AP BIOLOGY

ECOLOGY

CHEMICAL CYCLES

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
The formation of a dead zone starts with
A
algae growing abundantly
B
no oxygen is seen
C
excess fertilizers running off into a body of water
D
decomposers breaking down all the decaying material using lots of oxygen
Explanation: 

Detailed explanation-1: -The formation of the dead zone is the result of eutrophication-when the water body receives too many nutrients such as phosphorous and nitrogen. The excess of these nutrients which run off the land in the form of wastewater into the rivers and oceans stimulate an overgrowth of algae which sinks into the water.

Detailed explanation-2: -Dead zones form when the algae die, sink to the bottom, and are decomposed by bacteria-a process that strips dissolved oxygen from the surrounding water. Dense algal blooms also block sunlight, which prevents underwater grasses from growing.

Detailed explanation-3: -Dead zones begin to form when excess nutrients, primarily nitrogen and phosphorus, enter coastal waters and help fertilize blooms of algae. Major nutrient sources include fertilizers, wastewater, and the burning of fossil fuels.

Detailed explanation-4: -Dead zones develop when fertilizers and nutrients from farmland drain into oceans or lakes, creating an algae bonanza that eventually dies and decomposes. As the algae decomposes, it depletes the waters of oxygen, suffocating species that live in the area.

Detailed explanation-5: -Dead zones are generally caused by significant nutrient pollution, and are primarily a problem for bays, lakes and coastal waters since they receive excess nutrients from upstream sources. Excess nitrogen and phosphorus cause an overgrowth of algae in a short period of time, also called algae blooms.

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