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Cell membrane

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Biology Essay - Cell membrane a) Describe structure of cell membrane. b) Discuss how the structure of the membrane is related to its function for transport of materials across it (fat soluble, water soluble). c) Discuss briefly how prokaryotes and eukaryotes differ from one another with respect to the proportion of membrane present in these cells. a) (Fluid mosaic model) The cell membrane has a lipid bilayer (also known as a phospholipid bilayer) with a consistency similar to olive oil studded with a mosaic of globular proteins. Some of the proteins penetrate through and are found on both sides of the lipid bilayer whereas others are on one side or another. The lipid molecules are polarised which results in the non-polar tails facing inwards on each other and the polar heads facing outwards towards the outside or inside of the cell. ...read more.


Osmosis takes place as the solute molecules in the cell are unable to diffuse out due to the phospholipid bilayer, therefore the water molecules diffuse through the phospholipid bilayer by osmosis (where water travels from a high concentration of water to a low concentration of water). The fluidity of the membrane is also used for endocytosis and exocytosis. This is where the cell membrane makes vesicles to transport solids or liquids across the plasma membrane either into (endocytosis), or out of (exocytosis) the cell. A pore in the protein is used for simple diffusion (pore shown in the right protein in the diagram above), as some ions are too large to pass through the phospholipid bilayer. A carrier protein (shown at the left of the diagram) plays a role in facilitated diffusion. ...read more.


Prokaryotes are extremely small compared to eukaryotes, they are usually 0.5-0.10mm in diameter and Eukaryotic cells are usually 10-100mm in diameter. Cell walls are present in the prokaryotic cell, but are chemically different from those of plants and they contain mucopeptides. Eukaryotic cells have cell walls present in plants and fungi, however they do not contain mucopeptides. Prokaryotic cells have few organelles, membraneous structures absent or very simple and existing briefly in the cell. Eukaryotic cells have many organelles bounded by double membranes (for example, chloroplasts, mitochondria, nucleus) and single membrane (for example, Golgi apparatus, lysosome, vacuole, endoplasmic reticulum). The cell wall of a prokaryotic cell is rigid made of a protein and a polysaccharide. Murein is the main strengthening compound, whereas cellulose is not. Eukaryotic cells such as plants and algae have a rigid cell wall containing cellulose, which is the strengthening body. However fungi contains chitin and animal cells have no cell walls. 1 ...read more.

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