Interpret population dynamics and structure
Calculate population density and dependency ratio, interpret age structure and link demographic change to resource demand carefully.
Exam scope and assessment notes
Original StudyForA teaching and practice, not Cambridge-authored questions, mark schemes or official grades. Cambridge expects candidates to study all eight topics, carry out investigative work and learn teacher-selected case studies. This course does not replace a centre's named case-study examples, current local environmental data, supervised fieldwork or the candidate's own investigation. Practice datasets are illustrative, not observations from a real place. No official assessment or certification is provided. The examples and practice datasets in these lessons are fictional and formative; learners must add their centre's verified case studies and current local evidence.
Before you begin
- Cambridge recommends prior environmental/science study equivalent to IGCSE or O Level. This is an AS-only qualification; use the exam-year syllabus and confirm centre entry details.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What makes environmental evidence useful?
What you will learn
- Calculate population density and dependency ratio
- Explain how birth, death and migration rates affect population structure
- Compare dated population evidence without generalising across countries
Use measures accurately
Population density = population ÷ area with a stated area unit. Density averages can hide very crowded districts or sparsely populated regions.
Dependency ratio = [(population aged 0–14 + population aged 65+) ÷ population aged 15–64] × 100. It is a demographic indicator, not a direct count of employed and non-employed people.
Explain change through several drivers
Birth rates, death rates and migration alter population size and composition. An ageing population can mean lower tax revenues, higher pension spending, pressure on health care and pressure to raise the retirement age; effects depend on employment, productivity, services and policy.
Compare named high-income and low-income economies with dated age structures and environmental, economic, social, political and historical context. Income grouping alone does not explain every country's trajectory or every resident's circumstances.
Sources for this lesson
Pause and explain
What does the dependency ratio compare?
Worked example
A region has 12 million people across 60,000 km²; age counts are 3 million aged 0–14, 9 million aged 15–64 and 2 million aged 65+. Calculate both measures.
Show the worked solution
- Divide population by area.
- Add the two dependent age groups.
- Divide by the 15–64 group and multiply by 100.
Answer Density = 12,000,000/60,000 = 200 people per km². Dependency ratio = (3m+2m)/9m×100 ≈ 55.6 dependants per 100 people aged 15–64. These averages do not describe household or employment circumstances.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A city has 2.4 million residents and covers 800 km². Calculate population density.
Give me a hint
Divide residents by land area.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply calculate population density and dependency ratio to the stated context.
- Explain the inference and one limitation or trade-off.
Population density = 2,400,000÷800 = 3,000 people per km². This average can conceal local variation, so planning may also need neighbourhood-level data.
Look for these in your work
- Calculate population density and dependency ratio
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Birth and death rates fall while net migration is positive. What evidence is needed to predict age structure?
Give me a hint
Total population growth does not show which age groups change.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply explain how birth, death and migration rates affect population structure to the stated context.
- Explain the inference and one limitation or trade-off.
Check the ages of migrants and the existing age structure, then consider how long the birth and death trends persist. Positive migration may concentrate in working ages, while lower birth rates alter younger cohorts over time.
Look for these in your work
- Explain how birth, death and migration rates affect population structure
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
A country has a rising dependency ratio. Give two possible management implications and one qualification.
Give me a hint
Link the pattern to services and resource needs.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply compare dated population evidence without generalising across countries to the stated context.
- Explain the inference and one limitation or trade-off.
The ratio may indicate higher demand for healthcare, pensions or accessible transport and could affect the workforce available for services. The implications depend on employment, productivity, family support and policy; the ratio alone cannot predict them.
Look for these in your work
- Compare dated population evidence without generalising across countries
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Common mistakes
- Confusing population size with density
- Treating everyone aged 15–64 as employed
- Assuming every country follows the same population trajectory
What can you explain now?
What does the dependency ratio compare?
Compare with the explanation
People aged 0–14 and 65+ with people aged 15–64
It is a demographic ratio, not a count of workers and non-workers.
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Make it stick
Why is the dependency ratio not the same as the number of non-workers?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.