Triiodobenzoic acid (TIBA) inhibits auxin transport. If a tiny agar bead containing TIBA were placed off center on the tip of an intact coleoptile, which way would the coleoptile bend: toward the side of the bead or away from it?

To determine the direction in which the coleoptile would bend when a tiny agar bead containing TIBA is placed off center on its tip, we need to understand the role of auxin and its transport in plant growth.

Auxin is a plant hormone that plays a crucial role in various aspects of plant growth and development, including cell elongation. It is typically produced in the apical meristem and transported downwards through the plant, primarily via a process called polar auxin transport.

Polar auxin transport is a unidirectional movement of auxin from the apical meristem towards the base of the plant. This transport is driven and regulated by a group of efflux carrier proteins, known as PIN proteins, located in the plasma membrane of plant cells. These proteins actively pump auxin out of the cell, establishing auxin concentration gradients and controlling the direction of auxin flow.

Now, let's consider the scenario where a tiny agar bead containing TIBA is placed off center on the tip of an intact coleoptile. TIBA is known to inhibit auxin transport, meaning it disrupts or slows down the movement of auxin.

As a result, when the coleoptile tip is treated with TIBA, auxin transport from the apical meristem down will be inhibited in the cells near the TIBA bead. This would create an asymmetry in auxin distribution as compared to the untreated side of the coleoptile.

As auxin is essential for promoting cell elongation, the side of the coleoptile that has a higher concentration of auxin will experience greater cell elongation compared to the side with lower auxin levels. Consequently, the coleoptile will bend towards the side with lower auxin, i.e., away from the bead.

In conclusion, the coleoptile would tend to bend away from the side where the tiny agar bead containing TIBA is placed.