CIE iGCSE Biology-20.3 Pollution- Study Notes- New Syllabus
CIE iGCSE Biology-20.3 Pollution- Study Notes – New syllabus
CIE iGCSE Biology-20.3 Pollution- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Describe the effects of untreated sewage and excess fertiliser on aquatic ecosystems
- Describe the effects of non-biodegradable plastics, in both aquatic and terrestrial ecosystems
- Describe the sources and effects of pollution of the air by methane and carbon dioxide, limited to: the enhanced greenhouse effect and climate change
Supplement
- Explain the process of eutrophication of water, limited to:
• increased availability of nitrate and other ions
• increased growth of producers
• increased decomposition after death of producers
• increased aerobic respiration by decomposers
• reduction in dissolved oxygen
• death of organisms requiring dissolved oxygen in water
Effects of Untreated Sewage and Excess Fertilisers on Aquatic Ecosystems
1. Untreated Sewage
What it is: Sewage is wastewater from homes, factories, and toilets containing organic waste and harmful microorganisms.
⚠️ Harmful Effects:
- Deoxygenation of water: Bacteria decompose organic matter and consume dissolved oxygen.
- Kills aquatic life: Low oxygen levels cause fish and other aquatic organisms to suffocate.
- Disease spread: Pathogens in sewage can infect humans and animals using contaminated water.
2. Excess Fertilisers (Nitrates and Phosphates)
What it is: Fertilisers promote plant growth but may be washed into rivers and lakes by rain – this process is called leaching.
⚠️ Harmful Effects – Leads to Eutrophication:
- Algal bloom: Fertilisers cause excessive algae growth on the water surface.
- Sunlight blocked: Underwater plants die as they can’t photosynthesise.
- Decomposition: Dead plants and algae are broken down by bacteria, using up oxygen.
- Low oxygen levels: Aquatic animals die due to lack of oxygen.
- Result: The water becomes polluted and lifeless.
🧠 Summary Table:
| Pollutant | Effect on Aquatic Ecosystem |
|---|---|
| Untreated sewage | Reduces oxygen, spreads disease, kills aquatic life |
| Excess fertilisers | Causes eutrophication → algal bloom, low oxygen, plant/animal death |
Effects of Non-Biodegradable Plastics on Ecosystems
What Are Non-Biodegradable Plastics?
These are plastics that do not break down naturally by the action of bacteria or other decomposers. They can remain in the environment for hundreds of years, causing serious damage to ecosystems.
🌊 A. Effects in Aquatic Ecosystems (Rivers, Lakes, Oceans)
| Effect | Explanation |
|---|---|
| Harm to marine life | Animals like turtles, fish, and seabirds can swallow plastic or become entangled, leading to injury or death. |
| Blocking digestive systems | Swallowed plastics block the gut, causing starvation even when food is available. |
| Pollution of food chains | Tiny plastic particles (microplastics) can enter the food chain, affecting both animals and humans. |
| Water pollution | Floating plastic reduces water quality and harms aquatic plants and ecosystems. |
🌍 B. Effects in Terrestrial Ecosystems (Land Environments)
| Effect | Explanation |
|---|---|
| Harm to land animals | Livestock and wildlife may accidentally eat plastic, causing internal injury or death. |
| Soil degradation | Plastics alter soil structure, block water flow, and reduce fertility. |
| Land pollution | Accumulation of plastic waste ruins landscapes and clogs drains, increasing flood risk. |
| Harmful burning | Burning plastic releases toxic gases (like dioxins), which pollute air and harm health. |
🧠 Final Summary:
Non-biodegradable plastics are harmful because they persist in the environment, causing injury, pollution, and long-term damage to both aquatic and terrestrial life.
Air Pollution by Methane and Carbon Dioxide
What Are Methane and Carbon Dioxide?
Both are greenhouse gases – they trap heat in the Earth’s atmosphere and influence global climate patterns.
🔍 A. Sources of Carbon Dioxide (CO₂)
| Source | Explanation |
|---|---|
| Burning fossil fuels | Emitted from cars, factories, and power plants that use coal, oil, or gas. |
| Deforestation | Fewer trees mean less CO₂ is removed from the atmosphere via photosynthesis. |
| Respiration | All living organisms release CO₂ during respiration. |
🔍 B. Sources of Methane (CH₄)
| Source | Explanation |
|---|---|
| Livestock farming | Cows and sheep release methane during digestion (enteric fermentation). |
| Rice paddies | Flooded rice fields emit methane from anaerobic bacterial activity. |
| Landfills | Rotting organic waste in landfills produces methane gas. |
| Oil and gas extraction | Methane can leak during drilling, transport, and processing of fossil fuels. |
🌍 Effects – The Enhanced Greenhouse Effect
While the natural greenhouse effect keeps Earth warm enough for life, too much CO₂ and CH₄ from human activity causes global warming.
⚠️ Key Effects of Climate Change:
| Effect | Impact |
|---|---|
| Global temperature rise | Leads to melting ice caps, sea level rise, and more heatwaves. |
| Extreme weather | Increased droughts, floods, storms, and unpredictable seasons. |
| Rising sea levels | Floods coastal areas and threatens island communities. |
| Habitat loss | Ecosystems are disrupted; wildlife may not adapt in time. |
| Impact on farming | Crop failures and reduced food security in many regions. |
🧠 Final Summary:
Carbon dioxide and methane are major contributors to the enhanced greenhouse effect. Their build-up in the atmosphere leads to climate change, which disrupts ecosystems, affects weather patterns, raises sea levels, and impacts agriculture and human life worldwide.
Eutrophication – Step-by-Step Process
Eutrophication is a damaging process in aquatic ecosystems caused by excess nutrients (mainly nitrates and phosphates) from fertilisers or sewage entering lakes, rivers, or ponds. It often results in mass death of aquatic organisms.
1. Increased Availability of Nitrate and Other Ions
Fertilisers or sewage add extra nutrients (especially nitrates and phosphates) into the water.
📌 These nutrients promote excessive plant and algal growth.
2. Increased Growth of Producers (Algal Bloom)
Algae and aquatic plants grow rapidly due to high nutrient availability – forming an algal bloom.
📌 Algal bloom blocks sunlight from reaching submerged plants.
3. Death and Decomposition of Producers
Without light, deeper plants die. Overcrowded algae also begin to die.
📌 Dead plant matter settles at the bottom.
4. Increased Decomposition by Decomposers
Bacteria break down the dead plants and algae, using up a lot of oxygen in the process.
📌 Decomposition is highly oxygen-demanding.
5. Increased Aerobic Respiration by Decomposers
As decomposers respire aerobically, they further reduce the dissolved oxygen in the water.
📌 Oxygen levels drop sharply.
6. Reduction in Dissolved Oxygen
The low oxygen concentration causes stress to aquatic life that depends on oxygen.
7. Death of Aquatic Organisms
Fish and other aerobic aquatic animals suffocate and die.
📌 Their death leads to more decay and worsens the cycle.
🧠 Final Summary Table:
| Stage | What Happens |
|---|---|
| Extra nitrates enter water | From fertilisers or sewage |
| Algae and plants grow rapidly | Algal bloom occurs |
| Light blocked, plants die | Algae and deeper plants die |
| Decomposers break down dead matter | Bacteria increase, decomposition uses oxygen |
| Oxygen levels fall | Due to high aerobic respiration by decomposers |
| Fish and animals die | Lack of oxygen causes suffocation |