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Ordinary Level Revision Notes
Leaving Cert Ordinary Level Biology
Chapter 5: Study of an Ecosystem
Study Leaving Cert Ordinary Level Biology Study of an Ecosystem with ExamsLogic revision notes, diagrams, summaries, and exam-focused practice.
Subtopics Covered
- Chapter Overview
- Learning Outcomes
- Fieldwork Investigation
- Flora, Fauna and Keys
- Qualitative and Quantitative Surveys
- Quadrat Sampling
What This Pack Includes
- Structured chapter notes formatted for ExamsLogic website reading
- Exam-focused diagrams, definitions, and worked examples
- Interactive practice sections carried over from the source notes
- Independent study guidance based on the official curriculum
- Print-friendly layout for future PDF export when needed
This publication is an independent educational resource developed by ExamsLogic and compiled by experienced educators. It is based on publicly available official curricula, including Cambridge, Pearson Edexcel, IB, and the Irish Leaving Certificate. This product is not endorsed by, affiliated with, or sponsored by any examination board or governing authority. All registered trademarks remain the property of their respective owners.
1. Chapter Overview
This chapter explains how biologists study a local ecosystem using practical fieldwork methods. Students learn how to identify organisms, estimate abundance, use quadrats and transects, calculate population estimates, and explain adaptations that help organisms survive.
ExamsLogic Big Idea: Ecology fieldwork is about collecting evidence from real habitats and using that evidence to explain how organisms live, interact and survive.
2. Learning Outcomes
- I can describe how to study a selected local ecosystem.
- I can identify flora and fauna using keys.
- I can distinguish qualitative and quantitative surveys.
- I can explain how quadrats and transects are used.
- I can calculate percentage frequency and use percentage cover.
- I can use capture–recapture to estimate mobile animal populations.
- I can distinguish structural and behavioural adaptations.
3. Fieldwork Investigation
A fieldwork investigation is a practical study of organisms in their natural environment. Examples include woodland, grassland, rocky shore, pond or hedgerow.
| Stage | What the student does | Why it matters |
|---|---|---|
| Select ecosystem | Choose a named local ecosystem. | Gives the investigation a clear focus. |
| Identify organisms | Use keys to identify flora and fauna. | Ensures accurate species records. |
| Measure abiotic factors | Record temperature, light, pH or moisture. | Links organisms to environmental conditions. |
| Use sampling methods | Quadrats, transects or capture–recapture. | Produces quantitative data. |
| Record and analyse | Use tables, calculations and conclusions. | Turns observations into evidence. |
Examiner Tip: In a fieldwork answer, always name the ecosystem, state the method used, and explain how results were recorded.
4. Flora, Fauna and Keys
| Term | Meaning | Examples |
|---|---|---|
| Flora | Plants in an ecosystem. | Grass, moss, trees, flowering plants. |
| Fauna | Animals in an ecosystem. | Insects, worms, snails, birds. |
| Key | A tool used to identify organisms using visible features. | Dichotomous key. |
Dichotomous Keys
A dichotomous key gives two choices at each step. Each answer leads to another step until the organism is identified.
Examiner Trap: A key is not just a list of species. It uses features to identify organisms step by step.
5. Qualitative and Quantitative Surveys
| Survey type | Meaning | Example |
|---|---|---|
| Qualitative survey | Records what organisms are present. | Identifying species in a woodland using a key. |
| Quantitative survey | Records numerical data about organisms. | Using quadrats to estimate percentage cover. |
Student Common Mistake: Counting is quantitative. Qualitative means identifying what is present.
6. Quadrat Sampling
A quadrat is a square frame used to sample plants or slow-moving organisms in a known area. It is usually placed randomly to reduce bias.
| Measurement | Meaning |
|---|---|
| Frequency | How often a species occurs in quadrats. |
| Percentage frequency | Percentage of quadrats where the species is present. |
| Percentage cover | Estimated percentage of quadrat area covered by a species. |
Percentage frequency = (Quadrats containing species ÷ Total quadrats) × 100
Percentage cover = (Area covered ÷ Total quadrat area) × 100
Examiner Trap: Frequency is not the same as number of individual organisms. It tells how often a species appears in samples.
7. Transects
A transect is used to study how organisms change across a habitat gradient, such as from dry soil to wet soil or from shade to open light.
| Transect type | Description | Best use |
|---|---|---|
| Line transect | A tape or line is placed across the habitat and organisms touching the line are recorded. | Simple change across a habitat. |
| Belt transect | Quadrats are placed at intervals along a line. | More detailed sampling across a gradient. |
Examiner Tip: Use a transect when you expect organism distribution to change across an environmental gradient.
8. Capture–Recapture Method
Capture–recapture is used to estimate populations of mobile animals.
- Capture a first sample of animals.
- Mark them safely and release them.
- Allow time for them to mix back into the population.
- Capture a second sample.
- Count how many marked animals are recaptured.
- Use the formula to estimate population size.
Population estimate = (First sample × Second sample) ÷ Marked animals recaptured
Worked Example:
First sample = 20 animals. Second sample = 30 animals. Marked recaptured = 5.
Population estimate = (20 × 30) ÷ 5 = 120 animals.
First sample = 20 animals. Second sample = 30 animals. Marked recaptured = 5.
