ACT science practice test 59

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


Photosynthesis is the process by which organisms such as green plants, algae, and cyanobacteria convert light energy from the sun to chemical energy stored in the bonds of carbohydrates. Chlorophyll is a pigment employed by many autotrophic organisms to absorb the various wavelengths of visible light from the sun for use in photosynthesis. A variety of photosynthetic pigments exist; they are specifically adapted for absorbing different ranges of the visible light spectrum and reflecting others. The absorption spectrum of chlorophyll and accessory pigments can be obtained through spectrophotometry and later used to gain insight into plant growth, determine the abundance of photosynthetic organisms in fresh- or saltwater, and evaluate water quality.

The data in Figure 11.1 and Table 11.2 were collected by students measuring the absorption spectra of three commonly encountered photosynthetic pigments.

Figure 11.1

TABLE 11.2

1. Which of the following statements represents a valid assessment of the data?

A. Chlorophyll a and b absorb the most green light.
B. Neither chlorophyll a, b, nor the carotenoids absorb light in the wavelengths of 425 to 475 nm.
C. Chlorophyll a and b have the most reflection in the wavelengths of 525 to 625 nm.
D. Carotenoids absorb the most light in the red portion of the spectrum.

2. Using the information in Table 11.2, which of the following wavelengths of light would phycocyanin, a pale blue-colored accessory pigment, reflect most?

A. 400 nm
B. 460 nm
C. 550 nm
D. 750 nm

3. Based on Figure 11.1, which of the following wavelengths of visible light would be absorbed to promote the most photosynthetic activity in green plants?

A. 400 nm
B. 440 nm
C. 550 nm
D. 625 nm

4. Based on the information in Figure 11.1 and Table 11.2, which pigment has the highest relative absorbance in the red portion of the spectrum?

A. Chlorophyll a
B. Chlorophyll b
C. Carotenoids
D. All pigments absorb the same amount of light in this portion of the spectrum.

5. Which of the following statements about the relative absorbance levels of the pigments is most accurate?

A. Chlorophyll a absorbs 8 times as much light as chlorophyll b at 450 nm.
B. Carotenoids behave similarly to chlorophyll a and b at wavelengths greater than 550 nm.
C. Chlorophyll b has the lowest relative absorbance of violet light.
D. Carotenoids absorb approximately 60% as much light as chlorophyll b at 450 nm.

6. Which pigment would absorb the most violet light at a wavelength of 425 nm?

A. Chlorophyll a
B. Chlorophyll b
C. Carotenoids
D. All pigments absorb violet light equally.

7. Which wavelength represents the maximum absorbance of chlorophyll b?

A. 425 nm
B. 450 nm
C. 515 nm
D. 650 nm

8. From the information in the passage, one can conclude that chlorophyll appears green to the human eye because:

A. wavelengths of light between 550 and 600 nm are highly absorbed.
B. wavelengths in the green portion of the visible spectrum are absorbed.
C. wavelengths in the green portion of the visible spectrum are reflected.
D. wavelengths in the red portion of the visible spectrum are reflected.

9. Phycoerythrin is a photosynthetic pigment that is found in marine algae. It has absorption peaks at 495 nm and 566 nm and reaches its lowest values over 600 nm. Based on this information, one would expect phycoerythrin to:

A. appear very similar to chlorophyll a and b to the naked eye.
B. reflect green light and absorb red light.
C. reflect red light and absorb green light.
D. absorb red and green light equally.