Plants have different and noticeable reactions to light and dark. During the process of photosynthesis, plants use energy from the sun to produce oxygen, and in the darkness, plants respire and actually use oxygen and produce carbon dioxide. This can be shown by testing the gas around a plant. Plants are also phototropic, meaning they grow in the direction of a light source. Experiments can be used to to test these plant properties.
Phototropism
Plants demonstrate phototropism by physically bending toward a light source. Although scientists have shown that this growth is caused by a plant hormone, the process is still not fully understood. But, it is easy to demonstrate. To do this experiment, you will need to germinate two small colonies of fast growing plants, such as beans. Take one group of sprouts and place it on a window sill or in another place where the direction of the light source can be controlled. After a few days, you will observe that the plants seem to grow toward the light source in an attempt to maximize their leaf exposure to the light source in order maximize photosynthesis. Plants with the optimal level of light exposure will soon begin to grow more quickly than others.
Take the second group of sprouts and place it in a dark room or drawer. Within days, these plants will begin to lose their green color, their leaves will begin to fall off and they will ultimately die because they will be unable to produce the energy needed for cellular reproduction by photosynthesis without light.
Plant Breath Cycle
During photosynthesis plants produce oxygen, and in the dark, when photosynthesis is largely impossible, plants consume oxygen and produce carbon dioxide. This can be demonstrated by planting an aquatic plant, such as elodea, in a controlled environment using distilled water and taking regular pH measurements. During the day, leave the plant in a place where it gets plenty of sunlight so that it can photosynthesize and produce oxygen. Using a mid range pH indicator, measure the pH of the water several times throughout the day and record your results and any conditionals, such as whether or not the day was overcast. At sunset, place the plant in a dark closet or drawer overnight and measure the pH first thing in the morning when removing the plant from the drawer to place it back in the sunlight.
You will notice that the pH measurements during the day are much lower and thus more acidic in the morning. This is because when in the dark the plant is actually consuming oxygen and releasing carbon dioxide. Carbon dioxide reacts with water and forms a weak acid called carbonic acid which lowers the pH of the water. As you take measurements throughout the day, you will notice the pH level slowly returning to the neutral seven as the plant is exposed to sunlight, photosynthesizes, and releases oxygen. These is how plants breathe.
Tags: light source, produce oxygen, carbon dioxide, carbon dioxide This, dioxide This, direction light
