Free Man and His Environment MCQs with Answers

311. Which one of the following statements is correct?

• A. Legumes fix nitrogen only through the specialized bacteria that live in their roots.
• B. Legumes fix nitrogen independently of the specialized bacteria that live in their roots.
• C. Legumes fix nitrogen only through specialized bacteria that live in their leaves.
• D. Legumes are incapable of fixing nitrogen.

Explanation: The nitrogen­-fixing ability of leguminous plants is not a property of the plants as such but results from infection of their roots by bacteria in the soil, leading to the formation of nodules. These organisms are Gram­-negative motile rods that are classified in the genus Rhizobium.

312. Homeostasis is the:

• A. Tendency of biological systems to change with change in the environment
• B. Tendency of biological systems to resist change
• C. Disturbance of self regulatory system and natural controls
• D. Biotic materials used in homeopathic medicines

Explanation: The ability to maintain a steady state within a constantly changing environment is essential for the survival of living systems. The maintenance of a constant internal environment is called homeostasis.

313. Which of the following is correctly matched?

• A. Aerenchyma-Opuntia
• B. Age pyramid-Biome
• C. Parthenium hysterophorus-Threat to biodiversity
• D. Stratification-Population

Explanation: Parthenium hysterophorus is commonly known as congress grass or carrot weed. It is a herbaceous annual plant of the Family Asteraceae. It is a deadly invasive, noxious weed infesting cropped and non­cropped areas. It rapidly colonizes areas, replacing the native vegetation and causing a number of human health-related problems such as skin allergy, rhinitis, and eye irritations. Also, being toxic and unpalatable it causes fodder scarcity. Hence, it is considered a threat to the biodiversity.

314. Which one of the following statements is correct?

• A. Both Azotobacter and Rhizobium fix atmospheric nitrogen in root nodules of plants.
• B. Cyanobacteria such as Anabaena and Nostoc are not important mobilizers of phosphates and for plant nutrition in soil.
• C. At present it is not possible to grow maize without chemical fertilizers.
• D. Extensive use of chemical fertilizers may lead to eutrophication of nearby water bodies.

Explanation: Eutrophication is the excessive growth of algae, plants, and animals in water bodies due to nutrient enrichment, particularly with nitrogen and phosphate. Nutrients present in sewage, agricultural wastes, and fertilizers cause dense growth of plants and planktonic algae. The excessive growth of planktonic algae that causes the coloration of water is called algal bloom, which is toxic to animals and humans. Eutrophic water bodies also support the excessive growth of floating plants. Algal blooms and floating plants cut off light form submerged plants, resulting in their death. There is drastic decrease in oxygen replenishment inside water. Non­-availability of oxygen results in the death of aquatic animals such as fish, which further adds to organic loading of water. Decomposition is replaced by putrefaction which is anaerobic, leading to an absence of oxygen in water and the death of aquatic animals.

315. Which one of the following is a wrong statement?

• A. Anabaena and Nostoc are capable of fixing nitrogen in a free­living state also
• B. Root nodule-forming nitrogen fixers live as aerobes under free­living conditions
• C. Phosphorus is a constituent of cell membranes, certain nucleic acids, and all proteins
• D. Nitrosomonas and nitrobacteria are chemo­ autotrophs

Explanation: Phosphorus is present in the plasma membrane in the form of a phospholipid bilayer. It is an essential component of all nucleic acids- not 'certain' nucleic acids. Moreover, phosphorus is only sometimes found in proteins.

316. Biodiversity includes:

• A. Ecosystem and habitat diversity
• B. Species diversity and ecosystem diversity
• C. Species diversity, genetic diversity and ecosystem diversity
• D. Species diversity only

Explanation: c) Species diversity, genetic diversity, and ecosystem diversity:This is the correct answer. Biodiversity encompasses species diversity, which refers to the variety of different species within an ecosystem. It also includes genetic diversity, which refers to the genetic variation within a species. Additionally, biodiversity includes ecosystem diversity, which relates to the variety of ecosystems and habitats present on Earth.

317. Which of the following is the definition of the term niche?

• A. All the environmental factors that determine where an organism lives
• B. All the food webs in an ecosystem
• C. The place where an organism lives
• D. The role that a species fulfills in a community

Explanation: d) The role that a species fulfills in a community:This is the correct definition of niche. The niche of a species refers to the specific role it plays in its community, including its interactions with other species, its resource utilization, and its response to environmental conditions. It encompasses the species' habitat, feeding habits, reproductive strategies, and more.

318. A pond is an example of which ecosystem?

• A. Complete
• B. Incomplete
• C. Almost complete
• D. None of these

Explanation: Ecosystems with abiotic components, producers, consumers, and decomposers are considered as complete ecosystems. A pond fulfils the above prerequisites and hence constitutes a complete ecosystem.

319. Greenhouse gases are those that:

• A. Prevent entry of ultraviolet rays
• B. Prevent rainfall
• C. Prevent heat to escape
• D. All given options are correct

Explanation: Greenhouse gases are gases in Earth's atmosphere that trap heat. They let sunlight pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere. The other options are incorrect. Ultraviolet rays are not prevented by greenhouse gasses, and in fact, they can be harmful to living organisms if not filtered out by the ozone layer. Greenhouse gases also do not prevent rainfall, but they can indirectly affect precipitation patterns through their impact on global temperatures and weather patterns.

320. Grassland of Argentina is:

• A. Prairies
• B. Savana
• C. Boreal
• D. Pampas

Explanation: The Pampas in Argentina are most well known for the great biodiversity in the area. Pampas is a grassland ecosystem found in South America, particularly in Argentina and Uruguay, characterized by tall grasses and a subtropical climate with distinct wet and dry seasons.