1.3- LIPIDS

Question 1

1.Nutritionists investigated the relationship between eating oily and non-oily fish and the
incidence of asthma. They analysed the diets of children with asthma and the diets of
children without asthma

The pie charts show the results.

a) - What conclusions can you make from the data? (3)

Answer 1

1. Fewer children / less likely that children with asthma eat fish
2. Fewer children / less likely that children with asthma eat oily fish;
   MP1 and 2 − Allow use of numbers

3.Little / only 2% / no difference in (children with or without asthma who
eat) non-oily fish.
Do not accept arguments related to amount of fish eaten

Question 2

Describe how you could use the emulsion test to show the presence of oil in a
sample of fish. (3)

Answer 2

1. (Shake with) ethanol / alcohol;
2. Accept named alcohol
3. Then add (to) water;
4. Order must be correct
5. White / milky / cloudy (layer indicates oil).
6. Ignore forms emulsion as in stem
7. Ignore precipitate

Question 3

Describe how you would test a piece of food for the presence of lipid. (2)

Answer 3

1. Dissolve in alcohol, then add water;

2. White emulsion shows presence of lipid.

Question 4

The figure below shows a phospholipid.

The part of the phospholipid labelled A is formed from a particular molecule. Name
this molecule (1)

Answer 4

Glyercol

Question 5

Name the type of bond between A and fatty acid X. (1)

Answer 5

Ester

Question 6

Which of the fatty acids, X or Y, in the figure above is unsaturated? Explain your
answer. (1)

Answer 6

Y (no mark)

Contains double bond between (adjacent) carbon atoms in hydrocarbon chain

Question 7

Scientists investigated the percentages of different types of lipid in plasma
membranes from different types of cell. The table shows some of their results.

The scientists expressed their results as Percentage of lipid in plasma
membrane by mass. Explain how they would find these values. (2)

Answer 7

1. Divide mass of each lipid by total mass of all lipids (in that type of cell);
2. Multiply answer by 100.

Question 8

Cholesterol increases the stability of plasma membranes. Cholesterol does this by
making membranes less flexible.

Suggest one advantage of the different percentage of cholesterol in red blood cells
compared with cells lining the ileum. (1)

Answer 8

Red blood cells free in blood / not supported by other cells so cholesterol helps
to maintain shape;
Allow converse for cell from ileum – cell supported by others
in endothelium so cholesterol has less effect on maintaining
shape.

Question 9

E. coli has no cholesterol in its cell-surface membrane.
Despite this, the cell
maintains a constant shape. Explain why (2)

Answer 9

1. Cell unable to change shape;
2. (Because) cell has a cell wall;
3. (Wall is) rigid / made of peptidoglycan / murein

Question 10

Newborn babies can be fed with breast milk or with formula milk. Both types of milk contain
carbohydrates, lipids and proteins.
• Human breast milk also contains a bile-activated lipase. This enzyme is thought to
be inactive in milk but activated by bile in the small intestine of the newborn baby.
• Formula milk does not contain a bile-activated lipase.
Scientists investigated the benefits of breast milk compared with formula milk.
(a) The scientists used kittens (newborn cats) as model organisms in their laboratory
investigation.
Other than ethical reasons, suggest two reasons why they chose to use cats as
model organisms. (2)

Answer 10

1. (Are mammals so) likely to have same physiology / reactions as humans;
2. Small enough to keep in laboratory / produce enough milk to extract;
3. (Can use a) large number.

Question 11

Before starting their experiments, the scientists confirmed that, like human breast
milk, cat’s milk also contained bile-activated lipase.
To do this, they added bile to cat’s milk and monitored the pH of the mixture.

