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Lipids - Coggle Diagram
Lipids
Phospholipids
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Fatty acid molecules are hydrophobic (repel water), whereas phosphate molecules are hydrophilic (attract water).
A phospholipid is polar and is made up of two parts, a hydrophilic head and a hydrophilic tail.
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Phospholipids allow lipid soluble, non-polar and hydrophobic substances to enter and leave the cell.
Phospholipids prevent water soluble, polar and hydrophilic substances from entering and leaving the cell.
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TEST FOR LIPIDS: ETHANOL
- Take a completely dry and grease-free test tube.
- Add ethanol to the sample being tested.
- Shake the tube thoroughly to dissolve any lipid in the sample.
- Add water and shake gently.
- A cloudy-white colour indicates the presence of a lipid.
Roles of Lipids
Lipids can act as an energy source. When oxidised, lipids provide more than twice the energy as the same mass or carbohydrate and release valuable water.
Lipids can be useful as a waterproofing as they are insoluble in water. Both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.
Lipids can act as good insulators. Fats are slow conductors or 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.
Lipids are important for protection. Fat is often stored around delicate organs, such as the kidney. Fats are solids at room temperature and oils are liquids at room temperature.
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Triglycerides
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Saturated fatty acids have no double bonds, therefore they are normally solid at room temperatures.
Unsaturated fatty acids have double bonds and have low melting points, therefore they are normally liquid at room temperatures.