ACT: Questions

Passage 1

Various methods are used to estimate the number of microorganisms in a culture. One method utilizes a spectrophotometer to measure the density of organisms in a broth medium. Density indicates the quantity of organisms in a given volume.

In this method, a beam of light is passed through the broth medium. The density of microorganisms in the broth is inversely proportional to the intensity of the light that passes through the broth. A meter is used to indicate the percentage of light transmitted through the medium.

The spectrophotometric data are used to produce a graph, such as the one below, that relates optical density to cell number.

Question: In Figure 1, how does the growth of microorganisms in setup A compare to the growth in setup B?

Choices:


	A.		The greatest growth occurred in setup A.
	B.		The greatest growth occurred in setup B.
	C.		The growth is equal in setups A and B.
	D.		No growth occurred in either setup.

The correct answer is B.

This question requires you to draw a conclusion from the data. The meter reading is lower in setup B than in setup A.

This means that less light is striking the photoelectric cell in setup B. The graph tells us that this would be true only if the medium in which the microorganisms are growing in setup B is more optically dense due to the greater number of microorganisms in this setup.

Hence, there has been more growth in setup B than in setup A.

Primary Navigation

ACT: Questions

ACT: Science Question #1