Plant Hormones

Question 1

Explain how auxins cause a positive phototropism.

Answer 1

1. Auxin diffuses from the tip to the shaded side, causing elongation
2. Therefore the shaded side is longer, causing the stem to bend towards the light.

Question 2

How do shoots respond to gravity?

Answer 2

They grow up (negative geotropism).
When a plant is laid on its side, the auxins produced collect in the lower side of the stem. Auxins sped up growth in the lower side of the shoot, so the shoot curves up.

Question 3

How do roots respond to gravity?

Answer 3

They grow down (positive geotropism)
If a plant is laid on its side, the auxins produced collect in the lower side of the root. Auxins slow down growth on the lower side of the root, so the root curves down.

Question 4

What can plant hormones be used for?

Answer 4

• Gardening
• Agriculture
• Growing cuttings
• Killing weeds
• Ripening fruit