What do we have in common with Charles Darwin? Wondering about the weird and beautiful Green Alga Spirogyra doing the hokey pokey, moving all about, a little surprising in a filamentous photosynthetic true alga. What’s up with that?
If Darwin couldn’t figure it out, I can’t. Perhaps there is no function to it, with the movement being a byproduct of growth? Check it out and go figure:
See the Spirogyra in action in the brief footage below. The video has been sped up 10X:
CLICK HERE to see what Darwin saw (The tiny dancers are varied aquatic microbes.)
These freshwater algae have the world’s oddest chloroplasts, twisted like a ribbon running the entire length of each cell. It must be a good arrangement, as there are 400 different species, having anywhere from one to many helical ribbon chloroplasts per cell. We ask again, why? It looks like the spiral shape might be a consequence of the overall cell growth pattern. The cell wall grows in a helical pattern, and the shape of the chloroplast conforms. Like a spring, it is stretchable…a “plus” in a cell with the rare condition of each chloroplast running the length of the cell.
Those thickenings you see in the green chloroplasts are called pyrenoids (PIE-reh-noids). They are points of starch formation and storage.
Sometimes an algae-filled pond has a different look at the end of the day as opposed to dawn. Some algae and so-called blue-green algae rise and fall on a daily cycle, sinking during the night and bobbing to the surface during the day. In Spirogyra the simple and probably partially accurate explanation is that during the day oxygen from photosynthesis collects in the algal mat, causing it to float upward. That serves the alga well by placing it above the competition for sunbeams.
At night oxygen loss diminishes buoyancy, and the mat sinks. I think I’ve seen the mat rise sooner under sunny conditions, delayed by shade. You can see it too below. The Spirogyra you’ll see is on my back porch in a closed plastic bottle about a foot tall. It yo-yos up and down daily. The rise recorded in the short time-lapse video below was in bright sunshine. It resinks in the dark after my bedtime. The dark bodies dancing around are time-lapse snails.
CLICK HERE to see the Spirogyra rise up