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Transport across plasma membranes

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Introduction

Transport across plasma membranes In this essay I will discuss and explain the transport across plasma membranes, to do this, I shall refer to osmosis, diffusion, facilitated diffusion, active transport and finally, exocytosis and endocytosis. Like all other cellular membranes, the plasma membrane consists of both lipids and proteins. The fundamental structure of the membrane is the phospholipid bilayer, which forms a stable barrier between two aqueous compartments. In the case of the plasma membrane, these compartments are the inside and the outside of the cell. Proteins embedded within the phospholipid bilayer carry out the specific functions of the plasma membrane, including selective transport of molecules. The diagram opposite shows the fluid The plasma membrane is a selectively permeable barrier between the cell and the extracellular environment. Its permeability properties ensure that essential molecules such as glucose, amino acids, and lipids are able to readily enter the cell, leaving larger substances remaining in the cell. This allows the cell to maintain a constant internal environment. ...read more.

Middle

This is the process of facilitated diffusion. The transport protein involved is essential, it completely spans the membrane. It also has a binding site for the specific molecule or ion to be transported. After binding the molecule, the protein changes shape and carries the molecule across the membrane, where it is released. The protein then returns to its original shape, to wait for more molecules to transport. Glucose, sodium ions and chloride ions are just a few examples of molecules and ions that must efficiently get across the plasma membrane but to which the lipid bilayer of the membrane is virtually impermeable. Their transport must therefore be "facilitated" by proteins and provide an alternative route. This is sometimes referred to as 'Passive Transport'. This is due to no energy being needed. This is a diagram showing the facilitated diffusion process. If a substance requires to move across a membrane against a concentration gradient (i.e. from lower concentration to higher concentration) ...read more.

Conclusion

The cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane. It is used by all cells of the body because most substances important to them are large polar molecules, meaning they cannot pass through the hydrophobic plasma membrane or cell membrane. Endocytosis is used for bulk transport into the cell. The diagram below shows endocytosis and exocytosis happening. In conclusion, these six processes have enabled our body to function correctly by cells being able to control transport across their surface membrane. These processes are very important as they get rid of the waste carbon dioxide as when it reaches the blood vessels around the airways of the lungs, it passes out of the blood and into the air. Other reasons why this transport is essential is to maintain a suitable pH and ionic concentration within the cell for enzyme activity and obtain certain food supplies for energy and raw materials. Finally, it is vital to excrete toxic substances and secrete useful substances. The processes I have discussed allow this to occur. ?? ?? ?? ?? Faye Speddings 12AAR ...read more.

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A good overview of the key processes involved in the movement of substances through plasma membranes. Sometimes more specific detail and specific examples would have improved the work.

Marked by teacher Adam Roberts 05/09/2013

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