CELL TRANSPORT - SURFACE AREA TO VOLUME RATIO

• Cell membranes is used by a cell to allow materials to enter and leave. Only those materials that are needed by the cell ( e.g nutrients , O² , water ) should be able to enter the cell and wastes ( e.g CO² , metabolic waste ) should be able to leave the cell.
• Surface area to volume ratio = surface area / volume
• The surface area to volume ratio is important because it determines how quickly substances can diffuse into or out of cells
• If an object has a large surface area compared with its volume, then there will be more chance of particles colliding with the surface of the object than if the object had a small surface area relative to its volume.
• The larger the surface area, the greater the rate of diffusion across it.
• As cells get bigger they have more volume but less surface area so there is a smaller surface area to volume ratio which means that substances can diffuse into or out of the cell at a slower rate.
• This is why bacteria have a high surface area to volume ratio as this allows them to take up nutrients rapidly from their environment.
• The membrane is semi-permeable, allowing some substances to pass through it.
• What is diffusion?

  Diffusion is the movement of particles from an area of high concentration to an area if low concentration.
• What is osmosis

  Osmosis is the diffusion of water across a selectively permeable membrane.
• What happens in an isotonic solution?

  In an isotonic solution the concentration of solute is the same inside and outside the cell.
• what happens in an hypotonic solution?


  The prefix hypo means less. So there are less solutes(salt) molecules outside the cell , causing the cell to gain water and gro larger , making it to burst in animal cells or lysing. In plant cells , the central vacuole will and it becomes turgid.
• what happens in an hypersonic solution?


  The prefix hyper means more , means there are more solutes(salt) molecules outside the cell , which causes water to move out of the cell. In plant cells the vacuole loses water and the cells shrink , causing wilting , while in animal cells it also shrinks. The process of shrinking is called plasmolysis , in both plant and animal cells.