Lichens are very useful pioneers in succession on a bare rock, especially because:
1. they are sensitive to environmental pollution
2. they have various modes of nutrition
3. they help in the formation of soil
4. they would prevent colonization by parasites

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The correct sequence of seral stages in primary hydrarch succession [pioneer to climax] would be:

1.  Phytoplankton, Submerged plant stage, Submerged free floating plant stage, Reed swamp stage, Marsh-meadow stage, Scrub stage, Forest
2.  Phytoplankton, Submerged free floating plant stage, Submerged plant stage, Reed swamp stage, Marsh-meadow stage, Scrub stage, Forest
3.  Phytoplankton, Submerged plant stage, Submerged free floating plant stage, Marsh-meadow stage, Reed swamp stage, Scrub stage, Forest
4.  Phytoplankton, Reed swamp stage, Marsh-meadow stage, Submerged plant stage, Submerged free floating plant stage, Scrub stage, Forest

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The amount of nutrients present in the soil, at any given time, is referred to as:
1. Standing state
2. Standing crop
3. Primary productivity
4. Secondary productivity

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The nutrients in an ecosystem are:

1.  continuously lost from an ecosystem
2.  needed as a continuous supply from the outside
3.  recycled time and again indefinitely
4.  continuously synthesized by physical forces
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The reservoir is located in the Earth’s crust for:
I. Gaseous type of nutrient cycle
II. Sedimentary nutrient cycle
1. Only I
2. Only II
3. Both I and II
4. Neither I nor II

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The function of a reservoir of nutrient cycle is to:
1. synthesize minerals
2. transfer minerals to other ecosystems
3. meet any deficit
4. destroy the unwanted minerals

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The dry weight of living organisms is mainly made up of:

1.  Water 2.  Calcium
3.  Nitrogen 4.  Carbon
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The maximum percent of total global carbon is found:
1. in fossil fuels
2. in atmosphere
3. dissolved in oceans
4. in biomass of microbes

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The amount of carbon dioxide in the atmosphere is regulated mainly by:
1. the atmosphere itself
2. human activities
3. decomposition by microbes
4. the oceanic reservoir

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Carbon dioxide is returned to the atmosphere by all the following except:
1. photosynthesis by the primary producers
2. respiratory activities of producers and consumers
3. decomposers
4. volcanic activity

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