Water Cooler: Seed science for kids

Did you know that the sunflower seed in your snack mix is actually alive? It won’t be sprouting into a sunflower anytime soon, though. The conditions just aren’t right. So what does it take for a seed to turn into a plant anyway?

There are all kinds of seeds. Beans, popcorn kernels and peas are all seeds, and even though they seem different, they have the important things in common. A seed is made of three basic parts. On the outside of the seed is the seed coat. This protects the seed until it is time to start growing. Inside of the seed coat is the seed embryo, which is a tiny, immature plant. Surrounding the seed embryo and making up much of the body of the seed is the endosperm, which is a tissue that stores nutrients to help the seed grow until it can grow leaves and create its own food.

If seeds have everything they need to grow into a plant, what’s stopping the beans in your cupboard or the sunflower seeds in your snack mix from sprouting? Even though they have necessary nutrients and components to grow, the seeds will wait until they encounter the specific outside conditions that will ensure they can successfully grow into a plant. The main elements required for a seed to germinate, or begin to grow, are water, light, temperature and oxygen.

Seeds have an amazing ability to tell when the conditions are right and it is safe to start growing. In the meantime, they stay dormant, which means their growth and activity is put on pause. This is somewhat similar to how some trees lose their leaves and go dormant for the winter season. They’re not dead, they’re just waiting for safe conditions to grow again.

Seeds have two hormones, and these hormones function as chemical messengers. One sends the message to start growing and the other sends the message to stay dormant. The conditions outside the seed are signals. Once the seed senses all the right signals, like moisture and the perfect temperature, the growth hormone is sent out and the whole seed knows it is time to get busy.

Although most seeds need room temperature to germinate, a few seeds have more unique requirements for growing conditions. For example, some seeds only germinate after experiencing the hot temperatures of a forest fire, which cracks the seed coats. Other seeds require cold temperatures to end their dormant state.

Once the conditions are right, the seed begins to absorb water. This allows the cells inside the seed coat to swell and the seed’s food storage to break down into useful energy. The swelling will usually cause the seed coat to break, and out pop the roots. The seed is able to detect the Earth’s gravitational pull, so it always knows which way is up and which way is down.

Even though the seed needs water to start growing, it can’t have too much of it. This is because the seed also uses the surrounding oxygen molecules for energy. It converts the oxygen into energy through a process called aerobic respiration. If the seed is in sopping wet soil, it will not access enough oxygen.

Soon after the roots pop out of the seed coat, a sprout shoots up in the opposite direction. This small shoot will push its way out of the soil and into the open air and sunshine to form a plant stem and the plant’s first leaves. At this point, the seed is officially germinated.

Over the growing season, the plant will create brand new seeds, and the process happens all over again.