The effect of loss and gain of water in plants respectively. Image credit slideshare.net

The effect of loss and gain of water in plants respectively. Image credit slideshare.net

ZIMSEC O Level Integrated Science Notes: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.
turgid_flaccid-min

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.

To access more topics go to the Integrated Science Notes page.