Auxins & Phototropism

What happens to auxin distribution when light shines from one side of a shoot?

More auxin accumulates on the shaded side.

How does auxin cause a shoot to bend towards light?

Auxin stimulates greater cell elongation on the shaded side, causing the shoot to curve towards the light.

Which side of a shoot grows faster during positive phototropism?

The shaded side.

Why does the shaded side of a shoot grow faster?

It contains more auxin, stimulating greater cell elongation.

What happens when a shoot receives light equally from all directions?

It generally grows straight, assuming no other directional stimulus.

What happens when the tip of a shoot is removed?

Its phototropic response is greatly reduced or prevented.

Why does removing the shoot tip affect phototropism?

The tip is an important site of auxin production and light detection.

What happens when an opaque cap covers the shoot tip?

The shoot generally does not bend towards unilateral light.

Why does an opaque cap prevent the normal phototropic response?

It prevents the shoot tip from detecting the direction of light.

What happens when a transparent cap covers the shoot tip?

The shoot can still detect light and bend towards it.

What happens when an opaque sleeve covers only the lower part of a shoot?

The shoot can still show positive phototropism if the tip remains exposed.

What does the shoot-tip experiment demonstrate?

The shoot tip detects light and controls the growth response.

What happens to auxin on the illuminated side of a shoot?

Its concentration is generally lower than on the shaded side.

Why is phototropism useful for plant survival?

It helps shoots grow towards light for photosynthesis.

Why is phototropism considered a response to a stimulus?

Directional light causes a change in growth direction.