Science Snippets: Osmosis – it kinda sucks

Osmosis – that magic process by which plants suck up the water from the soil. Wierd. Here’s a quick explanation:

In osmosis water moves from a more dilute solution to a less dilute solution through some kind of semi-permeable membrane.

Diagram of osmosis

Circles are water molecules and squares are a solute.

Think of it as the way drivers will barge into the next lane over when it’s emptier. Water molecules are smarter than drivers though; they don’t keep doing it until the position is reversed, once equal dilution is reached the movement stops.

In a plant this starts at the root hairs with water being drawn from the soil into the plant through the cell wall. The water being drawn into the plant’s cells like this mantains their turgidity* and in non-woody plants provides much of the plants rigidity, which is why they collapse when they don’t have enough water.

It is possible to accidentally cause osmosis to work in the opposite direction to normal in a plant by feeding it a concentrated fertiliser when the soil is otherwise quite dry. This can push the levels of salts in the soil above the level of salts in the plant and when this happens osmosis starts to work in the opposite direction to normal; it starts drawing water out of the plant and into the soil. And that just sucks badly**.

– – – – –

* The English language is great. It brings us words such as ‘turgid’. I’m going to be finding ways to sneak it into conversation all week.

** Sorry, couldn’t help myself.

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9 responses to “Science Snippets: Osmosis – it kinda sucks

  1. It’s just like being back in the biology labs, minus the pickled insects. If you manage to get “turgid” into the conversation, go for extra bonus points and try and get “flaccid” in there too! Lol!

  2. Good post, Libby and not at all turgid. Osmosis is the only definition I can remember word perfect from school. I moved into new house a few years ago and hurriedly needed to water a very dry bamboo. Grabbed a bucket of water left by the previous owner, poured it into the bamboo pot and then realised that the bottom of the bucket was full of rock salt! A beautiful example of your reverse osmosis then occurred. D

    • Shame about the bamboo – bet it knew how a slug feels when you salt it. Did you save the day? Or was that The End for the poor thing.

      • Nah, bamboo very dead. It was the day of moving in and so I was rushing about unloading boxes and all the rest. I didn’t realise what I had done until it was too late. Sob!

  3. I remember all those turgid and flacid cell lessons…. osmosis frickin’ awesome!

  4. and so the driving force behibnd it all is really equilibrium.
    (Will review the car analogy when I’m on the motorway and everyone is hogging the middle lane)

  5. Pingback: Osmosis: How Plants Suck up Water « Gardora.net

  6. Wondered why liquid fertilizers say don’t apply to dry soil. I know why now..!

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