Tutor Hunt Questions

The coleoptile bends towards the light source. This is because IAA (an auxin) moves away from the light and causes the cells further away from the light to elongate.

A coleoptile exposed to a unilateral source of light will grow towards the light. The mechanism for this is related to plant hormones. When the tip of the shoot is exposed to the light, a plant hormone called auxin will move away from the light and gather on the dark side of the plant. The cells on the dark side of the plant are now exposed to high levels of auxin, while the cells on the light side are not.

Due to the effect of the auxin, the cells on the dark side start to grow by elongating. Therefore they are now longer than the cells on the light side of the plant. As the cells on the dark side are longer, this causes the plant to bend towards the light.

due to auxin plant hormone because more auxin will be store in dark side which are responsible for more elongation growth or bend to light area.

Dear Dedan,
First of all, let`s start from the fact that coleoptiles bend towards the light. For this to happen the part of the coleoptile that needs to be exposed to light is the tip. This observation was first recorded by francis Charles Darwin. But let`s see the structure of the coleoptile to understand few things about this `bending`. For example, grass has an emerging shoot which is covered by a protective sheath, the coleoptile. The bending takes place on the shoot. However, it is the tip that senses light because it contains photreceptor cells. Then a plant gromn hormone called auxin(now known to be indoleacetic acid IAA), is synthesised in the tip and moves to the shoot.This causes asymmetric growth of one side of the plant. As a result, the plant shoot will begin to bend toward a light source or toward the surface