4.17 understand the effects of deforestation, including leaching, sol erosion, disturbance of the water cycle and of the balance in atmospheric oxygen and carbon dioxide

Leaching

Trees leach nutrients when they are alive, but return nutrients to the soil when they die. When trees are cut down, nutrients gets leached but not returned, resulting in infertile soil.

Soil erosion

When trees are removed, soil can be washed away by rain etc as tree roots hold soil together (but there will be no tree roots, as there will be no trees).

Disturbance of the water cycle

Trees take up water, when they are cut down, water runs straight into rivers, causing flooding. also, the local climate gets drier as there is much less transpiration occurring.

Disturbance of the balance of carbon dioxide and oxygen

When trees die, carbon dioxide is naturally released. When they are burnt, all the carbon dioxide is released at once. alternatively, if wood is used in furniture etc, the carbon is stored and not released, disrupting the carbon cycle.

Fewer trees means fewer photosynthesis means less oxygen.

4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms causing depletion of oxygen

Like fertilisers, sewage also contains phosphates (from detergents) and nitrates (from faeces etc). If these are leaked into rivers, eutrophication occurs.

NOTE: Point 4.16 my help for understanding

4.16 understand that eutropication can result from leached minrals from fertiliser

Nitrates and phosphates can leak from mineral fertilisers that are put on fields. If it rains, they are easily leached into rivers and lakes. this results in eutrophication. Basically...

- The extra nutrients causes algae to grow super fast. This blocks out the light
- Plants in the river (before the algae) can not photosynthesise due to low light. They die.
- With more food (dead plants) available, microorganisms living in the water rapidly increase in number and deplete/use up all of the oxygen in the water.
- Organisms, like fish for example, that need oxygen, die.

4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences

Heat from the sun is naturally radiated off the earth and into space. Greenhouse gases naturally keep in some of the heat (otherwise we would all die of cold, basically). However, increasing the amount of greenhouse gases is blocking the heat from escaping (known as the greenhouse effect). effectively, this heats up Earth, which is global warming.

Consequences of global warming include climate change (e.g. change in rainfall pattern)

4.13 understand how human activities contribute to greenhouse gases

Okay so basically...

Contribution to carbon dioxide - Car exhausts, industrial processes (burning of fossil fuels etc), cutting down of trees

Contribution to methane - rice growing, cattle rearing

Contribution to nitrous oxides - fertilisers, vehicle engine, industrial engines

CFCS - all man-made

4.12 understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases

NOTE: You may be asked where the greenhouses originate from. Well, its not in the spec but it was in the 2015 paper so just to be safe I have included the info (its in red).

Greenhouse gases are bad as they trap heat from the sun in the earths atmosphere. Examples of greenhouse gases include...

- Water vapour
- Carbon dioxide (deforestation, industrial processes, car exhausts)
- Nitrous oxide (fertilisers, vehicle engines, natural release from bacteria)
- Methane (rotting plants, rice growing, cattle rearing)
- CFCs (NOTE: CFCS are man-made chemicals, they are basically not produced anymore but some still are and are leaking from old products that contain them)

4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide

Sulfur dioxide

When fossil fuels are burnt, sulfur dioxide is released (from sulfur impurities in the fuel). When it mixes with rain clouds is forms acid rain (dilute sulfuric acid). This kills fish and trees as it causes lakes to become more acidic and can damage leaves and release toxic substances from the soil, meaning it is hard for the tree to take up nutrients from the soil.

Carbon monoxide

When fossil fuels are not burnt with enough air (incomplete combustion), carbon monoxide is produced. this is a poisonous gas and binds to haemoglobin in red blood cells, preventing the red blood cells from carrying enough oxygen to your muscles.