Question 1

What is the term used to describe the variety of plant and animal species in a particular ecosystem or region?

Accepted Answer

Biodiversity (or biological diversity) refers to the variety of all living organisms—plants, animals, fungi, and microorganisms—and their genetic variations within ecosystems, habitats, and the entire biosphere.

Question 2

Which of the following practices helps reduce soil degradation and maintain soil fertility?

Accepted Answer

Crop rotation is an agricultural practice where different crops are planted in the same field in successive seasons. This prevents nutrient depletion, reduces pest buildup, and maintains soil health. It is a sustainable farming method that has been used for centuries.

Question 3

The layer of the atmosphere closest to Earth's surface, where weather occurs and where we live, is called the:

Accepted Answer

The troposphere is the lowest layer of Earth's atmosphere, extending from the surface to approximately 10-18 km altitude. It contains 75% of the atmosphere's mass and is where all weather phenomena occur. Temperature decreases with altitude in this layer.

Question 4

Which of the following is a non-renewable natural resource that, once depleted, cannot be replenished in human timescales?

Accepted Answer

Fossil fuels (coal, petroleum, natural gas) and minerals are non-renewable resources. They take millions of years to form and are being consumed much faster than they can be naturally replenished, making them finite resources.

Question 5

The process by which plants convert sunlight into chemical energy stored in glucose 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 the foundation of most food chains on Earth and is crucial for maintaining atmospheric oxygen levels.

Question 6

Which of the following practices is most effective in reducing soil erosion and maintaining soil fertility in agricultural areas?

Accepted Answer

Contour ploughing (ploughing along the contours of slopes rather than up and down) is highly effective in reducing soil erosion. Other effective practices include terrace farming, crop rotation, and maintaining vegetation cover. These methods prevent water runoff and nutrient loss.

Question 7

Which of the following gases is primarily responsible for the greenhouse effect and is released through the burning of fossil fuels?

Accepted Answer

Carbon dioxide (CO₂) is the primary greenhouse gas responsible for global warming. It is released when fossil fuels like coal, oil, and natural gas are burned for energy. While methane and nitrous oxide are also greenhouse gases, CO₂ is the most abundant and significant contributor to climate change.

Question 8

Which of the following is an example of a renewable energy source?

Accepted Answer

Solar energy is a renewable energy source because it is continuously replenished by the sun and does not deplete natural resources. Other renewable sources include wind, hydroelectric, geothermal, and biomass energy. These contrast with non-renewable sources like coal, oil, and natural gas.

Question 9

The 'Red Data Book' contains information about which of the following?

Accepted Answer

The Red Data Book (maintained by IUCN – International Union for Conservation of Nature) is a record of threatened and endangered species of plants, animals, and fungi. It categorises species into Extinct, Critically Endangered, Endangered, Vulnerable, etc. It does not deal with pollution or climate data.

Question 10

Which of the following best describes the concept of 'carrying capacity' in ecology?

Accepted Answer

Carrying capacity (K) is the maximum population size of a species that an environment can sustain indefinitely, given available resources (food, water, space, shelter). It is determined by limiting factors such as resource availability, predation, disease, and competition. When a population exceeds carrying capacity, resources become depleted, leading to increased mortality and decreased birth rates until equilibrium is restored. This is a fundamental concept in population ecology and conservation biology.

Question 11

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

Accepted Answer

Eutrophication is primarily caused by excess nutrient input (nitrogen and phosphorus) from agricultural runoff, sewage, and detergents. These nutrients trigger algal blooms, which deplete oxygen and create dead zones, harming aquatic life.

Question 12

Which of the following is the primary function of the ozone layer in Earth's atmosphere?

Accepted Answer

The ozone layer (located in the stratosphere, 15-35 km altitude) primarily absorbs ultraviolet (UV) radiation, particularly UV-B and UV-C rays. This protects life on Earth from harmful UV radiation that can cause skin cancer, cataracts, and immune system damage.

Question 13

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

Accepted Answer

Chlorofluorocarbons (CFCs) are synthetic chemicals that release chlorine atoms when exposed to ultraviolet radiation in the stratosphere. These chlorine atoms catalytically destroy ozone molecules, with a single chlorine atom capable of destroying up to 100,000 ozone molecules. CFCs were historically used in refrigerants, air conditioners, and aerosol propellants until their phase-out under the Montreal Protocol (1987).

Question 14

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

Accepted Answer

Chlorofluorocarbons (CFCs) are the primary cause of ozone layer depletion. When CFCs reach the stratosphere, UV radiation breaks them down, releasing chlorine atoms that catalytically destroy ozone molecules. One chlorine atom can destroy up to 100,000 ozone molecules.

Question 15

Which of the following is the primary cause of eutrophication in freshwater lakes and ponds?

Accepted Answer

Eutrophication is caused by excessive nutrient enrichment, primarily from nitrogen and phosphorus compounds. These nutrients come from agricultural runoff (fertilizers), sewage discharge, and detergents. The excess nutrients stimulate algal blooms, which consume dissolved oxygen when they decompose, creating hypoxic 'dead zones' where aquatic life cannot survive. This process is called cultural eutrophication when accelerated by human activities.

Question 16

Which of the following is the primary source of nitrogen fixation in terrestrial ecosystems?

Accepted Answer

Nitrogen-fixing bacteria, particularly those in the genus Rhizobium (which form symbiotic relationships with legume plants) and free-living bacteria like Azotobacter, are the primary biological sources of nitrogen fixation. These bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃), making it available to plants. This process is essential because most organisms cannot directly utilize atmospheric nitrogen.

Question 17

Which of the following is the primary cause of eutrophication in freshwater ecosystems, and what is its ecological consequence?

Accepted Answer

Eutrophication is caused by excess nutrient input (primarily nitrogen and phosphorus) from agricultural runoff, sewage, and detergents. This leads to algal blooms, oxygen depletion (hypoxia), and fish kills. Phosphorus is often the limiting nutrient in freshwater systems, making it the primary culprit in eutrophication.

Question 18

Which of the following best describes the process of eutrophication in aquatic ecosystems, and what is its primary cause?

Accepted Answer

Eutrophication is the process of nutrient enrichment (primarily nitrogen and phosphorus) in water bodies, leading to excessive algal growth, oxygen depletion, and death of aquatic life. The primary cause is nutrient runoff from agricultural fertilizers, sewage discharge, and industrial effluents. This creates anoxic (oxygen-free) zones called 'dead zones' where most aquatic organisms cannot survive.

Question 19

Which of the following correctly describes the concept of 'carrying capacity' in ecology, and what does it represent?

Accepted Answer

Carrying capacity (K) is the maximum population size of a species that an environment can sustainably support indefinitely, given available resources (food, water, habitat, etc.). It is determined by limiting factors such as food availability, predation, disease, and space. When a population exceeds carrying capacity, resource depletion leads to population decline through increased mortality or emigration.

Question 20

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

Accepted Answer

Carbon dioxide (CO₂) is the primary anthropogenic greenhouse gas driving climate change. As of early 2024, atmospheric CO₂ concentration exceeded 420 ppm (parts per million), marking a significant increase from pre-industrial levels of ~280 ppm. This elevated concentration is the main driver of global warming.

SSC CHSL Environment & Ecology

Environment & Ecology— Rules & Concept

Key Points to Remember

Exam-Specific Tips

Environment & Ecology — Practice Questions

60-Second Revision — Environment & Ecology