What is Osmosis | Essential for Plant Life

Non scientific explanation as to what Osmosis is, and why it is an essential part of plant life.

Osmosis is the ability of a strong solution to attract a weak solution though a semi permeable membrane such as the cell walls of a plant root system.

A semi-permeable membrane being a ‘skin’ that allows the passage of solution through it, but not solids.

A plant normally has a stronger chemical solution than the surrounding soil. This enables a plant to ‘suck in’ the soil water or solution through its cell walls – or the ‘skin’ of the root.

This ability to collect soil water – with its weaker solution of chemicals – from the surrounding area keeps the plan cells turgid. The soil moisture is replenished in the areas near the plant, by surrounding soil water being sucked towards the plant by capillary action. (The blotting paper effect!).

Osmosis and The semi-permeable Membrane

The essential element is Osmosis is the provision of a semi-permeable membrane – a skin or surface that allows solution to pass through – but not solids. So for the purpose of plant life, any chemicals applied to the soil by way of granular fertilisers – or organic manures such as bonemeal – have to be soluble in water to be used by the plant. Plants do not ‘eat’ they ‘drink’ via osmosis through to root walls and later by capillary action.

As long as the solution inside the plant is stronger than that of the adjacent soil, the osmotic action will continue. Following on from that, the solution inside the plant needs to go somewhere. Conveniently, the stem of the plant, attached to the root system has network of water transferring pipes – capillaries – which enables to life-supporting solution to be transferred upwards and sideways into the various parts of the plant.

The image shows a typical laboratory demonstration of Osmosis. The halves of the tube are separated by a semi-permeable membrane, then filled to equal volumes. The right side of the tube is 'strengthened by way of added chemicals, and resembles the inside of the plant root system  with its stronger solution.

The left side resembles normal soil solution, where the chemical make-up is weaker than that inside of the plant. As the weaker (soil) solution is forced into the plant by osmosis, the solution in the plant has to expand - thereby starting its assent through the plant and up to the leaves,

The traffic is not all one way of course, for there is a network of ‘veins’ – ‘arteries’ transporting the raw materials from the root up through the stems and into the leaves, where Photosynthesis takes place, and the changed raw materials of the soil moisture are then transferred to needy parts of the entire plant system as ‘sugars’ and carbohydrates. (Sounds familiar?)

Osmosis is the start of a complex set of events, that firstly keeps the plant rigid; starts the process of raw materials being taken up to the leaves (The factory) and then converted into sugars which the plant uses as basic energy – as do we humans, and importantly, the release of Oxygen into the atmosphere as a non-essential by-product for the plant.

Reverse Osmosis or Plasmolysis.

If the soil water/solution is chemically stronger than that inside the plant, then the reverse (plasmolysis) happens and the soil ’sucks’ the moisture out of the plant. The plant collapses and normally dies. This is precisely what happens if you over-apply feed to the soil, or you feed with liquid fertiliser when the soil is dry. The strong undiluted feed solution (stronger) in the soil, then attracts/sucks the (weaker) solution out of the plant.