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Question 1. Which property of water is primarily responsible for its high surface tension? A) Covalent bonding B) Hydrogen bonding C) Ionic bonding D) Van der Waals forces Answer: B Explanation: Hydrogen bonds between water molecules create a strong cohesive force, giving water a high surface tension. Question 2. As temperature increases, the solubility of most gases in seawater: A) Increases B) Decreases C) Remains constant D) First increases then decreases Answer: B Explanation: Higher temperatures give gas molecules more kinetic energy, reducing their ability to stay dissolved. Question 3. The primary factor that creates a thermocline in the ocean: A) Salinity differences B) Pressure gradients C) Temperature gradients D) Currents Answer: C Explanation: A thermocline is a layer where temperature changes rapidly with depth, separating warmer surface water from colder deep water. Question 4. In the carbonate system, which ion predominates at a pH of ~8.1 in seawater? A) CO₂ (aq)
B) HCO₃⁻
C) CO₃²⁻
D) H₂CO₃
Answer: B Explanation: At typical seawater pH, bicarbonate (HCO₃⁻) is the dominant dissolved inorganic carbon species. Question 5. Which type of plate boundary is most commonly associated with the formation of deep-sea trenches? A) Divergent B) Transform C) Convergent (subduction) D) Passive margin Answer: C Explanation: At convergent subduction zones, one plate is forced beneath another, creating a trench. Question 6. Mid-ocean ridges are primarily formed by: A) Erosion of continental crust B) Seafloor spreading and volcanic activity C) Sediment deposition D) Meteorite impacts Answer: B Explanation: Upwelling magma at divergent boundaries creates new oceanic crust, forming ridges. Question 7. Magnetic striping on the ocean floor provides evidence for: A) Sea-level change B) Plate tectonics C) Ocean currents D) Biological productivity
Explanation: Both species benefit: the fish gains protection, the anemone receives cleaning and nutrients. Question 11. In a marine food web, primary producers convert solar energy into chemical energy via: A) Chemoautotrophy B) Photosynthesis C) Respiration D) Fermentation Answer: B Explanation: Phytoplankton and macroalgae use photosynthesis to create organic matter. Question 12. The “10 % rule” in trophic transfer states that: A) 10 % of biomass is lost at each level B) Only 10 % of energy is transferred to the next trophic level C) 10 % of primary production is consumed by herbivores D) 10 % of predators are top-level consumers Answer: B Explanation: Roughly 10 % of the energy captured at one trophic level is available to the next due to metabolic losses. Question 13. Which nitrogen-fixing marine organism is a cyanobacterium that forms colonies called Trichodesmium? A) Rhizobium B) Anabaena C) Trichodesmium D) Nitrosomonas Answer: C Explanation: Trichodesmium is a free-floating cyanobacterium that fixes atmospheric N₂ in tropical oceans.
Question 14. Upwelling along a coast is most likely to occur when: A) Winds blow parallel to the shoreline toward the equator B) Winds blow parallel to the shoreline away from the equator C) Winds blow directly onshore D) There is a strong tidal current Answer: B Explanation: Offshore winds (e.g., the California Current) cause surface water to move away, allowing deeper nutrient-rich water to rise. Question 15. Which of the following best describes a keystone species? A) The most abundant organism in an ecosystem B) A species whose removal causes disproportionate changes in community structure C) A species that occupies the highest trophic level D) A species with the highest reproductive rate Answer: B Explanation: Keystone species have a critical ecological role; their loss triggers cascading effects. Question 16. The hierarchical level “Phylum” in taxonomy is directly above: A) Class B) Order C) Kingdom D) Genus Answer: A Explanation: The order of ranks is Kingdom, Phylum, Class, Order, Family, Genus, Species. Question 17. Which marine phylum includes organisms with a radula? A) Cnidaria B) Mollusca
Explanation: Opposite flow of water and blood creates a gradient that extracts up to 90 % of dissolved O₂. Question 21. Marine mammals such as whales regulate buoyancy primarily by: A) Swallowing air B) Adjusting lung volume and blubber density C) Producing gas bubbles in the bloodstream D) Using a swim bladder Answer: B Explanation: Lungs and blubber allow whales to fine-tune buoyancy; fish use a swim bladder, which mammals lack. Question 22. Euryhaline organisms are distinguished because they can: A) Tolerate a narrow salinity range B) Survive only in freshwater C) Osmoregulate across a wide salinity range D) Only inhabit hypersaline environments Answer: C Explanation: Euryhaline species, like salmon, can adjust to both fresh and marine salinities. Question 23. Which adaptation helps mangrove trees cope with anoxic soils? A) Deep taproots B) Pneumatophores for gas exchange C) Thick waxy cuticle only D) Salt-secreting glands on leaves Answer: B Explanation: Pneumatophores are aerial roots that transport oxygen to submerged root systems. Question 24. The primary cause of coral bleaching is:
