Naked Science Forum
General Discussion & Feedback => Guest Book => Topic started by: rotenbil on 18/07/2005 01:40:53
-
Why do trees grow in a vertical direction and vines climb trees?
Does centrifical force caused by the earth spinning have any thing to do with it?
-
Are you suggesting the gravity plays a part in the vertical growth of plants and trees?
Try posting on General Science to get a better response to your question.
You might also want to read a recent thread debating how water is lifted by trees, also posted on general science forum.
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
-
Plants have the ability to tell up from down and they use both light and gravity to guide them. Light controls the production of growth hormones in plant stems, pushing the leaves and shoots towards the greatest light intensity, whilst gravity is detected by intracellular 'spirit levels' comprising tiny starch grains that settle to the lowest point in the cell and signal downwards. Some parts of the plant have a stronger light-response (photo-tropism) e.g. the shoots, whilst others have a stronger gravity response (geo-tropism) e.g. roots.
Here's a link to a show containing an interview with NASA plant physiologist Volker Kern about how plants grow with and without gravity (http://www.thenakedscientists.com/HTML/Shows/2005.01.30.htm).
Chris
P.S. This thread will move to science from the guest book shortly.
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
-
Chris, any idea how far one would have to travel in space to become free of gravity, as erroneously stated by Volker Kern?
Orbiting the Earth does not negate the pull of gravity. One estimate is that there is still 90% of the Earth's gravitational pull. Centrifugal forces due to the speed in which a vehicle orbits the Earth does not take gravity away! And even the artificially induced environment aboard a vessel in orbit is termed as micro gravity, not zero gravity. To my knowledge, we have yet to experience truly zero gravity. the acceleration from gravity at 100 km is around 3% less than on the surface of the earth.
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
-
I think he was probably trying to simplify things. You're correct that in space one is never in zero gravity although the force of gravity at certain locations may be extremely small.
In orbit you are in perpetual freefall so it is more accurate to use the term 'weightless'. The mechanism by which plants detect gravity is through the interaction of starch grains within their cells with the cell skeleton. When they are in orbit both the cell and the starch grains within are in freefall and hence there is no net movement 'down' as there would be on Earth. Hence the experiment can be said to be taking place in the 'absence' of gravity, although what this actually means is in the absence of the 'effects' of gravity.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx