🏙️ Man and the Environment
Primary 6 Science — Summary Notes
Created by Miss Clarissa Ng · www.clartutors.com
1. 🌍 Man's Impact on the Environment
Whatever Man does affects the environment — sometimes for the worse, sometimes for the better.
The three main negative impacts
| Impact | What it means |
|---|---|
| Depletion of natural resources | As the world population grows, demand for resources rises, so they are used up faster than they can be replaced. |
| Deforestation | Large areas of forest are cleared by cutting or burning. |
| Pollution | Harmful matter is released into the air, water and land — and unwanted noise is produced. |
Deforestation leads to →
Soil erosion and water pollution · Reduced biodiversity · Global warming
2. 🔋 Natural Resources — Renewable or Non-renewable
- The growing world population has increased the demand for natural resources, putting non-renewable resources — such as fossil fuel and nuclear fuel — in danger of being depleted.
- Even renewable resources such as biomass are at risk, because Man uses them at a greater rate than nature can replace them.
| Type | What it means | Examples |
|---|---|---|
| Non-renewable | Resources that cannot be replaced easily within a relatively short period of time. | Fossil fuel, nuclear fuel |
| Renewable | Resources that can be replaced easily within a relatively short period of time. | Wind, solar energy, tides and water, geothermal energy, biomass (from plants and animals) |
3. 🐑 Living and Non-living Resources
- Man depends on natural resources for necessities such as food and shelter, and every natural resource comes from the environment.
- Resources can be living (biotic) — obtained from living things such as wildlife — or non-living (abiotic), which come from non-living things.
| Resource | Type |
|---|---|
| Animals | Living |
| Plants | Living |
| Fungi and bacteria | Living |
| Sand and clay | Non-living |
| Metals | Non-living |
| Air | Non-living |
| Water | Non-living |
4. 🪓 Deforestation
- Deforestation is what happens when large areas of forest are cleared by cutting down or burning the trees.
Why forests are cleared
- to obtain wood for buildings, houses and furniture;
- to make way for the construction of roads, highways and industrial areas;
- to create agricultural land for growing crops and rearing livestock.
5. ⛰️ Deforestation — Its Effects
Soil erosion
- Without the roots of trees to hold the soil firmly together, soil erosion occurs more easily. The soil then ends up in rivers and lakes, causing water pollution and the death of aquatic organisms.
- Soil that is washed into the water also makes it cloudier, so the submerged plants receive less light, photosynthesise less and grow poorly.
Disrupted rainfall
- With fewer trees, less water vapour is released during transpiration, so less condensation takes place and fewer clouds form.
- Fewer clouds mean less rain returns to the ground. This can lead to drought, and plants and animals that cannot cope with so little water may die out.
Reduced biodiversity
- Destroying or losing natural habitats puts species at risk of extinction.
- Tropical rainforests are home to a huge variety of living things — about 80% of all known species live there, so clearing them affects a very large number of species.
6. 🌡️ The Greenhouse Effect and Global Warming
- Heat from the Sun is trapped on Earth's surface by greenhouse gases such as carbon dioxide, water vapour, methane and ozone. These greenhouse gases make the planet warm enough for living things to survive. This is the greenhouse effect.
- When there are more greenhouse gases, more heat is trapped and average temperatures around the world rise. This is global warming.
Why the amount of greenhouse gases increases
- With fewer trees to take in carbon dioxide during photosynthesis, more carbon dioxide is left in the atmosphere.
- Burning fossil fuels in factories, power stations and motor vehicles releases carbon dioxide and methane.
Effects of global warming
- Polar ice caps melt and ocean waters gain heat and expand, so sea levels rise — low-lying coastal areas are then at risk of flooding.
- Temperature-sensitive wildlife may become extinct — for example, corals are sensitive to warmer waters.
- Climates become destabilised, bringing extreme weather.
