From Abracadabra to Zombies
In a nutshell: Plants don't have brains or nerves, yet some people believe plants can sense when someone is planning to cut them and they can feel pain. Is this possible? The science says no, though it is true that plants react to light and chemicals. Some plants can catch insects. Some can turn as the sun moves overhead.
Some people think plants can feel pleasure and pain. If you played music for one plant but not for another and the one you played music for grew healthier, you might think the plant was listening to and enjoying the music. If you hooked up a machine to a plant and saw a needle move on the machine when you came near the plant with a knife, you might think the plant was scared. If you saw a flower close up over an insect and saw chemicals begin to dissolve the insect, you might think the plant was hungry and was using its brain to get a meal.
Plants don't have nerves or a brain. Without nerves and a brain, living things can do many things that look like they're thinking. Some scientists even say that plants do think because they have evolved complex sensory mechanisms that allow them to survive in changing environments. Sunflowers will look like they are turning their heads to follow the path of the sun. Poppies will close up at night and open up when the sun comes out. Plants can take in sunlight, water, food (nutrients such as nitrogen), and a gas known as carbon dioxide. When they do this, they release oxygen, which animals like us need to live. Fruits that are ripening release chemicals which non-ripe fruits react to by starting to ripen. Changes in temperature cause plants to change themselves. The same genes that regulate the reaction to light in animals are present in plants.
Plants have evolved over millions of years to do many different kinds of things. The first land plants formed about 450 million years ago. (If you were 16 years old on July 22, 2011, and had started counting each second from the moment you were born, you would have gotten to about 450 million just in time for your 16th birthday party.) No plant has ever developed a brain or nerves. When plants look like they are thinking, they are responding automatically to a stimulus. A stimulus is something that causes an automatic response in something else, like when light causes a plant to close its petals or produce oxygen. No brain or nerves are needed to respond to a stimulus.
When plants respond to physical or chemical things, they are not thinking or feeling any more than we are when our bodies automatically respond to stimuli. Without a brain and nerves, a living thing can't be conscious of anything. It can't experience pleasure, pain, or any emotions. While it might be ok to say that plants are thinking when they respond automatically to physical or chemical things, it would not be ok to say that plants are conscious. They may have unconscious sense perception, but they don't have self-perception.
Without plants, there would be no animal life on Earth. We need plants for food and oxygen. We can't live without them, but even if they seem smart we must remember that they are without brains or anything like brains. So, if a plant in a music room does better than one in the garage, it probably is due to a difference in light, water, soil, or nutrients. Or it might just have been a healthier plant to begin with. But, there is only one way to find out for sure whether plants can respond to music or talking to them kindly.
You can set up a test to see if talking nicely to plants helps them grow better. It's easy. This type of experiment is called a control group study.
First, get some plants. I'd say you need at least a dozen. Either grow them from seeds from the same packet or buy plants from the same nursery. Divide the plants into two groups of six plants each. Talk nicely to one group, but not to the other group of plants. You could either not talk to that group at all or you could talk meanly to them. Give each plant the same amount of water, food, and light, and grow them in very similar places. The only difference between the two groups should be that one group of plants gets talked to nicely and the other doesn't.
Set a time for the test to run, say six weeks. At the end of the experiment compare the two groups of plants for such things as size, flowers, fruits, healthy leaves (make sure one group isn't in a place where there are more insects to chomp on the leaves!), and things like that.
Just in case one or more of the seeds or plants is very good or very bad compared to the others, you must randomize the plants before you divide them into the two groups. Give each plant a number from 1 to 12, put slips of paper with numbers from 1 to 12 in a hat, and draw six numbers. Those six plants will go into one group, say the one that gets talked to nicely (which is called the experimental group). The other six plants go into what is called the control group. (Click here to learn more about randomizing items in control group studies.)
If plants respond to nice talk, then the experimental group should do much better than the control group. But if they do, you still can't be sure your results aren't a fluke. It would be better if several kids in your class did the same kind of experiment. If you all get the same kind of result, then it's probably not a fluke.
p.s. Someone wrote in to warn experimenters about breathing on some plants and not others. Can you figure out why that should be a concern?