• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Transport Across Plasma Membrane

Extracts from this document...


Transport Across Plasma Membrane The plasma membrane covers all living cells, enabling the cells' contents to be held together and controls movement of substances into and out of the cell. Plasma membranes are made of phospholipids, proteins and carbohydrates. The phospholipids are essentially made out of two fatty acid chains and a phosphate-glycerol group. They are arranged in a bilayer with the hydrophilic phosphate head facing outwards and the hydrophobic fatty acid chains facing inwards and to each other in the middle of the bilayer. This effectively provides a barrier to all but the smallest molecules. In the membrane are proteins that have a number of functions. Those that span across the entire bilayer (from hydrophobic head to hydrophobic head) act as channels and carriers to transport substances across the membrane in active or facilitated diffusion. Those on the surface act as receptors with specific binding sites where hormones and other chemicals can bind. This binding in turn triggers other events in the cell. Finally, those that are on the inside surface maintains the cell's shape and motility, such as enzymes. ...read more.


Pure water has 0 kPa, so as the concentration of solutes increases, water potential will get increasingly negative. Therefore, water will always 'move' from a low to high water potential, where 0 kPa is the highest possible water potential. Different water potentials have different effects on animal and plant cells. Since an animal cell does not possess a cell wall, it is then effectively more vulnerable to the effects osmosis. Animal cells in a hypertonic solution (higher w.p outside cell) will have water moving out of it, leaving it shriveled and crenated. Animal cells in a hypotonic solution (lower w.p. outside cell) will have water moving inwards until it eventually burst. Plant cells however, will not burst in a hypotonic solution due to the protection of its cell wall. It will instead swell and become turgid. In a hypertonic solution, the cytoplasm becomes playsmolysed. In an isotonic solution (equal w.p outside cell), all cells will stay the cell due to no net movement of water through membranes. Facilitated Diffusion This is diffusion that can only occur with the aid of trans-membrane proteins. ...read more.


Pumping is therefore an active process, and is the only transport mechanism that can transport substances up their concentration gradient. Endocytosis and exocytosis via vesicles. These are the only processes where larger molecules can be moved into and out of a cell. Endocytosis is the transport of substances into the cell. As the molecules gets near the cell, the membrane forms a slight dip or pit. When they are close enough, they are enclosed by a fold of the membrane, which then pinches shut to form a closed vesicle. As the vesicle moves into the cell, the molecules are digested and the product molecules released. When the materials are small and often liquid particles, endocytosis is known as pinocytosis. When the materials are large and often solid particles, the process is known as phagocytosis. Exocytosis is the transport of materials out of a cell. It is the exact reverse of endocytosis. The molecules to be transported have to be enclosed in a membrane vesicle first, usually from the Golgi apparatus and RER. It then moves to the membrane and fuses with it, forcing the substances out. These processes are controlled and require energy. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Molecules & Cells section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Molecules & Cells essays

  1. Peer reviewed

    Transport across membranes How do substances cross into and out of cells.

    3 star(s)

    We can relate the above analogy to the cell membrane as the principles are the same. Though diffusion is a spontaneous and random event, the rate of diffusion from different substances is affected by a number of factors, firstly the steepness of the concentration gradient, as outlined and now

  2. Transport across Plasma Membranes

    Osmosis The definition of osmosis is- osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to an area of low water concentration. This process is also passive transport, as the water molecules move in the direction on the gradient.

  1. Write about the Transport across Plasma membranes

    On the inside of the cell, the ATP binds to the protein, causing it to split into ADP and a phosphate molecule. As a result, the protein molecule changes shape and allows the molecules or ions on the outside of the cell to bind to the protein.

  2. The Transport of Substances across the Plasma Membrane

    The resultant of the alignment of these two lines of lipids is a lipid bilayer. The lipid bilayer is primarily the foundation of any plasma membrane. A plasma membrane is a cell organelle that is actively controlling the passage of substances moving in and out of a cell.

  1. The Plasma Membrane

    act like enzymes which speed up chemical reactions at the edge of the membrane. Lastly the proteins also act like adhesion sites which help to stick some cells together. In the plasma membrane there are three types of protein arrangements, which are needed to gain stability and for different functions.

  2. Transport across plasma membranes.

    This is considerably faster then normal diffusion and is used to transport molecules such as glucose, fructose, non fat-soluble vitamins, urea and many ions across the membrane. Substances can pass in and out of cells along their concentration gradient in several different ways, none of which requires the input of energy.

  1. Transport across Plasma Membranes

    Plasma membranes contain many different types of protein channel, each type allowing only one kind of molecule or ion to pass through it. The movement of the molecules or ions is passive, just as in ordinary diffusion, and movement into or out of the cell will only take place down

  2. Transport Across Plasma Membranes.

    Passive transport is the movement of substances down the concentration gradient. This process is called diffusion. In a mixture of gases, diffusion cases each gas to spread out evenly through the space in which it is in. This is because every substance diffuses down its own concentration gradient and the

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work