UGC NTA NET/JRF Exam, Environmental Sciences, March-2023

Total Questions: 100

81. Correct order of soil horizons starting from top surface to bottom is:

(a) O
(b) A
(c) B
(d) E
(e) C
Choose the correct answer from the options given below:

Correct Answer: C. (a), (b), (d), (c), (e)
Solution:

The typical arrangement of soil horizons in a well-developed soil profile, starting from the top, is as follows:

O Horizon: This is the topmost layer comprised mainly of organic matter such as decomposing leaves, plants, and other materials. It's dark in color due to the organic content.

A Horizon: Known as the topsoil, this horizon is rich in minerals and organic matter. It's generally dark in color and is where most plant roots grow.

E Horizon: This is the eluviation or leaching layer where minerals and organic matter are leached to lower layers. It's often lighter in color.

B Horizon: Known as the subsoil, this horizon accumulates minerals and organic matter from above layers. It can be richer in clay and may have different colors based on its composition.

C Horizon: This is the parent material, which can be partially disintegrated rock or unweathered rock. The soil properties here are less influenced by the soil-forming processes.

This sequence reflects the natural processes of soil development, with organic matter accumulation at the top and mineral accumulation and leaching occurring as you move deeper.

82. Arrange the following stages of decomposition of landfill materials in their preferred sequence from initial to last.

(a) Acid phase
(b) Aerobic phase
(c) Unsteady methanogenesis
(d) Steady methanogenesis
Choose the correct answer from the options given below:

Correct Answer: B. (b), (a), (c), (d)
Solution:

Landfills go through several stages of decomposition:

• Aerobic Phase: Immediately after the waste is dumped, the available oxygen supports aerobic decomposition. This is a short phase characterized by a rapid rise in temperature.

• Acid Phase: As oxygen gets depleted, anaerobic decomposition starts. During this phase, acidogenic bacteria produce organic acids and gases like carbon dioxide and hydrogen. This phase is characterized by a drop in pH.

• Unsteady Methanogenesis: In this stage, the pH starts rising, and there's a shift towards methanogenic conditions. The production of methane begins but is not steady.

• Steady Methanogenesis: Here, methane production stabilizes, and the landfill starts emitting a steady stream of methane gas.

Understanding these stages is crucial for managing landfill emissions and harnessing methane for energy.

83. Following are the common procedural steps in ecological impact analysis process. Arrange them from the first to the last step.

(a) Focussing
(b) Impact Assessment
(c) Impact Evaluation
(d) Impact Mitigation
(e) Scoping
Choose the correct answer from the options given below: 

Correct Answer: A. (a), (e), (c), (b), (d)
Solution:

The steps for ecological impact analysis are:

Scoping: It identifies potential environmental impacts that might require a detailed analysis.

Focussing: This step prioritizes the identified impacts based on their significance.

Impact Assessment: At this stage, the magnitude and nature of each impact are assessed using various methodologies.

Impact Mitigation: This is the step where strategies to mitigate the negative impacts are designed and implemented.

Impact Evaluation: Finally, the success of the mitigation measures is evaluated. This systematic process ensures that all potential environmental impacts of a project are adequately addressed.

84. The three monthly moving average for rainfall in New Delhi for the monsoon periods, 2019, 2021 and 2022 was to be estimated. In calculation of the 95% confidence interval for rainfall, arrange the following sequence of steps in correct order.

(a) Choose confidence coefficient of 95%.
(b) Plot a time series graph on available data.
(c) Calculate three year moving average.
(d) Compute the standard error for estimate.
(e) Compute sample statistic 't'.
Choose the correct answer from the options given below:

Correct Answer: B. (b), (c), (d), (a), (e)
Solution:

When calculating the confidence interval for rainfall:

• Plot a time series graph on available data: This step helps in visualizing the data and spotting any trend or anomaly.

• Calculate three-year moving average: This smoothens the data and helps in identifying any underlying trend.

• Compute the standard error for estimate: Standard error measures the statistical accuracy of an estimate and is crucial for determining confidence intervals.

• Choose confidence coefficient of 95%: 95% is a common choice, meaning you are 95% confident that the interval contains the true mean.

• Compute sample statistic 't': The tstatistic, combined with the standard error. will determine the width of the confidence interval.

Using this sequence ensures an accurate and meaningful confidence interval.

85. Given below are two statements, one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): Natural Ecosystems are less vulnerable to catastrophic changes but adapted to weather changes.

Reason (R): Natural Ecosystems are mature from a succession point of view and rich in biotic diversity with less synchronisation of growth.
In light of the above statements, choose the correct answer from the options given below:

Correct Answer: A. Both (A) and (R) are true and (R) is the correct explanation of (A)
Solution:

Assertion (A) states that Natural Ecosystems are less vulnerable to drastic changes and are more adaptive to weather changes. This is correct because these ecosystems have evolved over a long time, creating a balance and resilience against various disturbances.

Reason (R) mentions that Natural Ecosystems are mature from a succession viewpoint and are biotically diverse with less synchronization of growth. This is also accurate.

A mature ecosystem, reached after successive stages of ecological succession, has a high level of biodiversity. Biodiversity provides an ecosystem with stability and resilience. When growth patterns are not synchronized, the ecosystem can better withstand shocks as not all species are affected at once.

