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LESSON L10 · EXPLAINER
Compulsory Practical 5: Germination
Four test tubes, one variable each. Germination is the perfect first controlled experiment.
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.
Conditions
Water, oxygen, suitable temperature (light not needed for most seeds).
Removing oxygen
Boiled cooled water + oil layer (or pyrogallol in an advanced set-up).
Growth measures
Length, leaf number, dry mass; average several seeds.
Seed drawing
Testa, micropyle, hilum, cotyledons, plumule, radicle; title + magnification.
EXAM TIPS & COMMON MISTAKES
Change only ONE condition per tube and say which tube is the control.
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 germination
Of 25 seeds kept at 25 °C, 22 germinated; of 25 kept at 10 °C, 6 germinated. Calculate the percentage germination for each and explain the difference.
Try it in your notebook first, then reveal the solution one step at a time.
Explain: germination depends on enzymes breaking down stored food. At 10 °C enzymes work slowly, so fewer seeds germinated in the time; 25 °C is closer to their optimum.
Answer. 88% at 25 °C; 24% at 10 °C. Low temperature slows the enzymes needed for germination.
Examiner’s tip. Using percentages lets you compare batches with different numbers of seeds.
Worked example 2
Growth rate of a radicle
Day
1
2
3
4
5
Radicle length (mm)
2
6
13
22
30
Calculate (a) the mean growth rate over days 1–5 and (b) the growth rate between days 3 and 4.
Try it in your notebook first, then reveal the solution one step at a time.
(a) Mean rate = change in length ÷ time = (30 − 2) ÷ (5 − 1) = 28 ÷ 4 = 7 mm per day.
(b) Days 3–4: (22 − 13) ÷ 1 = 9 mm per day.
The rate is not constant: growth speeds up as the seedling establishes itself.
Answer. (a) 7 mm per day. (b) 9 mm per day.
Examiner’s tip. Rate = change ÷ time, with units (mm per day). State which time interval you used.
On the board · Germination practical: one condition missing per tube
Tube
Water
Oxygen
Warmth
How the condition is removed
Control
✓
✓
✓
—
No water
✗
✓
✓
Dry cotton wool
No oxygen
✓
✗
✓
Boiled, cooled water under oil, or alkaline pyrogallol in a sealed tube
No warmth
✓
✓
✗
Refrigerator at about 4 °C
Each tube removes ONE condition; the control has all three.
Key terms
Percentage germination
Number of seeds germinated ÷ number planted × 100.
Radicle
Embryo root — the first part to emerge.
Growth rate
Change in size ÷ time taken.
Germination
The start of growth of a seed, shown by the radicle emerging.
Common misconceptions
✗ Seeds in the dark will not germinate.✓ Most seeds germinate in the dark; light is needed later for photosynthesis.
✗ Growth rate is the final length ÷ number of days.✓ Rate is the CHANGE in length ÷ time, starting from the first measurement.
✗ A few seeds are enough.✓ Use many seeds (e.g. 20–25 per condition) so percentages are reliable.
Memory aid
Rate = change ÷ time — always with units, e.g. mm per day.
Real-life link
Seed companies test the germination percentage of each batch and print it on the packet, so farmers know how many seeds to sow per bed.
Try this
Soak 20 bean seeds and keep 10 in the fridge and 10 at room temperature on damp paper. Count how many germinate after five days and calculate percentage germination.
Play & practise
Games
4 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 (7 marks in total). Your answers are saved on this device.
Based on SO B8.1–8.3 and SBA topic 5
Question 1 [7 marks]
A student investigates the conditions needed for germination of bean seeds.
(a) Describe four tubes that test water, oxygen and temperature, identifying the control. [4]
MARK SCHEME — (a) (max 4)
(b) State the expected results and explain why seeds need water. [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 topic 5 (germination); SO B8.1–8.3; Specimen Paper 01 Items 40–42