How do you set up an experiment to investigate phototropism?

To investigate phototropism, set up an experiment using seedlings, a light source, and a box with a single hole.

Start by selecting a plant species that is known to exhibit phototropism, such as sunflowers or cress. Plant the seeds in a suitable growing medium and allow them to germinate and grow until they are seedlings. It's important to ensure that the seedlings are all approximately the same size and health to ensure a fair test.

Next, prepare your experimental setup. You will need a box that is large enough to contain the seedlings and is completely opaque, so no light can enter. Cut a small hole in one side of the box. This hole will allow a single beam of light to enter the box and shine on the seedlings. Place your light source (a lamp or torch) at the hole, ensuring that the light beam is directed towards the seedlings.

Place the seedlings inside the box and close it, ensuring that the only light they receive is from the hole. Position the seedlings in such a way that they are initially growing straight up. Monitor the seedlings over several days, making careful observations and taking photographs if possible.

The seedlings should start to grow towards the light source, demonstrating phototropism. You can measure the angle of growth towards the light source each day to quantify the degree of phototropism.

To further investigate, you could set up additional boxes with the hole in different positions, to see if the seedlings grow towards the light from different angles. You could also use different types of light (e.g. different colours or intensities) to see if this affects the degree of phototropism. Remember to keep all other conditions the same in each box to ensure a fair test.