Cell recognition and Immune system

Question 1

Give two ways in which pathogens can cause disease.

Answer 1

• Release of toxins

- Kills cells

Question 2

Putting bee honey on a cut kills bacteria.
Honey contains a high concentration of sugar.

Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria.

Answer 2

• Water potential is higher in bacterial cells
• Water leaves bacteria by osmosis
• Stops metabolic reactions

Question 3

Whooping cough is a disease that affects some infants.
Doctors collected data relating to whooping cough between 1965 and 1996.

They collected data for:

• the number of cases of whooping cough reported
• the percentage of infants vaccinated against whooping cough.

The graph shows the data collected by the doctors.

( The graph has two graphs within it, one showing the number of reported cases of whooping virus, which is a fluctuating graph with sharp peaks, the other is the percentage of infants vaccinated which shows a minor “ U “ shape )

Suggest two reasons why the percentage of infants vaccinated decreased between 1973 and 1975.

Answer 3

• 1 - fewer cases of whooping cough

- 2 - fear of side effects

Question 4

Between 1980 and 1990, there were three peaks in the number of reported cases of whooping cough.
After 1981, the number of cases of whooping cough in each peak decreased.

Use the information from the graph to suggest why.

Answer 4

• Vaccination rate increases

- Fewer people to spread the disease

Question 5

The percentage of the population vaccinated does not need to be 100% to be effective in preventing the spread of whooping cough.

Suggest why.

Answer 5

• More people are immune

- Unvaccinated people are less likely to contact infected people

Question 6

Read the following passage.

Low-density lipoprotein (LDL) is a substance found in blood.
A high concentration of LDL in a person’s blood can increase the risk of atheroma
formation.
Liver cells have a receptor on their cell surface membranes that LDL binds to.
This leads to LDL entering the cell.
A regulator protein, also found in blood, can bind to the same receptor as LDL.
This prevents LDL entering the liver cell. People who have a high concentration of this regulator protein in their blood will have a high concentration of LDL in their blood. Scientists have made a monoclonal antibody that prevents this regulator protein working. They have suggested that these antibodies could be used to reduce the risk of coronary
heart disease.

A trial was carried out on a small number of healthy volunteers, divided into two
groups.
The scientists injected one group with the monoclonal antibody in salt solution.
The other group was a control group.
They measured the concentration of LDL in the blood of each volunteer at the start and after 3 months.
They found that the mean LDL concentration in the volunteers injected with the antibody was 64% lower than in the control group.

Use the information in the passage and your own knowledge to answer the following
questions.

The scientist gave an injection to a mouse to make it produce the monoclonal antibody used in this investigation (line 7).

What should this injection have contained?

Answer 6

• Regulator protein receptors

Question 7

LDL enters the liver cells (line 3-4).

( atheroma formation.
Liver cells have a receptor on their cell surface membranes that LDL binds to.
This leads to LDL entering the cell.
A regulator protein, also found in )

Using your knowledge of the structure of the cell-surface membrane, suggest how LDL enters the cell.

Answer 7

• Lipid soluble

- Enters through bilayer

Question 8

Explain how the monoclonal antibody would prevent the regular protein from working (lines 7-8).

( liver cell. People who have a high concentration of this regulator protein in their blood will have a high concentration of LDL in their blood. Scientists have made )

Answer 8

• Antibody has a specific tertiary structure

- Forms a complex with regulator protein

Question 9

Describe how the control group should have been treated.

LDL question about monoclonal antibodies

Answer 9

• Injected with salt solution

- Otherwise treated the same

Question 10

A mutation of a tumour suppressor gene can result in the formation of a tumour.

Explain how.

Answer 10

• Gene has become inactivated

- Rate of cell division is too fast

Question 11

Not all mutations result in a change to the amino acid sequence of the encoded polypeptide.

Explain why.

Answer 11

• Code is degenerate

- Mutation in intron

Question 12

Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor.
This stimulates the cancer cells to divide.

Scientist have produced a monoclonal antibody that stops the stimulation.

Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour.

