We living organisms are sacs of salty solution. That’s why we can be electrocuted. In my G-Chem class yesterday, we discussed electrolytes – solutions that conduct electricity. What do electrolytes have? Mobile charged particles, in this case ions from a dissolved soluble salt.
The black ghost is a knifefish – one of several species that include the electric eel in this family of electric fish. You can listen to the “sound” it makes by dipping an electrode in water set to detect the right frequency (~900 Hz). The black ghost generates an electric field which can be distorted by objects that have different conductivity compared to water. Thousands of electroreceptors on the body of the black ghost “listen” for these distortions. That’s how it detects its prey – the sacs of salty solution!
Perhaps “listen” is the wrong word. Should it be “see”? Our eyes detect electromagnetic radiation in the form of photons, although this isn’t akin to the electric field. Or maybe it should be “touch”. We have touch receptors all over our body, and essentially the black ghost extends its sense of touch when it generates the surrounding field. It costs valuable energy to generate an electric field so it doesn’t extend very far and quickly dies off with distance. You’re potential prey only if you get too close.
I’m learning all this re-reading An Immense World by Ed Yong, the best non-fiction book I read last year. Most of what I read is borrowed from the library. After my first read (last November!), Yong’s book is one that I knew I would return to on multiple occasions so I bought my own copy. (It’s the first non-work-related book I’ve bought in a decade.) Today’s post is from Chapter 10, “Living Batteries”.
What are the advantages of generating an electric field to detect prey? Yong writes: “It might be that electric fields are more reliable than almost any other stimulus. They aren’t distorted by turbulence… in fast-flowing rivers, where torrents and eddies befuddle the lateral line. Electric fields aren’t obscured by darkness or murkiness, so electric fish can stay active in turbid waters and nighttime hours. Electric fields aren’t blocked by barriers as light and smells are, so electric fish can sense through solid objects… it’s very hard to hide from these animals. They are sensitive to… capacitance… [an object’s] ability to store a charge.”
I also learned that these marvelous creatures turn their electric fields on and off to generate a particular rhythm – it’s akin to the “sound of their voice”. But this steady beat can also be modulated to communicate other sorts of information. Essentially living batteries are talking and listening to each other through pulsed electric fields. Yong writes: “These animals can’t hide from each other… A river full of electric fish must be like a cocktail party where no one ever shuts up, even when their mouths are full.” And some species, such as the elephantfish, have significantly sized oxygen-guzzling brains (as a percentage of body weight).
Reading Yong’s book inspired me to imagine teaching a class on the “Chemistry of Sense”. I already talk about photons in my G-Chem class and how we use them to “see”. I could bring in smell and taste by discussing molecular recognition and interactions. It requires molecules to “touch”, so to speak. While I hadn’t thought much about sound, I was reminded by our human limitations of hearing (20 Hz to 20 kHz) and what we might be missing, analogous to vision where I already discuss how organisms in other environments may have evolved different photoreceptors to detect different dominant wavelengths. And we could even speculate about sixth or seventh senses with electric fields as one possibility. After all, our electrolytic bodies are sacs of salty solution!
No comments:
Post a Comment