Explain why monitoring the pH of the mixture could show whether the cat’s milk
contained lipase. (2)

Answer 11

1. Hydrolysis of lipids produces fatty acids;

2. Which lower pH of mixture.

Question 12

The scientists then took 18 kittens. Each kitten had been breastfed by its mother for
the previous 48 hours.
The scientists divided the kittens randomly into three groups of six.
• The kittens in group 1 were fed formula milk.
• The kittens in group 2 were fed formula milk plus a supplement containing
bile-activated lipase.
• The kittens in group 3 were fed breast milk taken from their mothers.
Each kitten was fed 2 cm3
of milk each hour for 5 days.
The scientists weighed the kittens at the start of the investigation and on each day
for 5 days.
The figure below shows the scientists’ results.

What can you conclude from the figure about the importance of bile-activated lipase
in breast milk? (3)

Answer 12

1. (Bile-activated lipase / it) increases growth rate (of kittens);
2. Results for formula with lipase not (significantly) different from breast
   milk / are (significantly) different from formula milk alone;
3. Showing addition of (bile-activated) lipase is the likely cause (of
   increased growth);
4. Lipase increases rate of digestion of lipids / absorption of fatty acids.

Question 13

Q4.(a) Some seeds contain lipids. Describe how you could use the emulsion test to show
that a seed contains lipids. (3)

Answer 13

1. Crush / grind;
2. With ethanol / alcohol;
3. Then add water / then add to water;
4. Water must be added after ethanol for third mark.
5. Forms emulsion / goes white / cloudy;
6. Do not accept carry out emulsion test.

Question 14

The structure of a phospholipid molecule is different from that of a triglyceride.
Describe how a phospholipid is different. (2)

Answer 14

1. Phosphate / PO4;
   “It” refers to phospholipid.
2. Instead of one of the fatty acids / and two fatty acids;
3. Accept minor errors in formula. Do not accept phosphorus
   / phosphorus group.

Question 15

(iii) Use the diagram to explain what is meant by an unsaturated fatty acid. (2)

Answer 15

1. Double bonds (present) / some / two carbons with only one
   hydrogen / (double bonds) between carbon atoms / not saturated
   with hydrogen;
   Answer refers to unsaturated unless otherwise clearly
   indicated.
   May be shown in appropriate diagram.
2. In (fatty acid) C / 3

Question 16

(a) Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? (2)

Answer 16

Double bond(s);

(Bonds) between carbon;

Question 17

Scientists investigated the relationship between the amount of omega-3 fatty acids eaten per day and the risk of coronary heart disease. The graph shows their results.

Do the data show that eating omega-3 fatty acids prevents coronary heart disease?
Explain your answer.

(3)

Answer 17

) Graph shows negative correlation / description given;

Correlation does not mean causation / prevention / shows lower risk not
prevention;

May be due to another factor / example given;

Neutral: refs. to methodology e.g. sample size / line of best
fit
Q: Do not allow ‘casual’ relationship

Question 18

Olestra is an artificial lipid. It is made by attaching fatty acids, by condensation, to a
sucrose molecule. The diagram shows the structure of olestra. The letter R shows
where a fatty acid molecule has attached.

Name bond X. (1)

Answer 18

Glycosidic;

Question 19

A triglyceride does not contain sucrose or bond X. Give one other way in
which the structure of a triglyceride is different to olestra. (1)

Answer 19

Contains glycerol / three fatty acids / forms three ester bonds;

Neutral: contains less fatty acids
Answers must refer to a triglyceride
Ignore refs. to incorrect bond names
Neutral: olestra has eight fatty acids / R groups
Reject: contains three glycerol's

Question 20

Hydrogen bonds are important in cellulose molecules. Explain why. (2)

Answer 20

1. Holds chains / cellulose molecules together / forms cross links
   between chains / cellulose molecules / forms microfibrils, providing
   strength / rigidity (to cellulose / cell wall);
2. Hydrogen bonds strong in large numbers;x

Question 21

A starch molecule has a spiral shape. Explain why this shape is important to
its function in cells. (1)

Answer 21

Compact / occupies small space / tightly packed;
Answer indicates depth required. Answers such as “good for
storage”, “easily stored” or “small” are insufficient

Question 22

Triglycerides are taken into the body as part of a balanced diet. These triglycerides contain
fatty acids including omega-3 fatty acids. It has been discovered that omega-3 fatty acids
are associated with health benefits. The benefits include faster development of nerve cells
and clearer vision. Omega-3 fatty acids are also associated with protection from heart
disease, arthritis and cancer.
The following figure shows how omega-3 and other fatty acids are taken in and used by
the bodies of animals including humans.

