(a) Fig. 6.1 is a graph that shows the concentration of dissolved oxygen in the water at increasing distances along a river.
Untreated sewage is released into the river. This is marked on the graph in Fig. 6.1.
(i) Describe the results shown in Fig. 6.1.
(ii) Predict and explain the effect on the organisms in the river of the dissolved oxygen concentration at X in Fig. 6.1.
(b) Describe why it is important for humans that sewage is treated before entering rivers.
(c) Pollution can cause organisms to become extinct.
State three other factors that can cause extinction.
▶️ Answer/Explanation
(a)(i) The graph shows that initially, the dissolved oxygen concentration is high and stable. After untreated sewage is released, the oxygen level drops sharply, reaching a minimum at point X. Beyond X, the oxygen concentration gradually increases, eventually recovering to near its original level.
(a)(ii) Prediction: Organisms at point X will likely die or decrease in number. Explanation: The extremely low oxygen concentration at X cannot support aerobic respiration, leading to suffocation and death of aquatic life.
(b) Treating sewage is crucial to remove harmful pathogens and prevent waterborne diseases like cholera. It also protects aquatic ecosystems by maintaining oxygen levels and preventing contamination of food sources like fish.
(c) Three other extinction factors include: (1) Habitat destruction from deforestation or urbanization, (2) Overhunting/poaching of species, and (3) Climate change altering ecosystems faster than species can adapt.
Fig. 6.1 shows the total mass of plastics waste produced in the world since 2000 and what happens to that plastic. The data from 2020 to 2050 are predictions and are shown as dashed lines on Fig. 6.1.
(a)(i) Using the information in Fig. 6.1, describe the data for the total plastics waste production from 2000 to 2050.
(a)(ii) Using the information in Fig. 6.1, estimate the percentage of total plastics waste that will be discarded in 2050. Circle the correct percentage. 12% 25% 33% 50%
(a)(iii) Many plastics are made from oil. Oil is not a sustainable resource. Describe what is meant by the term sustainable resource.
(a)(iv) The combustion of plastics releases carbon dioxide gas into the atmosphere. Describe the consequences of releasing this carbon dioxide gas into the atmosphere.
(b) Fig. 6.2 shows plastic pollution in an ocean.
Describe the effects of plastic pollution on organisms in the oceans.
▶️ Answer/Explanation
(a)(i) The total plastics waste production shows a steady increase from 2000 to 2020, followed by an accelerated rise from 2020 to 2050. For example, the mass increases from ~300 million tonnes in 2000 to ~600 million tonnes in 2020, and is projected to exceed 1200 million tonnes by 2050.
(a)(ii) The correct percentage is 50% (circled), as the “discarded” portion in 2050 is roughly half of the total waste.
(a)(iii) A sustainable resource is one that can be replenished at the same rate as it is consumed, ensuring it does not deplete over time (e.g., solar energy, wind energy).
(a)(iv) Releasing CO2 from plastics combustion contributes to the greenhouse effect, leading to global warming, climate change, rising sea levels, and habitat destruction.
(b) Plastic pollution harms ocean organisms by:
1. Entanglement, causing injury or suffocation.
2. Ingestion, leading to digestive blockages or starvation.
3. Toxicity, poisoning marine life.
4. Disrupting food chains via bioaccumulation.