Plants utilize osmotic pressure and transpiration to move resources to their cells. Osmotic pressure is fueled by organs in the cell membrane. These organs utilize ATP to control the relative solution concentrations in the cells. It is efficient at doing this because the organs move the minor components of the solution and the pressure transport the greater mass of water. Transpiration is fueled by ambient heat. The heat evaporates water from leaves creating a negative pressure that draws water up the stem. It also keeps the plant cool.

Both processes require copious amounts of liquid water intake from outside the plants body and significant pressure. Space lacks both. How can plants overcome these limitations?

A possible solution is for the plant to create an enclosed system and have the Osmosis and transpiration occur within an environment contained by the plant. The environment would have to include a cycle of water evaporation and condensation.

A different solution would be to create system to collect resources other than Osmotic pressure or transpiration. There are plenty of none plant organisms that do this. They are called animals. Animal use ATP based mechanism to obtain resource, mechanisms such as digging, hunting, digesting, and breathing. The problem is there techniques require magnitudes more energy and they are therefore unable to synthesis non-organic resources or syntheses sugars and oxygen. This may not be a problem if sufficient source of energy can be tapped. Perhaps the much more intense radiation of space, nuclear, or heat.

The problem is that energy molecule synthesis in plants needs water as one of the reactants. Even if the problems of transpiration and transport, there is still the requirement for a source of water that is continuously replenished. A closed system would never support just plant life, it would need plant-eaters that would convert the carbohydrates produced by the plant back into water and carbon dioixide so the plant can produce more carbohydrates.

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Thank for responding to my postThere are sources of water as ice in space. Plants use the sugars they create to function metobolicaly and produce carbon dioxide as a waste product.

You were describing a compltely closed system. Plants alone cannot function in such a system[/quote]

Yes, but they produce for more energy than they consume.

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I met this wonderful girl at Macy's. She was buying clothes and I was putting Slinkies on the escalator.
-Steven Wright



My Website: The Black Cat's Web Page

A space-adapted plant would probably require most, if not all of the energy it produces simply to obtain more nutrient from its substrate, which is likely to be the dirty water ice of an asteroid or comet. But symbiotic bacteria or other organisms would no doubt help in the recycling of such nutrients.

How would such a plant extract water from ice? Two ways; one is by collecting and focusing solar energy onto the asteroid, and catching the volatiles which evaporate off; the second method is by establishing an internal greenhouse within a transparent membrane- ordinary, unfocused sunlight would then be sufficient to warm the asteroid surface enough for water to become liquid.

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The Biosphere project showed that a hermetically sealed environment is far trickier to bring to equilibrium than they imagined. The failure of the carbon cycle to arrest the gradual increase of carbon dioxide over the months/years...was a surprise to many. Nuclear submarines maintain it by a prodigious use of available energy.gas scrubbing...and electrolysis of water for oxygen. Navy food is stockpiled not grown. Star rations, anyone? Recycling water will be the real trick, as it is on the space staion. Reverse osmosis membranes fail in time. Ciao. Pete.

That is why you have large vehicles, so you can have margin.