Edexcel IAL Biology A2 Topic 6 Question Bank

[Maximum number: 8]

Two students, student P and student Q, each cultured bacteria in a liquid medium for 20 hours. The culture conditions used by both students were identical.

Every two hours, each student removed a sample of the culture to count the number of bacteria. Each student used a different method to count the number of bacteria in the samples.

The graph shows the bacterial growth curve that each student drew using their results. $\log _{10}$ number of bacteria per $\mathrm{cm}^{3}$

Figure for Question 1 — Edexcel A-Level Biology A2

(a)

Both students used aseptic techniques to culture the bacteria.

[ 4 ]

(i)

Explain the importance of using aseptic techniques to culture bacteria.

[ 2 ]

(ii)

Explain one aseptic technique that should be used when culturing bacteria.

[ 2 ]

(b)

Calculate the growth rate constant ( k ) of these bacteria between 2 hours and 6 hours of culture.

Use the equation: $\quad k=\frac{\log _{10} N_{t}-\log _{10} N_{0}}{0.301 \times t}$

where: $\log _{10} N_{t}=\log _{10}$ number of cells at 6 hours $\log _{10} N_{0}=\log _{10}$ number of cells at 2 hours.

[ 2 ]

3.2 (1)

- 3 / 2.7 / 2.66 / 2.658 (1)

ACCEPT 5.2-2=3.2

ECF 0.3 / 0.34 / 0.345 = 1 mark

Bald answer of $\{3 / 2.7 / 2.66 / 2.658\}=2$ marks Bald answer of 2.6578073089700996677 \{incorrectly rounded up to three decimal places max / correctly rounded to more than three decimal places\} = 1 mark Bald answer of 3.2 = 1 mark

Bald answer of $\{0.3$ / 0.34 / 0.345 $\}=1$ mark

(c)

The number of bacteria in the samples taken after 10 hours were:

398107171 in the culture of student P

6309573 in the culture of student Q.

[ 2 ]

(i)

Student P and student Q used different methods for determining the number of bacteria.

State which method each student used.

Give a reason for your answer. (2)

Student P

Student Q

[ 2 ]

[Maximum number: 7]

Rabies is a disease caused by a virus.

(a)

The diagram shows the structure of the rabies virus.

Figure for Question (a) — Edexcel A-Level Biology A2

[ 3 ]

(i)

The rabies virus has an envelope.

Which of the following pairs of viruses have an envelope?

A

Ebola virus and human immunodeficiency virus (HIV)

B

human immunodeficiency virus (HIV) and tobacco mosaic virus (TMV)

C

lambda phage ( $\lambda$ phage) and Ebola virus

D

tobacco mosaic virus (TMV) and lambda phage ( $\lambda$ phage)

[ 1 ]

(ii)

The structure of the rabies capsid is described as complex.

Which of the following has a complex capsid structure?

A

Ebola virus

B

human immunodeficiency virus (HIV)

C

lambda phage ( $\lambda$ phage)

D

tobacco mosaic virus (TMV)

[ 1 ]

(iii)

Rabies virus is an RNA virus.

How many of the following viruses are RNA viruses?
- Ebola virus
- human immunodeficiency virus (HIV)
- lambda phage ( $\lambda$ phage)
- tobacco mosaic virus (TMV)

A

1

B

2

C

3

D

4

[ 1 ]

(b)

Lemurs are found in Madagascar. It is thought that they might carry rabies viruses.

The photograph shows a lemur.

Figure for Question (b) — Edexcel A-Level Biology A2

(Source: Caroline Wilcox)

A person was bitten by a lemur.
This person did not receive any treatment for rabies until 18 days after being bitten.

Explain why doctors were worried that this person had left it too long for the treatment to be successful.

[ 4 ]

[Maximum number: 4]

Mycobacterium tuberculosis (Mtb) and human immunodeficiency virus (HIV) are two pathogens that infect people. When people infected with either pathogen become infected with the other pathogen the disease is worse.

