My pot plant is thirsty!
Evaporation and transpiration
Two processes need to take place in order for plants to “drink”– evaporation and transpiration. You are probably wondering what these words mean, right? You don't need to worry too much about the words, but it is good to know how it all works.
When you drink a soda using a straw, you suck the soda up into your mouth and then swallow it – right? Plants don't have mouths, or hands to hold the soda, but they also use straws to suck up the water!
“But if they don't have mouths, how can they suck?” I hear you ask...
Secondly, why do they need to take up water?
Well, check out this photo of some pumpkin plants in full sunlight on a hot day ...
... and this photo was taken at the same time. This pumpkin plant is in the shade, with moist soil - and as you can see, it is a much happier pumpkin plant!
So now that you have seen the visual evidence of why plants need water. Let's find out how they get it ...
let's do science!
The project – step by step
The Question
How do plants “drink”?
The Hypothesis
Evaporation
causes water to be drawn out of the plant through the leaves.
Transpiration
then allows water to be “sucked” up the plant by
diffusion
.
The Experiments
Understanding diffusion
How plants drink
Why these experiments?
Before you see how water is actually taken up into a plant, you need to understand why it happens. The first experiment shows you this. The second experiment will demonstrate the plant actually “sucking” (a more scientific term is “drawing”) up water using transpiration, which is caused by evaporation.
The Conclusion
From the above two experiments you can see that diffusion plays a big role in plants being able to draw up water. Diffusion is made possible because water is constantly being lost from the leaves through transpiration.
As transpiration takes place water is lost through the leaves, resulting in there being less water in the leaves than in the rest of the plant. Diffusion then causes water to be sucked (drawn) up out of the ground until a balance (or in the science world – equilibrium) is reached.
“Beef up your project” facts
You have shown in your experiments that diffusion makes it possible for plants to drink. Now, bowl the judges over by throwing the term “osmosis” into your project and display.
Osmosis
is diffusion across a membrane. All living cells have membranes. As water moves from cell to cell osmosis is taking place.
Look it up
I know the question that is spinning around in your ever inquiring scientific mind is ... “So if a plant needs water to keep standing upright and not wilting, why doesn't it just keep the water in itself instead of loosing it to evaporation?”
To answer your question, I am going to give you a couple of leading questions so that you can do a bit of background research (this is all part of science and this exercise may also help in the interview):
How and when do plants close their stomata? (
Click here
to go to the online science dictionary for a definition of stomata.)
What is brought into the plant from the soil with the water? (The answer to this would also explain why plants that do not wilt – such as trees – still use this system.)
How do desert plants, which are subjected to conditions where hectic evaporation takes place, and which do not have a chance to take up water on a daily, weekly or maybe even monthly basis, prevent all their water being lost through transpiration?
More...
Looking at the stomata of a plant is not only fascinating but will earn you brownie points with the judges. Set up a dissecting microscope focused on the underside of a large leaf. You should see stomata with the two guard cells surrounding it.
|
