1. : The study of freshwater ecosystems is called:
(A) Oceanography
(B) Limnology
(C) Hydrology
(D) Ichthyology
2. : The study of marine organisms and ecosystems is called:
(A) Limnology
(B) Oceanography
(C) Marine biology
(D) Ecology
3. : Which zone of a lake receives sufficient sunlight for photosynthesis?
(A) Aphotic zone
(B) Profundal zone
(C) Littoral and limnetic zones
(D) Benthic zone
4. : Organisms living at the bottom of oceans and lakes are called:
(A) Nekton
(B) Plankton
(C) Benthos
(D) Neuston
5. : Which of the following are microscopic drifting organisms in water?
(A) Nekton
(B) Benthos
(C) Plankton
(D) Mollusks
6. : Phytoplankton are important in aquatic ecosystems because they:
(A) Are top predators
(B) Act as primary producers
(C) Decompose organic matter
(D) Reduce oxygen in water
7. : The salinity of seawater is approximately:
(A) 1 ppt
(B) 15 ppt
(C) 35 ppt
(D) 100 ppt
8. : Eutrophication in freshwater bodies is mainly caused by:
(A) Oil spills
(B) Excess nutrients like nitrogen and phosphorus
(C) Overfishing
(D) High salinity
9. : Coral reefs are primarily built by:
(A) Sponges
(B) Mollusks
(C) Cnidarians (corals)
(D) Algae only
10. : Which gas is essential for fish survival in aquatic ecosystems?
(A) Carbon dioxide
(B) Oxygen
(C) Nitrogen
(D) Methane
11. : The zone of the ocean that extends to a depth of about 200 meters and receives sunlight is called:
(A) Aphotic zone
(B) Photic (euphotic) zone
(C) Abyssal zone
(D) Benthic zone
12. : Anadromous fishes are those that:
(A) Live only in freshwater
(B) Live only in oceans
(C) Migrate from sea to freshwater to spawn
(D) Migrate from freshwater to sea to spawn
13. : Catadromous fishes, like eels, migrate from:
(A) Freshwater to sea for spawning
(B) Sea to freshwater for spawning
(C) Lakes to rivers for spawning
(D) Estuaries to lakes for spawning
14. : The oxygen minimum zone (OMZ) in oceans is caused by:
(A) High photosynthesis
(B) Decomposition of organic matter
(C) Upwelling of cold water
(D) Strong wave action
15. : Estuaries are highly productive ecosystems because:
(A) They are nutrient-rich
(B) They receive inputs from both land and sea
(C) They support diverse species
(D) All of the above
16. : Freshwater constitutes about what percentage of Earth’s total water?
(A) 2.5%
(B) 10%
(C) 25%
(D) 50%
17. : Hypoxia in aquatic systems refers to:
(A) High oxygen concentration
(B) Low oxygen concentration
(C) High salinity concentration
(D) Absence of nutrients
18. : Which adaptation helps deep-sea fishes survive in darkness?
(A) Large eyes and bioluminescence
(B) Shallow-water spawning
(C) High oxygen consumption
(D) Migration to freshwater
19. : The process of mixing of surface and deep lake waters during autumn and spring is called:
(A) Stratification
(B) Turnover
(C) Eutrophication
(D) Upwelling
20. : Mangrove forests are found in:
(A) Freshwater lakes
(B) Estuarine and coastal intertidal zones
(C) Polar oceans
(D) Mountain rivers
21. : Which freshwater biome has the highest flow velocity?
(A) Pond
(B) Lake
(C) River/stream
(D) Wetland
22. : The primary cause of coral bleaching is:
(A) Overfishing
(B) Increase in seawater temperature
(C) Ocean salinity changes
(D) Oil spills
23. : Oligotrophic lakes are characterized by:
(A) High nutrient levels, low oxygen
(B) Low nutrient levels, high oxygen
(C) Shallow depth, high productivity
(D) Strong algal blooms
24. : Nekton refers to aquatic organisms that:
(A) Float passively with currents
(B) Live attached to the bottom
(C) Can actively swim against currents
(D) Only photosynthesize
25. : The ultimate importance of marine phytoplankton is that they:
(A) Form coral reefs
(B) Produce over 50% of Earth’s oxygen
(C) Are top predators in the food chain
(D) Regulate ocean salinity