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LESSON L6 · EXPLAINER
Compulsory Practical 1: Ecological Study
Your first SBA practical often happens outside. Here’s how to get it right before you leave the classroom.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Step 2 · Read
Key notes
Copy these into your notebook in your own words — that is how they stick.
Methods
Random quadrats (abundance), transects (distribution along a gradient), traps/nets/pooters (animals), capture–recapture (population).
Density = number ÷ area; % cover; kite diagrams along transects.
Ethics
Minimal disturbance; return organisms.
EXAM TIPS & COMMON MISTAKES
Always pair biotic counts with an abiotic factor so you can EXPLAIN the distribution.
Step 2 · Learn from examples
Worked examples & study resources
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Worked example 1
Percentage frequency from quadrats
Ten quadrats were placed along a transect from a pond edge. Water hyacinth was found in 4 of them; grass in 7; sensitive plant (Mimosa) in 2. Calculate the percentage frequency of each.
Try it in your notebook first, then reveal the solution one step at a time.
Percentage frequency = number of quadrats containing the species ÷ total number of quadrats × 100.
Water hyacinth: 4 ÷ 10 × 100 = 40%.
Grass: 7 ÷ 10 × 100 = 70%.
Sensitive plant: 2 ÷ 10 × 100 = 20%.
Answer. Water hyacinth 40%, grass 70%, sensitive plant 20%.
Examiner’s tip. Percentage frequency tells you how widespread a species is, not how many there are. For abundance use density (number per m²) or percentage cover.
Worked example 2
Linking a species to an abiotic factor
Along a transect away from a pond:
Distance from pond (m)
0
2
4
6
8
Soil moisture (%)
80
62
45
30
18
Percentage cover of moss
55
40
20
8
0
Describe and explain the distribution of moss.
Try it in your notebook first, then reveal the solution one step at a time.
Describe: moss cover decreases with distance from the pond, from 55% at the edge to 0% at 8 m.
Link to the abiotic factor: soil moisture also decreases (80% → 18%) — moss cover falls as the soil gets drier.
Explain: mosses lose water easily (no true roots or waxy cuticle) and need water for reproduction, so they grow best in moist soil.
Caution: this shows a correlation; other factors (light, competition) may also change along the transect.
Answer. Moss cover falls as distance from the pond increases and soil moisture falls; moss needs moist conditions, so moisture is likely the main factor (a correlation, not proof).
Examiner’s tip. Always measure abiotic factors at the same points as the organisms — otherwise you cannot link them.
On the board · Field study equipment and readings
Measure
Equipment
Plant abundance / cover
Quadrat (with grid), identification key
Change across an area
Measuring tape for a line or belt transect
Soil moisture
Moisture meter, or mass loss on drying a sample
Soil and air temperature
Thermometer / soil thermometer
Light intensity
Light meter
pH
Universal indicator or pH meter
Small animals
Pitfall traps, sweep nets, pooters
Pair each living-organism count with an abiotic reading taken at the same spot.
Key terms
Percentage frequency
Percentage of quadrats in which a species occurs.
Percentage cover
Percentage of the quadrat area covered by a species.
Density
Number of individuals per unit area.
Kite diagram
A chart showing how the abundance of species changes along a transect.
Correlation
A relationship between two variables — not necessarily cause and effect.
Common misconceptions
✗ High frequency means a species is abundant.✓ A species can occur in every quadrat (100% frequency) yet be very sparse.
✗ A correlation proves that one factor causes the other.✓ A correlation shows a link; other factors may be responsible.
✗ Fieldwork does not need a control or repeats.✓ Repeat transects and readings make field results more reliable.
Memory aid
Field study pairs: count the living, measure the non-living, at the same spot.
Real-life link
Ecologists monitoring Caribbean mangrove and seagrass areas use transects and quadrats every year to track changes after hurricanes, oil spills and coastal development.
Try this
Lay a 10 m string from a shady wall into an open sunny area. Every 2 m, count the plants in a 0.5 m quadrat and note whether the spot is shady or sunny.
Play & practise
Games
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
Step 3 · Practise
Paper 1 practice — multiple choice
6 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Step 4 · Apply
Practical-style questions
Write full answers, then reveal the mark scheme and tick the points you earned (8 marks in total). Your answers are saved on this device.
Based on CSEC Specimen Paper 02, Q1(a)–(b)
Question 1 [8 marks]
A class studies an area between a pond and a road.
(a) Plan a field study to find how plant species change from the pond to the road. [5]
MARK SCHEME — (a) (max 5)
(b) State TWO precautions and ONE safety measure. [3]
MARK SCHEME — (b) (max 3)
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Sources
Syllabus sources and past papers
Everything in this lesson is based on these parts of the CXC syllabus and papers.
CXC syllabus — SBA compulsory topic 1 (ecological study); SO A2.1; Specimen Paper 02 Q1
See also lesson A2 (Carrying out an ecological study)