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- List the undesirable effects of deforestation (to include extinction, loss of soil, flooding, carbon dioxide build-up).
- Species extinction through habitat loss – the destruction of habitats and/ or food sources for animals can result in their extinction. It should also be noted that the destruction of forest habitats also reduces the diversity of plants and animals, thus disrupting several food chains.
- Soil erosion – Fewer trees and flora, in general, mean that there are fewer roots to hold the soil. This means that each time it rains, a thin layer of soil is washed away. This causes soil erosion and leaching of minerals (leaching is when a soluble chemical or mineral is washed away from the soil by rainwater). The eventual result is that the land becomes a desert.
- Flooding – soil erosion is washed into rivers, causing them to fill up or become blocked. This causes flooding. The loss of flora also means that there are no plant roots to take up rainwater, which means more rainwater washes into nearby streams and rivers. This makes flooding easier.
- Carbon dioxide build-up – Forests have high rates of photosynthesis, which means a great deal of carbon dioxide is removed from the atmosphere by the flora in forests. Therefore, deforestation means that a lot less carbon dioxide will be removed from the atmosphere, causing an increase in the CO2 levels in the atmosphere.
- Describe the undesirable effects of overuse of fertilisers (to include eutrophication of lakes and rivers).
I’m going to tell you guys now – eutrophication is a really important concept and you must know this. Most of the past papers I’ve done have questioned me on this topic at least once, so make sure you’re really thorough with it.
Farmers use fertilisers to increase crop yield, but using an excess can be dangerous:
A high concentration of fertilisers around plant roots can cause the roots to lose water by osmosis, resulting in the wilting and death of plants.
Another effect is eutrophication.
Fertilisers are water soluble, so are easily leached out of the soil and washed into rivers and lakes. Algal bloom occurs – the algae absorb the fertilisers and grow rapidly. This means that the algae will blanket the surface of the lake, blocking sunlight from the plant life below. Algae and plants below the surface die as a result. Bacteria decompose the dead algae and plants, using up the oxygen in the water for respiration, causing the animals to die too.
- Describe the undesirable effects of pollution, to include:
- Water pollution by sewage and chemical waste
- Air pollution by greenhouse gases (carbon dioxide and methane) contributing to global warming.
Chemical wastes such as phosphates can cause eutrophication, which, as we have learned, can be disastrous. Some chemical wastes can be toxic to certain species of plants or animals, or two inert chemicals in combination could react to form a toxic compound, or, even if the chemicals weren’t dumped into water bodies, they could still be leached into water bodies. Even if a chemical only harms one species, this could disrupt a food chain and decrease the species diversity in that ecosystem. If such chemical wastes enter the drinking water supply, that could be extremely harmful.
Sewage, which consists of urine and faeces, contains high levels of nutrients such as phosphates, organic matter and bacteria. Phosphates act as fertilisers for algae, thus resulting in algal bloom.
Sewage also contains organic matter which bacteria breakdown by aerobic respiration, thus allowing them to multiply and deoxygenate the water.
Sewage may also contain disease-causing bacteria, which could get into drinking water supplies, causing serious maladies such as cholera or typhoid.
This part has already been explained in the previous unit, B10.0 – Energy Flow in Ecosystems, but I’ll explain it again in more detail here 😊
CO2 and methane (CH4) are both greenhouse gases. They’re called greenhouse gases because they trap heat in the Earth’s atmosphere in the same way a greenhouse traps heat.
CO2 is produced in the combustion of fossil fuels, and methane is produced in the decay of organic matter and as a waste gas from digestive processes in cattle.
As the concentration of these gases in the atmosphere rise, more heat is trapped, making the atmosphere warmer. This is called the enhanced greenhouse effect. It causes global warming – the rise of Earth’s average temperature.
Global warming can result in the melting of ice caps (which can destroy ecosystems near the poles), the rise of sea levels which causes flooding in coastal regions, deadly heat strokes, changing weather conditions due to flooding and reduced rainfall, and the extinction of some species that can’t survive at higher temperatures.
