Plants grow in many different conditions all over the world. Small, beautiful wildflowers grow high on many mountains, corn and wheat grow best in the midwest region of America, citrus fruits do very well in warm climates, and maple trees grow nicely in climates with very cold winters. It is important that plants can thrive in many conditions, because plant life is vital to the ecosystem of our planet.

Plants start out as seeds. With the proper water, light, and temperature, seeds become sprouts and start to grow. This process is called germination. Different types of seeds grow best under different conditions. Some seeds should be planted very early in the spring, and others should be planted later in the year. Some seeds thrive in wet conditions, while others grow best in drier areas.

In this Gizmo™, you can explore different growing environments for three fictional types of seeds (called Seed A, Seed B, and Seed C). You can run experiments in which you adjust the amount of water, the amount of light, and the temperature of the seeds' environment. The simulation will show you how many seeds sprout after five days under the conditions you selected. What conditions lead to the best rate of germination? Your answer could be different for different seeds.

Factors Affecting Germination Rate

  1. Select A for Seed type. (If the seed buttons are greyed out, click the Reset (reset button) button first.) Use the sliders to set the Water to 10 drops/hr, Light to 50%, and Temperature to 20°C (68°F). (You can quickly set a slider to a specific number by typing the number into the box to the right of the slider, and then pressing the ENTER key.) Press the Play (play button) button and watch as seeds sprout over 5 days. (Don't worry, the simulation does not really take 5 days!)
    1. Look at the Description tab. Out of the 100 seeds, how many have sprouted? How many have not yet sprouted? Write this down, along with the water, light, and temperature conditions you used.
    2. Click on the Graph tab. The line that starts at zero shows the number of seeds that had sprouted over time. The line that starts at 100 shows the number of seeds that had not yet sprouted. Does the sprouts line increase or decrease from left to right? Why? Does the seeds (not sprouted) line increase or decrease?
  2. Click on the Reset button on the Simulation tab. You will now repeat the same experiment, so be sure your conditions are still set on 10 drops of water per hour, 50% light, and 20°C. Also be sure that the Graph tab is selected. Then press the Play button. Watch the graph while the simulation plays.
    1. Why are both lines flat for a while at the beginning of the experiment?
    2. After the lines started moving, you should have seen that they moved together. Explain why.
    3. Click on the Description tab. Write down your results to this experiment along with your previous results.
    4. Repeat the experiment one more time, for a total of three trials. Write down your results again.
    5. Did you always get the same result when you performed the experiment several times using the same initial conditions? Why do you think it is important to perform this experiment more than once?
  3. Conduct a new series of experiments with Seed A where the temperature is kept at 20°C and the light is kept at 50%, but the amount of water given to the seeds varies. Start with a water supply of 30 drops/hour, and run the simulation three times. Write down your results each time. Then, do the same (three trials) for 40 drops of water per hour, then 50, and so on, until you reach 100 drops per hour. Be sure to write down your data for each trial.
    1. Make a graph of your results. Put the amount of water on the horizontal axis and the number of sprouts on the vertical axis. For each experiment you ran, plot a point on the graph.
    2. Look at your graph. What effect does the amount of water supplied to the seeds have on the number of sprouts that emerge for Seed A? Explain.
    3. What amount of water produced the largest number of sprouts?
    4. In this series of experiments, only the amount of water supplied to the seeds was changed. Why do you think the values of light and temperature were kept the same during these experiments?
  4. Conduct a similar series of experiments with Seed A where the temperature is kept at 20°C and the amount of water is kept at 50 drops/hr, but the amount of light supplied to the seeds is varied. Start with 20% as the amount of light supplied to the seeds, and run the simulation three times. Write down your results each time. Then, do the same (three trials) for 30% light, then 40%, and so on, until you reach 100% light. Be sure to write down your data for each trial.
    1. Graph your results. Did light have any effect on the number of sprouts for Seed A? Explain.
    2. Why might light not be a very important factor for some types of seeds? If possible, discuss your ideas with your classmates and teacher.
  5. Conduct another series of experiments with Seed A to test the effects of temperature on germination rate. Be sure to keep the amount of light constant at 50% and the amount of water constant at 50 drops/hr. Experiment with temperatures of 0°C (32°F) , 5°C, 10°C, and so on, up through 35°C (95°F).
    1. Make a graph of your results. What effect does the room temperature have on the number of sprouts that emerge for Seed A? Explain.
    2. What temperature produced the highest germination rate?
  6. In this experiment, you will try to produce the highest germination rate you can. Set up the conditions so that you are using the "best" amount of water, "best" amount of light, and "best" temperature for germination. (Use the values you found to be best in your experiments.) Run the simulation three times. Write down your data each time.
    1. On average, how many sprouts did you end up with under these conditions? How does the average value compare to the measurements you made in previous experiments? Explain.
    2. Try making small adjustments to the initial conditions to make the total number of sprouts as high as possible. Remember that it is often good to do the same experiment several times since each experiment can yield slightly different results. What do you think the ideal conditions for Seed A are? Explain your reasoning.

Further Considerations

  1. Design a series of experiments that will determine the ideal initial conditions for seed types B and C in the Gizmo. Describe the optimal climate for each type of seed. Which seed would you plant if you lived in a cool, sunny climate? Which would you plant in a warm, shady climate?
  2. Try performing experiments while viewing the graph on the Graph tab. Under the best conditions for each seed type, are there differences in the rate at which the seeds turn in to sprouts? For example, does one type of seed begin to sprout quickly? Does one type of seed sprout over a longer period of time? Describe how each type of seed acts over the five-day time period.
  3. Did one type of seed produce more sprouts than the other types did under the optimal conditions for each type of seed? Did one seed type seem to be more consistent under ideal conditions than another seed type?