Population estimate = (20 × 30) ÷ 5 = 120 animals.
| Assumption | Why it matters |
|---|---|
| Marks do not harm animals. | Marked animals must survive normally. |
| Marks do not rub off. | Marked animals must still be recognised. |
| Animals mix randomly. | The second sample must represent the whole population. |
| No major births, deaths or migration. | The population should remain stable during the study. |
9. Adaptations
An adaptation is a feature or behaviour that helps an organism survive in its habitat.
| Type of adaptation | Meaning | Example | Survival value |
|---|---|---|---|
| Structural adaptation | A physical feature of an organism. | Webbed feet in ducks. | Helps swimming. |
| Structural adaptation | A physical feature. | Thick fur in cold habitats. | Reduces heat loss. |
| Behavioural adaptation | A way an organism behaves. | Migration. | Avoids harsh conditions or finds food. |
| Behavioural adaptation | A behaviour. | Nocturnal activity. | Avoids daytime heat or predators. |
Examiner Tip: When describing an adaptation, always link the feature or behaviour to how it improves survival.
10. Common Student Mistakes
- Mixing qualitative and quantitative surveys.
- Using quadrats for fast-moving animals.
- Forgetting quadrats should usually be placed randomly.
- Confusing percentage frequency with percentage cover.
- Forgetting the capture–recapture formula.
- Ignoring capture–recapture assumptions.
- Confusing structural and behavioural adaptations.
11. Examiner Traps
Trap 1: Quadrats are mainly for plants and slow-moving organisms.
Trap 2: Capture–recapture is mainly for mobile animals.
Trap 3: Percentage cover is not the same as number of organisms.
Trap 4: A transect is best for studying change across a gradient.
Trap 5: Adaptation answers need feature + survival advantage.
12. Examiner Secrets
Secret 1: For fieldwork questions, write method + reason + result recorded.
Secret 2: For quadrats, mention random placement and repeated sampling.
Secret 3: For capture–recapture, marks often come from assumptions as well as the formula.
Secret 4: For adaptations, explain how the feature helps survival.
13. Section A: Multiple Choice Practice
- Which method is best for estimating percentage cover of plants?
A. Capture–recapture B. Quadrat C. Pooter D. Thermometer - Which method is best for mobile animal population estimates?
A. Quadrat B. Transect C. Capture–recapture D. Soil pH test - What does a qualitative survey record?
A. What organisms are present B. Exact population size C. Temperature only D. Percentage cover only - What type of adaptation is migration?
A. Structural B. Behavioural C. Edaphic D. Abiotic - Why are quadrats placed randomly?
A. To save time B. To reduce bias C. To avoid plants D. To increase light
14. Section B: Structured Practice Questions
- Describe how you would study a named local ecosystem. [6 marks]
- Distinguish between qualitative and quantitative surveys. [4 marks]
- Explain how a quadrat is used to estimate percentage frequency. [4 marks]
- When would a transect be more suitable than random quadrats? [2 marks]
- Use capture–recapture to estimate a population if first sample = 25, second sample = 40 and marked recaptured = 10. [3 marks]
- State two assumptions of the capture–recapture method. [4 marks]
- Give one structural adaptation and one behavioural adaptation, explaining their survival value. [4 marks]
15. Mark Scheme Answers
Section A:
1. B 2. C 3. A 4. B 5. B
Q1. Name ecosystem [1]; identify organisms using key [1]; use quadrats/transects/capture–recapture [1]; measure abiotic factor [1]; record data in table [1]; analyse/conclude [1].
Q2. Qualitative = records what organisms are present [2]; quantitative = records numerical data such as frequency/percentage cover/population estimate [2].
Q3. Place quadrats randomly [1]; record presence/absence of species [1]; repeat with many quadrats [1]; calculate percentage frequency using formula [1].
Q4. When studying change across an environmental gradient/habitat transition [2].
Q5. (25 × 40) ÷ 10 = 100 animals [3].
Q6. Marks do not harm/rub off [2]; animals mix randomly/no major births/deaths/migration [2].
Q7. Structural example + survival value [2]; behavioural example + survival value [2].
1. B 2. C 3. A 4. B 5. B
Q1. Name ecosystem [1]; identify organisms using key [1]; use quadrats/transects/capture–recapture [1]; measure abiotic factor [1]; record data in table [1]; analyse/conclude [1].
Q2. Qualitative = records what organisms are present [2]; quantitative = records numerical data such as frequency/percentage cover/population estimate [2].
Q3. Place quadrats randomly [1]; record presence/absence of species [1]; repeat with many quadrats [1]; calculate percentage frequency using formula [1].
Q4. When studying change across an environmental gradient/habitat transition [2].
Q5. (25 × 40) ÷ 10 = 100 animals [3].
Q6. Marks do not harm/rub off [2]; animals mix randomly/no major births/deaths/migration [2].
Q7. Structural example + survival value [2]; behavioural example + survival value [2].
16. Quick Revision Card
- Flora: Plants in an ecosystem.
- Fauna: Animals in an ecosystem.
- Qualitative: What organisms are present.
- Quantitative: Numerical data.
- Quadrat: Plants/slow organisms; frequency and percentage cover.
- Transect: Change across habitat gradient.
- Capture–recapture: Mobile animal population estimate.
- Structural adaptation: Physical feature.
- Behavioural adaptation: Action or behaviour.
17. Interactive Simulator: Fieldwork Method Detective
Choose the Best Method
Scenario: You want to estimate the percentage cover of daisies in a grassland.
Examiner Feedback
Ready
Choose the fieldwork method that matches the scenario.
Score: 0/0
18. Mastery Checklist
- I can describe how to study a named local ecosystem.
- I can identify flora and fauna using keys.
- I can distinguish qualitative and quantitative surveys.
- I can use quadrats for frequency and percentage cover.
- I can explain when transects are used.
- I can calculate capture–recapture population estimates.
- I can state assumptions of capture–recapture.
- I can distinguish structural and behavioural adaptations.
- I can answer OL fieldwork exam questions.