Is Transpiration a necessary evil?

[immortal]

Transpiration is the process of loss of water from the aerial parts of the body in the form of water droplets. It was Curtis who stated that Transpiration is a necessary evil. Transpiration is an effect which either opposes or favours the cause that produced it depending on the availability of water in the soil. It is just an emergent property which emerges out when there are pores on the surface of living organisms. They need this pores for the exchange of gases which is important for metabolic activities. The number of pores depend on the concentration of gas in the atmophere that has to be fixed. Animals have just two nostrils or pores because the concentration of oxygen was quite high when they appeared on land.

So when plants appeared on land around 400-500 million years ago the concentration of c02 in the paleozoic era was high and having pores between the epidermal cell of the body was sufficient to fix co2 and transpiration was not a problem as these plants were living in moist conditions. But at the end of the paleozoic era the conc of co2 decreased and this paved the way for evolution of stomata and leaves become broader as a result of increase in stomatal apparatus to fix co2 and this resulted in excess loss of water and this led to the evolution of passive absorption of water through the conduting system in order to compensate the loss of water and to maintain turgidity of cells.

Right from the 19th century many have looked at the process of transpiration and each one came up with a different conclusion.

One of the advantages of transpiration is that it reduces the temperature of the leaf (I don't know how far this is true) and if it does reduces the temperature then it must be advantageous to plants because we are begining to understand the importance of temperature in a cell and how it affects enzymes which maintain quantum coherence to carry out quick reactions.

Some claim that transpiration helps in translocation of mineral salts to the upper parts of the body. But studies show that only 1-2% of transpiration is sufficient to translocate the mineral salts.

If transpiration is both advantgeous as well as disavantageous to plants then natural selection may keep the advantageous effects and try to suppress the odd effects. But the problem is we don't know exactly what are the advantages of transpiration.

[thedarkshade]

Animals have just two nostrils or pores because the concentration of oxygen was quite high when they appeared on land.

But that doesn't mean that is the animal's main way of breathing! Take frogs for example! They breathe in two ways, by lungs (using nostrils) and by skin. But if we seal the pores on a frog's skin, the frog will soon die. That shows that it breathes more with skin than lungs, although when frogs appeared there was enough oxygen!

If transpiration is both advantgeous as well as disavantageous to plants then natural selection may keep the advantageous effects and try to suppress the odd effects. But the problem is we don't know exactly what are the advantages of transpiration.

You just mentioned one of the advantages, the keep of constant temperature. Changes in temperature have quite a lot effects in any organism. All organisms are sensitive to changes in temperature, so they have developed special methods of keeping the temperature constant and so they suffer not big changes, and one of them is transpiration!

 

We too have a sort of transpiration, sweat! And as far as I know, there is nothing bad with sweating (except the smell), because by sweat we keep the temperature constant in our organism!

[Mr Skeptic]

Some plants have a daily cycle of transpiring at night (a cycle that absorbs CO2) when they will lose less water, then using all that stored CO2 in the day. Tropical plants with lots of water will transpire during the day to cool themselves. Some plants with much sunlight and little water will shape themselves so as to reduce the amount of sunlight they get, as they cannot afford to transpire to cool themselves.

 

In as much as transpiring loses water and water is scarce, it is a necessary evil. It seems the membranes have to be wet to allow gas to diffuse, so transpiration in dryer air will result in the loss of water.

 

Oh, and BTW, nostrils are not pores, and you have a large number of pores and a large amount of lung surface area exposed to air.

[John Cuthber]

"Transpiration is the process of loss of water from the aerial parts of the body in the form of water droplets."

No, it's not.

http://en.wikipedia.org/wiki/Transpiration

Gutation is the process of forcing out water as a liquid (here's a nice picture as well as some text)

http://www.darklightimagery.net/52-6.html

Transpiration is losing water as a vapour.

"Animals have just two nostrils or pores because the concentration of oxygen was quite high when they appeared on land."

Er, no again.

Numerically, most animals are insects, which generally have a large number of pores called spiracles for breathing.

http://en.wikipedia.org/wiki/Spiracle

We humans also have a vast number of pores for sweating (I believe humans are some of the sweatiest animals on earth) but they couldn't do the job of keeping us supplied with air.

It's a safe bet that different plants have vastly different transpiration rates that suit their environments. Xerophytic plants, in particular, would have slow rates of water loss. Many plants are able to actively control the rate at which they transpire by opening and closing stomata, so it's hardly as if they have some fixed rate and have to put up with it.