Explain stationary growth and limiting factors
A population becomes stationary when additions and losses balance approximately; limited resources and other limiting factors can restrict further growth.
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Know population, community and ecosystem terms and read the axis labels on a graph.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What best explains a stationary phase?
What you will learn
- Explain a stationary phase with approximate balance
- Relate limited resources and limiting factors to growth
Stationary phase: numbers level off
In a stationary phase, population size changes little overall because additions to the population are approximately balanced by losses. In a limited-resource environment, food or another resource can restrict further increase. The population may fluctuate around a level rather than remain at one exact number.
Do not say stationary means births, deaths, immigration and emigration are each zero. The observed count is nearly stable overall; underlying processes can continue. The precise balance depends on the population and the interval measured.
Limiting factors restrict growth
A limiting factor is a condition that restricts population growth. The syllabus factors include food supply, competition, predation and disease. For example, scarce food can increase competition and reduce survival or reproduction; predation or disease can raise losses. Link a proposed factor to evidence in the scenario.
Carrying capacity is a useful model for the level an environment can support, but do not infer an exact value unless the data support it. A plateau in one graph does not identify which limiting factor caused it.
Pause and explain
What is a limiting factor?
Worked example
A population fluctuates between about 480 and 520 organisms while food remains limited. Explain the stationary section.
Show the worked solution
- The count changes little overall around a level.
- Limited food can restrict reproduction or survival.
Answer The population is in a stationary phase because numbers fluctuate around a similar level. Limited food may restrict growth so additions and losses are approximately balanced.
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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 population oscillates slightly around 700 individuals while food supply is limited. Explain why the curve may be stationary rather than perfectly flat.
Give me a hint
Distinguish near balance from zero change at every moment.
Compare my reasoning
- Small fluctuations occur.
- Additions and losses remain approximately balanced over the interval.
The population is approximately stationary because it fluctuates around 700 rather than changing greatly overall; additions and losses can vary while remaining roughly balanced.
Look for these in your work
- Approximate trend explained
- Fluctuations allowed
A pond population plateaus after disease is reported. What is a valid interpretation and what additional evidence is needed?
Give me a hint
A plateau shows little net change, not its cause.
Compare my reasoning
- The population may be stationary.
- Disease could be a limiting factor, but the graph alone does not prove it.
The plateau is consistent with a stationary phase. Disease could limit growth, but evidence linking disease to survival or reproduction and considering other factors is needed to establish its role.
Look for these in your work
- Phase interpreted
- Causation qualified
Food becomes limited and competition increases. Explain one route by which growth may slow.
Give me a hint
Link competition to access to resources and population change.
Compare my reasoning
- More individuals compete for limited food.
- Some may have lower survival or reproduction.
Greater competition for limited food may reduce access to resources, lowering survival or reproduction and slowing population growth.
Look for these in your work
- Factor connected
- Mechanism explained
Common mistakes
- Equating stationary with no births or deaths
- Assuming the graph identifies a specific limiting factor
- Treating the plateau as an exact universal carrying capacity
What can you explain now?
What best explains a stationary phase?
Compare with the explanation
Population additions and losses are approximately balanced overall
This produces little net change in population size.
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Make it stick
Explain how limited resources and approximate balance can produce a stationary phase.
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.