Environmental Sustainability
Human activity puts real pressure on the environment, so this chapter looks at where that pressure comes from and how it can be managed. It covers the main threats to air, water and land, the greenhouse effect and its link to global warming, and how biochemical oxygen demand (BOD) is used to judge how polluted a water sample is.
You should be able to connect a specific human activity to a specific environmental effect rather than describing pollution in only general terms. For example, burning fossil fuels releases both greenhouse gases that contribute to global warming and other pollutants that lower air quality, and each effect should be explained separately in an exam answer.
The chapter then moves to how ecosystems are protected and used sustainably: preservation keeps an area untouched, conservation manages resources so they are not used up, and restoration repairs ecosystems that have already been damaged. Ozone layer depletion and eutrophication are two further threats often tested here, each with its own distinct cause-and-effect chain.
The final section covers green technology and sustainable development, including renewable energy sources, waste reduction and an Environmental Impact Assessment (EIA) carried out before a development project is approved. A strong answer names a specific technology or practice and explains the mechanism behind why it reduces environmental harm, rather than simply calling it 'eco-friendly'.
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Content standards in this chapter
- 25.1 Threats to the Environment
- 25.2 Preservation, Conservation and Restoration of Ecosystems
- 25.3 Environmental Sustainability
- 25.4 Green Technology
Key concepts
- Threats to the environment
- Human activities such as burning fossil fuels, deforestation and improper waste disposal cause air, water and land pollution, alongside a rise in greenhouse gases that drives global warming. Each threat has a distinct cause, so an exam answer should name a specific activity and its specific effect rather than describing pollution in general terms. Open burning and vehicle exhaust, for example, are two separate sources of air pollution with different pollutants and different control measures.
- Greenhouse effect and global warming
- Greenhouse gases such as carbon dioxide and methane trap heat in the atmosphere that would otherwise escape into space, a natural effect that keeps Earth warm enough for life. Human activities release extra greenhouse gases, trapping more heat and raising the average global temperature, which is global warming.
- Biochemical oxygen demand (BOD)
- BOD measures how much oxygen microorganisms use to break down the organic matter in a water sample over a set time. A high BOD value means the water contains a lot of organic pollution, since more oxygen is used up, leaving less available for fish and other aquatic organisms. Comparing BOD values upstream and downstream of a discharge point is a common way to judge how much a specific source has polluted a river.
- Preservation, conservation and restoration
- Preservation protects an area of nature and keeps it untouched by human use, such as a strict nature reserve. Conservation manages the wise, sustainable use of a resource so it is not exhausted, such as controlled fishing. Restoration actively repairs an ecosystem that has already been damaged, such as replanting a cleared forest.
- Green technology
- Green technology reduces environmental harm compared with older methods, including renewable energy, recycling processes and cleaner production methods that release less pollution. Choosing a green technology usually involves weighing its environmental benefit against its cost and how practical it is to adopt widely. An electric vehicle, for example, produces no exhaust emissions itself, though the source of the electricity used to charge it also matters.
- Sustainable development
- Sustainable development meets the needs of people today without reducing the ability of future generations to meet their own needs. It balances economic growth, social wellbeing and environmental protection together rather than treating environmental protection as separate from development. Planting a fast-growing replacement crop for every tree logged in a plantation forest is one practical example of this balance.
- Ozone layer depletion
- The ozone layer in the upper atmosphere absorbs most of the sun's harmful ultraviolet (UV) radiation. Chemicals such as chlorofluorocarbons (CFCs), once common in aerosols and refrigerants, break down ozone molecules, thinning this layer and allowing more UV radiation to reach the Earth's surface, which raises the risk of skin damage and harm to some crops.
- Eutrophication
- Eutrophication begins when excess nutrients, often from fertiliser runoff or untreated sewage, enter a body of water and cause algae to grow rapidly, forming a dense bloom. When the algae die, decomposers use up large amounts of dissolved oxygen breaking them down, which can leave too little oxygen for fish and other aquatic life.
