To investigate phototropism, you can conduct a simple experiment using seedlings, a light source, and a box with a single opening.

Begin by selecting a plant species known for its phototropic behavior, such as sunflowers or cress. Plant the seeds in a suitable growing medium and allow them to germinate until they develop into seedlings. It is crucial to ensure that the seedlings are of comparable size and health to maintain the integrity of your experiment.

Next, prepare your experimental setup. Obtain a completely opaque box that is large enough to accommodate the seedlings. Cut a small hole in one side of the box; this opening will allow a single beam of light to enter and illuminate the seedlings. Position your light source, such as a lamp or torch, at the hole, directing the light beam toward the seedlings.

Place the seedlings inside the box and close it securely, ensuring that the only light they receive comes from the hole. Arrange the seedlings so that they are initially growing straight upward. Over the course of several days, monitor the seedlings closely, making careful observations and taking photographs when possible.

You should begin to see the seedlings grow toward the light source, demonstrating phototropism. To quantify the degree of phototropism, measure the angle of growth toward the light source each day.

For further investigation, consider setting up additional boxes with the hole positioned differently to determine if the seedlings exhibit growth toward the light from various angles. You can also experiment with different types of light (e.g., various colors or intensities) to assess how these factors influence phototropism. Remember to keep all other conditions constant in each box to ensure a fair test.