CBSE Questions for Class 12 Medical Biology Ecosystem Quiz 14 - MCQExams.com

Biogeochemical cycling means cycling of 
  • Energy in an ecosystem
  • Gases between plants and the atmosphere
  • Nutrients in an ecosystem
  • Water
Each successive trophic level has
  • Less total energy
  • More total energy
  • Increased total energy
  • Non-estimated energy contents
An ecologist estimates that there is an average of 27.3 kg/$$m^2$$ of plant growth within a British Columbia forest. What is the ecologist measuring?
  • Biomass
  • Food web
  • Trophic level
  • Food chain
The path through which nutrients are passed from one acceptor to the other is called _______.
  • Biogeochemical cycle
  • Biochemical cycle
  • Chemical cycle
  • None of the above
The carbon cycle is the movement of carbon on Earth by the processes of --- and ---- .
  • Plants and animals
  • Respiration and photosynthesis
  • Breathing in and breathing out
  • Oxygen and carbon dioxide
The excreta rich in phosphorus would be called as _________.
  • Organic excreta
  • Inorganic excreta
  • Guano deposits
  • Both B and C
Desert can be converted into green land by planting
  • Oxylophytes
  • Psammophytes
  • Halophytes
  • Green trees
Identify the wrong pair of statements.
I) During plant succession, some species colonise an area and populations become more numerous, whereas populations of other species decline and even disappear.
II) Both hydrarch and xerarch successions lead to mesic conditions.
III) Secondary succession is a slow process when compared to primary succession.
IV) In the successive seral stages, there is no change in the diversity of species of organisms.
  • II, III
  • I, II
  • III, IV
  • I, III
A keystone species is removed from an ecosystem. This will not cause
  • Decrease in species diversity
  • Increase in other community populations
  • Increase in the types of ecological interactions
  • Decrease in the carrying capacity for most of the community
  • Increase in the rate of growth of one or more populations

A rocky community near a pond has no vegetation or animal life. After a period of approximately 50 years, the community boasts a wide variety of flora and fauna, including trees, animals and insects. The process which has taken place can best be described as
  • Progression
  • Succession
  • Evolution
  • Habitation
  • colonization
A pollution free stream within a few miles downstream of a point at which a small amount of sewage is being dumped into it. This is the result of
  • Succession
  • Eutrophication
  • Evaporation
  • Photosynthesis
  • Decomposition
Plants growing in and around a pond eventually filling in the pond and converting it to a terrestrial habitat is an example of
  • Succession
  • Dispersion
  • Fertilization
  • Speciation
  • Mutation
Lichen is the pioneer vegetation on which succession?
  • Hydrosere
  • Lithosere
  • Psammosere
  • Xerosere
For a stable lake ecosystem, the net primary production (NPP) is equal to the
  • Phytoplankton present in the photic zone
  • Phytoplankton consumed by heterotrophs
  • Dissolved nutrients used by phytoplankton
  • Dissolved oxygen used by phytoplankton
  • Dissolved oxygen used by all consumers
The data given in the table shows species richness of mosses, shrubs and trees calculated for one hectare $$(10,000 m^2)$$ of land every 50 years for 200 years based on a long running ecological study.
YearMossesShrubsTrees
18001620
18502174
19001053
195013126
2000172814
The ecological process occurring according to the data is
  • Evolution
  • Succession
  • Destabilization
  • Primary growth
  • Artificial selection
Find the incorrect match.
IIIIII
i. CrabSacculinaInteraction $$++$$
ii. Human beingMosquitoInteraction $$- +$$
iii. Sea anemoneHermit crabInteraction $$++$$
  • i. only
  • ii. and iii.
  • iii. and i.
  • ii. only
Choose the correct statement regarding ecological succession.
  • It is a natural progression of plant types that cannot be reversed.
  • It always occurs over a short period time.
  • The rate can be changed by factors such as fire, clear cutting, and lava flows.
  • It only takes place on freshly cleared or new land such as islands.
  • The rate is very slow and constant.
The study of a pond revealed the presence of skimmers and minnows in it. Which of the following process is responsible for the conversion of pond into a swampy land after 15 years showing the prevalence of frogs and snakes?
  • Predation
  • Succession
  • Speciation
  • Natural disaster
  • Global warming
Which one of the following is true for a climax community?
  • The nitrogen cycle ceases to be important for primary producers.
  • There are no changes in seasonal population sizes in the community.
  • Predator-prey relationships between trophic levels in the food web remain constant from one generation to the next.
  • There is no loss of energy from one trophic level to the next.
  • There is only one species of primary producer.
The data from the study to determine metabolic rate shows the energy being released by respiration is less than the energy captured during photosynthesis. Which of the following condition takes place in terrestrial plant community?
  • Major plant species are dying.
  • Biomass of the community is increasing.
  • Biomass of the community is decreasing.
  • The rate of plant reproduction is increasing.
  • A secondary succession of plants is growing in an established community.
Which of the following is true about climax community?
  • Consists of only one species of life
  • Is populated mainly by so-called pioneer organisms
  • Is stable within a given climate
  • Is independent of the environment
  • Consists of decaying organic matter
In a food chain, if the grasses produce 1000 kcal of energy, how many kcal are theoretically available to the frogs?
  • 1000
  • 100
  • 10
  • 1
  • 0.5
The data given in the table shows species richness of mosses, shrubs and trees calculated for one hectare $$(10,000 m^2)$$ of land every 50 years for 200 years based on a long running ecological study.
According to the data natural disaster occurred during which time period?
YearMossesShrubsTrees
18001620
18502174
19001053
195013126
2000172814
  • 1750-1800
  • 1800-1850
  • 1850-1900
  • 1900-1950
  • 1950-2000
The data given in the table shows species richness of mosses, shrubs and trees calculated for one hectare $$(10,000 m^2)$$ of land every 50 years for 200 years based on a long running ecological study.
YEARMOSSESSHRUBSTREES
18001620
18502174
19001053
195013126
2000172814
Based on the data, has the community reached a climax?
  • Yes, all densities continue to change.
  • No, there is continual change in species' densities.
  • Yes, moss species are constantly present throughout time.
  • No, moss species are always present in high densities.
  • Yes, in 1800 there are relatively many more tree species found.
Which of the following will be the final succession climax stage of a freshwater lake?
  • Marsh
  • Grassland
  • Bog
  • Estuary
  • Deciduous forest
The following data shows the results based on the study of a meadow.
Organisms                                 Number
Hawk                                          $$3$$
Various birds                              $$50$$   
Spiders                                       $$500$$
Insects                                       $$3000$$
Shrubs and other plants        $$> 5000$$
The correct pyramid of biomass is
  • None of the above
A stable lake ecosystem shows net primary production which is equal to the 
  • Phytoplankton present in the photic zone
  • Phytoplankton consumed by heterotrophs
  • Dissolved nutrients used by phytoplankton
  • Dissolved oxygen used by phytoplankton
  • Dissolved oxygen used by all consumers
The given diagram shows the pyramid of energy at each trophic level. Choose the correct statement for the energy flow in the given pyramid. 
500171_6939d84fc87b4c83a1a38c8ae5cf4465.png
  • Energy is passed up the pyramid with the least energy at the top.
  • Energy is passed up the pyramid with the most energy at the top.
  • Energy is passed down the pyramid with the most energy at the top.
  • Energy is passed down the pyramid with the most energy at the bottom.
  • Energy is a constant in the pyramid.
Which of the following limits the number of trophic levels in an ecosystem?
  • The number of species
  • The population size
  • The loss of potential energy
  • The number of individuals
  • The hours of sunshine
Read the passage and answer the following question.