Explain why HIV infection causes tuberculosis (TB) to be worse.

[Maximum number: 2]

Two students, student P and student Q, each cultured bacteria in a liquid medium for 20 hours. The culture conditions used by both students were identical.

Every two hours, each student removed a sample of the culture to count the number of bacteria. Each student used a different method to count the number of bacteria in the samples.

The graph shows the bacterial growth curve that each student drew using their results. $\log _{10}$ number of bacteria per $\mathrm{cm}^{3}$

Figure for Question 4 — Edexcel A-Level Biology A2

The number of bacteria in the samples taken after 10 hours were:

398107171 in the culture of student P

6309573 in the culture of student Q.

Student P and student Q used different methods for determining the number of bacteria.

State which method each student used.

Give a reason for your answer. (2)

Student P

Student Q

[Maximum number: 2]

Two students, student P and student Q, each cultured bacteria in a liquid medium for 20 hours. The culture conditions used by both students were identical.

Every two hours, each student removed a sample of the culture to count the number of bacteria. Each student used a different method to count the number of bacteria in the samples.

The graph shows the bacterial growth curve that each student drew using their results. $\log _{10}$ number of bacteria per $\mathrm{cm}^{3}$

Figure for Question 5 — Edexcel A-Level Biology A2

Calculate the growth rate constant ( k ) of these bacteria between 2 hours and 6 hours of culture.

Use the equation: $\quad k=\frac{\log _{10} N_{t}-\log _{10} N_{0}}{0.301 \times t}$

where: $\log _{10} N_{t}=\log _{10}$ number of cells at 6 hours $\log _{10} N_{0}=\log _{10}$ number of cells at 2 hours.

3.2 (1)

- 3 / 2.7 / 2.66 / 2.658 (1)

ACCEPT 5.2-2=3.2

ECF 0.3 / 0.34 / 0.345 = 1 mark

Bald answer of $\{3 / 2.7 / 2.66 / 2.658\}=2$ marks Bald answer of 2.6578073089700996677 \{incorrectly rounded up to three decimal places max / correctly rounded to more than three decimal places\} = 1 mark Bald answer of 3.2 = 1 mark

Bald answer of $\{0.3$ / 0.34 / 0.345 $\}=1$ mark

[Maximum number: 2]

Methicillin-resistant Staphylococcus aureus (MRSA) is a disease causing worldwide concerns.

Methicillin is one of the antibiotics to which this pathogen has developed resistance.
Castaneroxy A is a molecule extracted from the European chestnut tree, endemic to Southern Europe and Turkey.

The effects of Castaneroxy A have been investigated.
The investigations have found that Castaneroxy A:
- does not affect the natural skin flora
- prevents MRSA from producing toxins
- weakens the MRSA bacteria
- reduces the size of skin infections caused by MRSA.

Explain why it is important that Castaneroxy A does not affect skin flora.

[Maximum number: 6]

Rheumatoid arthritis is an inflammatory condition caused by the overactivity of the immune system.

(a)

The photographs show the hand of a person with rheumatoid arthritis and the hand of a person without rheumatoid arthritis.

(Source: © Mediscan/Alamy Stock Photo)

Hand with rheumatoid arthritis
Magnification $\times 0.2$

Hand without rheumatoid arthritis
Magnification $\times 0.2$

[ 2 ]

(i)

Give one piece of evidence, shown in the photographs, that rheumatoid arthritis is an inflammatory condition.

[ 1 ]

(ii)

Give two other signs of inflammation that are experienced in the hand of a person with rheumatoid arthritis.

[ 1 ]

(b)

Tumour necrosis factor (TNF) is a protein that can be released by several types of cell. It plays an important part in the immune response.

This protein binds to specific receptors on the surface of cell membranes stimulating chemical reactions inside the cell. As a result, a number of responses may occur that include inflammation and the stimulation of phagocytosis by macrophages.

Antibodies to TNF are used to treat rheumatoid arthritis.
Scientists have used a virus that infects bacteria to produce antibodies to human TNF.

