This is the classic inquiry experiment of middle school biology. Its value goes beyond "knowing what seeds need": it walks students through the full scientific method — ask a question, make a hypothesis, set up a control, change one variable at a time, record data, and draw a conclusion.

All you need is a handful of mung beans and a few cups — but set aside 3 to 7 days. This is an experiment that rewards patience.

Safety first (read this section before you start)

  • The experiment itself is not dangerous, and students can do it on their own.
  • If you use the refrigerator, tell a parent first. Don't put the experiment cup next to food — seal it in a zip-top bag to keep it separate.
  • After a few days some cups may develop mold or an off smell (especially the flooded one). That is normal. Don't lean in and sniff — pour it all out, wash the container, and then wash your hands thoroughly.
  • Sprouted beans are experiment material — do not eat them. Neither the containers nor the conditions are food-safe.
  • Don't start with moldy seeds; results from them are unreliable.

Materials and equipment

  • About 60 plump, evenly sized mung beans (soybeans or adzuki beans work too, but use only one kind per run);
  • 5 clear cups or small bowls, labeled 1 through 5;
  • Paper towels or cotton wool, clean water, a dropper or small spoon;
  • 1 light-proof box or black paper bag (for the no-light group);
  • A refrigerator (for the cold group) and a zip-top bag;
  • A data table and pen; a thermometer is optional.

Step 1: design the controls — change only one variable

The core principle is one variable at a time: cup 1 is the control group with every condition favorable; each of cups 2–5 changes exactly one condition and keeps everything else identical to cup 1.

  • 1 — Control: moist paper towel (no standing water), room temperature (about 20–25 °C), in the light;
  • 2 — No water: paper towel kept dry; everything else same as cup 1;
  • 3 — No air: seeds fully submerged under water (water level at least 2 cm above the seeds); everything else same as cup 1;
  • 4 — Cold: placed in the refrigerator (about 4 °C); everything else same as cup 1;
  • 5 — No light: covered with a light-proof box; everything else same as cup 1.

Put 10 to 12 seeds in each cup — not just one.

Why a dozen seeds per cup: any single seed might be dead or shriveled, so a conclusion drawn from one seed could easily be a fluke. With a dozen seeds you can calculate a germination rate (sprouted ÷ total) and rule out individual differences. This is called replication — it's what makes the conclusion trustworthy, and it's the experimental-design point tests ask about most.

Step 2: set up and record

  1. Line the bottoms of cups 1, 2, 4 and 5 with 2–3 layers of paper towel; cup 3 gets no towel — just water.
  2. Wet the towels in cups 1, 4 and 5 until moist but not pooling (squeezed, they shouldn't drip); keep cup 2's towel completely dry.
  3. Spread 10–12 mung beans evenly in each cup — no piles.
  4. Fill cup 3 with water until the seeds are fully submerged; seal cup 4 in a bag and put it in the refrigerator; cover cup 5 with the black box.
  5. From then on, observe once a day at the same time. Record for each cup the number of sprouted seeds, sprout length, and any changes in appearance. Top up cups 1, 4 and 5 with water as needed to keep them moist.
  6. Keep observing for 3–7 days, until the control group has clearly sprouted and the other groups' results are stable.

Note: when checking cup 5, be quick — look, then cover it right back up. If it sits in the light too long, you've broken your own variable.

Interactive simulation: this experiment has a drag-and-play simulator in our Interactive Lab. The lab interface is currently Chinese-only — the controls are simple sliders and switches, so it is still easy to explore.

What you will see and record

The typical results look like this (germination rates vary a little from run to run, but the trend should hold):

  • 1 — Control: after 2–3 days, seeds sprout in large numbers; the embryonic root breaks through the seed coat first, and the germination rate is usually above 80%;
  • 2 — No water: no germination at all; the seeds look almost unchanged — still dry and hard;
  • 3 — No air: no germination, or almost none; the seeds swell and soften, often with an off smell or mold;
  • 4 — Cold: no germination; the seeds absorb water and swell, but no sprout appears;
  • 5 — No light: plenty of germination anyway! The rate is close to cup 1's — the sprouts are just paler, thinner, and longer-stemmed.

The science behind it

Comparing cup 1 with cups 2, 3 and 4 gives the three required conditions, one at a time:

  • Water: a seed must soak up enough water to germinate. Water softens the seed coat so the embryonic root can break through — and more importantly, the food stored inside the seed can only be broken down by enzymes and transported to the embryo when it is in solution.
  • Air (oxygen): germination burns a lot of energy, supplied by cellular respiration — and respiration needs oxygen. Submerged in cup 3, the seeds are starved of oxygen and can only respire anaerobically, which yields little energy and builds up alcohol and other by-products. So they fail to sprout and tend to rot — which is also why waterlogged fields rot their seed.
  • Suitable temperature: every chemical reaction in germination is catalyzed by enzymes, and enzyme activity depends heavily on temperature. At 4 °C the enzymes are barely active and the reactions all but stop, so cup 4 doesn't sprout. Note that these seeds are not dead: take cup 4 out of the refrigerator and back to room temperature, and most of them will still germinate normally — a follow-up check well worth doing.

Then compare cup 1 with cup 5 for the conclusion people most often get wrong: light is not a required condition for germination. A germinating seed lives off the food stored in its own cotyledons or endosperm — no photosynthesis needed — which is why seeds buried in dark soil sprout just fine.

But why are cup 5's sprouts pale, with longer stems? Because making chlorophyll requires light (this is exactly why bean sprouts are grown in the dark), and in darkness a plant stretches faster, "searching" for a light source. The lesson: light doesn't affect germination, but it does affect the growth and greening that come after. Once the true leaves appear and the stored food runs out, the seedling must live by photosynthesis — and from that point on, light becomes essential. That hands off neatly to the experiment proving green leaves make starch in the light.

Two more prerequisites are easy to overlook: the seed itself must be intact, alive, and past its dormancy period. A seed with a damaged embryo will never sprout, however good the conditions. These are the seed's internal conditions, to be kept separate in your notes from the three external conditions above.

Tips for teachers and parents

  • Time and grouping: the experiment spans three days, in pairs; observe at a fixed time each day.
  • Before hands go on equipment: the mung beans are not for eating.

The step most often skipped. Have students state for themselves what each of the five cups changes — the teacher only confirms. The light cup is a deliberately planted trap: hold the reveal until the results come in, and the inquiry lands with full force.

How to know they really understand. A student meets the bar when they can draw the five-group control table, name each group's variable and conclusion, and explain why cup 5 sprouted but came up pale.

Take it further

  • Prove the cold group isn't dead: take cup 4 out of the refrigerator, return it to room temperature, keep it moist, and watch whether it sprouts within a few days. This makes the "temperature controls enzyme activity" explanation stand on much firmer ground.
  • Find the optimum temperature: set up extra groups at 10 °C, 20 °C, 30 °C and 40 °C, tally the germination rates, and plot a temperature–germination curve to find mung beans' ideal sprouting temperature.
  • Measure the respiration of germination: pack sprouting mung beans into a thermos, stopper it, and insert a thermometer. After a few hours the temperature creeps up — direct evidence that respiration releases energy. The full version is in the sealed-jar respiration experiment with a candle, limewater and a thermometer.
  • Repeat with different seeds: run it again with soybeans or wheat and see whether the conclusions hold. Reproducing a result with different material is a key mark of a reliable conclusion.

When a student can draw up the five-cup control table, say what each cup changed and what it proved, and explain why cup 5 sprouted but stayed pale, the scientific method behind this inquiry is truly theirs.