Question 12 – 3.1 Communicable diseases - Questions

Name one chemical barrier the human body uses to defend itself against pathogens.

A student investigated the antimicrobial effect of tea tree oil at various concentrations on the survival of Staphylococcus aureus bacteria.

This is the method used:

Prepare four test tubes each with 15 cm³ of nutrient broth.
Add tea tree oil to adjust the concentrations to 0%, 2%, 4%, and 8%.
Add 1.5 cm³ of a Staphylococcus aureus bacterial culture to each test tube.
Take a 0.15 cm³ sample from each test tube immediately (0 hours) and record the number of live bacteria.
Incubate the test tubes at $37∘C37^\circ\text{C}$ for 16 hours.
Repeat step 4.

Table 1 shows some of the results.

Time in hours	Number of live bacteria at tea tree oil concentration
	0%	2%	4%	8%
0	480	480	480	485
16	400	Y	96	15

Name one chemical barrier the human body uses to defend itself against pathogens.

What fraction of the bacteria present at 0 hours for 4% tea tree oil concentration survived for 16 hours? Give your answer in its simplest form.

How many more bacteria were killed at 8% concentration than at 0% concentration in 16 hours? Complete the following steps:

A student calculated value Y in Table 1 to be 248. Suggest how the student calculated this value.

Name one chemical barrier the human body uses to defend itself against pathogens.

A student investigated the antimicrobial effect of tea tree oil at various concentrations on the survival of Staphylococcus aureus bacteria.

This is the method used:

Prepare four test tubes each with 15 cm³ of nutrient broth.
Add tea tree oil to adjust the concentrations to 0%, 2%, 4%, and 8%.
Add 1.5 cm³ of a Staphylococcus aureus bacterial culture to each test tube.
Take a 0.15 cm³ sample from each test tube immediately (0 hours) and record the number of live bacteria.
Incubate the test tubes at $37∘C37^\circ\text{C}$ for 16 hours.
Repeat step 4.

Table 1 shows some of the results.

Time in hours	Number of live bacteria at tea tree oil concentration
	0%	2%	4%	8%
0	480	480	480	485
16	400	Y	96	15

Name one chemical barrier the human body uses to defend itself against pathogens.

What fraction of the bacteria present at 0 hours for 4% tea tree oil concentration survived for 16 hours? Give your answer in its simplest form.

How many more bacteria were killed at 8% concentration than at 0% concentration in 16 hours? Complete the following steps:

A student calculated value Y in Table 1 to be 248. Suggest how the student calculated this value.

3.1 Communicable diseases