21.Estuary is a boundary where a freshwater ecosystem meets a saltwater ecosystem. Which of the following statements best describe an estuary? A. It is the deepest part of the ocean. B. It is also known as river and marsh. C. It is a body of water that drains into a stream D. It is a body of water between saltwater and freshwater.

22.Intertidal zone is the shallowest part of the ocean ecosystem. Which statement is NOT TRUE about the intertidal zone? A. It is an important food source. C. It is always flooded due to high tide B. This is found along coastlines. D. This is a habitat of numerous crustaceans Manong Tiago gathers mussels and other forms of food after high tide along the sea coast.


23.Which symbiotic relationship does it show? A. commensalism C. parasitism B. mutualism D. predation

24. What do you call the harmed organism in parasitism? A. host B. insect C. parasite D. prey


25. Which refers to a type of environment where organisms such as plants and animals and other organisms live? A. ecosystem B. estuaries C. habitat D. intertidal zone


26. Estuary is a body of water between saltwater and freshwater. Which is NOT a threat on estuaries? A. fertilizer or pet waste C. untreated sewage B. sedimentation D. use natural pesticides


27. Intertidal zone is covered or uncovered as the tide goes in and out. Which is NOT a threat in the intertidal zone? A. moisture C. responsible fishing practices B. pollution D. waves​