Cell elongation in plants is caused by

The substance related to phototropism in the shoot is

Give scientific reasons: Indole-$3$-acetic acid $(IAA)$ is not the only naturally occurring auxin.

Grass coleoptile tips bend towards the source of light because:

What is the result of removing the apical bud?

Levitt performed experiments. He observed that auxin-treated cells were able to absorb water even when kept in a hypertonic solution. Which explains this observation best?