Agriculture and Food 7–12 · Years 7–8

Germinating seeds at three temperatures, in light and in darkness

Food and agricultural practices

PracticalLow risk

The idea

A seed needs water, oxygen and a suitable temperature to germinate but does not need light, so temperature changes the rate of germination far more than darkness does.

What you need

white mustard (Brassica alba) or radish seed sold for sprouting (untreated), 30 seeds per dish
9 cm plastic Petri dishes with lids, 6 per group
filter paper discs to fit the dishes, 12
tap water in a wash bottle and a 10 mL measuring cylinder
aluminium foil to make 3 dishes light-proof
refrigerator (about 4 °C), classroom bench (about 20 °C) and an incubator set to 25 °C
3 thermometers, one left in each location
ruler graduated in millimetres, hand lens, marker pen

How to do it

Line each dish with two filter paper discs and wet them with 5 mL of water; tip off any excess.
Place 30 seeds on each dish in three rows of 10, using the SAPS grid template under the dish, and label the dish with its temperature and light treatment.
Wrap one dish from each pair in foil (dark) and leave the other unwrapped (light). Put one pair in the refrigerator, one on the classroom bench and one in the incubator. The closed refrigerator and incubator are dark inside, so both dishes there are in darkness and the light-or-dark comparison is made on the bench only.
Read the thermometer in each location at the start and end of each day and record the actual temperatures.
Count on every school day from day 1 to day 10, writing the day number beside each count. Weekends interrupt the run, so record which days were counted rather than assuming a count every day. At each count, count the seeds whose radicle (first root) has broken through the seed coat, and measure the radicle length of the same 5 marked seeds in each dish.
Add 1 mL of water to every dish whenever the paper starts to dry, so all dishes receive the same volume.
Calculate the percentage germinated for each dish on each day it was counted, plot percentage against day number for all six dishes on one graph with the uncounted days left as gaps, and pool the class results so each treatment has several replicate dishes.
At the first count on or after day 7, move the refrigerated dishes to the bench, and count them again at the day-10 count three days later.

What you should see

Germination percentage rises fastest in the 25 °C dishes and slowest in the refrigerated dishes, which show the fewest germinated seeds and the shortest radicles at the last count of the first week. On the bench the foil-wrapped dish germinates about as well as the unwrapped dish, because light is not needed for germination, and its seedlings are pale yellow instead of green. Both dishes in the refrigerator and both in the incubator are in darkness, so their seedlings are pale and each pair acts as two replicates for that temperature. Refrigerated seeds germinate once moved to the bench at the day-7 count and counted again on day 10, showing they were alive but slowed by the cold. The learner knows it worked when class replicates agree on the temperature ranking and the light and dark dishes on the bench give similar percentages.

What changes

What you change: temperature (about 4, 20 and 25 °C) and, on the bench, light (light or dark)
What you measure: percentage of seeds germinated each day; radicle length (mm) of 5 marked seeds
What you keep the same: seed batch and variety
30 seeds per dish
water volume added
dish and filter paper type
time of each count

Common misconceptions

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

Seeds need light before they can germinate.
Seeds that do not germinate in the refrigerator within a week must be dead.
A germinating seed makes its own food by photosynthesis from the start.

Safety card

Low riskLearners carry it out

Hazards

mould spores from dishes kept after the trial
water near the incubator's power supply

Controls

use untreated seed sold for sprouting so no fungicide dressing is handled
seal old dishes in a bag and put them in the bin without opening
fill dishes away from power points and wipe up spills
wash hands after the lesson

Note

No hazardous chemicals are used. General laboratory rules in NSW Department of Education, Chemical Safety in Schools (CSIS) 2021 Technical Update: Section 1 (general information for all staff) and Volume 2 Appendix D (generic risk assessment advice for each chemical). Complete a CSIS or RiskAssess site-specific risk assessment before the lesson.

Curriculum references

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

Agricultural Technology Years 7–10 Syllabus (2019)AG4-6 AG4-11 AG4-12
Technology 7–8 Syllabus (2023), focus area Food and agricultural practicesTE4-PPM-01
Australian Curriculum v9AC9TDE8K04AC9S7I02AC9S8I02

Sources

The pages the author read to write this activity.

All Concept Studio activities