biology unit 3-exchange of materials

exchange of materials 

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  • Created by: eleanor
  • Created on: 15-04-13 17:18


Osmosis- is the movement of water, randomly from a high concentration to a low concentration,

  • this is called following the concentration gradient. 
  • this is also going from a dilute solution to a more concentrated one. 
  • this only applies to water molecules(
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active transport

Active Transports- cells may need to absorb substances that are in short supply i.e. against the concentration gradient 

  • cells use active transport to absorb substances across partially permeable membranes 
  • active transports requires energy relesed in repiration
  • diffusion and osmosis do not need energy.(
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sports drink

  • after exercising you become hot and you sweat to cool down, sweat contains water and minerals ions. If you sweat a lot your body cells may become dehydrated. so you need to replace these ions. 
  • sport drinks are a solution of sugar and mineral ions. 
  • the drinks are designed to balance the concentration of body fluids and the concentration within the cells. 
  • some people think just water is fine but others argue sports drinks are better. 
  • an isotonic drink is one that matches the bodies fluids. 
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the lungs

  • large organisms need exchange surfaces 
    • they have large surface area
    • thin walls
    • or short diffusion paths 
  • the lungs are ventilated to maintain a steep concentration gradient 
  • the alveoli have all these adaptations to keep them efficient for gaseous exchange
  • (
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ventilating the lungs

  • when we breathe in-  
    • the intercostal muscles contract
    • the ribcage move up and out and the diaphragm flattens
    • the volume inthe thorax increases 
    • the pressure in the thorax decreases and air is drawn in 
  • when we breathe out-
    • the intercostal muscles of and the diaphragm relaxes
    • the ribcage move down and in and the diaphragm becomes domed
    • the pressure increases inside and air is forced out.(
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artificial breathing

  • there are reasons you may need artifical breathing
    • if the alveoli are damaged the surface area is damaged 
    • the tubes are narrowed 
    • if the person is paralysed 
  • the iron lung is for people who were paralysed. The person would lay in a sealed metal cylinder. when air was drawn out the pressure made the chest move up and down to make them breathe in and out. 
    • the vaccum which was formed in the cylinder would create negative pressure  
  • breathing aids which force air in to the lungs create positive pressure 
    • positive pressure is usually smaller and easier to use
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exchange in the gut

  • the food we eat is digested in the gut into small, soluble molecules. In the small intestines these solutes are absorbed into the blood. The villi line the inner suface of the intestine. 
    • they have great surface area 
    • the walls are thin
    • the capiilaries are close to the wall 
    • the products can be absorbed  through diffusion or active transport. (
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exchange in plants

  • gases diffuse in and out of leaves through tiny holes called stomata. The size of the stomata is controlled by the guard cells. They also lose water through the stomata.

  • water and minerals are taken up by the roots. Root hair cells increases the surface area of the roots.  

  • if the plant is losing more water than it can replace the stomata can close. 
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cross section of a leaf


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  • plant takes up water through the roots. the water passes through the plant to the leaves. In the leaves the water evaporates from the surfaces of leaf cells and the water vapour diffuses through the stomata. 
  • the movement of the water through the plant is called transpiration stream. 
  • evaporation is more rapid in dry, hot, windy or bright conditions. 
  • (
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A detailed set of revision notes on transpiration, osmosis, gaseous exchange and uptake in the gut. There are some useful diagrams and animations included. This topic is found in most GCSE specifications. It might also be useful to summarise the information after use by making  a mind map  of the key information.



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