Question 1a

Marks: 1

a)

EDTA is a compound that reacts with metal ions to form a stable harmless compound. It is commonly used to reduce levels of calcium in many medical procedures including dental work. EDTA has also been shown to have antimicrobial properties effective in the treatment of Staphylococcus aureus bacteria.

Scientists wanted to establish how effective EDTA could be in the treatment of infections from Escherichia coli bacteria. The growth of E.coli bacteria was monitored in response to treatment with EDTA over a period of 5 days. The chart below shows the results.

q3a_7-1_data_questions_medium_ib_sl_sq

State the reason for the group treated with no EDTA.

Question 1b

Marks: 1

b)

Calculate the percentage difference between the number of bacteria in the sample treated with EDTA and the number of bacteria in the untreated sample after 5 days.

Question 1c

Marks: 2

c)

Outline the effect of EDTA on the growth of bacteria.

Question 1d

Marks: 1

d)

The presence of antibiotic resistance within E.coli populations was studied and presented in the graph below.

Identify which antibiotic has been shown to be the least effective against E.coli.

Question 1e

Marks: 2

e)

Compare the levels of antibiotic resistance shown in E.coli to the antibiotics studied.

Question 1f

Marks: 3

f)

The table below shows some of the side effects associated with the antibiotics studied.

Antibiotic	Side effects
EDTA	Abdominal cramps, nausea, vomiting, diarrhoea, headache, low blood pressure, skin problems and fever.
Amoxicillin	Abdominal cramps, back and leg pains, bloating, blood in urine, chest pains
Tetracycline	Nausea, vomiting, diarrhoea, loss of appetite, mouth sores, black hairy tongue, sore throat, headache
Pivmecillinam hydrochloride	Diarrhoea, feeling sick, thrush

Using all the information provided, evaluate whether EDTA is the best candidate antibiotic to treat E.coli.

Question 1g

Marks: 1

g)

Suggest a different method that could be used to help reduce the development of antibiotic resistance.

Question 2a

Marks: 1

a)

State the reason why enzymes are referred to as biological catalysts.

[1 mark]

Key Concepts

Structure of Enzymes

Question 2b

Marks: 3

b)

The image below shows a representation of an enzyme-controlled reaction.

Describe the events taking place in the image.

[3 marks]

Key Concepts

Enzyme Activity

Question 2c

Marks: 2

c)

State what is meant by the term 'enzyme specificity'?

[2 marks]

Key Concepts

Structure of Enzymes

Question 3a

Marks: 3

a)

The ends of a DNA strand are referred to as the 3’ end and the 5’ end.

Describe the aspects of DNA structure that give rise to this naming system.

[3 marks]

Key Concepts

Double Helix Structure

Question 3b

Marks: 2

b)

Adenine/thymine and guanine/cytosine form hydrogen-bonds with each other in complementary base-pairing within the DNA double helix. These bases can also form bonds with other molecules in order to carry out their function.

i)

Suggest one other molecule that might form bonds with the bases in a DNA molecule.

[1 mark]

ii)

State the role of the molecule identified in part i).

[1 mark]