The diagram summarises this process.

[ 4 ]

(i)

Patients being treated with antibodies to TNF are more susceptible to tuberculosis (TB), which can be fatal.

Explain why patients being treated with antibodies to TNF can die from TB.

[ 4 ]

[Maximum number: 3]

There are four types of immunity.

Natural active immunity can develop when a person is infected with a virus.

Describe the role of macrophages in the development of natural active immunity to a virus, following infection.

[Maximum number: 4]

There are four types of immunity.

Natural active immunity can develop when a person is infected with a virus.

Explain why both T helper cells and T killer cells are needed in the immune response to a virus.

[Maximum number: 3]

There are four types of immunity.

Artificial immunity develops when a person is immunised by an injection.

The table gives some statements about artificial immunity.
For each statement, put one cross ∖ in the appropriate box, in each row, to show which statements are correct for the types of artificial immunity.

Table for Question 10 — Edexcel A-Level Biology A2

[Maximum number: 2]

Methicillin-resistant Staphylococcus aureus (MRSA) is a disease causing worldwide concerns.

Methicillin is one of the antibiotics to which this pathogen has developed resistance.
Castaneroxy A is a molecule extracted from the European chestnut tree, endemic to Southern Europe and Turkey.

The effects of Castaneroxy A have been investigated.
The investigations have found that Castaneroxy A:
- does not affect the natural skin flora
- prevents MRSA from producing toxins
- weakens the MRSA bacteria
- reduces the size of skin infections caused by MRSA.

Explain why the development of this drug is an example of an 'evolutionary race' between humans and this pathogen.
(2)

[Maximum number: 3]

Aquaculture is the controlled cultivation of aquatic organisms such as fish, shellfish and plants. It is an important source of food in many countries of the world. The photograph shows freshwater aquaculture ponds in Africa.

Figure for Question 12 — Edexcel A-Level Biology A2

(Source: © E.Westmacott/Alamy Stock Photo)

Vibrio are bacteria that are common in aquatic habitats. They cause diarrhoea and cholera and are also pathogenic to shellfish. The resistance of Vibrio to antibiotics and to heavy metals in aquaculture ponds in Nigeria was investigated.

(a)

The samples of Vibrio taken from each pond were spread on agar containing different antibiotics.

[ 3 ]

(i)

Some of the antibiotics used were bacteriostatic and some were bactericidal.

State the difference between a bacteriostatic antibiotic and a bactericidal antibiotic.

[ 1 ]

(ii)

The method did not distinguish between bacteriostatic and bactericidal antibiotics because no colonies grew. Suggest how the method would need to be modified to show which antibiotics were bacteriostatic and which were bactericidal. Give a reason for your answer.

[ 2 ]

[Maximum number: 3]

The resistance of bacteria to antibiotics can be studied using a mast ring.
A mast ring is made of filter paper.
Each part of the mast ring contains a different type of antibiotic or different mass of the same antibiotic.

The diagram shows a mast ring placed on agar in a Petri dish that has been spread with bacteria.

The table shows the mass of each antibiotic in the mast ring.

Figure for Question 13 — Edexcel A-Level Biology A2

Clear zones around the mast ring indicate that the growth of the bacteria has been inhibited.

The greater the diameter of the zone of inhibition, the more effective the antibiotic.

Explain how the results shown in the diagram can help a doctor decide how to prescribe antibiotics to a patient who is infected with this type of bacteria.

An explanation that includes three of the following points:

- not A and D because {they have no effect / the bacteria are resistant to them / there is no zone of inhibition} (1)

- B as it {is most effective / has the largest zone of inhibition} (1)

- use {high mass / $200 \mu \mathrm{~g}$ } antibiotic C as lower masses are not effective (1)

-use antibiotic B at $10 \mu \mathrm{~g}$ as higher masses are no more effective (1)

ACCEPT use antibiotics B, C and E
as {they are effective / the
bacteria are not resistant to them
/ they have a zone of inhibition}
PIECE TOGETHER

(3)

Answer

Mark

[Maximum number: 2]

The photograph shows parts of Tussilago farfara. This is a native species of plant that grows in North Africa and Central Asia.

