5.2.6Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Core Practical 11: Quadrat and Transect Study — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 6 parts Lesson 21 of 36 Unit quiz
Curriculum Equation Key معادلة التنفس الخلوي الهوائي الموزونة - Balanced Cellular Respiration EquationFast Exam Solution
C₆H₁₂O₆ + 6O₂ ➔ 6CO₂ + 6H₂O + 36-38 ATP
Word Equation & Conditions: Glucose + Oxygen -> Carbon Dioxide + Water + Energy (36-38 ATP) | جلوكوز + أكسجين ← ثاني أكسيد كربون + ماء + طاقة
Location & Specifications: الميتوكوندريا (Mitochondria) والسيتوسول.
Part 1 of 6Sampling Methods
It is usually impossible to count every organism, so a sample is taken.
Random sampling
- Random sampling Quadrat positions are chosen using random numbers, which avoids bias in where samples are placed.
Systematic sampling
- Systematic sampling Samples are taken at fixed intervals, such as every metre along a line.
Quadrat
- Quadrat A frame of known area, such as 0.25 m², placed on the ground to sample plants.
Sample size
- Sample size More quadrats give a more reliable estimate and reduce the effect of unusual areas.
Part 2 of 6Measuring Abundance
Measuring Abundance
Frequency
- Frequency The percentage of quadrats in which a species is present.
Density
- Density The number of individuals per unit area.
Percentage cover
- Percentage cover An estimate of the area covered by a species, useful for plants that are hard to count.
Estimate
- Estimate Population size = mean number per quadrat x total area / quadrat area.
Part 3 of 6Using a Transect
A belt transect shows how species change along an environmental gradient.
1
Stretch a measuring tape in a straight line across the habitat, for example from the shore upwards.
2
Place the quadrat at set intervals along the tape and record the species present.
3
Measure abiotic factors such as light intensity, soil moisture and pH at each point.
4
Compare the changes in species with the abiotic factors, using a statistical test such as Spearman's rank correlation.
Part 4 of 6Reliable Results
Identification
- Identification Use a key and be consistent when identifying species.
Repeat
- Repeat Repeat the study in other areas or at other times to check the results.
Environment
- Environment Avoid damage to habitats and wear suitable clothing, with permission to enter the site.
Limitations
- Limitations Mobile animals are hard to sample this way, so other methods are needed.
| Method | Use |
|---|---|
| Random quadrats | Estimate abundance across an area |
| Belt or line transect | Study change along a gradient |
| Percentage cover | Plants that are hard to count |
Part 5 of 6Worked Example
Question
- A field of 400 m² is sampled with 0.25 m² quadrats.
- Mean count of daisies per quadrat is 3.5.
- Estimate the population.
- Number of quadrat areas in the field = 400 / 0.25 = 1 600.
- Population = 3.5 x 1 600.
- = 5 600.
Answer About 5 600 daisies.
Part 6 of 6Exam Checklist & Tips
5.2.6 – Key Points for the Exam
- Quadrat A square frame of known area used to sample organisms.
- Transect A line or belt along which samples are taken to study change across a habitat.
- Random sampling Choosing sample positions by chance to avoid bias.
- Systematic sampling Sampling at regular intervals.
Common Mistakes
- Throwing a quadrat over the shoulder and calling it random; use random coordinates.
- Using too few quadrats for a reliable estimate.
- Forgetting to measure the abiotic factors along the transect.
- Mixing up the area of the quadrat and the total area when scaling up.
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