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100 questions in this collection · Page 7 of 10
Question 61 of 100
📘 CLASS XII
Environmental Issues
Regarding Algal Blooms and the water hyacinth, consider the following statements:
I. Presence of large amounts of nutrients in water causes excessive growth of free-floating planktonic algae. II. Algal blooms significantly improve water quality and increase dissolved oxygen levels. III. Water hyacinth (Eichhornia crassipes) was introduced in India because of its beautiful purple flowers and leaf shapes. IV. Water hyacinth is also known as the "Terror of Bengal" because it grows faster than our ability to clear it.
Which of the statements given above are correct?
Algal blooms occur due to excessive nutrient enrichment and deteriorate water quality by reducing dissolved oxygen, often causing fish mortality. Eichhornia crassipes was introduced for its ornamental value and is called the "Terror of Bengal" because of its rapid growth. Therefore, Statement II is incorrect.
Question 62 of 100
📘 CLASS XII
Environmental Issues
Read the following statements regarding industrial wastewater and pathogens:
I. Sewage from homes and hospitals is likely to contain many pathogenic micro-organisms. II. Disposal of untreated sewage can cause outbreaks of serious diseases like typhoid, jaundice, and cholera. III. Industrial wastewater often contains heavy metals, defined as elements with a density greater than 5 g/cm3. IV. Toxic substances like mercury, cadmium, copper, and lead are examples of heavy metals.
Which of the statements given above are correct?
All four statements are correct. Domestic and hospital sewage contains disease-causing microorganisms, untreated sewage spreads water-borne diseases, and industrial effluents often contain toxic heavy metals such as mercury, cadmium, copper and lead.
Question 63 of 100
📘 CLASS XII
Environmental Issues
With reference to the process of Biomagnification, consider the following statements:
I. Biomagnification is the increase in concentration of a toxicant at successive trophic levels. II. It occurs because toxic substances accumulated by an organism cannot be metabolized or excreted. III. This phenomenon of accumulation is particularly well-known for calcium and sodium ions. IV. High concentrations of DDT interfere with calcium metabolism in birds, causing thinning of eggshells and premature breaking.
Which of the statements given above are correct?
Biomagnification is the progressive increase in concentration of persistent toxic substances along successive trophic levels because they cannot be metabolized or excreted. It is characteristic of pollutants such as DDT and mercury, not calcium or sodium. High DDT concentrations interfere with calcium metabolism, causing eggshell thinning in birds.
Question 64 of 100
📘 CLASS XII
Environmental Issues
Analyze the concentration of DDT at successive trophic levels of an aquatic food chain:
I. The concentration of DDT starts in water at a level of 0.003 ppb. II. Through biomagnification, the concentration in zooplankton reaches 0.04 ppm. III. Small fish and large fish accumulate DDT to concentrations of 2 ppm and 5 ppm respectively. IV. The final concentration reached in fish-eating birds is approximately 25 ppm.
Which of the statements given above are correct?
The textbook values are: water = 0.003 ppb, zooplankton = 0.04 ppm, small fish = 0.5 ppm, large fish = 2 ppm, and fish-eating birds = 25 ppm. Therefore, Statement III contains incorrect values.
Question 65 of 100
📘 CLASS XII
Environmental Issues
Consider the following statements regarding the Natural Eutrophication of lakes:
I. Eutrophication is the natural aging of a lake by nutrient enrichment of its water. II. In a young lake, the water is cold and clear, supporting very little organic life. III. Over time, streams introduce nutrients like nitrogen and phosphorus, encouraging aquatic growth. IV. As organic debris piles up, the lake grows deeper and colder, favoring cold-water organisms.
Which of the statements given above are correct?
Natural eutrophication is the gradual aging of lakes through nutrient enrichment. Young lakes are cold and clear with little organic life. Nutrients gradually accumulate and increase biological productivity. As sediments accumulate, lakes become shallower and warmer, not deeper and colder. Hence Statement IV is incorrect.
