Term
| What characteristics do all lipids share? (4) |
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Definition
-They contain carbon, hydrogen and oxygen.
-The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates.
-They are insoluble in water.
They are soluble in organic solvents such as alcohols and acetone. |
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Term
| What are the main groups of lipids?(2) |
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Definition
| Triglycerides (fats and oils) and phospholipids |
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Term
| What are some of the roles of lipids? (5)and explain each one. |
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Definition
1.Cell membrane- phospholipids contribute to the flexibility of membranes and transfer of lipid- soluble substances across them.
2. source of energy- When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water.
3. Waterproofing- Lipids are insoluble in water and therefore useful as waterproofing. Both plants and insects have waxy, lipid cuticles that converse water, while mammals produce a oily secretion from the sebaceous glands on the skin.
4.Insulation- Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells.
5.Protection- Fat is often stored around delicate organs, such as the kidney. |
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Term
| At what temperature are fats solid? |
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Definition
| Room temperature (10-20°C) |
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Term
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Definition
| 3 fatty acids (tri) combined with glycerol (glyceride).Each fatty acid forms an ester bond with glycerol in a condensation reaction. Hydrolysis of a triglyceride therefore produces glycerol and three fatty acids. |
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Term
| What stays the same and what varies in each triglyceride? |
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Definition
| The glycerol molecule in all triglycerides is the same, the same, the differences in the properties of different fats and oils come from variations in the fatty acids. There are over 70 different fatty acids and all have a carboxyl (-COOH)group with a hydrocarbon chain attached. |
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Term
| Describe the difference between saturated, mono-unsaturated and polyunsaturated. |
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Definition
| If the chain has no carbon-carbon double bonds, the fatty acid is then described as saturated, because all the carbon atoms are linked to the maximum possible number of hydrogen atoms, in other words they are saturated with hydrogen atoms. If there is a single double bond, it is mono- unsaturated- if more than one double bond is present, it is polyunsaturated. |
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Term
| Why are triglycerides an excellent source of energy? |
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Definition
| Triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms and are therefore an excellent source of energy. |
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Term
| Why are triglycerides good storage molecules? |
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Definition
| Triglycerides have low mass to energy ratio, making them good storage molecules because much energy can be stored in a small volume. This is especially beneficial to animals as it reduces the mass they have to carry as they move around. |
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Term
| How are triglycerides insoluble in water? |
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Definition
| They are large, non-polar molecules and as a result their storage does not affect osmosis in cells or the water potential of them. |
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Term
| Why do triglycerides release water when oxidised? |
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Definition
| They have a high ratio of hydrogen to oxygen atoms. They therefore provide an important source of water, especially for organisms living in hot deserts. |
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Term
| What is different about the structure of a phospholipid to a lipid? |
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Definition
| Phospholipids are similar to lipids except that one of the fatty acid molecules is replaced by a phosphate molecule. |
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Term
| What is the difference between fatty acid molecules and phosphate molecules? |
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Definition
| Fatty acid molecules repel water (are hydrophobic), phosphate molecules attract water (are hydrophilic) |
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Term
| What are the two parts a phospholipid is made up of? |
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Definition
A hydrophilic 'head', which interacts with water (is attracted to it) but not with fat
A hydrophobic 'tail', which orients itself away from water but mixes readily with fat. |
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Term
| What is meant when molecules are said to be polar? |
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Definition
| Molecules have two ends (poles) that behave differently |
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Term
| What happens when these polar phospholipid molecules are placed in water? |
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Definition
| They position themselves so that the hydrophilic heads are as close to the water as possible and the hydrophobic tails are as far away from the water as possible. |
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Term
| What is the test for lipids known as? |
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Definition
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Term
| Describe the emulsion test |
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Definition
1. Take a dry and grease free test tube
2. To 2cm3 of the sample being tested, add 5cm3 of ethanol.
3. Shake the tube thoroughly to dissolve any lipid in the sample.
4. Add 5cm3 of water and shake gently.
5. A cloudy-white colour indicates the presence of a lipid.
6. As a control, repeat the procedure using water instead of the sample; the final solution should remain clear. |
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Term
| What causes the cloudy colour? |
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Definition
| It due to any lipid in the sample being finely dispersed in the water to form an emulsion. Light passing through this emulsion is refracted as it passes from oil droplets to water droplets, making it appear cloudy. |
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