Chapter Wise Ecology & Environment MCQ’s With Explanation

Today’s Topic:Ecosystem: Structure and Function

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Today’s Topic:Ecosystem: Structure and Function

Q1. Consider the following statements:

  1. Ecosystem receives nutrients from external sources and stores them for further use through biological processes.
  2. Significant amount of nitrogen is lost in gaseous form by the gentrification process in soil.

Which of the statements given above is/are correct?

a) Only 1                       b) Only 2                        c) Both 1 and 2                        d) Neither 1 nor 2

Ans:     C

Explanation:    Ecosystem receives nutrients from external sources and stores them for further use through biological processes. For example, nutrients in a dissolved state are gained from rainfall or in particulate from dust fall. Nutrients are moved out of an ecosystem and many become input to another ecosystem. For example, considerable loss of nutrients like calcium and magnesium occurs through runoff water, or through soil erosion. A significant amount of nitrogen may be lost in gaseous form by the denitrification process in soil.

Q2. Which of the following add nutrients in the Ecosystem?

  1. Rainfall                       2. Runoff water                           3. Dustfall                          d    4. Denitrification

a) Only 1 and 2                           b) Only 1 and 3                       c) Only 2 and 4                        d) Only 1, 2 and 4

Ans:     B

Explanation:    Ecosystem receives nutrients from external sources and stores them for further use through biological processes. For example, nutrients in a dissolved state are gained from rainfall (wet deposition) or in a particulate state from dust fall (dry deposition). Through runoff water and the denitrification process in soil nutrients are moved out of the ecosystem.

Q3. Which of the following moved nutrients out of the ecosystem?

  1. Symbiotic biological fixation of nitrogen.
  2. Harvesting agricultural crops.
  3. Soil erosion.

a) Only 1 and 2                        b) Only 1 and 3                       c) Only 3                     d) Only 2 and 3

Ans:     D

Explanation:    Nutrients are moved out of an ecosystem and many become input to another ecosystem. For example, considerable loss of nutrients like calcium and magnesium occurs through runoff water, or through soil erosion. Harvesting of agricultural crops, or transportation of logs from the forest, represent nutrient loss from these ecosystems. Symbiotic biological fixation of nitrogen in soil represents an input of nutrients in the ecosystem.

Q4. Consider the following statements:

  1. Weathering of soil parent materials moved nutrients out of the ecosystem.
  2. Severe disturbances in the ecosystem may make the nutrient cycles unbalanced and the ecosystem unstable.

Which of the statements given above is/are correct?

a) Only 1                           b) Only 2                           c) Both 1 and 2                        d) Neither 1 nor 2

Ans:     B

Explanation:    Weathering of soil parent materials, which releases available nutrients from their fixed state adds nutrients in the ecosystem.In an undisturbed ecosystem (i.e., an ecosystem in which human activities are absent or nearly so) the input of nutrients may approximately equal the output of nutrients, rendering the nutrient cycles more or less balanced. Severe disturbances in the ecosystem (e.g. tree felling, insect outbreak, fire, soil erosion, etc.) may make the nutrient cycles unbalanced and the ecosystem unstable.

Q5. Consider the following statements:

  1. In an undisturbed ecosystem, the input of nutrients is less than the output of nutrients.
  2. Removal of natural vegetation leads to the rapid loss of soil by erosion.

Which of the statements given above is/are correct?

a) Only 1                           b) Only 2                            c) Both 1 and 2                        d) Neither 1 nor 2

Ans:     B

Explanation:    In an undisturbed ecosystem j(i.e., an ecosystem in which human activities are absent or nearly so) the input of nutrients may approximately equal the output of nutrients, rendering the nutrient cycles more or less balanced. Severe disturbances in the ecosystem may make the nutrient cycles unbalanced and the ecosystem unstable. The soil can be lost rapidly by erosion after removal of natural vegetation.

Q6. Consider the following statements:

  1. The ultimate source of nitrogen to the ecosystem is molecular nitrogen in the atmosphere.
  2. Nitrogen fixation in the terrestrial ecosystem is called out by symbiotic microbes.

Which of the statements given above is/are correct?

a) Only 1                                 b) Only 2                     c) Both 1 and 2                        d) Neither 1 nor 2

Ans:     C

Explanation:    The ultimate source of nitrogen to the ecosystem is molecular nitrogen in the atmosphere, which cannot be directly metabolized by plants of animals. Native rocks do not contain nitrogen, so do not contribute nitrogen to plants or animals. Nitrogen fixation in the terrestrial ecosystem is predominantly carried out by symbiotic microbes, ecosystems is done by free-living microbes.

Q7. Consider the following statements:

  1. Native rocks predominantly contribute nitrogen to plants or animals.
  2. Nitrogen fixation in aquatic ecosystems is done by free-living microbes.

Which of the statements given above is/are correct?

a) Only 1                     b) Only 2                     c) Both 1 and 2                        d) Neither 1 nor 2

Ans:     B

Explanation:    The ultimate source of nitrogen to the ecosystem is molecular nitrogen in the atmosphere, which cannot be directly metabolized by plants or animals. Native rocks do not contain nitrogen, so do not contain nitrogen, so do not contribute nitrogen to plants or animals. Nitrogen fixation in terrestrial ecosystems is carried out by symbiotic microbes, whereas the bulk of fixation in aquatic ecosystems is done by free-living microbes.

Q8. Which of the following are nitrogen-fixing cyanobacteria?

  1. Anabaena                           2. Aulosira                           3. Nostoc
  2. a) Only 1 and 2                        b) Only 1 and 3                       c) Only 2 and 3                        d) 1, 2 and 3

Ans:     D

Explanation:    A variety of cyanobacteria are mainly responsible for nitrogen fixation in flooded rice fields in the tropics. Anabaena, Aulosira and Nostoc rank amongst the important nitrogen-fixation cyanobacteria.

Q9. Match the following:

List-I                            List-II

A. Clostridium                           1. Nitrogen-fixing actinomycete.

B. Nostoc                                  2. Free-living nitrogen-fixing bacteria.

C. Frankia                                 3. Nitrogen-fixing cyanobacteria.

Code:

A         B          C

a) 2          3          1

b) 2          1          3

c) 1           2          3

d) 1           3          2

Ans:     A Azotobacter and Clostridium are important free-living nitrogen-fixing bacteria residing in the soil.

Anabaena, Aulosira, and Nostoc are important nitrogen-fixing cyanobacteria. Frankia is a nitrogen-fixing actinomycete.

Q10. Which of the following statements is correct?

a) Nitrosomonas converts ammonia into nitrite.

b) Nitrobacter converts nitrite into nitrate.

c) Pseudomonas is a denitrifying bacterium thriving under poorly aerated and detritus-rich conditions.

d) All of the above.

Ans.     D

Explanation:    Ammonia is converted to nitrite by the bacterium Nitrosomonas, followed by the conversion of nitrite into nitrate by Nitrobacter. If the soil is waterlogged and anaerobic, another group of microbes, the denitrifiers, become active. Pseudomonas, the most common denitrifying bacterium, Thrives best under poorly-aerated and detritus-rich conditions.

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