A) Increased predation by crown-of-thorns starfish B) Elevated sea-surface temperature disrupting zooxanthellae symbiosis C) Ocean acidification reducing calcium carbonate deposition D) Overfishing of herbivorous fish Answer: B Explanation: Heat stress forces corals to expel zooxanthellae, leading to loss of color and reduced nutrition. Question 25. Which type of reef is formed when a volcanic island sinks and coral growth keeps pace with subsidence? A) Fringing reef B) Barrier reef C) Atoll D) Patch reef Answer: C Explanation: Atolls encircle a lagoon where the original island has subsided. Question 26. In the intertidal zone, organisms that can tolerate both submerged and exposed conditions are described as: A) Pelagic B) Benthic C) Eurytopic D) Stenotopic Answer: C Explanation: “Eurytopic” species have broad tolerance to environmental variation. Question 27. Which of the following is a primary productivity indicator for coastal waters? A) Dissolved oxygen concentration B) Chlorophyll-a concentration C) Salinity
Explanation: Mercury biomagnifies, reaching highest concentrations in apex predators. Question 31. Ocean acidification reduces the saturation state of which mineral, making it harder for organisms to form shells? A) Halite (NaCl) B) Calcite (CaCO₃) C) Gypsum (CaSO₄·2H₂O) D) Silica (SiO₂) Answer: B Explanation: Lower pH decreases carbonate ion availability, reducing calcite (and aragonite) saturation. Question 32. The term “thermohaline circulation” refers to: A) Surface currents driven solely by wind B) Deep ocean currents driven by density differences from temperature and salinity C) Tidal currents in estuaries D) Seasonal upwelling near coasts Answer: B Explanation: Thermohaline circulation is the global “conveyor belt” caused by density gradients. Question 33. Which of the following is NOT a typical indicator of eutrophication in coastal waters? A) Algal blooms B) Hypoxic zones C) Increased water clarity D) Decline of benthic fauna Answer: C Explanation: Eutrophication usually reduces clarity due to high phytoplankton density.
Question 34. In a mark-release-recapture study, a major source of bias occurs when: A) Marks are permanent and harmless B) Recaptured individuals are not randomly sampled C) The population size is very large D) The study period is short Answer: B Explanation: Non-random recapture skews the proportion of marked individuals, leading to inaccurate estimates. Question 35. Which of the following best describes the role of mycosporine-like amino acids (MAAs) in marine organisms? A) Antifreeze proteins B] Osmoregulation agents C) UV-protective pigments D) Nitrogen fixation enzymes Answer: C Explanation: MAAs absorb UV radiation, protecting organisms such as corals and algae. Question 36. The primary driver of the seasonal monsoon circulation in the Indian Ocean is: A) Differential heating of land and sea B) Tidal forces C) Coriolis effect alone D) Oceanic current interaction with the Antarctic Circumpolar Current Answer: A Explanation: Land heats faster than ocean, creating pressure gradients that reverse seasonally, generating monsoons. Question 37. Which of the following best explains why seawater has a higher boiling point than freshwater?
D) CO₂ + Mg²⁺ → MgCO₃ Answer: A Explanation: CO₂ reacts with water to form carbonic acid (H₂CO₃), initiating the carbonate system. Question 41. Which of the following processes contributes most to the formation of deep-sea hydrothermal vent chimneys? A) Sedimentation of siliceous ooze B) Precipitation of metal sulfides from vent fluids C) Bioturbation by benthic organisms D) Coral reef growth Answer: B Explanation: Hot, metal-rich fluids mix with cold seawater, causing sulfide minerals to precipitate and build chimneys. Question 42. The term “bioturbation” refers to: A) The breakdown of organic matter by bacteria B) The mixing of sediments by living organisms C) The formation of biogenic silica shells D) The release of methane from the seabed Answer: B Explanation: Organisms such as worms and burrowing crustaceans rework sediments, influencing oxygen penetration and nutrient cycling. Question 43. Which of the following best describes the role of the Antarctic Circumpolar Current (ACC)? A) It transports warm tropical water to the poles. B) It isolates Antarctica, contributing to its cold climate. C) It drives upwelling along the western coasts of continents. D) It is a surface current driven solely by wind. Answer: B
Explanation: The ACC circles Antarctica, preventing warm water intrusion and maintaining the continent’s frigid environment. Question 44. In the context of marine protected areas (MPAs), a “no-take” zone means: A) Only recreational fishing is allowed. B) All extractive activities, including fishing, are prohibited. C) Only non-destructive research is permitted. D) Limited quota fishing is permitted. Answer: B Explanation: No-take zones ban all forms of extraction to preserve biodiversity and habitats. Question 45. Which of the following is a direct consequence of sea-level rise on coastal mangrove ecosystems? A) Increased salinity in the canopy B) Inland migration of mangrove forests C) Decreased tidal flushing D) Reduction in sediment deposition rates Answer: B Explanation: As sea level rises, mangroves can move landward if suitable substrate is available. Question 46. The “oxygen minimum zone” (OMZ) in the ocean is primarily caused by: A) High rates of photosynthesis at depth B) Limited water mixing and high respiration of organic matter C) Excessive wind-driven turbulence D) Direct injection of oxygen-rich water from the atmosphere Answer: B Explanation: Decomposition of sinking organic material consumes oxygen, and weak circulation prevents replenishment, creating an OMZ.
