Re: HOW DOES PHOTOTROPISM AFFECT PLANTS?

Plants need light to grow. They will do everything they can to get as much of it as possible. One of the ways plants maximize their amount of light is phototropism or "moving toward light". Since most plants cannot really move their whole body, they move part of it.

When light is all around, the plant grows straight, but if light is coming from only one side (for instance, from a window) plants will start to grow toward the source of the light. The way the plant does this is by making one side of the stem grow faster than the other side. This causes the plant to bend. Contrary to what one might think at first, the part away from the light (the DARKER part) grows faster! But this has the effect of getting the rest of the plant closer to the light.

The way the plant does this is using a plant hormone called auxin. Auxin is produced at the tip of the plant and then goes down causing the cells in the stem to get longer. When one side is darker than the other, more of the auxin goes to the darker side and it then grows faster, bending the stem toward the light.

You can do experiments to see this effect. The original experiments used young oat seedlings ( a few days after germination) but you can use other plants. Beans work well also. Try different plants if you have time. You will see the effect better if the plants are very young (usually 1-2 inches). One way is to put the seedlings (young plants) in a box with bright light coming through a "window" on one side. You can also put different colors of plastic wrap over the windows to see the effects. (Plants do not respond equally to all colors of light.)

Another way is to put a small cap of dark paper over the tip of some of the plants to see if this inhibits the plants from "seeing" the light.

Good luck and enjoy your science project.