Exchange Systems in Plants

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  • Created by: Katherine
  • Created on: 17-03-13 11:09

Exchange Systems in Plants

In plants carbon dioxide enters leaves by diffusion.

Most of the water and mineral ions are absorbed by the roots

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Root Hair Cells

  • Specialised for absoribing water and minerals.
  • The surface area of the roots are increase by root hairs.
  • This gives the plant a large surface area for absorbing water and minerals form the soil.
  • Root hair cells take in minerals using ACTIVE TRANSPORT
  • The concentration of minerals is usually higher in the root hair cell than in the soil around it. 
  • Active transport allows the plant to absorb minearls from a very dilute soultion, against a concentration gradient.
  • This is essential for growth
  • But active transport need energy frfom respiration to make it work.

(http://www.bbc.co.uk/bitesize/ks3/science/images/plant_root_cell.gif)

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Leaves

  • The structure of a leaf is adapted to let gases diffuse in and out of cells easily
  • Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens. 
  • The underneath of the leaf is an exchange surface
  • It's covered in stomata which carbon dioxide diffuses in through
  • Oxygen (produced in photosynthesis) and water vapour diffuses out through the stomata
  • The size of the stomata are controlled by guard cells, which surround them. These close the stomata if the plant is losing water faster than it is being replaced by the roots. Without these guard cells the plant would soon wilt.
  • The flattened shape of the leaf and internal air spaces increase the area of this exchange so that it's more effective.

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Water Loss

  • Plants mainly lose water vapour from their leaves.
  • Most of the loss of water vapour takes place through the stomata.
  • Evaporation is more rapid in hot, dry and windy conditions
  • The water vapour escapes by diffusion because it is more concentrated inside the leaf than the air outside. 

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