- Renewable energy
- Renewable energy sources, such as solar, wind and hydroelectric power, generate electricity without burning fossil fuels, which reduces the greenhouse gases released compared with coal or oil power plants. Adopting them at a larger scale usually requires weighing the upfront cost of infrastructure against the long-term reduction in emissions.
- Environmental Impact Assessment (EIA)
- An Environmental Impact Assessment is a formal study carried out before a development project, such as a new highway or factory, is approved. It identifies the project's likely effects on the surrounding environment so that mitigation steps can be planned, rather than approving a project without considering its environmental consequences.
How this chapter is examined
SPM Biology is assessed over three papers. Paper 1 has 40 objective questions (40 marks) in 1 hour 15 minutes; Paper 2 carries 100 marks across Sections A, B and C in 2 hours 30 minutes; Paper 3 is the practical, testing science process skills. Content from this chapter can appear in any of them, so lessons drill recall for Paper 1 and structured answers for Paper 2.
Common exam angles
- Linking a specific human activity to its specific effect on the environment.
- Explaining the greenhouse effect and distinguishing it from global warming.
- Interpreting BOD data to compare the pollution level of different water samples.
- Explaining how CFCs lead to ozone layer depletion and its effects on living things.
- Describing the stages of eutrophication from nutrient runoff to a drop in dissolved oxygen.
- Evaluating a named renewable energy source or green technology as a solution to a specific environmental threat.
Common mistakes
What students write: Confusing preservation and conservation.
What earns the mark: Preservation keeps nature untouched; conservation is the careful, sustainable use and management of resources. A protected forest reserve where logging is completely banned is preservation; a forest where logging is limited and controlled is conservation.
What students write: Saying high BOD means clean water.
What earns the mark: High BOD means more organic pollution, because microorganisms use more oxygen to break it down. A very low BOD value is what indicates cleaner water with less organic pollution.
What students write: Writing that the greenhouse effect is entirely harmful.
What earns the mark: A natural greenhouse effect keeps Earth warm enough for life; the problem is the extra warming from too much greenhouse gas. Without any greenhouse effect at all, Earth's average temperature would be far too cold to support life as it exists today.
What students write: Treating deforestation as only a loss of trees.
What earns the mark: Deforestation also reduces biodiversity, disturbs the carbon and water cycles, and causes soil erosion. Removing forest cover can also increase the risk of landslides and flooding by reducing how much rainwater the soil can absorb.
What students write: Believing ozone layer depletion is the same issue as global warming.
What earns the mark: Ozone depletion is about more ultraviolet radiation reaching Earth's surface; global warming is about heat being trapped by greenhouse gases. Some chemicals contribute to both, but the two problems have different mechanisms.
What students write: Saying eutrophication is caused by too little nutrients in water.
What earns the mark: Eutrophication is caused by an excess of nutrients, often from fertiliser or sewage, which triggers rapid algae growth and later a drop in dissolved oxygen.
What students write: Assuming green technology only means solar panels.
What earns the mark: Green technology is a broad category that also includes wind and hydroelectric power, biofuel, efficient waste treatment and electric vehicles, each reducing environmental harm in a different way. A good exam answer names the specific technology being discussed rather than referring to green technology as a single, uniform idea.
What students write: Believing an Environmental Impact Assessment removes all negative effects of a project.
What earns the mark: An EIA identifies a project's likely environmental effects before approval so mitigation steps can be planned; it does not remove every impact, only helps manage and reduce it. A project can still be approved with conditions attached, such as a required buffer zone or a wastewater treatment step.
Study this chapter
Experiments in this chapter
Frequently asked questions
What is the difference between preservation and conservation?
What does biochemical oxygen demand (BOD) tell us?
How does the greenhouse effect cause global warming?
What causes ozone layer depletion?
What is eutrophication?
Source:SRC-DSKP-EN, SRC-FORMAT
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