Figure for Question 14 — Edexcel A-Level Biology A2

Scientists have isolated antibacterial compounds from plants such as Tussilago farfara.

Explain how the code of practice for prescribing antibiotics helps to control infections.

[Maximum number: 6]

Quince are fruit that grow on trees.
When a quince falls from the tree, two processes take place: browning and decomposition.

A quince fruit is made up of cells and contains a lot of juice.

The table shows the composition of carbohydrates in the juice of one species of quince.

Table for Question 15 — Edexcel A-Level Biology A2

Explain the role of decomposition in returning the carbon present in the carbohydrates in the quince fruit back into the atmosphere.

Use the information given in part (b) to support your answer.

[Maximum number: 2]

Madagascar is a large island off the southeast coast of mainland Africa.
Lemurs are endemic to Madagascar.

Lemurs have been found on another island close to Madagascar.

Scientists have used DNA profiling to show that these lemurs originated from those on Madagascar.

Explain the role of the polymerase chain reaction (PCR) in DNA profiling.

[Maximum number: 2]

Gel electrophoresis is used to separate DNA fragments of different lengths.
The rate at which the DNA fragments move through the gel depends on several factors including:
- molecular size of the DNA fragment
- shape of the DNA fragment
- concentration of the gel.

(a)

Fragments of double-stranded DNA move through the gel at a relative rate ( $\mathrm{M}_{\mathrm{r}}$ ) that is inversely proportional to the log of their molecular weight (MW).

[ 1 ]

(i)

The diagram shows the position of a DNA fragment with a MW of 10000, after gel electrophoresis.

Complete the diagram to show the position of a DNA fragment with a MW of 100000.

Use the information in the question.

Figure for Question (i) — Edexcel A-Level Biology A2

[ 1 ]

(b)

The fragments move more slowly through a higher concentration of gel. Suggest why the fragments move more slowly through a higher concentration of gel.

[ 1 ]

[Maximum number: 2]

Madagascar is a large island off the southeast coast of mainland Africa.
Lemurs are endemic to Madagascar.

Lemurs have been found on another island close to Madagascar.

Scientists have used DNA profiling to show that these lemurs originated from those on Madagascar.

Explain how DNA profiling could show that these lemurs originated from the lemurs on Madagascar.

[Maximum number: 14]

The time of death of a mammal can be estimated in a number of ways.

(a)

Measuring the body temperature of a corpse is one method used to estimate the time of death.

The graph shows a calibration curve that can be used in this method.

[ 5 ]

(i)

Describe how the time of death of a person can be estimated using this method.

[ 3 ]

(ii)

Explain the limitations of this method.

[ 2 ]

(b)

Scientists are looking for other methods to estimate the time of death, using the presence of chemicals in the blood.

One study used blood taken from five rat corpses and two pig corpses at intervals after death.

[ 9 ]

(i)

The graphs show some of the results of this study.

Levels of lactate in blood / a.u.

Comment on the usefulness of using these chemicals for determining the time of death of rats and pigs.

Use the information in the graphs to support your answer.

[ 6 ]

(ii)

Discuss whether these chemical tests are likely to be useful in determining the time of death of a human.

[ 3 ]

Edexcel A-Level Biology A2 6 Microbiology Immunity and Forensics Questions

Exam points

Covered syllabus points

Covered syllabus points

Question 1

Question (a)

Question (i)

Question (ii)

Question (b)

Question (c)

Question (i)

Question 2

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Question (i)

Question (ii)

Question (iii)

Question (b)

Question 3

Question 4

Question 5

Question 6

Question 7

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Question (i)

Question (ii)

Question (b)

Question (i)

Question 8

Question 9

Question 10

Question 11

Question 12

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Question (ii)

Question 13

Question 14

Question 15

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Question 17

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Question 19

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Question (ii)