Light's Effect on Plants

A photoperiod is the amount of time that an organism experiences sunlight as well as night time. Photoperiodism is a physiological response to photoperiod, typically for the purpose of flowering. It also helps the plant be able to detect seasonal changes.

Photoperiodism influences flowering because it allows the plant to know when they should flower according to whether they are short-day plants or long-day plants. Short-day plants tend to flower in seasons such as winter due to their lack of need for sunlight. Long-day plants require long term exposure to the sun, so they tend to flower during seasons such as spring and summer.

Plants can also grow in response to light that they are exposed to. In the picture below, it shows the plants' growth being manipulated in accordance to the little variables present.

In the control, the plant leans towards the light, growing in the direction of the illuminated side. Since the tip of the plant is the main variable in the detection of light due to the high numbers of photoreceptors. As the tip of the plant is removed, the plant grows straight upwards. The same occurs when the tip is covered by an opaque cap. The plant with the tip covered with the opaque cap grows straight because phototropism only occurs if the tip is exposed to light, and light is being completely shielded from the tip. A plant with the tip covered in a transparent cap is the closest resemblance to the control as the transparent cap does not prevent the tip from being exposed to the light, thus promoting the plant to lean towards the light source. The base covered by the opaque shield does curve towards the source of light, but the base remains straighter than that of the control. Since the tip is exposed to light, it is supposed to lean, but the base is voided from light thus making it grow straight. The tip separated by a gelatin block does not do much in preventing the curvature of the plant towards the light. The gelatin block is similar to the transparent cap as it allows light to penetrate through and come into contact with the plant. The tip separated by mica is a unique case. Although the tip is separated by the impermeable mica suggested that the chemical signal was a growth stimulant as the phototropic response involves faster cell elongation on the shady side than on the illuminated side.

http://www.sciencebuddies.org/Files/3834/5/PlantBio_img032.jpg