A population study of plants was done in an abandoned field. Each year for $$3$$ years the vegetation was sampled. The chart indicates the results of the body.

YearNumber of Plants per Acre
SandspurRagweedTimothy GrassGoldenrodWire Grass
$$1$$$$3,800$$$$4,900$$$$600$$$$0$$$$412$$
$$2$$$$1,500$$$$2,209$$$$1,185$$$$75$$$$796$$
$$3$$$$752$$$$180$$$$2,234$$$$790$$$$1,643$$$

Which of the following are initially most successful in succession?
  • Sandspur and ragweed
  • Sandspur and timothy grass
  • Ragweed and timothy grass
  • Ragweed and wire grass
  • Sandspur and goldenrod
According to the theories of succession, what will be the result?
491603_91e09687e2ae4afba6c4f21bc14549f2.png
  • The lake will get deeper and the trees more numerous
  • The lake will get shallower and the trees will be replaced by grass
  • The lake will dry up
  • The trees will become coniferous types
  • There is no fixed order to the replacement of species
Which one of the following areas is an example of secondary succession if the succession takes place in/on?
  • Abandoned farm land
  • Newly cooled lava
  • Newly created pond
  • Bare rock
Which biological process is responsible for the appearance of these plants in a burned area?
  • Evolution by natural selection
  • Succession
  • Mutation
  • Eutrophication
  • Recombination
Highest value in g C m$$^{−2}$$ yr$$^{−1}$$ of a grassland ecosystem  would be
  • Gross primary production
  • Net primary production
  • Secondary production
  • Tertiary production
In plant succession, the net productivity of climax community
  • Continuous to increase
  • Becomes stable
  • Becomes halved
  • Reduced to $$10\%$$
  • Becomes zero
Number of individuals decreases from producer level to consumer level in
  • Pyramid of numbers
  • Pyramid of energy
  • Pyramid of biomass
  • All of the above
The animal species controlling the ecosystem functioning is known as
  • Edge species
  • Pioneer species
  • Keystone species
  • Umbrella species