Use the information in the figure to explain two ways in which fatty acids are important in
the formation of new cells. (4)

Answer 22

Fatty acids used to make phospholipids;
Phospholipids in membranes;
More phospholipids more membranes made;

Fatty acids respired to release energy;
More triglycerides more energy released;
Energy used for cell production / production of named cell component;
Do not allow credit for ‘making’ energy

Question 23

Mucus produced by epithelial cells in the human gas exchange system contains
triglycerides and phospholipids.
Compare and contrast the structure and properties of triglycerides and phospholipids.
[5 marks]

Answer 23

1. Both contain ester bonds (between glycerol and
   fatty acid);
2. Both contain glycerol;
3. Fatty acids on both may be saturated or
   unsaturated;
4. Both are insoluble in water;
5. Both contain C, H and O but phospholipids also
   contain P;

D-

6. Triglyceride has three fatty acids and
   phospholipid has two fatty acids plus phosphate
   group;
7. Triglycerides are hydrophobic/non-polar and
   phospholipids have hydrophilic and
   hydrophobic region
8. Phospholipids form monolayer (on
   surface)/micelle/bilayer (in water) but
   triglycerides don’t;

Question 24

Compare and contrast the structure and properties of triglycerides and phospholipids (5)

Answer 24

1. Both contain ester bonds (between glycerol and
   fatty acid);
2. Both contain glycerol;
3. Fatty acids on both may be saturated or
   unsaturated;
4. Both are insoluble in water;
5. Both contain C, H and O but phospholipids also
   contain P;
6. Triglyceride has three fatty acids and
   phospholipid has two fatty acids plus phosphate
   group;
7. Triglycerides are hydrophobic/non-polar and
   phospholipids have hydrophilic and
   hydrophobic region;
8. Phospholipids form monolayer (on
   surface)/micelle/bilayer (in water) but
   triglycerides don’t;

Question 25

The structure of a phospholipid molecule is different from that of a triglyceride.
Describe how a phospholipid is different. (2)

Answer 25

1. Phosphate / PO4
   ;
   “It” refers to phospholipid.
2. Instead of one of the fatty acids / and two fatty acids;
3. Accept minor errors in formula. Do not accept phosphorus /
   phosphorus group.

Question 26

S In an investigation, the effects of caffeine on performance during exercise were
measured. One group of athletes (A) was given a drink of decaffeinated coffee.
Another group (B) was given a drink of decaffeinated coffee with caffeine added. One
hour later the athletes started riding an exercise bike and continued until too exhausted
to carry on. Three days later the same athletes repeated the experiment, with the
drinks exchanged.
(a) (i) The researchers added caffeine to decaffeinated coffee. Explain why they did not

just use normal coffee. (1)

Answer 26

(i) in case normal coffee differs in some other way /

to control concentration of caffeine;

Question 27

The performance of the athletes might have been influenced by how they
expected the caffeine to affect them. How could the researchers avoid this
possibility? (1)

Answer 27

not telling them what the drink contained / purpose of experiment;

Question 28

Describe the effect of caffeine on exercise performance. (1)

Answer 28

able to continue for longer; (not just increases performance)
(disqualify if also refers to fatty acids and glycerol)

Question 29

suggest 1 explanation for the hugher gycerol and fatty acid conc in the blood plasma of the athletes after they were given caffine (2)

Answer 29

breakdown of fats;

at increased rate / by mobilisation of fat stores;