Question

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?

• A. Sunlight caused the plant to bend.
• B. The plant exhibited gravitropism.
• C. Auxin stimulated cell division on the opposite side of the plant.
• D. Auxin stimulated cell division on the same side of the plant.
• E. Auxin stimulated cell growth toward a light.

Answer 1

The correct option is C Auxin stimulated cell division on the opposite side of the plant.

If gelatin/auxin block was applied to the left side of the cut edge, the plant will grow and bend towards the light. This will result in the mitotic cell division on the opposite side of the plant. Thus the plant will bend towards the light. When a coleoptile tip that has previously been illuminated from one side is placed on two separated agar blocks, the block on the side that had been shaded accumulates almost twice as much auxin as the block on the previously lighted side. Auxin is the phytohormone which promotes cell division.