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Investigating Osmosis - Coggle Diagram

- - - - Ventilation - Replenishing the alveoli with fresh oxygen from the air.
      - For example a steep concentration gradient between oxygen in the alveolus and oxygen in the blood is maintained by:
      - Circulation - Moving the oxygenated blood away along the pulmonary artery.
      - For fast movement it is important to maintain a steep concentration gradient (i.e. a large difference in concentration between the higher and lower regions).
    - - If you increase the temperature in a system the particles have more kinetic energy so move faster.
      - Particles in liquids and gases have kinetic energy. This allows them to move down concentration gradients.
    - - Cell B: Consider another one, but this one to have a surface area of 24 cm2 and a volume of 8 cm3. So the surface area to volume ratio is 24:8 or 3:1.
      - Although cell B has a larger surface area it also has a proportionally larger volume, so the rate of diffusion into the centre of the cell will be much slower.
      - Cell A would easily be able to obtain oxygen by diffusion as there is a large surface area to supply a small volume.
      - This explains why cells that need to move substances by diffusion, osmosis and active transport maximise their surface area (for example, root hair cells having a long projection or cells lining the alveolus being very thin and flat.)
      - Cell A: Consider a cell that is a cube to have exactly 1cmx1cmx1m its surface is 6cm2 and its volume is 1cm3, so its surface area to volume ratio is 6: 1.
  - - - We use the term water potential to describe how 'free' the water molecules are to move. Pure water has the highest possible water potential as there are no solute molecules to attract water molecules.
      - The diagram below shows two sucrose solutions separated by a partially permeable membrane. There is the same number of water molecules on each side of the partially permeable membrane, but there are more sucrose molecules on the left.
      - There are many more free water molecules on the right-hand side because most of the water molecules on the left hand side are attracted to the sucrose molecules. Thus there is a region of higher concentration of water molecule on the right hand side and e say it has a higher water potential
      - Osmosis is a special type of diffusion that refers only to the movement of water through partially permeable membranes (i,e. the cell membrane or visking tube
    - - Small, uncharged molecules (crucially, oxygen and carbon dioxide) can diffuse freely across the cell membrane
    - - Sometimes a cell needs to take in a molecule when there is little of it outside the cell ( i.e. against the concentration gradient). To do this is uses energy from respiration to power a protein pump embedded in the membrane that moves the molecule across the membrane (e.g. mineral ion uptake in the root hair, glucose absorption in the ilium).
  - - - Remove from solutions and dab dry with paper towel.
      - Leave for 30 minutes
      - Find new masses and record percentage change.
      - Soak each in a salt solution of different
        concentration (0%,25%,50%,75%,100% Nacl).
      - Results: Rods soaked in pure water should gain mass, as the contents of the potato cells have a lower water potential than the external solution, so water moves in by osmosis down the water potential gradient and through the partially permeable cell membrane. Rods soaked in a strong salt solution should lose mass, as the contents of the potato cells have a higher water potential than the external solution,so water moves out by osmosis down the water potential gradient and through the partially permeable cell membrane. If a chip shows no gain or loss in mass the concentration of salt inside its cells must be equal to the concentration of salt in the external solution.
      - Method: 1. Cut 5 potato rods of equal diameter and length and find their masses.