AQA GCSE Combined Science (8464), Higher tier · Biology › Ecology › Biodiversity and the effect of human interaction on ecosystems
Practise Waste management. 11 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
A growing human population with a rising standard of living uses more resources and makes more waste, which can pollute water, air and land. Expect questions on the sources of pollution and how pollution reduces biodiversity, often with data.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Name sources of water, air and land pollutionWater: sewage, fertiliser, toxic chemicals. Air: smoke, acidic gases. Land: landfill, toxic chemicals.
4
Explain why more waste is producedThe human population is growing rapidly and the standard of living is rising, so more resources are used.
5
Explain how pollution reduces biodiversityPollution kills plants and animals, so fewer species survive in the area.
6
Explain the effects of acidic gasesGases such as sulfur dioxide dissolve in rain to make acid rain, which damages trees and makes lakes acidic.
7
Explain how fertiliser run-off kills aquatic lifeAlgae grow, block light, plants die, decomposers respire and use up oxygen, so fish die.
Notes
Why there is more waste
The human population is growing rapidly and the standard of living is increasing.
So more resources are used and more waste is produced.
Unless waste and chemical materials are properly handled, more pollution will be caused.
Where pollution happens
Water: from sewage, fertiliser and toxic chemicals.
Air: from smoke and acidic gases.
Land: from landfill and toxic chemicals.
Pollution kills plants and animals, which can reduce biodiversity.
Examples of the effects
Acidic gases, such as sulfur dioxide from burning fuels, dissolve in rainwater to make acid rain. This damages trees and can make lakes and rivers too acidic for many organisms.
Smoke contains tiny solid particles that can harm the lungs of animals and coat leaves, reducing photosynthesis.
Landfill takes up land that could be a habitat, and toxic chemicals can leak from it into the soil and water.
Toxic chemicals, such as pesticides, can kill organisms other than the pests they are meant to kill.
Fertiliser and sewage in water grade 7+
Fertiliser washed into a lake or river adds mineral ions such as nitrates, so algae and surface plants grow rapidly.
They block the light, so plants lower down cannot photosynthesise enough and die.
Decomposers (bacteria) feed on the dead plants and algae. Their numbers increase, and their respiration uses up the oxygen in the water.
Fish and other animals die from lack of oxygen, so biodiversity falls.
Untreated sewage also feeds decomposers, so it can use up the oxygen in the same way.
Cheatsheet
More people + higher standard of living → more resources used → more waste
Water pollution: sewage, fertiliser, toxic chemicals
Air pollution: smoke, acidic gases
Land pollution: landfill, toxic chemicals
Pollution kills plants and animals → lower biodiversity
Acidic gases (e.g. sulfur dioxide) → acid rain
Fertiliser in water → algae grow → light blocked → plants die → decomposers respire → oxygen used up → fish die grade 7+
How to answer each type of question
Recall: name a source of pollution
1 to 3 marks3
Match the source to where it pollutes: water, air or land.
Be specific: 'fertiliser' or 'sewage', not just 'waste'.
Example. Give one source of pollution for each of: (a) water (b) air (c) land.
Link both to more resources used and more waste made.
Example. Explain why the amount of waste produced by humans has increased over the last 100 years.
Show the model answer
The human population has increased rapidly (1). The standard of living has increased, so each person uses more resources and produces more waste (1).
Describe and explain pollution data
2 to 3 marks5
Describe the pattern with numbers.
Link the pollutant to the number of organisms or species.
Explain using the chain of effects.
Example. Scientists counted the invertebrate species in samples from a river. Upstream of a sewage outlet: 14 species. 100 m downstream: 3 species. 1 km downstream: 9 species. Describe and explain the pattern. (3 marks)
Show the model answer
The number of species is lowest just below the outlet (3), compared with 14 upstream and 9 further downstream (1). Bacteria break down the sewage and their respiration uses up oxygen, so fewer species can survive just below the outlet (1). Further downstream the sewage has been diluted or broken down, so there is more oxygen and more species survive (1).
Explain how a pollutant reduces biodiversity
3 to 5 marks7
Name the pollutant and where it goes.
Explain the chain of effects step by step, one point per sentence.
Finish with organisms dying, so there are fewer species.
Example. After heavy rain, fertiliser from a field washed into a lake. Several weeks later, many fish in the lake died. Explain why. (5 marks)
Show the model answer
The fertiliser adds mineral ions (nitrates) to the lake, so algae grow rapidly (1). The algae block the light, so plants below the surface cannot photosynthesise and die (1). Decomposers / bacteria feed on the dead plants and increase in number (1). The decomposers respire, using up the oxygen in the water (1). The fish cannot get enough oxygen for respiration, so they die (1).
the standard of living has increased, so each person uses more resources
(e)
it kills plants and animals
Question 2Medium6 marks
Burning coal in power stations releases acidic gases such as sulfur dioxide. These gases dissolve in rain water. Scientists measured the pH of the water in lakes in one region and counted the number of fish species in each lake. {table} shows the results.
[object Object]
(a) Describe the relationship shown in {table}.[1]
(b) Suggest why fewer species of fish live in more acidic lakes.[2]
(c) Acidic gases released in one country can reduce biodiversity in another country. Suggest why.[1]
(d) Explain why rapid growth in the human population can lead to more pollution.[2]
Show the answer and mark scheme
(a)
as the pH decreases (more acidic), the number of fish species decreases
(b)
some species cannot survive at low pH (e.g. the acid damages gills / kills eggs)
enzymes in the fish may be denatured at low pH
the plants and invertebrates that fish eat are killed, so there is less food
(c)
the gases are carried by the wind / clouds and fall as acid rain in other countries
(d)
more people use more resources / burn more fuel
(so) more waste / pollutants are produced, which cause pollution unless handled properly
Question 3Hard6 marks
Sewage from a village is sometimes released into a river without being treated.
Explain how untreated sewage entering a river could reduce the biodiversity of the river.[6]
Show the answer and mark scheme
sewage contains organic matter and mineral ions such as nitrate and phosphate
the mineral ions cause rapid growth of algae (and plants) in the water
a layer of algae at the surface blocks light, so plants below cannot photosynthesise and die
bacteria (decomposers) feed on the organic matter in the sewage and on the dead algae and plants
the number of bacteria increases, and they use oxygen in aerobic respiration
so the concentration of dissolved oxygen falls
fish and invertebrates that need a high concentration of oxygen die or move away
only a few species that can tolerate low oxygen survive, so biodiversity falls
sewage may also contain pathogens or toxic chemicals that kill organisms
Marked with levels of response: the full level descriptors are in the app.