Seed Germinator

1. Soak the seeds overnight in water.
2. Set aside the top of the petri dish, or open the CD case. Cut the paper towel (or coffee filter) to fit inside.
3. With a ruler and pencil, draw a straight line across the middle of the paper towel. Lay the marked-up paper in the bottom of the dish (or inside the CD case) so the line sits horizontally across the center. If you’re using a CD case, be sure the hinged edge is at the top or side (not bottom).
4. Pour a little water into the dish to wet the paper towel. Smooth out any bubbles and tip out any extra water not absorbed by the paper. Later, when you stand the dish on its edge, the wet paper should remain stuck to the inside of the dish or CD case.
5. Place 6 to 10 seeds on the paper towel, evenly spaced along the reference line. Then put the lid on the petri dish, or close the CD case.
6. Stretch the rubber bands, set close to one another, around the center of the straight-sided plastic container (see photo below). Stand the petri dish (or CD case) between the rubber bands, and adjust the setup so it’s secure, standing on edge, upright in the container. With gentle handling, the seeds should stick to the moistened paper towel. If they move, put them back in their places on the line.

   

7. Pour water into the container to a depth of about 1 inch (2 to 3 cm). The water should seep into the petri dish or CD case and contact the paper towel, keeping it moist as the seedlings begin to sprout.
8. Put your seed germinator in a warm place (room temperature or slightly higher), away from direct sunlight.

Check on your seeds once or twice a day, and notice what changes or emerges (see photo below). (It’s fine to open the seed germinator; just handle it carefully so the seeds don’t move.) Do shoots with green tips emerge first, or do white roots emerge first? Do each seed’s roots and shoots sprout in the same direction, or in different directions? Use a magnifying glass to examine the growing structures in more detail. How do they change over time?

Measure the growth of the roots and shoots over time. You may want to collect data to graph average root length vs. time, and average shoot length vs. time. (Note that it’s helpful to measure time in total elapsed hours, rather than days.) Which grows faster, the shoots or the roots?

Inside a seed is the embryo of a plant, plus a food source for that embryo, all contained within a protective seed coat. Here, you can observe seed germination, in which the embryo begins to digest the food and grow into a seedling. While this process usually happens in soil, the key component for germination is water.

At appropriate temperatures, most seeds begin their germination by absorbing water through a tiny hole in the seed coat. The moisture starts the metabolic processes of the embryo that’s contained within the seed. When hydrated by absorption of water, enzymes in the seed are activated. They begin digesting the food stored inside to generate energy for the embryo’s growth.

The developing root emerges from the seed first. As the root grows longer and thicker, it develops tiny root hairs, which help the developing plant take up water and nutrients. Shoots with pale-green leaflike structures emerge after the roots. Eventually, these leaves will turn a deeper green color and begin to photosynthesize, capturing and storing light energy and carbon dioxide from the air.

Photosynthesis in leaves supplies the plant with the energy and matter it needs to grow. Newly germinated seedlings, however, are not yet photosynthesizing. Instead, in early stages of growth, the embryo digests and assimilates the energy and matter from the food present in the seed. Depending on the type of seed, this food store contains a mixture of proteins, fats, sugars, and starches. This stored food isn’t just important to the developing plant embryo; it’s also important to human diets. About 45 percent of the calories humans consume globally comes from seed grains like rice, wheat, and corn.

A common misconception is that plants get their mass from soil. In this soil-free experiment, you can prove to yourself that plants don’t strictly require soil to grow. In fact, many plants grow very well hydroponically in water cultures, as long as the appropriate nutrients such as nitrogen, phosphorous, and potassium are provided. Your seedlings will eventually need more space than the seed germinator can provide, but given the right lighting conditions, they’ll begin to photosynthesize, accumulating mass from the carbon dioxide in the air and the water you provide.

This seed germinator makes it easy to design and perform experiments to determine the materials and conditions seeds need in order to germinate and grow. The effects of temperature, light levels, and water conditions (such as pH or salinity), as well as the presence or absence of various nutrients are all factors you can investigate. Experimenting with the position and lighting of the seed germinator can help you determine the conditions necessary for roots to grow down, and for shoots to grow up. Do roots sense gravity? Do they sense light? Or are they affected by other factors?

As noted in the What’s Going On? section above, this experiment can be used to begin investigating where a plant’s mass comes from. To do this, weigh the seeds before you soak them. Allow the seedlings to grow under good light conditions for several days, so they begin to accumulate mass through photosynthesis. Then take them out, let them dry, and check their mass again. Comparing the initial mass of the seeds to the dry mass of the germinated seedlings can help show students that a plant’s mass does not come from soil or water.