PEARSON EDEXCEL BIOLOGY
Unit 1 - 3
PRACTICE EXAM Q & A
2024
,Unit 1:
1. A patient with type 2 diabetes has been advised to follow
a low-carbohydrate diet. Explain how this diet can help to
control the blood glucose level of the patient. (4 marks)
Answer: A low-carbohydrate diet can help to control the
blood glucose level of the patient by reducing the intake of
glucose from food sources. This can lower the demand for
insulin, which is the hormone that regulates the uptake of
glucose into cells. Insulin resistance is a common feature of
type 2 diabetes, which means that the cells do not respond
well to insulin and do not take up enough glucose from the
blood. By reducing the glucose intake, the patient can
avoid high blood glucose levels that can cause
complications such as nerve damage, kidney damage and
cardiovascular disease. (4 marks)
2. A researcher is investigating the effect of different types
of lipids on the membrane fluidity of red blood cells. She
extracts the lipids from the membranes of red blood cells
and separates them by thin-layer chromatography (TLC).
She then measures the distance travelled by each lipid on
the TLC plate and calculates the Rf value for each lipid.
The Rf value is the ratio of the distance travelled by the
lipid to the distance travelled by the solvent. She obtains
the following results:
| Lipid | Rf value |
|-------|----------|
, | Phospholipid | 0.75 |
| Cholesterol | 0.60 |
| Saturated fatty acid | 0.40 |
| Unsaturated fatty acid | 0.80 |
a) Explain why unsaturated fatty acids have a higher Rf
value than saturated fatty acids. (2 marks)
Answer: Unsaturated fatty acids have a higher Rf value
than saturated fatty acids because they are more polar than
saturated fatty acids. Unsaturated fatty acids have one or
more double bonds between carbon atoms, which create
kinks in their hydrocarbon chains. These kinks increase the
polarity of the molecule, making it more soluble in polar
solvents and more likely to travel further on the TLC plate.
Saturated fatty acids have no double bonds and have
straight hydrocarbon chains, which make them less polar
and less soluble in polar solvents and less likely to travel
far on the TLC plate. (2 marks)
b) Explain how cholesterol affects the membrane fluidity of
red blood cells. (2 marks)
Answer: Cholesterol affects the membrane fluidity of red
blood cells by acting as a buffer, preventing the membrane
from becoming too fluid or too rigid. Cholesterol is an
amphipathic molecule, which means that it has both
hydrophilic and hydrophobic regions. It can insert itself
between the phospholipids in the membrane, forming
hydrogen bonds with them. At high temperatures,
Unit 1 - 3
PRACTICE EXAM Q & A
2024
,Unit 1:
1. A patient with type 2 diabetes has been advised to follow
a low-carbohydrate diet. Explain how this diet can help to
control the blood glucose level of the patient. (4 marks)
Answer: A low-carbohydrate diet can help to control the
blood glucose level of the patient by reducing the intake of
glucose from food sources. This can lower the demand for
insulin, which is the hormone that regulates the uptake of
glucose into cells. Insulin resistance is a common feature of
type 2 diabetes, which means that the cells do not respond
well to insulin and do not take up enough glucose from the
blood. By reducing the glucose intake, the patient can
avoid high blood glucose levels that can cause
complications such as nerve damage, kidney damage and
cardiovascular disease. (4 marks)
2. A researcher is investigating the effect of different types
of lipids on the membrane fluidity of red blood cells. She
extracts the lipids from the membranes of red blood cells
and separates them by thin-layer chromatography (TLC).
She then measures the distance travelled by each lipid on
the TLC plate and calculates the Rf value for each lipid.
The Rf value is the ratio of the distance travelled by the
lipid to the distance travelled by the solvent. She obtains
the following results:
| Lipid | Rf value |
|-------|----------|
, | Phospholipid | 0.75 |
| Cholesterol | 0.60 |
| Saturated fatty acid | 0.40 |
| Unsaturated fatty acid | 0.80 |
a) Explain why unsaturated fatty acids have a higher Rf
value than saturated fatty acids. (2 marks)
Answer: Unsaturated fatty acids have a higher Rf value
than saturated fatty acids because they are more polar than
saturated fatty acids. Unsaturated fatty acids have one or
more double bonds between carbon atoms, which create
kinks in their hydrocarbon chains. These kinks increase the
polarity of the molecule, making it more soluble in polar
solvents and more likely to travel further on the TLC plate.
Saturated fatty acids have no double bonds and have
straight hydrocarbon chains, which make them less polar
and less soluble in polar solvents and less likely to travel
far on the TLC plate. (2 marks)
b) Explain how cholesterol affects the membrane fluidity of
red blood cells. (2 marks)
Answer: Cholesterol affects the membrane fluidity of red
blood cells by acting as a buffer, preventing the membrane
from becoming too fluid or too rigid. Cholesterol is an
amphipathic molecule, which means that it has both
hydrophilic and hydrophobic regions. It can insert itself
between the phospholipids in the membrane, forming
hydrogen bonds with them. At high temperatures,
