They contain carbon, hydrogen and oxygen. They are insoluble in water. They are soluble in organic solvents such as alcohols.
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What are the two main groups of lipids?
Triglycerides (fats and oils) and phospholipids
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What is the role of lipids in the cell-surface membrane?
Phospholipids make up the a bilayer in all plasma membrane, they contribute to the flexibility of the membrane and allow the transfer of lipid-soluble substances across them.
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How are lipids used as a source of energy?
When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release water
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How are lipids used for waterproofing?
Lipids are insoluble in water so can be used for waterproofing. Both plants and insects have waxy lipid cuticles that conserve water.
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How are lipids used for insulation?
Fats are slow conductors of heat and when stored beneath the body surface to help retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells
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How are lipids used for protection?
Fat is often stored around delicate organs to protect them
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What is the structure of a triglyceride?
Three fatty acids combined with glycerol
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What bond forms between the fatty acids and the glycerol?
An ester bond forms between each fatty acid with the glycerol in condensation reactions
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What is a saturated fat?
A triglyceride with fatty acids that don't have any double bonds between carbon atoms
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What is an unsaturated fat?
A triglyceride with fatty acids that have double bonds between carbons. They can be monounsaturated (one double bond) or polyunsaturated (multiple double bonds)
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How are triglycerides a good source of energy?
There is a high number of energy-storing carbon-hydrogen bonds
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Why are triglycerides good storage molecules?
Because they have a low mass to energy ratio, so a lot of energy can be stored in a small volume
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Why is this especially beneficial to animals?
Because it reduces the mass that they have to carry around
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Why are triglycerides insoluble in water and how does this make them suited for storage?
Because they are non-polar molecules, being insoluble, they don't change the water potential of the cell so water doesn't move in or out of the cells by osmosis
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How do triglycerides provide a source of water?
They have a high ratio of hydrogen to oxygen atoms so they release water when oxidised
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What is the main difference between triglycerides and phospholipids?
One of the fatty acid molecules is replaced by a phosphate molecules
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Name the two parts that make up a phospholipid
A hydrophilic head and a hydrophobic tail
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What are these parts made up of?
The hydrophilic head is the phosphate molecule (attracted to water). The hydrophobic tail is the fatty acid molecules (repelled by water).
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Phospholipids are polar, why does this suit them to their function in the cell-surface membrane?
The phospholipid molecules create a bilayer in an aqueous environment creating a hydrophobic barrier between the inside and outside of the cell
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How do phospholipids create glycolipids?
They combine with carbohydrates in the cell-surface membrane
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What is the test for lipids?
The emulsion test
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How do you carry out the emulsion test?
Add ethanol to the sample being tested and shake thoroughly, then add an equal amount of water and shake gently. If a cloudy white precipitate forms it shows a lipid is present
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Other cards in this set
Card 2
Front
What are the two main groups of lipids?
Back
Triglycerides (fats and oils) and phospholipids
Card 3
Front
What is the role of lipids in the cell-surface membrane?
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