18.1 The Human Population Explosion

A free GCSE Biology lesson for AQA (8461) from OBA School: biodiversity, why it matters, human population growth and managing our waste. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Define biodiversity and explain why a high biodiversity makes an ecosystem more stable
• Describe how the human population has grown and why this uses up more resources
• Explain how more people and higher living standards produce more waste and pollution
• Describe where pollution happens (water, air and land) and how waste can be managed
• Calculate a percentage increase from population or waste data

Key words

• Biodiversity: The variety of all the different species of organisms on Earth, or within one ecosystem.
• Ecosystem: All the living organisms in an area together with the non-living (abiotic) parts of their environment.
• Resource: Something people take from the environment and use, such as land, water, food, fossil fuels, metal ores or timber.
• Pollution: Harmful substances or energy released into the environment, which can damage living organisms.
• Landfill: A large hole in the ground where household and industrial waste is buried.
• Sewage: Waste water from toilets, homes and factories, containing human waste and dissolved chemicals.

Biodiversity and why it matters

An ecosystem with a high biodiversity contains many different species. Each species depends on others for food, shelter and keeping the physical environment steady (for example, plants hold soil together and keep it moist).

• Stability: in a food web with many species, if one food source becomes scarce, animals can switch to another. Populations rise and fall less sharply.
• Less dependence on one species: no single species is essential for the whole ecosystem to keep working.
• Value to humans: wild species give us food, medicines, timber and genes for breeding crops. Many have not even been discovered yet.

Worked example: two meadows

Meadow P has 45 plant species. Meadow Q is a field sown with one type of grass.
A new fungal disease kills that one grass species. Meadow Q loses almost all its plants, so the insects, voles and birds that fed there also go.
In meadow P, the other 44 plant species keep growing, so most animals still have food.

Answer: the meadow with higher biodiversity is more stable and recovers better

Key fact: The future of the human species on Earth relies on us keeping a good level of biodiversity. Many human activities are reducing biodiversity, and only recently have we started to take action to slow this down.

The human population explosion

For most of history the human population grew slowly, because of disease, famine and war. Since about 1800, better farming, clean water, sanitation and medicine have let far more people survive. The population is now growing very fast.

Worked example: percentage increase

The world population was about 2.5 billion in 1950 and about 8.2 billion in 2025. Work out the percentage increase.
Increase = 8.2 − 2.5 = 5.7 billion
Percentage increase = 5.7 ÷ 2.5 × 100 = 228%

Answer: about 228%

Living standards are also rising in many countries. People own more goods, travel more and use more energy, so each person uses more resources and makes more waste than in the past.

More people, more resources, more waste

Rapid growth in the human population and an increase in the standard of living mean that more resources are used and more waste is produced. Unless waste is handled properly, more pollution is caused.

• Water; Main sources of pollution Sewage, fertiliser running off fields, toxic chemicals from industry; Example of harm Fish and other water life die; drinking water is contaminated
• Air; Main sources of pollution Smoke and acidic gases (sulfur dioxide, nitrogen oxides) from burning fuels; Example of harm Acid rain damages trees and lakes; smoke harms lungs
• Land; Main sources of pollution Landfill sites, toxic chemicals such as pesticides and herbicides; Example of harm Habitats are lost; poisons pass along food chains

Exam tip: Pollution kills plants and animals, which reduces biodiversity. Building, quarrying, farming and dumping waste also reduce the land available for other animals and plants.

Managing waste

We cannot stop producing waste, but we can manage it so that less of it pollutes the environment.

• Sewage; How it can be managed Treated at sewage works so it is safe before the water returns to rivers or the sea.
• Household waste; How it can be managed Reduce, reuse and recycle; compost food and garden waste; less goes to landfill.
• Toxic chemicals; How it can be managed Stored and disposed of safely; strict laws on what factories and farms may release.
• Waste gases; How it can be managed Filters (scrubbers) in power station chimneys; cleaner fuels; catalytic converters in cars.

Worked example: waste per household

A town of 20 000 households each sends 0.45 tonnes of waste to landfill per year. A recycling scheme cuts this by 30%.
Before: 20 000 × 0.45 = 9000 tonnes per year
Saving: 30% of 9000 = 0.30 × 9000 = 2700 tonnes
After: 9000 − 2700 = 6300 tonnes per year

Answer: 6300 tonnes of waste to landfill per year

Common mistakes

• Defining biodiversity as “the number of animals”. It is the variety of species (plants, animals and microorganisms), not the number of individuals.
• Saying a high biodiversity makes an ecosystem “healthy” without explaining why. Say it is more stable, because species are less dependent on any one other species.
• Forgetting that it is both more people and higher living standards that increase resource use and waste.
• Working out a percentage increase by dividing by the new value. Always divide the increase by the original value.

Revision questions

Try these, then check your answers below each one.

Question 1. Which statement best describes biodiversity? (Choose from: The total mass of all the living things in a habitat, The number of plants in a food web, The variety of all the different species in an ecosystem or on Earth, The total number of animals living in an area.)

Answer: The variety of all the different species in an ecosystem or on Earth

Working: Biodiversity is the variety of all the different species of organisms on Earth or within an ecosystem.

Question 2. True or false? An ecosystem with a high biodiversity is more stable, because its species depend less on any one other species.

Answer: True

Working: True. With many species, animals can switch food sources and no single species is essential, so populations are more stable.

Question 3. The population of a town rose from 18 000 to 27 000. Calculate the percentage increase.

Answer: 50 %

Working: Increase = 27 000 − 18 000 = 9000. 9000 ÷ 18 000 × 100 = 50%.

Related lessons

• Previous lesson: 17.5 Required Practicals: Organising an Ecosystem
• Next lesson: 18.2 Land and Water Pollution
• In this chapter: 18.3 Air Pollution
• In this chapter: 18.4 Deforestation and Peat Destruction
• In this chapter: 18.5 Global Warming

Continue in the full course

This lesson is section 18.1 (AGCBH1801) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.