Chapter Wise Ecology & Environment MCQ’s With Explanation

Today’s Topic: Ecosystem: Structure and Function-2

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Today’s Topic: Ecosystem: Structure and Function-2

Q1. Consider the following statements:

  1. Within the same climatic conditions, the decomposition rate of detritus is slower if the detritus is rich in substances like lignin and chitin.
  2. The nitrogen-rich detritus having low amounts of lignin decomposes rapidly.

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 accumulation of certain substances in the detritus either promotes or retards decomposition rate. The chemical quality of detritus is determined by the relative proportions of water-soluble substances, polyphenols, lignin and nitrogen. Within the same climatic conditions, the decomposition rate is slower if the detritus is rich in substances like lignin and chitin. The nitrogen-rich detritus, having low amounts of lignin, decomposes relatively rapidly.

Q2. Which of the following determined the chemical quality of detritus?

  1. Polyphenols                       2. Lignin                       3. Nitrogen

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

Ans:     D

Explanation:    The accumulation of certain substances in the detritus either promotes or retards decomposition rate. The chemical quality of detritus is determined by the relative proportion of water-soluble substances (including sugars), polyphenols, lignin and nitrogen. Within the same climatic conditions, the decomposition rate is slower if the detritus is rich in substances like lignin and chitin. The nitrogen-rich detritus, having low amounts of lignin, decomposes relatively rapidly.

Q3. Consider the following statements:

  1. Energy flow is a key function in the ecosystem.
  2. In an ecosystem, the transfer of food energy from one organism to another leads to degradation and loss of a major fraction of food energy.

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:    Energy flow is the key function in the ecosystem. The storage and expenditure of energy is the ecosystem is based on two basic laws of thermodynamics. In an ecosystem, the transfer of food energy from one organism to another leads to degradation and loss of a major fraction of food energy as heat due to metabolic activities, with only a small fraction being stored in living tissues or biomass.

Q4. Consider the following statements:

  1. Only the visible light or photosynthetically active radiation (PAR) which carries about 50 percent of the energy of total incident solar radiation is available to producers for absorption.
  2. The calorific value is determined by burning known weight of dry biomass in a bomb calorimeter in the presence of oxygen and measuring heat evolved.

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:    It is useful to examine the relationship between incident radiant energy and the energy captured by the producers in the food they manufacture. Only the visible light or the photosynthetically active radiation (PAR) which carries about 50 percent of the energy of total incident solar radiations is available to producers for absorption. By multiplying the estimated productivity with the calorific value of biomass, the energy captured can be determined.

Q5. Consider the following statements:

  1. All trophic levels in an ecosystem are connected by transfer of food or energy.
  2. Food chain is the transfer of energy from one trophic level to the next trophic level.

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:    All trophic levels is an ecosystem are connected by transfer of food or energy. The transfer of energy from one trophic level (e.g. producers) to the next trophic level (e.g. consumers) is called the food chain. Two types of food chains can be distinguished in all ecosystems, grazing food chain and detritus food chain.

Q6. Which of following are biotic constituents of the grazing food chain?

1.Cattle grazing in grasslands                       . 2. Deer browsing in the forest.                       3. Insects feeding on crops and trees.

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

Ans.     D

Explanation:    The transfer of energy from one trophic level to the next trophic level is called the food chain. Two types of food chains can be distinguished in all ecosystems, grazing food chain and detritus food chain. Grazing food chain extends from producers through herbivores to carnivores. Cattle grazing in grasslands, deer browsing in a forest, and insects feeding on crops and trees are most common biotic constituents of the grazing food chain.

Q7. Consider the following statements:

  1. Detritus food chain begins with dead organic matter and passes through detritus feeding organism in the soil to organisms feeding on detritus feeders.
  2. A specific herbivore of one food chain may serve as the food of carnivores of several other food chains.

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 transfer of energy from one trophic level to the next trophic level is called the food chain. Two types of food chains can be distinguished in all ecosystems, grazing food chain and detritus food chain. Detritus food chain begins with dead organic matter and passes through detritus-feeding organisms in the soil to organisms feeding on detritus-feeders. Different food chains are often interconnected, e.g., a specific herbivore of one food chain may serve as a food of carnivore of several other food chains. Such an interconnected matrix of the food chain is called food web.

Q8. Which of the following statements is/are correct?

  1. Energy flows from producers through herbivores to carnivores and transferred in the reverse direction.
  2. The amount of energy flow increases with successive trophic levels:

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

Ans:     D

Explanation:    Two aspects with respect to energy flow in an ecosystem need careful consideration. First, the energy flows one way, i.e., from producers through herbivores to carnivores; it cannot be transferred in the reverse direction. Second, the amount of energy flow decreases (not increases) with successive trophic levels.

Q9. Which of the following statements is /are correct?

  1. A small fraction of solar energy is captured by producers.
  2. Part of the energy captured in gross production of producers is used for maintenance of their respiration and for providing food to herbivores.

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

Ans:     C

Explanation:    Producers capture only a small fraction of solar energy (1-5 percent of total solar radiation), and the bulk of the unutilized energy is dissipated mostly as heat. Part of the energy captured in gross production of producers is used for maintenance of their respiration and for providing food to herbivores (herbivory). The unutilized net primary production is ultimately converted to detritus, which serves as the energy source to decomposers.

Q10. Consider the following statements:

  1. The respiration cost decreases along successive higher trophic levels.
  2. The length of food chains in an ecosystem is limited to 3-4 trophic levels.

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 respiration cost increases sharply along successive higher trophic levels. On an average, respiration of producer consumes about 20 percent of its gross productivity. Herbivores consume about 30 percent of the assimilated energy in respiration. The proportion of assimilated energy consumed in respiration rises to about 60 percent in carnivores. Because of their tremendous loss of energy at successively higher trophic levels. The residual energy is decreased to such an extent that no further trophic level can be supported. Therefore, the length of food chains in an ecosystem is generally limited to 3-4 trophic levels.

 

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