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Cell Membrane and Transport Material

Essay by   •  September 10, 2017  •  Course Note  •  1,237 Words (5 Pages)  •  976 Views

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Prokaryotic cells

  • Extremely small.
  • Have a simple internal structure with no membrane-bound organelle.
  • No membrane-bound nucleus.
  • E.g bacteria.

  • Eukaryotic cells
    Have a complex internal structure.
  • Many membrane-bound organelles.
  • Membrane-bound nucleus.

Plasma membrane

  • The plasma membrane is the boundary between the inside and outside environment of the cell.
  • Ultra thin and pliable (can bend).
  • Too thin to see with a light microscope because it has a thickness of 0.001mm.
  • Made of phospholipid bilayer ( a double layer of phospholipid molecules.
  • Phospholipids are from the lipid family.
  • Plasma is also called the fluid mosaic model. Because it can pass those liquids and everything through. the proteins embedded in here in the channels allow substances to pass through.
  • Antigens (research what antigens are) are protein which combine with the carbohydrates.
  • The plasma membrane is partially permeable (allows some substances through and others now.


  • In terms of biology, it is the overall movement of particles from a high concentration to a low concentration.
  • For diffusion to occur, there needs to be a high concentration outside the cell, which will then move to the inside. If there is high concentration inside the cell, it will move outside.
  • It will stop diffusion when there is the same concentration inside and outside (when it is equal in concentration).
  • Diffusion can occur for gases. E.g If you spray something in a room, the gas particles will diffuse to take up all the available space it can.
  • Hydrophilic: substances that readily dissolve in water (water loving)
  • Lipophilic: substances that have low water solubility or do not dissolve in water are able to dissolve in or mix with lipids.
    Lipophilic substances can cross the plasma membrane readily.
    E.g alcohol

  • The difference in concentration provides a concentration gradient.
  • The steeper the gradient, the faster the rate of diffusion- until the equilibrium is reached.
  • Does not require energy because it’s just a net movement.

Size matters

  • Small molecules (oxygen, water, carbon dioxide) can pass through the cell membrane by diffusion. This is because we need all three of these things readily.
  • Bigger ones can pass by protein channels.
  • Channel mediated: substances that are unable to carry out simple diffusion, cross the membrane with the assistance of protein channels. Does not need energy for this.
  • Glucose molecules are huge and need help to get into the cell.
  • Carrier mediated: substances are attached to the protein molecules to get across the cell membrane. This is also known as facilitated diffusion.

[pic 1][pic 2]


  • It is the diffusion of water molecules.
  • Water is the medium in which all biochemical process take place, it helps keep cell shape and is universal solvent.
    [pic 3]
  • In the diagram, the sugar is still gonna stay, we are talking about in terms of osmosis. But the water molecules will move through. It will dilute through. As you add more water to it, it will dilute it. Therefore you are undertaking the process of osmosis.

Active transport

  • The net movement of dissolved
  • Uses energy. Because it’s against the net movement, imagine walking against the wind, you use more energy.

Bulk transport

  • Endocytosis: bulk transport of materials into a cell.
  • Exocytosis: bulk transport of materials of outside the cell.

[pic 4]

Solute: the stuff that is dissolving.

Solvent: the liquid which the solute is dissolved into.

Solutions and cells

Isotonic: the concentration is the same on both sides on the membrane.

  • Particles move in both directions.

Hypotonic: the external concentration of the cell is lower than the inside, the particles will diffuse into the cell.

  • Water particles will move into the cell.
  • If the outside is of low concentration, particles are gonna move into the cell to allow that balance. it will move from high concentration to low concentration.
  • Needs to be more plump.

Hypertonic: the external concentration of the cell is higher than the inside.

  • Water particles will move out of the cell.
  • If the concentration in a cell is much higher, it is plump and expanded. So it needs to shrink more. Therefore, water particles will move out of the cell.

[pic 5]

Cell walls and water



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