The following experiment was performed to test the effect of auxin on plant growth: Study and answer question.
The auxin was dissolved in a gelatin block; gelatin does not affect the biological activity of the auxin. Several plant seedlings were prepared in a gelatin block; gelatin does not affect the biological, activity of the auxin. Several plant seedlings were prepared as described above and growth was measured every 5 days.
Based on the results of the experiment, one can conclude that the tip of the plant contains ....................
In a separate experiment, an auxin/gelatin block applied to only half the cut edge of the tip caused the plant to grow and bend in the opposite direction. For example, if the auxin/gelatin block was applied to the left side of the cut edge, the plant grew and bent toward the light.
Which of the following is the most likely explanation for this observation?
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To test the effect of an auxin on plant growth, the auxin was dissolved in a gelatin block. Several plant seedlings were prepared and growth was measured every five days.
| Plant | Growth after 5 days | Growth after 10 days |
| 1 | 15 mm | 29 mm |
| 2 | 4 mm | 9 mm |
| 3 | 5 mm | 10 mm |
| 4 | 14 mm | 31 mm |
| 5 | 8 mm | 20 mm |
In a separate experiment, an auxin/gelatin block applied to only half the cut edge of the tip caused the plant to grow and bend in the opposite direction. For example, if the gelatin block was applied to the left side of the cut edge, the plant grew and bent toward the right. Which of the following is the most likely explanation for this observation?
If the light is coming from right the plant will bend to the right and cells on the left side of the plant must grow faster than cells on the right. If the light is coming from left then the plant will bend to the left and the opposite must occur; cells must grow faster on the right than on the left. Auxin applied to half the plant causes the plant to bend in the opposite direction; for example, auxin on the left stimulates bending to the right. Bending to the right means growth on the left; therefore, auxin must stimulate growth on the same side of the plant to which it is attached.
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To test the effect of an auxin on plant growth, the auxin was dissolved in a gelatin block. Several plant seedlings were prepared and growth was measured every five days.
| Plant | Growth after 5 days | Growth after 10 days |
| 1 | 15 mm | 29 mm |
| 2 | 4 mm | 9 mm |
| 3 | 5 mm | 10 mm |
| 4 | 14 mm | 31 mm |
| 5 | 8 mm | 20 mm |
Based on the results of the experiment, one can conclude that the tip of the plant contains
Growth rate in intact plant 1 is 3 mm per day which is reduced in plant 2 upon removal of tip to 1 mm per day. The growth rate is resumed to 3 mm per day upon application of auxin as in plant 4. This means plant tip contain auxin and removal of tip resulted in truncated growth.
Therefore, the correct answer is option C.
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