Human Influences on the Environment (Edexcel IGCSE Biology: Double Science)

Large quantities of food are wasted every year. Waste food needs to be disposed of using methods that do not harm the environment.

The table shows the mass of each gas released into the air from three different methods of waste disposal.

Calculate how much carbon dioxide would be released from 125 kg of waste food when using an anaerobic digester.

Give your answer to two significant figures and in kilograms. 

Some scientists have claimed that anaerobic digesters are the most environmentally friendly method of waste disposal.

Evaluate this claim using data from the table and your own knowledge.

Farmers may add chemical fertilisers to their soil.

Explain how chemical fertilisers can increase crop yield.

These fertilisers may leak into rivers.

A scientist measures the oxygen content of water in two different locations of the same river during the month of April.

In location A he finds that the mean dissolved oxygen was 6 mg per litre and at location B he finds that the mean dissolved oxygen was 3 mg per litre.

He concludes that the use of fertiliser in the field has affected the oxygen content of the river.

Discuss his conclusion.

Some farmers use alternative substances to chemical fertilisers.

Suggest one alternative substance that a farmer may use.

There is a general consensus amongst the scientific community that increased levels of carbon dioxide emissions, as a result of human activity, are causing global warming due to an enhanced greenhouse effect. 

Explain how increases in the proportions of greenhouse gases in the atmosphere have led to global warming.

Global warming, and the climate change that it brings, have an overall detrimental effect on biodiversity and ecology in general.

Suggest and explain one effect of global warming that may be beneficial to an individual species.

The graph below shows the total greenhouse gas emissions from Europe and China from the years 1990 to 2019.

The emission data is given using the unit billion tonnes. 

Describe the data in the graph. 

(3)

Give two reasons that could explain the trends shown in the graph. 

(2)

The diagram shows a river and the location of a fertiliser factory. The arrows indicate the direction of the flow of the river.

Calculate the mean nitrate concentration found at site B.

The scientist observed algae and some dead fish in the river at site B. These were not present at site A.

Give an explanation for these observations.

Scientists carried out another test and found higher than normal levels of sulfuric acid dissolved in the water in the stream at both sites. 

Explain a series of events that could have led to sulfuric acid washing into the river. 

A dairy farmer hoses down the floors of his milking shed at the end of each day's milking. The waste water flows from the shed floor and is pumped into a storage tank. This waste water contains urine and faeces from the cattle.

On one occasion the waste water storage tank overflowed and entered a nearby stream. 

Explain the effect that this event will have on the plants and animals living in the stream.

Farmers keep cows to produce milk.

Injecting cows with growth hormone (GH) will increase milk production.

This allows farmers to obtain the same volume of milk from fewer cows.

Digestion in cows releases methane gas into the atmosphere.

A scientist claims that injecting GH into cows would reduce climate change.

Comment on this claim.

The table below gives data about how the carbon dioxide (CO₂) concentration of the earth's atmosphere has changed over time. 

Plot the data from the table on the graph paper provided below. 

 Explain why carbon dioxide concentrations in the atmosphere are changing.

In 2022 a climate activist claimed that, to arrest global warming, the atmospheric CO₂ level should be brought back to the level of the year 1900.

Using the data from the table in part (a), calculate the percentage decrease that the climate activist claims would be needed to return the atmospheric CO₂ level to its 1900 level. 

When fossil fuels are burned sulfur dioxide gas (SO₂) can also be released into the atmosphere. 

Flue gases from the burning process can be captured and desulfurised, a process which traps the flue gases and reacts with the sulfur dioxide with calcium hydroxide.

A further step results in the formation of calcium sulfate which is a major component of plasterboard used in the building industry. 

Ca(OH)_2(s) + SO_2(g) → CaSO_3(s) + H₂O_(l)

Apart from supplying the building industry, explain one benefit of the process of flue gas desulfurisation. 

Describe the potential consequences for living organisms of failing to carry out flue gas desulfurisation. 

There are currently two main ways in which household rubbish is disposed of by local authorities in the UK.

These are:

• Landfill: rubbish is buried underground
• Incineration: rubbish is burned at 1000 °C

The table below outlines some of the features of both methods. 

Use the data in the table and your knowledge of waste treatment to evaluate both methods of waste disposal.