Science and Technology K–6 · Year 6

Rising salt: how salty water affects germinating seeds

Science understanding: Biological sciences

PracticalLow risk

The idea

Salt in soil water is a physical condition that is rising in parts of Australia's farmland, and as its concentration increases fewer seeds germinate, they germinate later and their roots grow shorter.

What you need

5 saucers or petri dishes, each lined with 2 layers of paper towel
100 untreated radish seeds (20 per dish)
table salt, weighed on a kitchen balance reading to 0.1 g: 0, 2.5, 5.0, 10.0 and 20.0 g
5 labelled 1 L bottles of tap water
a 10 mL measuring syringe
cling wrap, a ruler in millimetres and tweezers

How to do it

Make five solutions by dissolving 0, 2.5, 5.0, 10.0 and 20.0 g of salt each in 1 L of tap water. Label the bottles in grams per litre.
Wet the towel in each dish with 10 mL of its solution and lay 20 seeds on it, evenly spaced. Cover with cling wrap and keep all five dishes together at room temperature, out of direct sun.
Every day for 7 days, count the seeds with a root at least 2 mm long in each dish and record the count. Add 2 mL of tap water, not solution, only if the towel starts to dry: evaporation takes away water but leaves the salt behind, so topping up with solution would make the dish saltier.
On day 7, measure the root length of 5 seedlings from each dish and work out the mean.
Work out percentage germination (seeds germinated / 20 x 100) and pool the class's dishes so each concentration has 100 seeds or more.
Graph percentage germination and mean root length against salt concentration.
Write a short letter to a farmer whose bore water has become salty, advising which water to use on seedlings, with your graph as the evidence.

What you should see

The fresh-water dish germinates first and most and grows the longest roots. As the salt concentration rises, germination is delayed, the day-7 percentage falls and the roots are shorter; the 20 g/L dish, 57 percent of the salt in sea water (about 35 g/L), has the fewest seeds up and the shortest roots, while the lowest concentration, 2.5 g/L, is only 7 percent of sea water. Salty water makes it harder for the seed to take up the water it needs, and the salt harms its cells. The downward trend across all five concentrations, not any single count, is the finding; a group whose dishes do not follow it checks for dishes that dried out.

What changes

What you change: salt concentration (0, 2.5, 5, 10, 20 g/L)
What you measure: percentage of seeds germinated by day 7 and mean root length
What you keep the same: seed type and number
solution volume
temperature and light
towel type
days

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Salt is a plant food because plants need minerals.
Salty soil is only a problem near the beach.
A seed that has not germinated by day 7 is dead (in salty water many are only delayed).

Safety card

Low riskLearners carry it out

Hazards

seed dressings on some packet seeds
salt solution stings cuts and eyes

Controls

use untreated seed
no tasting
wash hands after handling seeds and solutions

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-4LW-S ST3-5LW-T ST3-1WS-S
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-SCI-01 ST3-PQU-01 ST3-CWT-01
Australian Curriculum v9AC9S6U01AC9S6H02AC9S6I02AC9S6I03AC9S6I04AC9S6I06

Sources

The pages the author read to write this activity.

All Concept Studio activities