The movement of molecules in plants: Diffusion

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The movement of molecules in plants: Diffusion

Coloured ink droplets falling and diffusing in a glass of water. Image credit pinterest.com

Coloured ink droplets falling and diffusing in a glass of water. Image credit pinterest.com

ZIMSEC O Level Integrated Science Notes:The movement of molecules

  • Both plants and animals contain a large amount of water in their tissue.
  • Plants like water melons and cucumbers have a lot of water which sometimes constitute 95% of their weight.
  • Most animal tissue is at least 70% water.
  • Water must be able to enter and leave both plant and animal cells.
  • The process by which water enters plants is called diffusion.
  • All matter is made up of molecules.
  • The kinetic theory states that all molecules and particles are always in constant movement.
  • In gasses and liquids particular these molecules are able to move freely from one place to another.
  • If there is a higher concentration of certain molecules in one place than in another, they ( molecules)will move from where there is a higher concentration to regions where the concentration is lower.
  • This movement is referred to as diffusion.
  • Water vapor molecules in the air and inside leaves move by diffusion.
  • These molecules will continue to move as long as there is a difference in concentration between the two places involved.
  • The difference in the concentration of a certain molecule in one place from another creates what is known as a a concentration gradient.
Molecules move (diffuse) from higher concentration to lower concentration areas.

Molecules move (diffuse) from higher concentration to lower concentration areas.

Diffusion of water

Demonstrating diffusion using a semi-permeable membrane and equal concentrations of water.

Demonstrating diffusion using a semi-permeable membrane and equal concentrations of water.

  • Water molecules are always moving because they have enrgey.
  • If water is separated into two sections by a thin membrane which is permeable, as shown in the diagram above,
  • molecules will pass through and move in both directions.
  • There is equal movement of the water molecules in each direction.
When sugar is added to the left side of the partition more water molecules move there.

When sugar is added to the left side of the partition more water molecules move there.

  • If salt/sugar is added to the water on the left side of the partition as shown in the diagram above,
  • There will be relatively more water molecules on the right side of the membrane.
  • The membrane is semi-permeable as it only allow water but not salt/sugar molecules to pass.
  • More water molecules will move from the right to the left than will move to the left from the right.
  • The diffusion of water across a semi-permeable membrane from higher concentration to lower concentration places is known as osmosis.
  • Osmosis-the diffusion of water molecules from regions of higher concentration to regions of lower concentration via a semi-permeable membrane.

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

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By | 2017-01-17T11:16:14+00:00 December 31st, 2015|Notes, O Level Science Notes, Ordinary Level Notes|0 Comments

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