UGC NTA NET/JRF Exam, Environmental Sciences, January-2025

Total Questions: 100

91. (Qs. No. 91 to 95): Read the following passage and answer the questions given below:

The first phototrophs were anoxygenic and likely used H₂S as electron donor for CO₂ fixation, generating elemental sulphur (S⁰) as a waste product. How could the first phototrophs have evolved at a time when life existed mostly near hydrothermal systems?

A clue came from the recent discovery of anoxygenic phototrophs living at hydrothermal vents in the complete darkness of the deep ocean. These phototrophs actually carry out photosynthesis using infrared radiation generated by the heat of hydrothermal vents.

Likewise, the first photosynthetic organisms likely lived in the dark, at hydrothermal vents where H₂S and infrared radiation were abundant. Diversification of anoxygenic phototrophs led to species that were able to use a range of electron donors including Fe²⁺, which was abundant throughout Earth’s early oceans.

The ability to use Fe²⁺ as an electron donor likely allowed early phototrophs to escape from hydrothermal systems and colonize shallow regions of Earth’s early oceans where light was abundant but where overlying water still provided protection from UV radiation.

The ability to use solar radiation as an energy source allowed phototrophs to diversify extensively. By 2.5-3.3 bya, the cyanobacterial lineage evolved a photosystem capable of oxygenic photosynthesis in which H₂O supplanted H₂S as the reductant for CO₂, thereby generating O₂ as a waste product.

About a billion years later, eukaryotic oxygen phototrophs appeared and can be seen in the microfossil record.

Which of the following chemical species played a crucial role in the early phototrophs' colonization in the shallow waters of Earth's early oceans?

Correct Answer: 3. Fe²⁺
Solution:

"Diversification of anoxygenic phototrophs led to species that were able to use a range of electron donors including Fe²⁺, which was abundant throughout Earth's early oceans.

The ability to use Fe²⁺ as an electron donor likely allowed early phototrophs to escape from hydrothermal systems and colonize shallow regions..."

This clearly indicates that Fe²⁺ was the key electron donor that enabled colonization of shallow waters by early phototrophs.

92. The first photosynthetic organisms likely released:

Correct Answer: 1. S°
Solution:

"The first phototrophs were anoxygenic and likely used H₂S as electron donor for CO₂ fixation, generating elemental sulphur (S°) as a waste product." Hence, the correct answer is S° not O₂ or CO₂.

93. Identify the most probable time when the ability to use water for photosynthesis developed in the organisms.

Correct Answer: 2. 3 billion years ago
Solution:

"Вy 2.5-3.3 billion years ago, the cyanobacterial lineage evolved a photosystem capable of oxygenic photosynthesis in which H₂O supplanted H₂S..."

This implies the ability to use water for photosynthesis evolved around 3 billion years ago.

94. The early photosynthetic organisms likely existed in:

Correct Answer: 4. Deep in the oceans at specific places in ocean bottoms
Solution:

"The first photosynthetic organisms likely lived in the dark, at hydrothermal vents where H,S and infrared radiation were abundant." Such vents exist deep in the ocean on the seafloor, confirming the correct habitat.

95. The first phototrophs used which of the following types of radiations for photosynthesis?

Correct Answer: 3. Infrared
Solution:

"These phototrophs actually carry out photosynthesis using infrared radiation generated by the heat of hydrothermal vents. "Likewise, the first photosynthetic organisms likely lived... where infrared radiation was abundant.

" Thus, the first phototrophs used infrared radiation for photosynthesis.

96. (Qs. No. 96 to 100): Read the following passage and answer the questions given below:

Waves expend their energy when they reach the coastline. But, the amount is surprisingly large. For example, the energy expended on a 400 km length of open coastline by waves with a height of about 1 m over a given period of time is approximately equivalent to the energy produced by one average-sized nuclear power plant over the same time period.

Wave energy is approximately proportional to the square of the wave height. Thus, if wave height increases to 5 m, which is typical for large storms, then the energy expended, or wave power, increases 25 times over that of waves with a height of 1 m.

When waves enter the coastal zone and shallow water, they impinge on the bottom and become steeper. Wave steepness is the ratio of wave height to wave length. Waves are unstable when the wave height is greater than about 10 per cent (0.1) of the wave length. As waves move into shallow water, the wave period remains constant, but wave length and velocity decrease and wave height increases.

The waves change shape from the rounded crests and troughs in deep water to peaked crests with relatively flat troughs in shallow water close to shore. Perhaps the most dramatic feature of waves entering shallow water is their rapid increase in height. The height of waves in shallow water, where they break, may be as much as twice their deep-water height.

When waves move into shallow water, which of the following would NOT change?

Correct Answer: 4. Wave period
Solution:

"As waves move into shallow water, the wave period remains constant, but wave length and velocity decrease and wave height increases."

This clearly means the wave period does not change, making it the correct answer.

97. Energy expended by waves of height 2 m on a 1000 km length of open coastline would be approximately equivalent to the energy produced by how many average sized nuclear power plants?

Correct Answer: 1. 10
Solution:

98. Which of the following corresponds to an unstable wave?

Correct Answer: 2. Wave height = 2.5 m, Wavelength = 20 m
Solution:

99. Which of the following is a characteristic of the shallow water close to shore?

Correct Answer: 3. Flat troughs
Solution:

"The waves change shape from the rounded crests and troughs in deep water to peaked crests with relatively flat troughs in shallow water close to shore." Thus, a key characteristic of shallow-water waves is: flat troughs.

100. If wave height increases by 3 times, wave energy would increase by:

Correct Answer: 3. 9 times
Solution:

Wave energy is:
Wave energy (Wave height)²
If wave height increases 3 times:
(3)² = 9
So, the wave energy would increase by 9 times.