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iPhone.jpgIs the iPhone 4 More Aware of Its Surroundings Than a Typical Plant?

That’s the question that I posed in my previous post.

Because of the array of sophisticated sensors included in the new iPhone, could this inanimate object actually be better at sensing its environment than a living plant?

Last time, I started with the iPhone’s ambient light and proximity sensors.

Today, let’s consider the next iPhone sensor on the list:

The Compass

As reported by AppleInsider, the newer iPhones use a sophisticated magnetometer or “digital compass”, specifically, the “…Asahi Kasei’s azimuth sensor No. AK8973, a 16-pin leadless IC package measuring 4mm square and 0.7mm thick…” (An exhaustive description of this IC can be found here (PDF), a very small portion of which: “AK8973 is a geomagnetism detection type electronic compass IC. The small package of AK8973 integrates magnetic sensors for detecting geomagnetism in the X-axis, Y-axis, and Z-axis, and arithmetic circuit for processing the signal from each sensor.”)

Thus, the iPhone 4 can sense the Earth’s geomagnetic field, and using the compass application, can tell you which direction the iPhone is facing.

Can plants sense the Earth’s magnetic field to obtain directional information? And, if so, why?

The ability to sense the Earth’s magnetic field or magnetoreception has been known to occur in birds and other animals for nearly fifty years. “Dozens of experiments have now shown that diverse animal species, ranging from bees to salamanders to sea turtles to birds, have internal compasses.” (from Ref. 1 below)

But what about plants?

compass.jpgCompared to animal magnetoreception, “…little is known about magnetoreception in plants, although early studies on plants were initiated more than 70 years ago….” (from Ref. 2 below) The authors of this review continue: “The central questions in this context, i.e. (1) whether or not plants can perceive the Earth’s magnetic field, (2) what is the physical nature of the magnetoreceptor(s), and (3) whether or not the geomagnetic field has any bearing on their survival, have remained largely unanswered.”

These authors should be commended for plowing through the scientific literature regarding a myriad of alleged geomagnetic effects on plants, which they describe as “bewildering”.

Perhaps the following best describes the history of geomagnetic-sensing research in plants: “The scientific literature describing the effects of weak magnetic fields on living systems contains a plethora of contradictory reports, few successful independent replication studies and a dearth of plausible biophysical interaction mechanisms. Most such investigations have been unsystematic, devoid of testable theoretical predictions and, ultimately, unconvincing.” (from Ref. 3 below)

These investigators were responding to recent reports (abstracts here and here) of cryptochrome-mediated magnetoreception in Arabidopsis. Harris, et al. (ref 3) could not replicate these results and concluded that there is no reliable evidence for such magnetic effects in plants.

So, what do I conclude?

After a brief review of the recent literature on this subject, I found that there is little or no well-founded, reproducible evidence that plants can sense geomagnetic fields. Moreover, there are no clear reasons that it would be to a plant’s advantage to be able to do so. Therefore, I think it is unlikely that plants have geomagnetic sensors.

Score one for the iPhone.

Next-time: The Accelerometer

References

1. Johnsen, S. and K.J. Lohman (2008) “Magnetoreception in animals.” Physics Today, March 2008, pp. 29-35. (PDF)

2. Galland, P. and A. Pazur (2005) “Magnetoreception in plants.” Journal of Plant Research Vol. 118, pp. 371–389. (Abstract)

3. Harris, S.-R., K.B. Henbest, K. Maeda, J.R. Pannell, C.R. Timmel, P.J. Hore, and H. Okamoto (2009) “Effect of magnetic fields on cryptochrome-dependent responses in Arabidopsis thaliana.” Journal of the Royal Society Interface Vol. 6, pp. 1193 –1205. (PDF)

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