Water and ion uptake in plants

• When plant cells are surrounded by water, the water enters by osmosis until the cells are full of water.
• The water enters the plants because there is relatively more water outside the cells than within.
• These plant cells are surrounded by a strong cellulose cell wall that prevents them from bursting.

Plamolysed (flaccid) vs turgid cell with arrows showing the direction of water diffusion. Image credit kshitij-pmt.com

• When cells are full of water they are said to be turgid.
• If plan cells are placed in a strong sugar/salt solution they lose water via osmosis.
• Plasmolysis is the movement of water out of the cells.
• Plasmolysis occurs because there is relatively more water outside the cells than within the cells.
• When water moves out of the cells they become soft as the cell walls sag in.
• When this occurs the cells are said to be flaccid.
• Plants gain water continuously by osmosis through microscopic root hairs if there is enough water in the soil.
• Water will only enter the plants if there is a higher concentration outside the roots than on the inside.
• Dissolved minerals enter into plants at the same time as water.
• The minerals are in the form of ions.
• Ions are charged particles.
• These ions are absorbed actively i.e. energy inside the roots is used to pull the ions.
• This is because the ion in the soil are in lower concentrations which means they cannot be taken up via osmosis.
• The ions that would otherwise enter the plant by diffusion would be insufficient to sustain the plant.
• The ions are thus absorbed via active uptake against the diffusion gradient.
• The minerals and water enter the plants via the roots and move up to all parts of the plant.

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