Passage VI
Plant roots can respond to a stimulus. Response to light is phototropism; response to gravity is gravitropism. Growth toward a stimulus is a positive tropism; growth away from a stimulus is a negative tropism.
For 2 experiments with wild-type (WT) and mutant (M) Arabidopsis seeds, nutrient agar was put into each of 8 petri dishes (PD1-PD8).
Experiment 1
Six WT Arabidopsis seeds were placed in each of PD1 and PD2. Six M Arabidopsis seeds were placed in each of PD3 and PD4. Then, PD1 and PD3 were placed in the dark for 70 hr, and PD2 and PD4 were exposed to light from above for 70 hr. Figure 1 shows the growth of the hypocotyls (seedling stems) above the surface of the nutrient agar and the growth of the radicles (seedling roots) below the surface of the nutrient agar in each dish at 70 hr.
Experiment 2
Six WT Arabidopsis seeds were placed in each of PD5 and PD6. Six M Arabidopsis seeds were placed in each of PD7 and PD8. Then, PD5-PD8 were exposed to light from above for 70 hr. After 70 hr, each petri dish was turned 90° such that each dish was vertical and the seedlings in each dish were approximately horizontal (see Figure 2).
Then, PD5 and PD7 were exposed to light from above for 25 hr while PD6 and PD8 were exposed to light from below for 25 hr. At various times during the 25 hr, the downward curvature, in degrees (°), of the radicle (relative to its starting position) of each seedling in each dish was measured. The average downward curvature of the radicles in each dish at each measurement time is shown in Figure 3.
34. Which of the following figures best shows the orientation of PD5 before the petri dish was turned 90°？
Your Answer is
Correct Answer is H
Explanation
According to the description in the text part of Experiment 2, it can be seen that the WT seeds were planted in PD5, and they received 70 hr of light before being turned 90°, which means that this is the same as PD2 in Experiment 1, so it should be Consistent with the graphics of PD2