Pheretima and its close relatives obtain nourishment from
  • Decaying fallen leaves and soil organic matter
  • Soil insects
  • Small pieces of fresh fallen leaves of Maize and others
  • Sugarcane roots
Source of maximum sulphur is/reservoir of sulphur is
  • Ocean
  • Lakes
  • Land
  • Rocks
Community dynamics is related to
  • Population growth in an ecosystem
  • Recycling of nutrients in an ecosystem
  • Flow of energy in an ecosystem
  • Ecological succession
Which of the following is a correct trend of succession in hydroseric succession?
  • Rooted submerged $$\rightarrow$$ Phytoplankton $$\rightarrow$$ Reed swamp $$\rightarrow$$ Sedge meadow
  • Phytoplankton $$\rightarrow$$ Reed swamp $$\rightarrow$$ Rooted submerged $$\rightarrow$$ Sedge meadow
  • Phytoplankton $$\rightarrow$$ Sedge medow $$\rightarrow$$ Reed swamp $$\rightarrow$$ Root submerged
  • Phytoplankton $$\rightarrow$$ Rooted submerged $$\rightarrow$$ Reed swamp $$\rightarrow$$ Sedge meadow
Which of the following represents the graphical portrayal of biomass present in a unit of the territory of different trophic levels.
  • Pyramid of biomass
  • Pyramid of number
  • Pyramid of energy
  • All of the above
Which of the following is the correct trend of succession in hydroseric succession?
  • Phytoplankton $$\rightarrow$$ Rooted submerged $$\rightarrow$$ Reed swamp $$\rightarrow$$ Sedge meadow.
  • Phytoplankton $$\rightarrow$$ Reed swamp $$\rightarrow$$ Rooted submerged $$\rightarrow$$ Sedge meadow.
  • Phytoplankton $$\rightarrow$$ Sedge medow $$\rightarrow$$ Reed swamp $$\rightarrow$$ Sedge meadow.
  • Rooted submerged $$\rightarrow$$ Phytoplankton $$\rightarrow$$ Reed swamp $$\rightarrow$$ Sedge meadow.
Identify the incorrect statement for the following.
  • Pyramids of number and biomass may be either upright or inverted
  • Pyramid of biomass in sea is generally inverted as biomass of fish far exceeds that of phytoplankton
  • Food chains are generally short with few trophic levels as only 10% of the energy is transferred to higher trophic level from lower one
  • Pyramid of energy is mostly upright but sometimes it may be inverted
Gross primary productivity of an ecosystem is 170 tons of organic matted and amount used in respiration is 50 tons. Calculate the net primary productivity of the ecosystem.
  • 120 tons
  • 100 tons
  • 70 tons
  • 12 tons
  • 17 tons
Consider the components of a food chain producers $$ \rightarrow\ $$ herbivores $$ \rightarrow\ $$ carnivores $$ \rightarrow\ $$ top carnivores. Eventually what happens to all the energy passed from one element to the next?
  • It recycles back to the producers
  • It results in a much larger decomposer population
  • It gets dissipated into the environment.
  • It is recaptured by another food chain
Which of the following statements about productivity is true?
  • Primary productivity of all ecosystems is a constant
  • Annual net primary productivity of the whole of the biosphere is 17 billion tons (dry weight) of organic matter
  • Net primary productivity is the amount of biomass available for consumption by carnivores
  • Secondary productivity is defined as the rate of formation of new organic matter by decomposers
  • Primary productivity depends upon the plant species inhabiting a particular area
All of the following statements are true for ecological pyramid except
  • Energy available at a lower trophic level is always more than that at a higher level
  • The pyramid of numbers in a parasitic food chain is inverted
  • Pyramid of biomass in sea is upright normally
  • In a tree ecosystem, squirrels are primary consumers and ticks are secondary consumers
Quantities of mineral nutrients in soils of tropical rainforests are relatively low because
  • standing crop is small
  • microorganisms that recycle chemicals are not very abundant in tropical soils
  • decomposition of organic refuse and reassimilation of chemicals by primary productivity occur rapidly
  • nutrient cycles occur at a relatively slow rate in tropical soils
Read the following statements regarding ecological pyramids and choose the correct answer.
(a) Relationship between organisms at different trophic levels is expressed in terms of number, biomass and energy.
(b) Any calculations of energy content, biomass or number has to include one group of organisms at that trophic level.
(c) In most ecosystems, all the pyramids of number, biomass and energy are upright.
(d) The pyramid of biomass in sea is generally inverted.
(e) Pyramid of energy is always inverted and can never be upright.
  • a, c and d are wrong
  • a is wrong
  • b and e are wrong
  • a and e are wrong
  • d and e are wrong
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