ACT Science Quiz #3

Based on Activity 1, which of the nutrient broths appears to produce the slowest doubling time for the bacteria populations? 

• Broth A

• Broth B

• Broth C

• Broth D

Answer explanation

The data in Table 1 shows that Broth C produces larger doubling times than any of the other broths. 

If the student needed to produce a very large sample of a bacteria population as quickly as possible, which bacteria species should he grow under which light? 

• E. coli under blue light

• Salmonella under blue light 

• Streptococcus under red light 

• Shigella under yellow light 

Answer explanation

Table 2 gives data on bacteria doubling time under different lights. Bacteria grown under the blue light has the smallest doubling times, meaning this light can produce more bacteria in less time. Of the four bacterial species, E. coli has the smallest doubling time. E. coli under blue light would be the best combination. 

According to Activity 2, if the student began growing a population of 1,000 Salmonella bacteria under red light, he should expect to have 4,000 in how many minutes? 

• 30

• 32

• 34

• 36

Answer explanation

Salmonella grown under red light has a doubling time of 18 minutes. If there are 1,000 Salmonella bacteria initially, then after 18 minutes this population will have grown to 2,000. This population will double again 18 minutes later to 4,000. 18 + 18 = 36 minutes 

If the student were to introduce a fifth bacterium into Activity 2 with a doubling time of 28 minutes in Broth D under yellow light, which of the following doubling times (in minutes) might he most likely expect the fifth bacterium to have under blue light? 

• 27

• 28

• 29

• 30

Answer explanation

According to Table 2, bacteria grown under blue light consistently has a doubling time one minute less than bacteria grown under yellow light. Therefore, it is likely that a bacteria with a doubling time of 28 minutes under yellow light will have a doubling time of 27 minutes under blue light. 

In working with the bacterial growth equation in Activity 3, the student notices a correlation between the growth constant k and the doubling time of the bacterial populations. Which of the following correlations is most likely true? 

• As k increases, doubling time increases. 

• As k increases, doubling time decreases. 

• As k increases, doubling time is unaffected. 

• There is no correlation between k and doubling time. 

Answer explanation

Compare the data in Tables 2 and 3. The largest values of k correspond to the smallest doubling times and vice versa. This most likely implies that as k increases, doubling time decreases.