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Messing With Your Mind: Grass answer not entirely correct...

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ezach4381
1169700.  Thu Jan 14, 2016 9:56 pm Reply with quote

In the Messing With Your Mind episode, Stephen correctly says that plants develop strategies to not be eaten; ie: becoming prickly, thorny, etc. He then goes on to say that "it seems that grass does not try and stop itself from being eaten." That's not true. If you've ever smelled that "freshly cut grass" smell, that's grass trying to save itself. The smell is a bunch of chemicals that do a few things: stimulate the growth of new cells to heal the wound faster, act as an antibiotic, cause the production of defensive hormones in unharmed parts of the plant, and act as a distress signal. So for example, if Bug A is eating the grass, and Bug B likes to eat Bug A, the smell emitted by the grass will attract Bug B to it to eat Bug A, which in turn defends the grass. (One of many sources: http://www.sciencedaily.com/releases/2014/09/140922145805.htm)

So while I don't know that these hormones would prevent larger animals like cows from eating them (though it would be reasonable that the plants would evolve so that the smell is unappealing) or humans from mowing, I don't think it's correct to say that grass does not try and stop itself from being eaten.

 
Alfred E Neuman
1169702.  Fri Jan 15, 2016 1:12 am Reply with quote

On the mowing front, grass screwed up quite badly - most humans I know like the smell of freshly mown grass. Cows seem to tolerate it quite well too.

 
Jenny
1169848.  Fri Jan 15, 2016 11:11 am Reply with quote

Hi ezach 4381 and welcome to the forums. Interesting post!

 
Troux
1170143.  Sun Jan 17, 2016 4:40 am Reply with quote

Quote:
defensive hormones in unharmed parts of the plant

What would these be? When I think of defensive chemicals in biology, I think of the tools that protect against microscopic threats - bacteria, illnesses, etc. In this case, we are talking about a macroscopic threat, so are the hormones acting to prevent a beetle from taking another bite, or are they something like white blood cells crowding a vulnerable wound?

Quote:
So for example, if Bug A is eating the grass, and Bug B likes to eat Bug A, the smell emitted by the grass will attract Bug B to it to eat Bug A, which in turn defends the grass.

Wouldn't Bug B also eat the grass which is the source of the smell? I can follow if the grass triggers an odious emission to get Bug A off, but it seems a stretch to find that the grass could smell more like Bug A than Bug A, so perhaps it's some kind of Pavlovian trigger to Bug B - the distinct and localized smell of freshly cut grass indicates a delicious bug with a full stomach is near. In that case, it seems more an evolution of Bug B's pattern recognition.

FYI, the link didn't work....

 

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