Lipids (3.1.3)

Question 1

what are two groups of lipid?

Answer 1

triglycerides and phospholipids

Question 2

what are the main functions of lipids?

Answer 2

major source of energy in human diet, form adipose tissues under skin in humans which acts as energy store, helps insulate the body and protects internal organs eg. kidneys, used to waterproof eg. oils coat feathers of aquatic birds, major part of membranes

Question 3

how are triglycerides formed?

Answer 3

from the condensation of one molecule of glycerol and three molecules of fatty acids

Question 4

what does a condensation reaction between glycerol and a fatty acid form?

Answer 4

an ester bond

Question 5

what are fatty acids?

Answer 5

long hydrocarbon chains with a carboxyl group (COOH) on one end (RCOOH)

Question 6

what can the R group of a fatty acid be?

Answer 6

saturated or unsaturated

Question 7

in what ways may fatty acids vary?

Answer 7

the length of the hydrocarbon chain and how saturated the molecule is

Question 8

what are the features of saturated fatty acids?

Answer 8

they only contain single C-C bonds
all carbon atoms are fully saturated with hydrogen atoms
they are solid at room temperature

Question 9

what are the features of unsaturated fatty acids?

Answer 9

they contain one or more double C=C bonds
some carbon atoms are not fully saturated with hydrogen atoms
they are liquid at room temperature

Question 10

what does monounsaturated mean?

Answer 10

only one double C=C bond

Question 11

what does polyunsaturated mean?

Answer 11

more than one double C=C bond

Question 12

what does a glycerol molecule look like?

Answer 12

three carbon atoms bonded in a chain, one OH group bonded to each one on the same side and H atoms filling in the rest of the bonds

Question 13

how many water molecules are produced when a triglyceride forms?

Answer 13

3

Question 14

what are key features of triglycerides?

Answer 14

they are non-polar (don’t dissolve in water) - used as waterproofing
lots of energy can be released from them because they contain many carbon and hydrogen atoms

Question 15

how are phospholipids different to triglycerides?

Answer 15

in phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group

Question 16

what is the key feature of the phosphate group on a phospholipid?

Answer 16

it is hydrophilic/polar so it attracts water (known as the head)

Question 17

what is the key feature of the fatty acid molecules on a phospholipid?

Answer 17

they are hydrophobic/non-polar so they repel water (known as the tail)

Question 18

what do phospholipids do in water?

Answer 18

they position themselves so they hydrophilic head interacts with the water molecules
the hydrophobic tails cluster together away from the water molecules
this creates a phospholipid bilayer

Question 19

what is the role of lipase in the digestive system?

Answer 19

it breaks the ester bonds in triglycerides which releases the glycerol and fatty acids (hydrolysis reaction)

Question 20

how do you test for lipids?

Answer 20

1. don’t filter the food mixture as the lipids may stick to the filter paper
2. add 3cm^3 of food solution to a test tube
3. add 3cm^3 of ethanol followed by 3cm^3 of water
4. shake the solution
5. if lipids are present, a cloudy white emulsion will form, and if not then the solution will remain clear