3.1 Communicable diseases

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

A student investigated the effect of different concentrations of a disinfectant on the survival of bacteria.

This is the method used:

Prepare four test tubes each with $cm310\text{ cm}^3$ of nutrient broth.
Add disinfectant to adjust the concentrations to $0%0\%$ , $1%1\%$ , $2%2\%$ , and $4%4\%$ .
Add $cm31\text{ cm}^3$ of a bacterial culture to each test tube.
Take a $cm30.1\text{ cm}^3$ sample from each test tube immediately (0 hours) and record the number of live bacteria.
Keep the test tubes at $35∘C35^\circ\text{C}$ for 12 hours.
Repeat step 4.

Table 1 shows some of the results.

Time in hours	Number of live bacteria at disinfectant concentration
	0%	1%	2%	4%
0	320	320	320	325
12	280	Y	80	16

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

[1]

What fraction of the bacteria present at 0 hours for 2% disinfectant survived for 12 hours? Give your answer in its simplest form.

[2]

How many more bacteria were killed at 4% disinfectant than at 0% disinfectant in 12 hours? Complete the following steps:

[3]

A student calculated value Y in Table 1 to be 180. Suggest how the student calculated this value.

[2]

3.1 Communicable diseases

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

A student investigated the effect of different concentrations of a disinfectant on the survival of bacteria.

This is the method used:

Prepare four test tubes each with $cm310\text{ cm}^3$ of nutrient broth.
Add disinfectant to adjust the concentrations to $0%0\%$ , $1%1\%$ , $2%2\%$ , and $4%4\%$ .
Add $cm31\text{ cm}^3$ of a bacterial culture to each test tube.
Take a $cm30.1\text{ cm}^3$ sample from each test tube immediately (0 hours) and record the number of live bacteria.
Keep the test tubes at $35∘C35^\circ\text{C}$ for 12 hours.
Repeat step 4.

Table 1 shows some of the results.

Time in hours	Number of live bacteria at disinfectant concentration
	0%	1%	2%	4%
0	320	320	320	325
12	280	Y	80	16

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

[1]

What fraction of the bacteria present at 0 hours for 2% disinfectant survived for 12 hours? Give your answer in its simplest form.

[2]

How many more bacteria were killed at 4% disinfectant than at 0% disinfectant in 12 hours? Complete the following steps:

[3]

A student calculated value Y in Table 1 to be 180. Suggest how the student calculated this value.

[2]

3.1 Communicable diseases

3.1 Communicable diseases Questions