IB ESS Topic 4.4

A coastal inlet is currently experiencing an overpopulation of phytoplankton. Which of the following is a likely cause of this phenomenon?

• The introduction of sea otters into the bay

• The decrease in agricultural activity on land drained by the river

• The establishment of fish farms in the bay

• The overfishing of salmon

Answer explanation

Phytoplankton grows in response to increased nutrients in the water which is most significantly done by keeping fish captive in overstocked cages. While sea otters would also add to nutrients through their waste, they are free to leave and are generally added in much lower numbers.

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An example of an organic pollutant is

• Radioactive waste from a nuclear power plant

• Chemical fertilizer applied to fields

• Animal manure from a feedlot

• An oil spill in the ocean

Answer explanation

The only example of organic pollution is animal manure. The others are inorganic.

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An example of an inorganic pollutant is

• biological detergents used in laundry

• pathogens from human waste

• noise pollution from aircraft taking off from an airport

• pesticides used in agriculture

Answer explanation

Noise pollution from transport is inorganic. All others are organic.

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Which of the following pollutants contributes to eutrophication?

• pesticides

• chemical fertilizers

• heavy metals

• oil

Answer explanation

Only chemical fertilizer contain nitrogen and phosphorous that drive eutrophication.

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Nitrogen in groundwater is more likely when

• located near/under forested areas

• located near/under agricultural fields

• located near/under industrial areas

• soils are exposed to acid deposition

Answer explanation

Nitrogen is not typically a natural component of groundwater and usually indicates fertilizer contamination from agriculture and/or failed septic systems. The other options are not sources for nitrogen in groundwater.

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NGSS.MS-ESS2-4

Nutrient rich runoff from fertilized fields causes

• adaptation

• eutrophication

• biomagnification

• denitrification

Answer explanation

The addition of nutrients into water bodies from fertilized fields will most likely lead to eutrophication and not biomagnification as nutrients are biodegradable. Eutrophication is the increase of nitrates in water, while denitrification reduces nitrates concentrations.

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Eutrophication is:

• the decrease in oxygen content of water due to an explosion of decomposers

• an important energy flow in the nitrogen cycle

• a process used to purify water

• the gradual improvement of water quality in lakes and rivers

Answer explanation

Eutrophication starts with the increased input of nutrients which results in an increase in surface algae that block out sunlight to deeper parts of the water body. The increase in algae results in a temporary increase of smaller consumers but as they can't keep up with algal growth, much of the algae remains uneaten and when it dies falls to the bottom where decomposers increase using up oxygen. Larger consumers begin to die resulting in more decomposers until the complete food web collapses.

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Which of the following does NOT occur at the end stage of eutrophication?

• Average dissolved oxygen content of water decreases

• Water nutrient content increases

• Producers increase

• Diversity increases

Answer explanation

As eutrophication progresses and dissolved water content decreases, the food web collapses, reducing diversity.

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Biochemical oxygen demand is measured in

• percent (%)

• parts per billion (ppb)

• milligrams per liter (mg/L)

• grams per liter (g/L)

Answer explanation

The correct units of measurement are milligrams per Liter or parts per million (ppm).

The cheapest strategy for reducing pollution is

• Clean up and restoration of polluted sites once development is complete

• Altering human activity that produces the pollution

• Regulating and reducing the pollutants at the point of emission

• Develop and instal technology to reduce pollution at acceptable levels

Answer explanation

Preventing pollution of the environment is always going to be much cheaper and effective in the long run than cleaning up once the ecosystem is already polluted. Even if all of the pollution can be removed, restoring the ecosystem to what it was before is almost impossible. While pollution reducing technology can minimize ecosystem impact, the cost of its development is often more expensive than changing the human behavior.

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