Light! Right Between My Eyes!


One of our “Many” readers had a question on this plant growth at day vs night story..

See: “Plants Grow Faster at Night.”

So off I went to clear things up….OUCH!…I took a hit right between the eyes…BUT…I did not fall!

First, to get a “crash course” in photosynthesis follow these videos…

Crash Course Biology Photosynthesis # 8 Hank Green

A little childish, heavy on the chemistry but certainly not boring…


Photosynthesis: Light reaction, Calvin cycle, Electron Transport [3D Animation]

Great animation, narrator’s voice is sweet and could put you to sleep, but explained well. Don’t drown in the terms.


Photosynthesis Boseman Science by Paul Anderson

Best of the three, even though Mr. Anderson got in a couple of good shots….At one point he said, “The dark reaction [Calvin Cycle] is a silly term, because it only happens in the light.”


But plants grow FASTER in the DARK!

No, Mike…they only LOOK like they are growing faster…

“While rapid cell elongation causes plants to appear longer, it is not actually growth. The process is more comparable to stretching. Plant cells mostly expand upward when exposed to total darkness, because that is generally where they can access light; this process is known as geotropisim. Green plants require photosynthesis in order to experience actual growth; plants left in total darkness for an extended period of time eventually die.”


But “APPEAR LONGER” and “STRETCHING” is not “GROWING”?   Grrrrrrr.

“Plant growth is driven by photosynthetic carbon fixation during the day. Some photosynthate is accumulated, often as starch, to support nocturnal metabolism and growth at night. The rate of starch degradation in Arabidopsis leaves at night is essentially linear, and is such that almost all of the starch is used by dawn……..Thus, starch degradation is under circadian control to ensure that carbohydrate availability is maintained until the next anticipated dawn, and this control is necessary for maintaining plant productivity.”

My take on this last quote is this….Starch is used to make cellulose to make the cell wall to ELONGATE the cells which looks like “GROWING” but is actually reaching out in panic searching for the light.

I need to stop but I wanted to get this out to “Mad Scientist Juls”. This post is not pretty and is riddled with errors…but I did have fun getting schooled.





About Mike

Retired science teacher that is learning to blog...

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