Question 1

Which of the following is the primary greenhouse gas responsible for climate change?

Accepted Answer

Carbon dioxide (CO₂) is the most significant anthropogenic greenhouse gas driving global climate change. While methane and nitrous oxide are also greenhouse gases, CO₂ has the longest atmospheric lifetime and accounts for the majority of radiative forcing.

Question 2

The process by which plants convert sunlight into chemical energy is called:

Accepted Answer

Photosynthesis is the biochemical process where plants, algae, and some bacteria use sunlight, water, and carbon dioxide to produce glucose and oxygen. This is fundamental to all life on Earth as it forms the base of most food chains.

Question 3

Which of the following is a renewable source of energy?

Accepted Answer

Solar energy is a renewable resource because the sun continuously provides energy without depletion. Other renewable sources include wind, hydroelectric, geothermal, and biomass energy. Non-renewable sources like coal, petroleum, and natural gas have finite reserves.

Question 4

The layer of the atmosphere closest to Earth's surface is called:

Accepted Answer

The troposphere is the lowest layer of Earth's atmosphere, extending approximately 8-18 km above the surface. It contains about 80% of the atmosphere's mass and is where all weather phenomena occur. Temperature decreases with altitude in this layer.

Question 5

Which of the following is an example of a biodegradable waste?

Accepted Answer

Biodegradable waste is organic material that can be decomposed by microorganisms into natural substances like water, carbon dioxide, and biomass. Paper is biodegradable as it is made from plant cellulose that bacteria and fungi can break down naturally.

Question 6

Which of the following gases is primarily responsible for the depletion of the ozone layer in the Earth's stratosphere?

Accepted Answer

Chlorofluorocarbons (CFCs) contain chlorine atoms that, when released into the stratosphere, catalytically destroy ozone molecules. One chlorine atom can destroy up to 100,000 ozone molecules. CFCs were commonly used in refrigerants, air conditioners, and aerosol propellants before being phased out under the Montreal Protocol (1987).

Question 7

Which of the following is an example of a primary pollutant that is directly emitted into the atmosphere from a source?

Accepted Answer

Primary pollutants are those emitted directly from sources such as vehicles, factories, and power plants. Carbon monoxide (CO) is emitted directly from incomplete combustion of fossil fuels in vehicle engines and industrial processes. Secondary pollutants (like ozone and PAN) are formed in the atmosphere through chemical reactions.

Question 8

Which of the following is the primary cause of eutrophication in freshwater bodies?

Accepted Answer

Eutrophication is caused by excess nutrients, primarily nitrogen and phosphorus, entering water bodies from agricultural runoff, sewage discharge, and detergents. These nutrients cause algal blooms, which deplete oxygen (hypoxia) when they decompose, creating 'dead zones' where aquatic life cannot survive.

Question 9

Which of the following is the correct definition of 'carrying capacity' in ecology?

Accepted Answer

Carrying capacity (K) is the maximum population size that an environment can sustain indefinitely given available resources (food, water, space, etc.). It is determined by limiting factors such as food availability, predation, disease, and habitat space. When a population exceeds carrying capacity, it experiences decline due to resource scarcity.

Question 10

Which of the following is the primary greenhouse gas responsible for climate change, and what is its approximate concentration in the atmosphere as of 2024?

Accepted Answer

Carbon dioxide (CO₂) is the most significant anthropogenic greenhouse gas driving climate change. As of 2024, atmospheric CO₂ concentration has exceeded 420 ppm (parts per million), marking a continuous increase from pre-industrial levels of ~280 ppm. This elevated concentration traps heat in the atmosphere, causing global warming and associated climate impacts.

Question 11

The Montreal Protocol (1987) was designed to protect the ozone layer by phasing out which class of chemicals?

Accepted Answer

The Montreal Protocol targeted Ozone-Depleting Substances (ODS), primarily Chlorofluorocarbons (CFCs), Halons, and Hydrochlorofluorocarbons (HCFCs). These chemicals release chlorine and bromine atoms in the stratosphere, which catalytically destroy ozone molecules. The protocol has been highly successful, with the ozone hole showing signs of recovery.

Question 12

The process by which nitrogen gas (N₂) in the atmosphere is converted into ammonia (NH₃) by certain microorganisms is called:

Accepted Answer

Nitrogen fixation is the biogeochemical process by which atmospheric N₂ (which is inert and unavailable to most organisms) is converted into ammonia (NH₃) or nitrate (NO₃⁻) by nitrogen-fixing bacteria and archaea. Key organisms include Rhizobium (in legume root nodules), Azotobacter, and cyanobacteria. This process is essential for the nitrogen cycle and agriculture.

Question 13

Which of the following is the primary mechanism by which invasive species reduce native biodiversity in an ecosystem?

Accepted Answer

Invasive species reduce native biodiversity primarily through competitive exclusion (outcompeting natives for resources like food, water, light, and space), predation on native species, habitat degradation, and disease transmission. The most common mechanism is resource competition, where invasive species are often better adapted to the new environment or lack natural predators, allowing rapid population growth.

Question 14

Which of the following is the primary greenhouse gas responsible for the majority of anthropogenic climate change, and what is its approximate atmospheric concentration as of 2024?

Accepted Answer

Carbon dioxide (CO₂) is the primary anthropogenic greenhouse gas, accounting for approximately 60% of radiative forcing from long-lived greenhouse gases. As of 2024, atmospheric CO₂ concentration has exceeded 420 ppm (parts per million), having risen from pre-industrial levels of ~280 ppm. This is measured by organizations like NOAA and is a critical indicator of climate change severity.

SSC GD Constable Environment & Ecology

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60-Second Revision — Environment & Ecology