Given both the Assertion and the Reason are true and the Reason correctly explains the Assertion, the answer is "Both (A) and (R) are true and (R) is the correct explanation of (A)".

86. Given below are two statements, one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): Humic acid is less soluble in acid solution compared to fulvic acid.
Reason (R): Molecular weight of humic acid is 100 to 1000 times higher compared to fulvic acid and also its oxygen content is lower.

In light of the above statements, choose the correct answer from the options given below:

Correct Answer: A. Both (A) and (R) are true and (R) is the correct explanation of (A)
Solution:

Humic and fulvic acids are principal components of humic substances, which are organic compounds found in the soil. Humic acid is less soluble in acidic solutions when compared to fulvic acid.

The reason for this behavior primarily relates to their molecular structures. Humic acid has a much larger molecular weight compared to fulvic acid, often ranging from 100 to 1000 times more.

This significant difference in molecular weight affects its solubility. Additionally, humic acid generally contains less oxygen content than fulvic acid.

The oxygen content in a molecule can influence its solubility in water due to the presence of functional groups that can participate in hydrogen bonding or other interactions. Therefore, both the molecular weight and the oxygen content are factors influencing the solubility of humic acid, especially in acidic solutions.

87. Given below are two statements:

Statement I: Soluble phosphorus is referred to as soluble reactive phosphorus and is a limiting nutrient in aquatic systems.
Statement II: Speed of phosphorus movement between biotic and abiotic components, makes it difficult to differentiate between Zooplankton-p, bacterial-p, algae-p or even inorganic-р.

In light of the above statements, choose the most appropriate answer from the options given below:

 

Correct Answer: A. Both Statement I and Statement II are correct
Solution:

Soluble reactive phosphorus (SRP) is the form of phosphorus that is available for plants and algae in aquatic systems. It's often considered a limiting nutrient because its availability can dictate the growth rate of aquatic plants and algae.

When in excess, SRP can lead to eutrophication, which is an overabundance of nutrients in water bodies leading to excessive plant and algal growth.

On the other hand, the rapid interchange of phosphorus between its biotic (living) and abiotic (non-living) forms in aquatic systems, including Zooplankton-p, bacterial-p, algaep, or inorganic-p, makes it challenging to differentiate between them.

This rapid cycling emphasizes the need for effective phosphorus management in aquatic ecosystems.

88. Given below are two statements:

Statement I: Alien species are a significant direct threat affecting 30% of all threatened birds, 15% of all threatened plants and 10% of all threatened mammals.

Statement II: At ecosystem level, alien species affect structural diversity, cause local extinction of native species, change fire and nutrient regimes and nutrient cycling patterns as well as produce allelochemical substances.

In light of the above statements, choose the most appropriate answer from the options given below:

 

Correct Answer: A. Both Statement I and Statement II are correct
Solution:

Alien species, also referred to as invasive species, can cause significant ecological disruption when introduced to new environments.

They can outcompete, prey on, or bring diseases to native species, sometimes leading to reductions or extinctions of native species.

The statistics mentioned, such as affecting 30% of threatened birds, is indicative of the severity of the impact of alien species. At an ecosystem level, the introduction of invasive species can bring about a multitude of changes.

These can include impacting structural diversity, causing local extinction of native species, altering fire frequencies and patterns, disrupting nutrient cycling, and even introducing new chemicals into the environment, such as allelochemicals, which can inhibit the growth of other plants.

89. Given below are two statements:

Statement I: With reference to solid waste, 'Rubbish' includes both combustible and non-combustible solid waste.
Statement II: Trash is part of rubbish but rubbish does not include garbage.

In light of the above statements, choose the most appropriate answer from the options given below:

Correct Answer: A. Both Statement I and Statement II are true
Solution:

In the context of solid waste management, rubbish can be broadly classified into two categories: combustible and non-combustible.

Combustible rubbish includes items like paper, wood, and certain types of textiles, while non-combustible rubbish consists of materials like glass and metals.

Trash is often used synonymously with rubbish and typically includes waste items that do not decompose quickly, such as paper, glass, and metals.

On the other hand, garbage refers to waste items that decompose quickly, especially food wastes. Therefore, while trash can be considered a subset of rubbish, rubbish doesn't include garbage.

90. Given below are two statements:

Statement I: Past data records help in forecasting weather conditions.

Statement II: The statistical methods of correlation help ONLY in forecasting weather conditions.

In light of the above statements, choose the most appropriate answer from the options given below:

Correct Answer: C. Statement I is true, but Statement II is false
Solution:

Past data records are indeed invaluable for forecasting weather conditions. Historical data, when analyzed, can provide patterns or trends which become the foundation for predicting future weather conditions.

For instance, understanding past monsoon patterns might help meteorologists predict upcoming monsoon intensities or timings. However, Statement II is not accurate.

While statistical methods, including correlation, are pivotal tools in forecasting weather conditions, they are not exclusive to this purpose. Statistical methods find applications in a plethora of fields, from economics to biology.

In meteorology, apart from statistical methods, numerical weather prediction models, which solve complex equations to predict future weather conditions, are also extensively used. Thus, while correlation and other statistical methods are important, they are not the only tools used for weather forecasting.