Answer 12

• Antibody has a specific tertiary structure
• Complementary to the receptor protein
• Prevents growth factor from binding

Question 13

Read the following passage.

Herpes simplex virus (HSV) infects nerve cells in the face, including some near the
lips.
Like many other viruses, HSV can remain inactive inside the body for years.
When HSV becomes active, it causes cold sores around the mouth.

Human cells infected with a virus may undergo programmed cell death.
While HSV is inactive inside the body, only one of its genes is transcribed.
This gene is the latency-associated transcript (LAT) gene that prevents programmed cell death of an infected nerve cell.

Scientists have found that transcription of the LAT gene produces a microRNA.
This microRNA binds to some of the nerve cell’s own mRNA molecules.
These mRNA molecules are involved in programmed cell death of nerve cells.
The scientists concluded that production of this microRNA allows HSV to remain in the
body for years.

Use information from the passage and your own knowledge to answer the following
questions.

HSV infects nerve cells in the face (line 1).
Explain why it infects only nerve cells.

( Herpes simplex virus (HSV) infects nerve cells in the face, including some near the )

Answer 13

• The virus has antigens on its surface
• With a complementary shape to the receptor on the membrane of cells
• The receptor is found only on the membrane of nerve cells

Question 14

HSV can remain inactive inside the body for years (line 2-3).

( lips. Like many other viruses, HSV can remain inactive inside the body for years.
When HSV becomes active, it causes cold sores around the mouth. )

Explain why this virus can be described as inactive.

Answer 14

• No more nerve cells are infected

- Virus isn’t replicating

Question 15

Suggest one advantage of programmed cell death (line 4).

Human cells infected with a virus may undergo programmed cell death. While HSV

Answer 15

• Prevents replication of virus

Question 16

The scientist concluded that production of this microRNA allows HSV to remain in the body for years (lines 10-12).

( mRNA molecules are involved in programmed cell death of nerve cells. The
scientists concluded that production of this microRNA allows HSV to remain in the
body for years. )

Explain how this microRNA allows HSV to remain in the body for years.

Answer 16

• mircroRNA binds to mRNA by specific base pairing
• Prevents mRNA being read by ribosomes
• So prevents translation
• of proteins that cause cell death

Question 17

Malaria is a disease caused by parasites belonging to the genus Plasmodium.
Two species that cause malaria are Plasmodium falciparum and Plasmodium vivax.

A test strip that uses monoclonal antibodies can be used to determine whether a person is infected by Plasmodium.
It can also be used to find which species of Plasmodium they are infected by.

• A sample of a person’s blood is mixed with a solution containing an antibody, A, that
  binds to a protein found in both species of Plasmodium.
  This antibody has a coloured dye attached.
• A test strip is then put into the mixture. The mixture moves up the test strip by capillary action to an absorbent pad.
• Three other antibodies, B, C and D are attached to the test strip.
  The position of these antibodies and what they bind to is shown in Figure 1.

( Figure 1 shows a test strip from a chromatograpghy which has different sections; Pad of absorbment material to soak up liquid, Position of antibody B - this binds to antibody A, Position of antibody C - this binds only to the protein from Plamodium vivax, Position of antibody D - this binds to only the protein from Plasmodium falciparum, Mixture of antibody A and sample of blood, from top to bottom )

Explain why antibody A attaches only to the protein found in species of Plasmodium.

Answer 17

• Antibody has a tertiary structure

- Complementary to the binding site on the protein

Question 18

Antibody B is important if this test shows a person is not infected with Plasmodium.

Explain why antibody B is important.

Answer 18

• Prevents false negative results

- As it shows that antibody A has moved up the strip

Question 19

One of these test strips was used to test a sample from a person thought to be
infected with Plasmodium.
Figure 2 shows the result.

( Figure 2 shows coloured dye on the first and second part of the strip from the top, dye for antibody B and C parts )

What can you conclude from this result?

Explain how you reached this conclusion.

Answer 19

• Person is infected with plasmodium
• infected with vivax
• coloured dye where antibody C is present
• which only binds to protein from vivax