Daily Static MCQs for UPSC & State PSC Exams - Environment & Ecology (28 October 2023)

Daily Static MCQs Quiz for UPSC, IAS, UPPSC/UPPCS, MPPSC. BPSC, RPSC & All State PSC Exams

Subject : Environment & Ecology

1. What would happen if phytoplankton of an ocean is completely destroyed for some reason?

1. The ocean as a carbon sink would be adversely affected.
2. The density of ocean water would drastically increase.
3. The food chains in the ocean would be adversely affected.

How many of the above statements is/are correct?

(a) Only one
(b) Only two
(c) All three
(d) None

Answer: (B)

Explanation: Phytoplanktons are food factories of the ocean, it fixes atmospheric carbon dioxide in large quantities (Carbon Sink) and produce food. So, if phytoplanktons are removed completely it leads to catastrophic failure of ocean ecosystem. It doesn’t influence the density of ocean water. Hence, statement 2 is not correct.

2. Consider the following:

1. Blue-green algae
2. Lightning
3. Uptake of soil nutrients by plants
4. Terrestrial Food chain

How many of the above play a role in the Nitrogen cycle on earth?

(a) Only one
(b) Only two
(c) Only three
(d) All four

Answer: (D)

Explanation: Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen. Lightning also fixes atmospheric nitrogen. Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins. The atmospheric nitrogen cannot be taken directly by plants and animals. Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds. When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant. Hence, all are correct.

3. Which one of the following is the best description of the term ‘standing crop’?

(a) It is the total mass of living material at a particular time in an ecosystem.
(b) It is the total amount of energy produced in a food chain.
(c) It is the amount of biomass of a forest.
(d) It is the number of primary producers in an ecosystem.

Answer: (A)

Explanation: Standing crop is defined as the total amount or number of living things or of one kind of living thing (such as an uncut farm crop, the fish in a pond, or organisms in an ecosystem) in a particular area at any given time. Hence, statement (a) is correct.

4.Which of the following shows the symbiotic relationship (partially or fully) between Rhizobium bacteria and the plants they colonise?

1. Rhizobium bacteria colonize plant cells within root nodules, where they convert nitrous oxide from the soil into ammonia and provide organic nitrogenous compounds to the plants.
2. The plant, in turn, provides the Rhizobium bacteria with organic compounds made using photosynthesis.

Select the correct answer using the code given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Answer: (C)

Explanation: Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. Rhizobium forms a symbiotic relationship with certain plants such as legumes, fixing nitrogen from the air into ammonia, which acts as a natural fertilizer for the plants. The plant, in turn, provides the bacteria with organic compounds made by photosynthesis. This mutually beneficial relationship is true of all of the rhizobia, of which the genus Rhizobium is a typical example. Hence, both statements are correct.

5. Tropics harbour more species than temperate or polar areas. What could be the possible reasons that tropics account for greater biological diversity than temperate regions?

1. There is more solar energy available in the tropics.
2. Unlike temperate regions which were subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years.
3. Tropical environments are less seasonal, relatively more constant and predictable unlike temperate regions.

Select the correct answer using the code given below:

(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3

Answer: (D)

Explanation: What is so special about tropics that might account for their greater biological diversity? Ecologists and evolutionary biologists have proposed various hypotheses; some important ones are:
(a) Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification,
(b) Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity and
(c) There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.
Hence, all statements are correct.