A) Open ocean waters B) Riverine or stream habitats C) Intertidal rocky shores D) Deep-sea hydrothermal vents Answer: B Explanation: “Lotic” describes flowing freshwater systems; while marine, it can refer to estuarine channels. Question 51. Which of the following is a major source of marine microplastics? A) Natural sediment erosion B) Fragmentation of larger plastic debris C) Dissolution of salt crystals D) Volcanic ash deposition Answer: B Explanation: Larger plastics break down into micro-sized particles through mechanical, photolytic, and biological processes. Question 52. The term “biofouling” describes: A) The accumulation of dead organic matter on the seafloor B) The colonization of submerged surfaces by organisms such as barnacles and algae C) The process of coral bleaching due to temperature stress D) The spread of invasive fish species Answer: B Explanation: Biofouling is the growth of sessile organisms on man-made structures, affecting ship hulls and aquaculture gear. Question 53. Which of the following best describes the role of mycorrhizal fungi in coastal salt marshes? A) They fix atmospheric nitrogen. B) They enhance phosphorus uptake for salt-tolerant plants.
C) They produce calcium carbonate for sediment stabilization. D) They are primary producers of methane. Answer: B Explanation: Mycorrhizae increase nutrient acquisition, especially phosphorus, aiding plant growth in nutrient-limited marshes. Question 54. The “El Niño Southern Oscillation” (ENSO) primarily affects marine ecosystems by: A) Increasing sea-surface salinity globally B) Altering upwelling patterns, leading to reduced productivity in some regions C) Raising atmospheric CO₂ concentrations directly D) Causing permanent shifts in continental drift Answer: B Explanation: El Niño suppresses upwelling along the Pacific coasts, decreasing nutrient supply and affecting fisheries. Question 55. Which fish group exhibits a “lateral line” system used for detecting water movements? A) Chondrichthyes (sharks) B) Osteichthyes (bony fish) C) Cephalopoda (octopuses) D) Echinodermata (sea stars) Answer: B Explanation: The lateral line is a mechanoreceptive organ in bony fish that senses vibrations and flow. Question 56. The most abundant form of dissolved inorganic nitrogen in most oligotrophic oceanic waters is: A) Ammonium (NH₄⁺) B) Nitrate (NO₃⁻) C) Nitrite (NO₂⁻) D) Organic nitrogen
Explanation: Toxic substances such as mercury become more concentrated as they move up the food chain. Question 60. The “Great Pacific Garbage Patch” is primarily composed of: A) Floating kelp mats B) Micro- and macro-plastic debris concentrated by gyre currents C) Sunken shipwrecks D) Aggregated fish eggs Answer: B Explanation: Converging currents in the North Pacific subtropical gyre trap plastics, forming a large debris field. Question 61. Which mineral is the principal component of the shells of foraminifera? A) Silica (SiO₂) B) Calcite (CaCO₃) C) Aragonite (CaCO₃ polymorph) D) Iron oxide (Fe₂O₃) Answer: B Explanation: Foraminiferal shells are made of calcite, a common form of calcium carbonate. Question 62. The term “marine snow” refers to: A) Fresh snowfall over the ocean surface B) Falling organic particles that transport carbon from surface waters to the deep sea C) Ice crystals forming in polar seas D) Large aggregations of fish schools Answer: B Explanation: Marine snow consists of dead plankton, fecal pellets, and detritus sinking and providing food for deep-sea organisms.
Question 63. Which of the following is a direct physiological effect of hypercapnia (elevated CO₂) on fish? A) Increased gill surface area B) Decreased blood pH (acidosis) C) Enhanced oxygen carrying capacity of hemoglobin D) Reduced metabolic rate Answer: B Explanation: Elevated CO₂ leads to increased dissolved carbonic acid, lowering blood pH and causing acidosis. Question 64. The “critical depth hypothesis” in phytoplankton ecology proposes that: A) Phytoplankton growth is limited only by nutrient availability. B) Bloom initiation occurs when the mixed layer becomes shallower than a depth where photosynthesis exceeds respiration. C) Light attenuation is irrelevant for primary production. D) All phytoplankton die at a fixed depth. Answer: B Explanation: When mixing brings phytoplankton into the euphotic zone less often, net production can become positive, leading to blooms. Question 65. Which of the following best characterizes a “cold-water coral” species? A) They are found only in tropical shallow reefs. B) They rely on symbiotic zooxanthellae for nutrition. C) They can thrive in deep, low-light, cold environments without zooxanthellae. D) They are primarily composed of silica. Answer: C Explanation: Cold-water corals (e.g., Lophelia pertusa) live in deep, dark waters and obtain nutrients by filter feeding, not photosynthesis. Question 66. The main driver of the “Ekman transport” in the upper ocean is:
