Which Is More Intelligent? An iPhone Or A Plant? – Part 3

rollercoaster.jpg3D Motion Sensing – iPhone Versus Plant

If an iPhone can sense its surroundings better than a plant can, does that make the iPhone more “intelligent”?

To try to answer this question, in previous posts, I compared the iPhone’s light and proximity sensors and the geomagnetic sensor to the equivalent (if it existed) in plants.

Now, on to the accelerometer…

The iPhone uses an accelerometer to sense “…orientation, acceleration, vibration shock, and falling.”

An excellent description about how the accelerometer works from an online article published by Macworld:

“Today, like everything else electronic, the iPhone employs micro-electromechanical systems (MEMS). These devices have tiny (3 microns thick and 125 to 150 microns long) polysilicon arms with small hammer-like blocks on the end. They act like springs and hold the MEMS structure above a substrate. Acceleration causes the arms to deflect from their center position. And just like in the old electro-mechanical devices, the movement of that tiny mass is detected, by capacitors in this case, and a signal is generated.”

The actual IC board used in the iPhone can be purchased here for about $20. And an example of how some people actually take advantage of the iPhone’s accelerometer can be seen below:

You might think that it’s unlikely that plants would have sensors analogous to the iPhone’s accelerometer. After all, plants are sessile organisms. What conceivable use would a plant have for a motion detector?

Well, if you think this, then you’d be incorrect.

Plants have very sensitive cellular mechanisms to detect the wind, for example, and even to detect touch. Think Venus flytrap, for example.

This is called “mechano-stimulation”, and is nicely summarized in the following excerpt from the abstract of Ref. 1 below.

“In nature, plants are challenged with hurricane winds, monsoon rains, and herbivory attacks, in addition to many other harsh mechanical perturbations that can threaten plant survival. As a result, over many years of evolution, plants have developed very sensitive mechanisms through which they can perceive and respond to even subtle stimuli, like touch.”

Plant responses to this mechano-stimulation range from movement (thigmonasty) to changes in plant development, such as the fact that plants in windy areas tend to have thicker and shorter stems. The latter is an example of thigmomorphogenesis.

Although how mechano-stimulation is perceived by plant cells is currently unknown, several hypotheses regarding these mechanosensory mechanisms are presented here.

Briefly, one hypothesis is based on localized changes in turgor pressure within plant cells as a result of mechano-stimulation. Another hypothesis is that wind or touch may cause the cell membranes to be stretched, which may trigger stretch-activated ion channels in the membranes. Still another involves mechanical perturbation to the plant cells’ cytoskeleton, sort of like pushing one side of a spider’s web.

All of the above lead to complex biochemical interactions within the cells, including enzyme activation and changes in gene regulation, for example, all culminating in the responses that we can observe.

Though plants have cellular mechano-sensors that allow them to detect motion, these sensors really aren’t acting like the accelerometer in the iPhone.

However, the cellular mechanisms that plants use to sense gravity may be more analogous to accelerometers. We’ll have a peek at these next-time, when I get to the last iPhone sensor on the list, namely, the gyroscope.


1. E. Wassim Chehab, Elizabeth Eich and Janet Braam (2009) “Thigmomorphogenesis: a complex plant response to mechano-stimulation.” Journal of Experimental Botany Vol. 60, pp. 43-56. (Full Text)

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