AS ADAPTATION AND SELECTION
UPDATED ACTUAL Exam Questions and
CORRECT Answers
Clostridium difficile is a bacterium that is present in the gut of up to 3% of healthy adults and
66% of healthy infants.
(i) C. difficile rarely causes problems, either in healthy adults or in infants. This is because its
numbers are kept low by competition with harmless bacteria that normally live in the intestine.
Use this information to explain why some patients treated with antibiotics can be affected by C.
difficile - CORRECT ANSWER - Antibiotics kill other bacteria / Clostridium is resistant;
Less/no competition so (Clostridium)
reproduces/replicates/multiplies/increases in number
Suggest why older people are more likely to be affected by C. difficile. - CORRECT
ANSWER - Immune system less effective / more likely to have other infections/been in
hospital;
Accept: 'Weak/lower' immune system'
The antibiotic methicillin inhibits the enzyme transpeptidase. This enzyme is used by some
bacteria to join monomers together during cell wall formation. Methicillin has a similar structure
to these monomers. Use this information to explain how methicillin inhibits the enzyme
transpeptidase. - CORRECT ANSWER - Attaches to active site (of enzyme);
(Methicillin) is a competitive inhibitor / prevents monomers/substrate attaching (to enzyme);
MRSA is a variety of Staphylococcus aureus. It is difficult to treat infections caused by this
bacterium because it is resistant to methicillin and to some other antibiotics. As a result, some
patients who are already very ill may die if they become infected with MRSA. The graph shows
the number of deaths in England and Wales between 1994 and 2008 caused by MRSA. It may be
difficult to identify MRSA as the actual cause of death. Explain why. - CORRECT
ANSWER - Have other illness/medical condition/'weak' immune system/disease/infection
, Describe the change in the number of deaths caused by MRSA in England in the period shown in
the graph.
DECRIBE WHAT YOU SEE - CORRECT ANSWER - Increase up to 2006/20 (per 100 000)
then decreases
Describe how gene transmission and selection have increased the difficulty of treating bacterial
infections with antibiotics - CORRECT ANSWER - 1. (Antibiotic) resistant gene/allele;
2. Vertical (gene) transmission;
3. Resistant bacteria (survive and) reproduce / population of
resistant bacteria increases;
4. Increase in frequency of (resistant) allele/gene (in future generations);
5. Horizontal (gene) transmission;
6. Plasmid;
7. Conjugation / pilus (tube);
8. (Horizontal transmission/ conjugation) can occur
between bacteria of different species
Penicillin was first used to treat infections in the 1940s.
Describe how penicillin prevents the growth of bacteria - CORRECT ANSWER - stop cell
walls forming / lysis;
The bacterium Staphylococcus aureus is a common cause of life-threatening infections. By the
1960s it had already become resistant to the antibiotic penicillin.Describe one mechanism of
resistance to penicillin - CORRECT ANSWER - penicillinase produced / enzyme breaks
down penicillin;
or
capsule/wall and membrane complex that does not allow penetration/ penicillin pumped out
Explain how S. aureus evolved resistance to penicillin - CORRECT ANSWER - mutation;
UPDATED ACTUAL Exam Questions and
CORRECT Answers
Clostridium difficile is a bacterium that is present in the gut of up to 3% of healthy adults and
66% of healthy infants.
(i) C. difficile rarely causes problems, either in healthy adults or in infants. This is because its
numbers are kept low by competition with harmless bacteria that normally live in the intestine.
Use this information to explain why some patients treated with antibiotics can be affected by C.
difficile - CORRECT ANSWER - Antibiotics kill other bacteria / Clostridium is resistant;
Less/no competition so (Clostridium)
reproduces/replicates/multiplies/increases in number
Suggest why older people are more likely to be affected by C. difficile. - CORRECT
ANSWER - Immune system less effective / more likely to have other infections/been in
hospital;
Accept: 'Weak/lower' immune system'
The antibiotic methicillin inhibits the enzyme transpeptidase. This enzyme is used by some
bacteria to join monomers together during cell wall formation. Methicillin has a similar structure
to these monomers. Use this information to explain how methicillin inhibits the enzyme
transpeptidase. - CORRECT ANSWER - Attaches to active site (of enzyme);
(Methicillin) is a competitive inhibitor / prevents monomers/substrate attaching (to enzyme);
MRSA is a variety of Staphylococcus aureus. It is difficult to treat infections caused by this
bacterium because it is resistant to methicillin and to some other antibiotics. As a result, some
patients who are already very ill may die if they become infected with MRSA. The graph shows
the number of deaths in England and Wales between 1994 and 2008 caused by MRSA. It may be
difficult to identify MRSA as the actual cause of death. Explain why. - CORRECT
ANSWER - Have other illness/medical condition/'weak' immune system/disease/infection
, Describe the change in the number of deaths caused by MRSA in England in the period shown in
the graph.
DECRIBE WHAT YOU SEE - CORRECT ANSWER - Increase up to 2006/20 (per 100 000)
then decreases
Describe how gene transmission and selection have increased the difficulty of treating bacterial
infections with antibiotics - CORRECT ANSWER - 1. (Antibiotic) resistant gene/allele;
2. Vertical (gene) transmission;
3. Resistant bacteria (survive and) reproduce / population of
resistant bacteria increases;
4. Increase in frequency of (resistant) allele/gene (in future generations);
5. Horizontal (gene) transmission;
6. Plasmid;
7. Conjugation / pilus (tube);
8. (Horizontal transmission/ conjugation) can occur
between bacteria of different species
Penicillin was first used to treat infections in the 1940s.
Describe how penicillin prevents the growth of bacteria - CORRECT ANSWER - stop cell
walls forming / lysis;
The bacterium Staphylococcus aureus is a common cause of life-threatening infections. By the
1960s it had already become resistant to the antibiotic penicillin.Describe one mechanism of
resistance to penicillin - CORRECT ANSWER - penicillinase produced / enzyme breaks
down penicillin;
or
capsule/wall and membrane complex that does not allow penetration/ penicillin pumped out
Explain how S. aureus evolved resistance to penicillin - CORRECT ANSWER - mutation;
