Step 1: Ask a question and plan a fair test
A project question must be small and testable: "Does adding more sugar change how fast a piece grows?" Pick:
- One variable to change (for example sugar amount: low or normal).
- Things to keep the same: light, warmth, jar size, plant type and piece size.
- A control: a jar with the normal mix, to compare with.
- Repeats: use at least 3 jars for each choice, so one lucky or unlucky jar does not mislead you.
Step 2: Prepare materials and the work area
List what you need: jars with lids, jelly food (medium) made from water, sugar, minerals and agar or a safe jelly, a knife or blade, forceps, alcohol, a flame, a notebook, labels and a lamp. The jelly food and jars are sterilised by heating in a pressure cooker (autoclave) and then closed until use. Label each jar with the date, mix and your name. In school labs, an adult prepares the sterilising step.
Step 3 and 4: Work clean and plant the pieces
- Wash hands. Wipe table and hands with 70% alcohol.
- Flame the knife and forceps, then let them cool.
- Cut a small clean piece from a healthy, disinfected plant part (for example a shoot tip or a bud).
- Open a jar for only a moment, place the piece on the jelly, and close the lid.
- Put the jars in a bright, warm place (about 25 °C), out of direct sun.
See the lesson Plant structure and aseptic technique to revise the cleaning steps.
Step 5: Watch the growth
Every 2–3 days, look without opening. Typical stages: the piece stays small or swells (days 0–7), a soft shapeless lump called callus grows (days 8–17), then shoots with tiny leaves appear (after about day 18). Hormones in the jelly guide this: more auxin leads to roots and callus, more cytokinin leads to shoots. Cloudy, slimy or fuzzy jars are contaminated: close them and discard them safely, and note the day.
Step 6: Record, compare and share
A results table has columns: Date, Jar, What you see, Height (mm), Notes. Draw a simple graph of height against days for each jar. Compare the control with the changed jar. Write one sentence: "In my test, ___ grew better because ___, but I need more jars to be sure." Share your findings with the class, say what failed, and say what you would change next time. Failed jars are valuable data.
Try it: make a results table for the 3D jars at days 5, 15 and 25.
Key formulas and definitions
- Key term: Variable = the one thing you change in a test
- Key term: Control = a jar with the normal mix, used for comparison
- Key term: Callus = a soft lump of dividing plant cells
- Key term: Contamination = germs growing in the jar
- Growth rate = change in height ÷ number of days
- Contamination rate (%) = contaminated jars ÷ total jars × 100
Worked examples
1. A shoot grows from 2 mm to 14 mm in 6 days. What is the average growth rate?
Change = 14 − 2 = 12 mm. Rate = 12 ÷ 6 = 2 mm per day.
2. In a test, 3 of 24 jars were contaminated. What is the contamination rate?
3 ÷ 24 × 100 = 12.5%.
3. You want to test whether more sugar helps growth. List the variable, two things to keep the same and a control.
Variable: amount of sugar. Keep the same: light, temperature (also jar size). Control: jar with normal sugar.
4. Jar A has a shoot at day 25 but Jar B has green fuzz. Both were planted the same day with the same mix. What is a likely reason?
Jar B was contaminated with a fungus, probably through a dirty tool, hands or air. The mix was not the cause, because both had the same mix.
Common mistakes
- Changing many things at once (sugar, light and jar size). Then you cannot tell what caused the difference.
- Opening jars every day to look. Each opening lets germs in. Look through the glass.
- Skipping the notebook. If you do not write it down, you will not remember what happened.
- Throwing away contaminated jars without noting them. They are data.