• Increasing human population has led to an increase in pollution. Some of this is due to:
• more fossil fuels being burnt for heat and power
• more food being grown
• land taken over for industry and housing.

As a result there has been an increase in levels of water pollution.

• Nitrate fertilisers are very soluble in water and are easily washed off fields by the rain and then into rivers and reservoirs. Because nitrates are all soluble they cannot easily be removed from the water.
• Pesticides used by farmers to kill weeds or insects may be washed or blown into streams and rivers.
• Sulfur dioxide in the air can dissolve in water to form an acidic solution.

The most common source of air pollution is the combustion of fossil fuels. This usually happens in vehicle engines and power stations.

smoke- Deposits soot on buildings and trees, causing them damage. Permeates the air, making it difficult for living creatures to breathe

carbon dioxide- greenhouse gas that contributes to global warming

sulfurdioxide- contributes to acid rain

This makes lichens natural indicators of air pollution. For example:

• bushy lichens need really clean air
• leafy lichens can survive a small amount of air pollution
• crusty lichens can survive in more polluted air

In places where no lichens are growing, it's often a sign that the air is heavily polluted with sulfur dioxide.

Most rubbish is buried in landfill sites and not all of it comprises safe materials. Even common household items can contain toxic chemicals such as poisonous metals. Many smoke alarms contain radioactive americium. Industrial waste is also discharged onto the land. Many farmers apply pesticides to improve their crops, but these can damage living things. Toxic chemicals can be washed from the land into rivers, lakes and seas.

Forestry is sustainable as long as forests are allowed to replace themselves, or are replanted after felling, but often this is not done. The result is that the world’s forests are steadily shrinking.

loss of biodiversity- The term biodiversity refers not only to the number of different species, but also to all the variations within and between species, and all the differences between the habitats and ecosystems that make up the Earth’s biosphere.

The loss of forests reduces biodiversity and we run the risk of losing organisms that might have been useful in the future - for example as sources of new medicines. There is also a moral responsibility to look after the planet and its resources.

This process is called deforestation. It has some important consequences:

• forest habitats are destroyed
• soil erosion increases, which causes barren land, flooding and land slides
• atmospheric pollution is caused when forests are cleared by burning trees

• causes big changes in climate
• rise in sea level
• reduces biodiversity 
• migration patterns
• changes in distribution of species.  

Biofuels come from the products of living organisms, such as methane biogas from decaying manure and sewage. Vegetable oils are also used as fuels for vehicles. Some of this biodiesel is made from waste cooking oil and rapeseed oil.

Advantages of using biofuels

Biofuels are carbon neutral, which means that they release only as much carbon dioxide when they burn as was used to make the original oil by photosynthesis.

However, some people are concerned about whether it is ethical to use food crops in this way, instead of using them to feed hungry people.This helps to reduce global warming (see next section).

Ethanol is the type of alcohol found in alcoholic drinks such as wine and beer. It is also useful as a fuel. For use in cars and other vehicles it is usually mixed with petrol.

it can be distilled from the fermentation product to be used in cars.

fermentation- This converts sugar from sugar cane or sugar beet into ethanol and carbon dioxide. Single-celled fungi, called yeast, contain enzymes that are natural catalysts for making this process happen:

C₆H₁₂O₆ 2C₂H₅OH + 2CO₂

Biogas- Bacteria break down sewage in a digester. Then The methane in biogas can be used as a fuel for heating homes

Intensive farming

Food production in this field has been increased by growing high-yield crops, removing other plants and pests and adding fertiliser to the soil. Other intensive farming practices include keeping animals indoors - often in restricted spaces. Many of these practices have unwelcome side effects and some raise ethical concerns. 

• a shorter food chain means that less energy is wasted therefore it is more efficient to eat plants than animals.
• preventing animals from moving so that it doesn't waste energy but this is seen as cruel to the animal.
• keeping them in warm sheds so they don't waste energy on maintaining body temperature.  

• one way is restricting fishermen taking too many fish. 
• the fungus fusarium is grown to produce mycoprotien. this is a protein rich food suitable for vegetarians. fusarium is grown aerobically on cheap sugar syrup. 
• microorganisms can be grown on a large scale industrial fermenters
• the conditions must be controlled for maximum growth. 

it has:

an air supply providing oxygen 

a stirrer to keep them spread out at an even temperature

a water- cooled jacket around the outside which the microorganisms heat

pH and temperature sensors