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Practice biomes-and-habitats with 20 free MCQ questions covering environment-and-ecology. Detailed explanations in English and Hindi, perfect for UPSC, SSC, and competitive exam preparation.
Attempt the quiz above first, then review every question with its correct answer and a short explanation below.
Q1.Which of the following is a semi-enclosed coastal body of water where freshwater from rivers mixes with saltwater from the ocean?
Explanation: An estuary is a dynamic transition zone between a river and the sea, where freshwater and saltwater mix (brackish water). They are highly productive because they receive nutrient-rich sediments from rivers and are influenced by ocean tides.
Q2.The symbiotic relationship between coral polyps and which microscopic algae is responsible for the building of coral reefs?
Explanation: Corals share a mutualistic symbiotic relationship with Zooxanthellae (photosynthetic dinoflagellate algae). The algae live inside the coral tissues, performing photosynthesis to provide food and assist in calcium carbonate skeleton deposition, while the coral polyp provides shelter and carbon dioxide.
Q3.A circular or horseshoe-shaped coral reef that surrounds a central deep lagoon with no central island is classified as a/an:
Explanation: According to Charles Darwin's reef classification (NCERT Geography), an atoll is a circular reef structure surrounding a central lagoon. Lakshadweep Islands in India are a classic example of atoll formations.
Q4.Coral bleaching is primarily triggered by which environmental stress factor?
Explanation: Coral bleaching occurs when corals expel their symbiotic zooxanthellae algae due to stress, primarily caused by elevated sea temperatures (even 1-2°C above normal summer limits) or ocean acidification. This leaves the coral white and vulnerable to starvation and death.
Q5.The primary producers in the aphotic, extreme-pressure ecosystems of deep-sea hydrothermal vents are:
Explanation: NCERT Class 12 Biology, Chapter 14 states that deep-sea hydrothermal ecosystems are exceptions to the solar rule. Primary producers here are chemosynthetic bacteria that synthesize organic matter using energy from the oxidation of chemical compounds like hydrogen sulfide (H2S).
Q6.Which of the following adaptations is commonly found in deep-sea fishes to locate prey and communicate in complete darkness?
Explanation: Bioluminescence is a key adaptation in the deep sea. Organisms possess specialized light-producing organs (photophores) containing luciferin and luciferase, which react to emit light used for attracting prey, camouflaging, or finding mates.
Q7.Average salinity of the open ocean is approximately:
Explanation: According to NCERT Geography and Biology, the average salinity of the world's oceans is about 35 parts per thousand (35 grams of dissolved salt per 1000 grams of water).
Q8.The process by which wind-driven currents bring cold, nutrient-rich water from the ocean depths to the surface is called:
Explanation: Upwelling is an oceanographic phenomenon where offshore winds push surface waters away, causing cold, dense, and nutrient-rich deeper waters to rise to the photic zone. This supports massive phytoplankton growth, creating rich fishing grounds.
Q9.Absorption of excess anthropogenic carbon dioxide by the oceans leads to which major threat to calcifying marine organisms?
Explanation: When CO2 dissolves in seawater, it forms carbonic acid, lowering the ocean's pH (acidification). This reduces the concentration of carbonate ions, making it difficult for corals, mollusks, and calcareous plankton to build and maintain their calcium carbonate shells/skeletons.
Q10.The area of floating Sargassum seaweed in the North Atlantic Ocean gyre, forming a unique ecosystem with no land borders, is the:
Explanation: The Sargasso Sea is a region in the middle of the North Atlantic Ocean, bounded by ocean currents forming a gyre. It is famous for hosting massive floating mats of Sargassum seaweed, which provides shelter, food, and breeding grounds for many unique marine species.
Q11.In marine ecosystems, what percentage of global atmospheric oxygen production is contributed by marine phytoplankton?
Explanation: Marine phytoplankton perform massive photosynthesis, capturing solar energy and fixing carbon dioxide. They are estimated to produce about 50% of the Earth's oxygen supply, making marine ecosystems vital for planetary oxygen balance.
Q12.Organisms that live in the intertidal zone of a rocky shore must possess adaptations to deal with which daily stress?
Explanation: The intertidal zone is covered by water during high tide and exposed to air during low tide. Organisms here adapt to survive drying out (desiccation), high solar heat, and physical impact of crashing waves by having hard shells, suction-like attachments (e.g., limpets, barnacles), or flexible bodies.
Q13.Which of the following marine zones receives enough light to support photosynthesis?
Explanation: The photic or euphotic zone is the upper layer of the ocean (usually down to 200 meters) where sunlight is sufficient for photosynthesis. Almost all marine primary production occurs in this zone.
Q14.The Great Barrier Reef, the largest coral reef system in the world, is classified as which type of reef?
Explanation: As classified by Darwin, a barrier reef is separated from the mainland or island coast by a deep, wide channel or lagoon. The Great Barrier Reef of Australia is the largest barrier reef in the world, running parallel to the northeastern coast.
Q15.Which of the following is considered the main environmental limit for the geographical distribution of reef-building corals?
Explanation: Reef-building (hermatypic) corals require warm, shallow, and clear tropical waters. They cannot survive where water temperatures drop below 18-20°C or exceed 30°C for long periods, restricting them to tropical and subtropical latitudes.
Q16.Coral reefs are often called the 'rainforests of the sea' because:
Explanation: Although coral reefs cover less than 0.1% of the ocean floor, they support about 25% of all marine species (fishes, mollusks, crustaceans). This extraordinary concentration of biodiversity and high productivity earns them the nickname 'rainforests of the sea'.
Q17.In India, major coral reef formations are found in which of the following areas?
Explanation: India's major coral reefs are located in the Gulf of Mannar, Gulf of Kutch, Lakshadweep (atolls), and Andaman and Nicobar Islands (fringing reefs). Corals do not grow near river deltas like the Ganga-Brahmaputra mouth because corals require clear water free from high silt/sediment and freshwater inflow.
Q18.Why do estuary habitats support very high productivity despite having fluctuating salinity levels?
Explanation: Estuaries act as nutrient traps. Rivers wash down nutrients from agricultural and forest soils, and tides mix these nutrients with seawater. This abundance of nutrients, along with shallow, sunlit waters, drives high primary productivity by phytoplankton and marsh grasses.
Q19.Calcifying marine organisms use carbonate ions to build shells. Ocean acidification reduces the availability of carbonate ions by converting them into:
Explanation: When excess hydrogen ions (H+) from carbonic acid react with carbonate ions (CO3^2-), they form bicarbonate ions (HCO3^-). This reaction 'steals' carbonate ions, making them unavailable for marine organisms to bind with calcium to form calcium carbonate shells.
Q20.Pelagic marine organisms differ from benthic marine organisms because pelagic systems refer to:
Explanation: Marine habitats are divided into pelagic zone (the open water column where organisms swim or float, e.g., tuna, sharks, jellyfish) and benthic zone (the ocean floor, including sediments, where crawlers and attached species live, e.g., sea anemones, crabs, starfish).
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