Question 66 of 100
📘 CLASS XII
Environmental Issues
With reference to Cultural Eutrophication and Thermal Wastewater, read the following statements:
I. Pollutants from human activities, such as effluents from industries and homes, radically accelerate the aging of lakes. II. This human-induced acceleration is termed cultural or accelerated eutrophication. III. Nitrates and phosphates are prime contaminants that act as plant nutrients and overstimulate algal growth. IV. Thermal wastewater from power plants always enhances the growth of all temperature-sensitive indigenous organisms.
Which of the statements given above are correct?
Human activities accelerate eutrophication through nutrient-rich domestic and industrial effluents. Nitrates and phosphates stimulate excessive algal growth. Thermal wastewater generally harms temperature-sensitive indigenous organisms, although it may enhance growth only under special cold conditions. Hence Statement IV is incorrect.
Question 67 of 100
📘 CLASS XII
Environmental Issues
Consider the following statements about the wastewater treatment case study of Arcata, California:
I. The project successfully combined artificial and natural purification processes. II. In the first stage, conventional sedimentation, filtering, and chlorine treatments are carried out. III. After conventional treatment, dangerous pollutants like dissolved heavy metals are completely removed. IV. The natural purification stage consists of six connected marshes spread over 60 hectares of marshland.
Which of the statements given above are correct?
The Arcata Marsh project combines conventional wastewater treatment with natural marsh-based purification. Even after conventional treatment, dissolved heavy metals remain and are removed through the marsh ecosystem. Therefore, Statement III is incorrect.
Question 68 of 100
📘 CLASS XII
Environmental Issues
Read the following statements regarding Ecological Sanitation (EcoSan) toilets:
I. EcoSan is a sustainable system for handling human excreta using dry composting toilets. II. EcoSan toilets require a continuous water pressure of at least 5 litres per flush. III. By this composting method, human excreta can be recycled into a valuable organic resource (fertilizer). IV. Working EcoSan toilets are currently operational in many areas of Kerala and Sri Lanka.
Which of the statements given above are correct?
EcoSan is a dry composting toilet system that does not require water for flushing. It safely converts human excreta into organic fertilizer and has been successfully implemented in several areas of Kerala and Sri Lanka. Hence, Statement II is incorrect.
Question 69 of 100
📘 CLASS XII
Environmental Issues
With reference to Municipal Solid Wastes and Landfills, consider the following statements:
I. Municipal solid wastes comprise papers, food wastes, plastics, glass, metals, rubber, leather, and textiles. II. Burning reduces the volume of solid waste, though it is generally not burnt to completion. III. Sanitary landfills were adopted as a cleaner alternative to open-burning dumps. IV. In a sanitary landfill, wastes are compacted in a trench and covered with dirt every day.
Which of the statements given above are correct?
All four statements are correct. Municipal solid waste consists of papers, food waste, plastics, glass, metals, rubber, leather and textiles. Burning reduces waste volume but is generally incomplete. Sanitary landfills are cleaner alternatives to open-burning dumps, where compacted waste is covered daily with soil.
Question 70 of 100
📘 CLASS XII
Environmental Issues
Consider the following statements regarding waste categorization and recycling:
I. All waste generated can be categorized into biodegradable, recyclable, and non-biodegradable types. II. Biodegradable materials can be put into deep pits in the ground and left for natural breakdown. III. Non-biodegradable packaging materials like plastic and polystyrene contribute heavily to pollution. IV. Kabadiwallahs and rag-pickers perform the crucial task of sorting and separating out biodegradable waste.
Which of the statements given above are correct?
Waste is broadly categorized into biodegradable, recyclable and non-biodegradable types. Biodegradable waste decomposes naturally in pits, while plastics and polystyrene contribute significantly to pollution. Kabadiwallahs and rag-pickers mainly collect recyclable materials, not biodegradable waste. Therefore, Statement IV is incorrect.