top of page

B17.1 The Human Population Explosion

GCSE Combined Science · AQA · Chapter B17: Biodiversity and Ecosystems

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: biodiversity, why it matters, and how a growing human population puts it under pressure. 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 give examples of areas with high and low biodiversity
  • Explain why a high biodiversity makes an ecosystem more stable
  • Describe how the human population has grown and why more people and higher living standards use more resources and make more waste
  • Explain how building, quarrying, farming and dumping waste reduce the land available for other species
  • Calculate percentage change and population density from data

Key words

  • Biodiversity: The variety of all the different species of organisms (plants, animals, fungi and microorganisms) 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.
  • Population density: The number of individuals living in each unit of area, e.g. people per km².
  • Sustainable: Describes an activity that can continue for a long time without damaging the environment.

Biodiversity and why it matters

An area with a high biodiversity contains many different species. Tropical rainforests, coral reefs and ancient woodlands have very high biodiversity. Deserts, polar regions and large fields of one crop have low biodiversity.

  • 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: species rely on each other for food, shelter and keeping the physical environment steady. With many species, no single one is essential.
  • Value to humans: wild species give us food, medicines, timber and useful genes. Many have not yet been discovered.

Worked example: two hedgerows

Hedge X contains 14 species of shrub. Hedge Y was planted with one species only.
A disease kills that one species of shrub. Hedge Y dies back completely, so caterpillars, birds and mice that lived in it lose food and shelter.
In hedge X the other 13 shrub species survive, so most animals still have food and nesting places.

Answer: the hedge with higher biodiversity is more stable

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

The human population explosion

For most of history the human population grew slowly, held back by famine, disease and war. Since about 1800, better farming, clean water, sewers and medicine have let far more people survive. The population now grows very fast.

Worked example: percentage increase

The world population was about 1.6 billion in 1900 and about 6.1 billion in 2000. Work out the percentage increase.
Increase = 6.1 − 1.6 = 4.5 billion
Percentage increase = 4.5 ÷ 1.6 × 100 = 281%

Answer: about 281%

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 living close together also lets communicable diseases spread more easily.

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 properly handled, more pollution is caused.

  • Water; Main sources of pollution Sewage, fertiliser and toxic chemicals; Example of harm Fish and other water life die; disease spreads in dirty water
  • Air; Main sources of pollution Smoke and acidic gases from burning fuels; Example of harm Acid rain damages trees and lakes; smoke harms lungs
  • Land; Main sources of pollution Landfill and toxic chemicals such as pesticides and herbicides; Example of harm Habitats are lost; soil and water are poisoned

Exam tip: Pollution kills plants and animals, and this reduces biodiversity.

Land use

Ten thousand years ago a few small groups of people hunted and gathered over huge areas, so their effect on the environment was tiny. Today the population density is far higher. Humans reduce the land available for other animals and plants by:

  • building homes, roads, factories and whole cities
  • quarrying and mining for stone, metal ores and coal
  • farming crops and animals, often in huge single-crop fields
  • dumping waste, for example in landfill sites

Worked example: population density

A district has an area of 250 km². In 1950 it had 30 000 people; today it has 92 500.
Density in 1950 = 30 000 ÷ 250 = 120 people per km²
Density today = 92 500 ÷ 250 = 370 people per km²

Answer: density has risen from 120 to 370 people per km²

Common mistakes

  • Defining biodiversity as “the number of animals”. It is the variety of species (plants, animals, fungi 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 the use of resources and the amount of 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. What is meant by biodiversity? (Choose from: The total number of animals living in a habitat, The variety of all the different species of organisms in an ecosystem or on Earth, The mass of all the plants in an area, The number of food chains in a food web.)

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

Working: Biodiversity is the variety of all the different species (plants, animals, fungi and microorganisms) on Earth or within an ecosystem.

Question 2. Use the graph of world population. About how long did it take for the population to double from 4 billion to 8 billion? (Choose from: About 25 years, About 50 years, About 100 years, About 175 years.)

Answer: About 50 years

Working: The population was 4 billion in about 1975 and 8 billion in about 2023, so it doubled in about 48 years, roughly 50 years. Earlier, it took about 125 years to double from 1 to 2 billion.

Question 3. True or false? An ecosystem with high biodiversity is more stable, because its species depend less on any one other species for food, shelter and maintaining the environment.

Answer: True

Working: True. With many species, animals can switch to other foods and no single species is essential, so the ecosystem is more stable.

Related lessons

Continue in the full course

This lesson is section B17.1 (AGCSC1701) of our free GCSE Combined Science 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 Combined Science course.

 

 

 

 

 

 

 

bottom of page