A week before the activity, test the mung bean seeds if they come from a food store (sometimes foods are irradiated which will kill seeds): sandwich between wet paper towels in the dark and warm; check after a few days.
If seeds are from a plant nursery they will be fine.
We’ll test what seeds need for them to germinate and grow into plants.
Work in table groups to set up the experiments:
1. seeds on wet paper towel (get water and air and light) - crunch up a paper towel in the bottom of the tub, wet it, then lay over a folded paper towel to make a damp, flat surface for the seeds. Layer some saran wrap over the top of the tub with small holes punched in it, to let in the light, but keep water from evaporating away as fast.
2. dry seeds in tub (get air and light, no water)
3. seeds under water (get water and light, no air) - put seeds in a tub filled with water.
4. seeds on wet paper towel in a tub (as 1.), and wrap the tub in aluminium foil (get water and air, no light)Open each day briefly to let plenty of oxygen in.
5+ Add other variables that students come up with that are dooable e.g. adding soil (the seeds have water and air, but no light if they are buried in the soil). e.g. keeping the seeds cold e.g. damaging the seeds (mimic damage by pests by puncturing or cutting the seeds)
Optional: make predictions about what will happen. I suggest keeping these predictions private, as they are emotionally heavy for students and therefore can get in the way of thinking through the scientific process. It doesn’t matter whether you predict correctly or not. It means you are thinking around the topic.
Leave tubs in a warm spot for a week. Make sure the damp conditions stay damp - check at least once a day. The seeds under water will need to have their water changed, so that mould growth does not take over.
One week to 10 days later:
Did you have a look during the week at your seeds? What did you notice? Look at all your experiment dishes. What do you see?
The long white thing coming out of the seed is the root, and comes first. Then the shoot, which is green, and might have distinct leaves.
Record average root and shoot length for each of the tubs. Combine results into a class chart.
Expected results:
The seeds with no water (#2) did not grow at all.
The seeds with water and light but no air (#3) grew the next best. They had split open and had sent out a root, but it stopped growing pretty quickly.
The seeds with water, air and light grew the next best (#1). They had roots, but they had turned brown at the ends and very few had shoots. This is likely surprising to students, as they assume plants need light even at the beginning of their growth.
The seeds in the dark with water and air (#4) grew the most in a week - they had long roots and many had shoots too. Germination happens best in the dark.
Conclude as a class what seeds need to most successfully germinate (water, air, darkness).
This makes sense as seeds germinate when they are covered in soil (so in darkness), where they stay moist and are protected from animals.
And this is why we store seeds dry, so that they do not germinate before we want them to.
Possible additional variables and results:
Seeds with soil grow well (they have darkness, wet, oxygen and also nutrients from the soil).
Seeds in the cold do not grow well (discuss: seed germination is triggered by the warmth of spring).
Seeds that are damaged sometimes germinate (discuss: probably depending on whether the plant embryo (new root and leaves) is been damaged or just the cotyledons (food storage part)).
Optional continuation of experiment:
Continue the experiment with the plants that are growing OK (should be the seeds in the darkness either on the wet paper towels or in soil), to find out what the plants need once they have germinated.
Results should show that plants need light after the leaves appear. With no light, the leaves are present but pale green.
