The role of the microvilli in increasing the surface area of cell-surface membranes.

Microvilli protrusions of the cell surface membrane which are tightly packed- spread out they would cover a larger surface area but because they are in a wavy line they don't take up much space but do increase the surface area a lot.

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The arrangement of phospholipids, proteins and carbohydrates in the fluid-mosaic model of membrane structure.

The fluid mosaic model is the name for the cell-surface membrane and all the stuff in it; it is knows as fluid because the things in it can move around.

Phospholipids

The phosphate group is attracted to water (hydrophilic), where as the other end of fatty acids are not (hydrophobic)- this means that phospholipids will form a layer on water:

Phospholipids come together so that their tails are facing in and their heads facing out in contact with water. This is called a phospholipid bilayer and is what the cell-surface membrane is made of.

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Proteins

Intrinsic proteins go from one side of the bilayer through to the other. Some are enzymes and others are protein channels which carry substances across the membrane.

Extrinsic proteins are embedded in but do not span the membrane. Some act as structural support; others join with glycolipids to be receptors.

Intrinsic right, extrinsic left:

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Carbohydrates

Carbohydrates bond with lipids and proteins to form receptors. The carbohydrate branch acts as a recognition site in glycoproteins, as does the whole glycolipid, to detect chemicals like hormones and toxins.

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The emulsion test for lipids.

Take 2ml of the sample and 5ml of ethanol, then shake- this should dissolve any resent lipids.
Then add 5ml of water and shake again to mix.
If the mixture turns cloudy it is because water is being refracted as it changes between the density of water and lipids: so the cloudy appearance indicates the presence of lipids.

In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate group.

A phospholipid is made up of fatty acids, glycerol and a phosphate group: PO4(3-).

Phosphate group; glycerol; fatty acids

The R-group of a fatty acid may be saturated or unsaturated.

Fatty acids are made up of oxygen, carbohydrate and hydrogen.

In some all of the bonds are being used to join together the separate elements- these are called saturated.

In others not all of the possible bonds that can be made have been, these are unsaturated; this happens because carbons are double bonded (these can be made into single bonds freeing up another space.)

If a fat is unsaturated, its double bonds will cause kinks in the chain- this means that the fats cannot line up and compact into a solid, so they are liquid at room temperature.

Glycerol and fatty acids combine by condensation to produce triglycerides.

A triglyceride is a neutral fat, is formed when one glycerol bonds to three fatty acids.
An 'ester' bond is formed by a three stage condensation reaction.

Glycerol; fatty acids; triglyceride; water molecules