3.1.3 Lipids

Question 1

What are lipids made of?

Answer 1

Carbon, hydrogen and oxygen

Question 2

Proportion of oxygen to carbon and hydrogen is…

Answer 2

Smaller than in carbs

Question 3

Solubility in water and why

Answer 3

Insoluble-lipids are non-polar molecules while water is polar molecule, so there is no way for water to attach to a lipid molecule. Instead, the non-polar lipids will bind to themselves, which is why oils and fats form droplets on the surface of water

Question 4

Solubility in organic solvents e.g alcohols, acetone

Answer 4

Soluble

Question 5

What are the two main groups-draw them (if paper not available draw in air)?

Answer 5

Triglycerides (fats and oils)
Structure- Glycerol attached to fatty acid chains
Phospholipids (make up cell (plasma) membranes
Structure- Phosphate head, glycercol attached to fatty acid chains

Question 6

What do phospholipids contribute to?

Answer 6

The flexibility of membranes and the

transfer of lipid-soluble substances across them

Question 7

Roles of lipids

Answer 7

source of energy- when oxidised, lipids provide more than TWICE energy as the same mass of carbs + release valuable water.

waterproofing- lipids are insoluble in water, plants+insects have waxy, lipid cuticles- conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.

insulation- fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. Also act as electrical insulators in the myelin sheath around nerve cells.

protection- often around delicate organs e.g kidneys

Question 8

Triglycerides have…

Answer 8

Three fatty acid groups

One glycerol group

Question 9

What bonds do the fatty acids form with the glycerol?

Answer 9

An ester bond in a condensation reaction

Question 10

What does hydrolysis of triglyceride produce?

Answer 10

Glycerol and fatty acids

Question 11

Where do the different properties come from?

Answer 11

The variations in fatty acids- glycerol molecules are always the same

Question 12

How many fatty acids are there?

Answer 12

Over 70

Question 13

All triglycerides have

Answer 13

Carboxyl (-COOH) group with hydrocarbon chain attached and vary in lengths and bonds

Question 14

What does saturated mean?

Answer 14

The hydrocarbon chain contains no double carbon-carbon bonds?

Question 15

What does mono-unsaturated mean?

Answer 15

The hydrocarbon chain has one double carbon-carbon bond

Question 16

What does poly-unsaturated mean?

Answer 16

The hydrocarbon chain has more than one double carbon-carbon bond

Question 17

What do the double bonds cause?

Answer 17

the molecule to bend. They cannot therefore pack
together so closely making them liquid
at room temperature. i.e. they are oils

Question 18

Structure of triglycerides related to their properties

Answer 18

High ratio of energy storing carbon-hydrogen bonds to carbon atoms so an excellent source
of energy.
Low mass to energy ratio- so good storage molecules as much energy can be stored in a small volume
Large, non-polar molecules- insoluble in water, doesn’t affect osmosis or water potential in cells
High ratio of hydrogen to oxygen atoms- release water when oxidised

Question 19

Why are triglycerides properties beneficial to animals?

Answer 19

HROESingCHBCA- excellent energy source
LNPM-their storage doesn’t affect osmosis in cells or
the water potential of them
LMER- Reduces mass that needs to be carried
HRHOA- an important source of water, especially for organisms living in dry deserts.

Question 20

Compare and contrast saturated/unsaturated fatty acids

Answer 20

Saturated- only single c-c bonds, straight chain molecules w/more contact points, higher m.p=solid at room temp, in animals
Unsaturated- double c-c bonds, kinked molecules w/fewer contact points, found in plant oils

Question 21

Describe the structure of the phospholipid bilayer

Answer 21

A phosphate hydrophilic head, glycerol molecule, two fatty acids (hydrocarbons) so hydrophobic

Question 22

Structure of phospholipids related to properties

Answer 22

Polar molecule (philic head, phobic tail)- aqueous environment, form a bilayer within cell-surface membranes- hydrophobic barrier
formed between the inside and outside of a cell.
Hydrophilic phosphate ‘heads’ -
to hold at the surface of the cell-surface membrane
Phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane

Question 23

Emulsion test for lipids

Answer 23

Take a completely dry and grease free test tube

To 2cm3 of the sample being tested add 5cm3 of ethanol

shake the tube thoroughly to dissolve any liquid in the sample

Add 5cm3 of water and shake gently

A milky-white emulsion indicates the presence of a lipid

(Simple- Sample+ethanol-shake-add water-shake-milky white emulsion)

Question 24

Function of the phospholipid bilyaer

Answer 24

Allows lipid soluble substances to
enter and leave cells

Prevents water soluble
substances entering and leaving
cells

Makes the membrane flexible

Question 25

Compare phospholipids and triglycerides.

Answer 25

● Both have glycerol backbone.
● Both may be attached to a mixture of
saturated, monounsaturated &
polyunsaturated fatty acids.
● Both contain the elements C, H, O.
● Both formed by condensation reactions.

Question 26

Contrast phospholipids and triglycerides.

Answer 26

phospholipids:
● 2 fatty acids & 1
phosphate group attached
● Hydrophilic head &
hydrophobic tail
● Used primarily in
membrane formation

triglycerides:
● 3 fatty acids attached
● Entire molecule is
hydrophobic
● Used primarily as a
storage molecule
(oxidation releases
energy)

Question 27

Are phospholipids and triglycerides

polymers?

Answer 27

No- they aren’t made from a small repeating unity- they’re macromolecules