CBSE Class 6 Answered

Hi Sunil,

Auxins are found in tips of the shoots and roots but can diffuse to other areas.

The hormones affect the rate of elongation of plant cells.

Effect of auxins:

• Shoot cells to grow more quickly
• Root cells to grow less quickly

Phototropism

• Auxins diffuse to the shaded areas of shoots and roots.
• In shoots the high concentration of auxin causes the shaded shoot cells to grow more quickly.
• The result is a shoot that bends towards the light.
• In roots the high concentration of auxin causes the shaded cells to grow more slowly.
• The result is a root that bends away from the light.

Gravitropism

• Auxins are affected by gravity.
• In horizontal shoots there is a higher concentration of auxin at the bottom.
• This causes the bottom cells to grow more quickly, pushing the shoot up against gravity.
• In horizontal roots, there is also a higher concentration of auxin at the bottom.
• This causes the bottom cells to grow less quickly than the top cells, pushing the root into the ground.