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LESSON B16 · EXPLAINER
Growth and Germination
A bean the size of your fingernail becomes a plant taller than you. What happens in the first few days?
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Explore in 3D
Germination in 3D
Watch a seed grow into a seedling.
Step 2 · Read
Key notes
Copy these into your notebook in your own words — that is how they stick.
Growth
Permanent increase in size/mass/complexity by cell division, enlargement and differentiation.
Measuring growth
Length/height, fresh mass, dry mass (most reliable), number of leaves.
Growth curve
Sigmoid; time on x-axis; measure of growth on y-axis.
Enzymes break down stores (II) → soluble products move to embryo (III) → embryo uses food to grow radicle and plumule (I).
Dry mass
Falls at first (stores respired), rises once photosynthesis begins.
EXAM TIPS & COMMON MISTAKES
P1: “Units of time” is the INCORRECT y-axis label on a growth graph.
Germination order in P1: II → III → I (enzymes → movement → growth).
For a germination experiment, the controls must change only ONE condition at a time.
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
Which conditions do seeds need?
Bean seeds were set up in four test tubes and left for five days.
Tube
Conditions
Result
A
Moist cotton wool, 25 °C, air
Germinated
B
Dry cotton wool, 25 °C, air
No germination
C
Boiled, cooled water with a layer of oil on top, 25 °C
No germination
D
Moist cotton wool, 4 °C (refrigerator), air
No germination
State what each tube shows.
Try it in your notebook first, then reveal the solution one step at a time.
Tube A has all three conditions — water, oxygen, warmth — and is the control.
Tube B lacks only water → water is needed: it softens the testa, lets the seed swell and activates enzymes; enzymes work in solution.
Tube C: boiling removed dissolved oxygen and the oil stops more dissolving → oxygen is needed for aerobic respiration to release energy for growth.
Tube D lacks only warmth → a suitable temperature is needed, because enzymes work too slowly in the cold.
Answer. Germination needs water (B), oxygen (C) and a suitable temperature (D); tube A, with all three, is the control.
Examiner’s tip. In each tube only ONE condition is changed compared with the control — that is what makes the test fair. Say so if asked about the design.
Worked example 2
Dry mass of a germinating seedling
Day
0
4
8
12
16
Dry mass (g)
2.0
1.6
1.4
1.9
3.0
Describe and explain the changes in dry mass.
Try it in your notebook first, then reveal the solution one step at a time.
Days 0–8: dry mass falls from 2.0 g to 1.4 g.
Explanation: stored food in the cotyledons is broken down and used in respiration to release energy for growth; carbon dioxide is lost. No leaves yet, so no photosynthesis.
Days 8–16: dry mass rises to 3.0 g.
Explanation: the first green leaves open and photosynthesise; the seedling now makes more food than it uses in respiration.
Answer. Dry mass falls at first as stored food is respired (no photosynthesis yet), then rises once leaves photosynthesise faster than the seedling respires.
Examiner’s tip. Dry mass is the best measure of growth because water content changes from hour to hour; its drawback is that the plants must be killed (dried) to measure it.
On the board · Parts of a bean seed
Part
Function
Testa
Protective seed coat
Micropyle
Tiny hole where water enters at the start of germination
Hilum
Scar where the seed was attached to the pod
Cotyledons
Seed leaves that store food for germination
Plumule
Embryo shoot
Radicle
Embryo root — the first part to emerge
Draw the seed split open and label these parts — the drawing is a favourite SBA and exam task.
Key terms
Growth
A permanent increase in size and dry mass.
Germination
The start of growth of a seed into a seedling.
Dry mass
Mass after all water has been removed.
Testa
The seed coat.
Plumule
The embryo shoot.
Radicle
The embryo root.
Dormancy
A resting period when a seed does not germinate even if conditions are suitable.
Common misconceptions
✗ Seeds need light to germinate.✓ Most seeds need water, oxygen and warmth, not light. Light is needed later, by the seedling, for photosynthesis.
✗ Fresh mass is the best measure of growth.✓ Fresh mass changes with water content. Dry mass measures the real increase in material.
✗ Growth just means getting taller.✓ Growth is a permanent increase in size and dry mass; it can be measured as length, area, volume or mass.
Memory aid
Germination needs WOW: Water, Oxygen, Warmth.
Real-life link
Caribbean farmers plant crops such as corn and pigeon peas at the start of the rainy season, when the soil is warm and moist — the conditions seeds need to germinate.
Try this
Grow three bean seeds in a jar against damp paper towel. Measure the root and shoot every day for ten days and draw a growth curve.
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
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Step 4 · Apply
Paper 2 practice — structured questions
Write full answers, then reveal the mark scheme and tick the points you earned (17 marks in total). Your answers are saved on this device.
Based on CSEC P2 May/June 2024, Question 3(c)
Question 1 [11 marks]
A graph shows that during germination, starch and protein in a seed decrease while sugar increases.
(a) Describe the structure of a dicotyledonous seed (you may draw and label it). [4]
MARK SCHEME — (a) (max 4)
(b) Explain the decrease in protein and starch as the seed germinates. [4]
MARK SCHEME — (b) (max 4)
(c) State THREE conditions necessary for germination and the role of each. [3]
MARK SCHEME — (c) (max 3)
Based on SO B8.1 (growth investigation)
Question 2 [6 marks]
A student measured the height of a corn seedling every 2 days for 20 days.
(a) Describe the expected shape of the graph and explain it. [3]
MARK SCHEME — (a) (max 3)
(b) Suggest TWO other ways of measuring growth and ONE advantage of dry mass. [3]
MARK SCHEME — (b) (max 3)
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Sources
Where this topic appears in CSEC papers
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.