iGCSE Biology (0610)-20.3 Pollution – iGCSE Style Questions Paper 1

Question

The bloodworm is an organism that is found in heavily polluted water.
        The diagram shows where raw sewage flows into a river.
        Where would there be fewest bloodworms?

▶️Answer/Explanation

A

The presence of bloodworms in water bodies is often an indicator of poor water quality and pollution. Bloodworms (the larvae of chironomid midges) are known to thrive in environments with high levels of organic matter, especially decaying sewage and other pollutants. These organisms are adapted to tolerate low oxygen levels and can survive in heavily polluted waters.

In the context of the given diagram, the point of input for raw sewage is between points A and B, which means that the highest concentration of pollutants, including organic matter and sewage, would be present in the water between these two points. Therefore, the area where there would be the fewest bloodworms would likely be point A, which is upstream from the input of raw sewage. As you move downstream towards points B, C, and D, the pollution level increases, leading to a higher likelihood of bloodworm presence.

Question

The diagram shows the results of a survey on the types of animals found along a stretch of river
        near to a factory.

Which of the following animals lives in the most polluted water?
blood worm
B  caddis fly larva
C  leech
D  stonefly nymph

▶️Answer/Explanation

A

Blood worms are often considered to be the most pollution-tolerant among the options listed (blood worm, caddis fly larva, leech, and stonefly nymph). This is due to their unique adaptations that allow them to survive in low-oxygen and polluted environments. Blood worms are a type of aquatic worm that can thrive in areas with organic pollution, where there might be high levels of nutrients and low levels of oxygen. They are often found in areas where organic matter and pollution accumulate, such as sewage-contaminated water bodies. The presence of blood worms in the survey results suggests that the water in that stretch of the river is polluted, as they are commonly found in environments with poor water quality. They have developed mechanisms to survive in these conditions, such as hemoglobin in their blood that helps them extract oxygen even in low-oxygen situations. 

On the other hand, the caddis fly larva, leech, and stonefly nymph are comparatively less tolerant of pollution. They are typically found in cleaner and better-oxygenated waters. As pollution levels increase, these organisms may not be able to survive, which is why the blood worm is considered to inhabit the most polluted water among the options given.

 

Question

The graph shows how oxygen concentration and the number of bacteria change when sewage is
        added to a river.

What describes the oxygen concentration and the number of bacteria between the point at which
sewage is added and point P?

Oxygen concentration and number of bacteria stay the same.
B  Oxygen concentration decreases and number of bacteria increases.
C  Oxygen concentration increases and number of bacteria decreases.
Oxygen concentration remains the same and number of bacteria increases.

▶️Answer/Explanation

B

The graph represents the relationship between the oxygen concentration and the number of bacteria in a river when sewage is introduced into it.  At the starting point, before sewage is introduced to the river, the oxygen concentration is relatively high, and the number of bacteria is relatively low. This is typical for a healthy and unpolluted river ecosystem, where oxygen levels are sufficient to support aquatic life, and bacterial populations are under control. When sewage is added to the river (introduced at the indicated point), the dynamics start to change. Sewage often contains organic matter, nutrients, and pollutants that can affect the water quality. As you move from the sewage addition point to point P on the graph, two key changes are observed:

    • Decrease in Oxygen Concentration: The graph shows a decrease in the oxygen concentration. This could be due to the decomposition of organic matter present in sewage. Bacteria and other microorganisms feed on this organic material, consuming oxygen during the process of decomposition. This can lead to a decrease in dissolved oxygen levels in the water.
    • Increase in Bacteria Population: Simultaneously, the graph indicates an increase in the number of bacteria. The introduction of organic matter from sewage serves as a food source for bacteria. As they consume this organic matter, their population grows rapidly. This increase in bacteria can contribute to the breakdown of the organic pollutants but can also lead to an imbalance in the ecosystem.

 The organic matter in sewage is promoting bacterial growth, which in turn is consuming more oxygen, potentially leading to a decrease in the overall water quality and negatively impacting aquatic life that depends on sufficient oxygen levels. This situation is characteristic of pollution in water bodies, where untreated sewage or pollutants can lead to imbalances in the natural ecosystem and potential harm to the environment.

Question

On the map shown, sulfur dioxide is produced at X. Which region is most likely to experience acid
         rain?

                 

▶️Answer/Explanation

A

The region which is most likely to experience acid rain is at point A.

Sulfur dioxide (SO2) is a primary contributor to the formation of acid rain. It is produced primarily through the combustion of fossil fuels, particularly in power plants, industrial facilities, and vehicles. When released into the atmosphere, sulfur dioxide can undergo chemical reactions that lead to the formation of sulfuric acid (H2SO4), a major component of acid rain. This sulfuric acid can then be carried by the wind and atmospheric conditions to distant regions where it falls to the ground as acid rain.

Acid rain can travel long distances from its source due to prevailing wind patterns. Downwind regions can experience the effects of acid rain even if they don’t have as many local emissions.  If sulfur dioxide is being produced at point X on the map, the regions most likely to experience acid rain would be downwind of that location, typically in the direction of prevailing winds. So, the region most likely to experience acid rain would be the A where high concentration of SO2 emissions occurs.

 

Question

Which process may result in eutrophication in a lake?

A    bleach entering from a factory
B    fertilisers entering from farmland
C    hot water entering from a power station
D    pesticides entering from farmland

▶️Answer/Explanation

 B. Fertilizers entering from farmland

Eutrophication is the process by which a body of water, such as a lake, becomes enriched with nutrients, particularly nitrogen and phosphorus. These nutrients can come from various sources, but in this case, the main source is fertilizers entering from farmland. When fertilizers are applied to agricultural fields, excess nutrients can run off into nearby water bodies during rainfall or irrigation. These nutrients then promote the growth of algae and other aquatic plants in the lake. As these plants die and decompose, bacteria break down the organic matter, consuming oxygen in the process. This can lead to a depletion of oxygen in the water, causing harm to aquatic life and creating dead zones where little to no life can thrive.

Option A (bleach entering from a factory) could lead to water pollution, but it’s less directly related to eutrophication. Option C (hot water entering from a power station) could cause thermal pollution, affecting aquatic life, but it’s not a direct cause of eutrophication. Option D (pesticides entering from farmland) could also contribute to water pollution, but it’s not a primary cause of eutrophication either.

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