystems
b) Released by respiration
c) Converted into sugars
d) Stored in petroleum, coal, or wood
Answer: d

Question: Which of the following changes would NOT result in an increase in net primary production?
a) Increased precipitation in an arid area
b) Increased soil fertility
c) Increased latitude (moving toward poles)
d) Moving down a mountain to warmer temperatures
Answer: c

Question: Chemosynthetic bacteria around deep-sea vents are examples of–
a) Producers
b) Decomposers
c) Chemical cycling
d) Secondary productivity
Answer: a

Question: A plant in the dark uses 0.02 ml of O₂ per minute. In sunlight it releases 0.14 ml of O₂ per minute. The gross primary production is–
a) 0.02 ml/min
b) 0.12 ml/min
c) 0.14 ml/min
d) 0.16 ml/min
Answer: d

Question: The open ocean and tropical rain forest are the two largest contributors to Earth’s net primary productivity because–
a) Both have high rates of net primary productivity
b) Both cover huge areas of Earth
c) Nutrients cycle fastest in these ecosystems
d) The ocean covers a huge area and the rainforest has high productivity
Answer: d

Question: What is true about photolithotrophs?
a) Obtain energy from radiation and hydrogen from organic compounds
b) Obtain energy from radiation and hydrogen from inorganic compounds
c) Obtain energy from organic compounds
d) Obtain energy from inorganic compounds
Answer: b

Question: The nature’s cleaners are–
a) Producers
b) Consumers
c) Decomposers and scavengers
d) Symbionts
Answer: c

Question: Primary productivity–
a) Equals the standing crop of an ecosystem
b) Is greatest in freshwater ecosystems
c) Is the rate of conversion of light to chemical energy in an ecosystem
d) Is inverted in some aquatic ecosystems
Answer: c

Question: In light, a plant fixes 0.12 ml of CO₂ per hour. In the dark, it releases 0.04 ml per hour. Net primary production is–
a) 0.04 ml/hour
b) 0.08 ml/hour
c) 0.12 ml/hour
d) 0.16 ml/hour
Answer: b

Question: Which biogeochemical cycle has a major reservoir in sedimentary rock?
a) Carbon cycle
b) Nitrogen cycle
c) Phosphorus or sulfur cycle
d) More than one cycle
Answer: d

Question: Most of Earth’s nitrogen is in–
a) The atmosphere
b) The oceans
c) Fresh water
d) Soil
Answer: a

Question: Green plants constitute–
a) 1st trophic level
b) 2nd trophic level
c) 3rd trophic level
d) 4th trophic level
Answer: a

Question: Which of the following is NOT true of a pyramid of productivity?
a) Only about 10% of the energy in one trophic level is passed into the next level
b) Because of energy loss, most food chains are limited to 3–5 steps
c) The pyramid of productivity of some aquatic ecosystems is inverted because of large zooplankton at the primary consumer level
d) Eating grain-fed beef is inefficient for obtaining energy from photosynthesis
Answer: c

Question: Deer in a forest ecosystem acts as–
a) Primary consumer
b) Secondary consumer
c) Decomposer
d) None
Answer: a

Question: Grasslands can support greater grazing rates by herbivores than forests because–
a) Grasslands receive more sunlight
b) The net production of grasslands is greater
c) Grasslands produce less woody plant tissue
d) More of the grassland production is above ground
Answer: c

Question: Which of the following could NOT be considered an ecosystem?
a) A small pond
b) All the fish in a coral reef
c) Earth
d) A pile of dung in a pasture
Answer: b

Question: Biogeochemical cycles are global for elements–
a) That are found in the atmosphere
b) That are found mainly in the soil
c) Such as carbon, nitrogen, and phosphorus
d) That are dissolved in water
Answer: c

Question: Which of the following organisms and trophic levels is mismatched?
a) Algae — producer
b) Phytoplankton — primary consumer
c) Fungi — detritivore
d) Bobcat — secondary consumer
Answer: b

Question: The gas that is removed from the atmosphere by plants and algae is–
a) Nitrogen
b) Oxygen
c) Carbon dioxide
d) Methane
Answer: c

Question: In an ecosystem–
a) Energy is recycled through the trophic structure
b) Energy is captured from sunlight by producers, passed to consumers, and lost to detritivores as heat
c) Chemicals are recycled between biotic and abiotic components, whereas energy flows one-way
d) Energy is lost as heat, and chemical elements leave the ecosystem through runoff
Answer: c

Question: In biogeochemical cycles, elements that cycle fastest–
a) Are found in organisms
b) Are scarce
c) Have a gaseous phase
d) Do not become fixed into sediment
Answer: c

Question: Density and distribution of the plant and animal species vary along–
a) Stratification
b) Secession
c) Gradation
d) Zonation
Answer: d

Question: Which of the following biogeochemical cycles is characterized by a major reservoir that is gaseous, and a major inorganic form usable only by a small group of bacteria and cyanobacteria?
a) Carbon cycle
b) Nitrogen cycle
c) Phosphorus cycle
d) Sulfur cycle
Answer: b

Question: What do primary producers have available to convert into biomass?
a) 10% of secondary productivity
b) Energy used for respiration
c) Gross primary productivity
d) Net primary productivity
Answer: d

Question: In succession, ______ is a crucial factor.
a) Time
b) Direction
c) Height
d) Space
Answer: a

Question: Water logging occurs in–
a) Sandy soil
b) Gravel soil
c) Loamy soil
d) Clay soil
Answer: d

Question: Which of the following statements regarding the hydrological cycle is false?
a) Most input to the oceans occurs via river runoff
b) More water evaporates from oceans than falls as rain over them
c) Less water evaporates from land than falls as rain over it
d) Water in sedimentary rock is constantly exchanged with the ocean
Answer: d

Question: Which of the following statements about food chains and energy flow through ecosystems is false?
a) A single organism can feed at several trophic levels
b) The lower the trophic level, the more energy available
c) Detritivores feed at all trophic levels except producers
d) Food webs include two or more food chains
Answer: c

Question: Most of the world’s carbon is found–
a) As carbon dioxide in the atmosphere
b) In living organisms
c) As bicarbonate and carbonate ions dissolved in the oceans
d) As carbonate minerals in sedimentary rock
Answer: c

Question: Secondary productivity–
a) Is measured by the standing crop
b) Is the rate of biomass production in consumers
c) Is greater than primary productivity
d) Is 10% less than primary productivity
Answer: b

Question: Which of the following is NOT an objective of integrated pest management?
a) To eliminate the use of chemicals in agriculture
b) To develop pest-resistant strains
c) To use natural biological control methods
d) To reduce agriculturally-caused pollution
Answer: a