7. 🏭 Pollution — The Four Types
Pollution happens when harmful matter is released into the environment. Most of it is caused by Man's activities and by using natural resources irresponsibly.
| Type | Main causes |
|---|---|
| Air pollution | Burning fuels in factories, power stations and motor vehicles; burning forests and rubbish; smoking |
| Water pollution | Dumping untreated sewage, waste or litter into water bodies; oil spills; fertilisers and chemical nutrients washed into the water |
| Land pollution | Dumping of rubbish; littering; excessive use of herbicides and pesticides |
| Noise pollution | Road traffic; construction equipment; factories; loudspeakers |
8. 💨 Air Pollution
| Cause | Effect |
|---|---|
| Dust and smoke from burning fuels, forests, rubbish and cigarettes | Damages the lungs, irritates the eyes and may cause breathing difficulties. |
| Acidic gases released when fuels are burnt | Dissolve in rainwater to form acid rain, which corrodes buildings and statues and makes soil and water too acidic for living things. |
| Chlorofluorocarbons (CFCs) from coolants, aerosol sprays and styrofoam | Destroy the ozone layer, so more harmful UV rays from the Sun reach us — causing sunburn, eye problems and skin cancer. |
How to reduce air pollution
- Switch off vehicle engines when they are not needed, and use public transport or carpool where possible.
- Choose CFC-free products such as CFC-free refrigerators and aerosol sprays.
9. 💧 Water Pollution
| Cause | Effect |
|---|---|
| Dumping of untreated sewage, waste or litter | Bacteria in untreated sewage spread diseases such as cholera. Harmful substances such as oil and mercury are taken in by living things and build up along the food chain. |
| Oil spills and plastic waste | Toxic waste and oil spills poison aquatic life. Oil on a bird's feathers makes it hard for the bird to float, fly and keep warm, and marine animals may eat plastic or get tangled in it and die. |
| Fertilisers washing into the water | Cause eutrophication — the chain below shows how this kills aquatic animals. |
1. Fertilisers wash into the water, feeding the algae and floating plants.
2. They grow quickly and block sunlight from the submerged plants, which then die.
3. Decomposers breaking down the dead plants use up the dissolved oxygen in the water.
4. With too little dissolved oxygen, the aquatic animals suffocate and die.
How to reduce it
- Keep rubbish out of water bodies such as drains, canals and rivers, and treat wastewater before releasing it.
- Use less fertiliser on farms near water bodies.
10. 🗑️ Land Pollution
- Causes: dumping of rubbish and littering; excessive use of herbicides and pesticides.
- Health problems: rubbish carries harmful germs, and food waste attracts pests such as houseflies, cockroaches and rats, which spread disease.
- Rubbish that cannot rot: biodegradable rubbish such as paper and food is broken down by decomposers, but non-biodegradable rubbish such as plastics, metals and glass is not. It piles up in landfills and may give off poisonous gases when burnt.
- Poisons in the soil: herbicides and pesticides can kill useful organisms in food chains and upset the balance of the ecosystem.
- How to reduce it: throw rubbish in the proper place, reduce, reuse and recycle non-biodegradable items, and use natural predators of pests instead of chemicals.
11. 🔊 Noise Pollution
- Noise is any sound that is unwanted and unpleasant to hear. Its main sources are road traffic, construction equipment, factories and loudspeakers.
- Health problems: noise disturbs rest and causes stress, and being exposed to loud noise for a long time may cause deafness.
- Environmental problems: stress from noise makes animals leave their habitats. Animals such as whales and dolphins, which find their way using echolocation, are badly affected by noise from engines and sonar.
- How to reduce it: turn down the volume of televisions and radios, and wear earplugs or earmuffs when working in noisy places.
12. ✅ Man's Positive Impact — Conservation and Reforestation
Conservation: reduce, reuse, recycle
| Action | What it means | Examples |
|---|---|---|
| Reduce | Cut down on what you use. | Switch off lights and fans when you leave a room; take a reusable bag to the shops instead of taking new plastic bags; print on both sides of a sheet of paper. |
| Reuse | Use an item again instead of throwing it away. | Store food in washed plastic containers; refill a reusable water bottle instead of buying new ones; pass on old books and clothes to someone else. |
| Recycle | Send used materials to be made into new products. | Put drink cans, glass jars, plastic bottles and newspapers into recycling bins; old glass jars are melted down to make new glass products. |
⭐️ KEY POINT
Reducing has the greatest effect. Reusing and recycling still help, but energy has already gone into making the products we use, so buying only what we truly need prevents the most resources from being wasted.
Reforestation
- Reforestation means planting seeds and young plants in areas where trees were cut down, so that habitats for endangered species can be restored.
- It moderates the harm caused by deforestation, such as global warming and water pollution.