- Discuss the causes and effects on the environment of acid rain, and the measures that might be taken to reduce its incidence.
When fossil fuels with impurities such as sulfur or nitrogen are combusted, Sulfur dioxide and oxides of nitrogen are released into the air. Nitrogen oxides are also a pollutant gas that may be released in car exhaust fumes. Another way that Nitrogen oxides are made is during lightning.
About 78% of the Earth’s atmosphere consists of nitrogen gas and 21% is oxygen. Nitrogen gas, N2, is extremely unreactive. However, under extreme conditions, it may react. So, when lightning strikes and the surrounding air is heated to a very high temperature and severely ionised, nitrogen reacts with oxygen to form nitrous oxides.
Nitrous oxides and sulfur dioxide can travel very high into the atmosphere, and be carried long distances by the wind. When they mix and react with the water in the atmosphere, they form acidic pollutants such as sulfuric acid (H2SO4), sulphurous acid (H2SO3), nitric acid (HNO3) and nitrous acid (HNO2). These acids dissolve in water, and fall back to Earth when it rains, causing acid rain.
Acid rain has a number of causes including:
- Damage to leaves, killing plants
- Acidification of lakes, killing animals (this is a major effect)
- The release of aluminium from the soil into lakes and aluminium is toxic to fish (also a major effect)
- Increased risk of asthma attacks and bronchitis in humans
- Corrosion of stonework on buildings, especially structures made of marble (marble contains calcium carbonate, which readily reacts with acids).
There are several measures that could be taken to reduce the reduce the incidence of acid rain:
Changing power stations from coal and oil to renewable energy sources will reduce the emission of several waste gases, including sulfur dioxide.
Using ‘scrubbers’ in power station chimneys removes sulfur dioxide from the exhaust gases. ‘Scrubber’ is the informal name for flue gas desulfurization (FGD).
Using catalytic converters in car exhausts ensures that oxides of nitrogen are converted to harmless nitrogen gas.
Another possible route is switching to electric cars instead of traditional fuel powered cars.
- Explain how increases in greenhouse gases (carbon dioxide and methane) are thought to cause global warming.
This has already been pretty clearly explained in point 3.
- Describe the need for conservation of:
- Species and their habitats
- Natural resources (limited to water and non-renewable materials including fossil fuels).
Why we should conserve species and their habitats:
- Ethical reasons – it is our responsibility to look after the Earth and all life on it.
- Many species are in danger of extinction due to habitat destruction, the introduction of alien species (they are called alien species as they are foreign to that ecosystem), international trade, pollution, hunting, poaching, etc.
- Loss of species also means that genes are lost – these may be important in future for genetic engineering.
- The presence of rare species and/or beautiful habitats could be an important source of money for poor communities, through tourism.
- Many plants have important medicinal value.
- The species may play an important role in a food chain so its endangerment could lead to the endangerment of several other species
- Aesthetic value – flora and fauna are often very pleasing to the eye.
Habitats can be conserved by introducing legislation that protects the habitat, such as fining on pollution, cutbacks on carbon emissions, laws against hunting and poaching, etc. Using wardens to protect habitats, and creating national parks and wildlife reserves are also very useful. Reducing or controlling public access to these habitats also goes a long way in their conservation (the public may litter in or damage the habitat). Controlling factors such as water drainage and grazing could also help preserve the habitat.
Natural resources are non-renewable, and therefore need to be conserved.
They can be conserved by increasing the use of renewable resources and improving the efficiency of energy (e.g. better insulation, smaller car engines, more public transport, using more energy efficient appliances, etc.). Another method is replanting the trees as they are cut down, preventing the increase of the greenhouse effect, and allowing habitats to be maintained.
And with that, we have concluded biology! Hallelujah!
Notes submitted by Sarah.
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