5.5.4 Auxins and Apical Dominance

Question 1

What do auxins do?

Answer 1

• Synthesised at tip of roots and shoots (meristems)
• Stimulates cell elongation growth (ie. Roots or shoots grow upwards / downawrds)
• Stops lateral growth (prevents side buds from growing)

Question 2

What is apical dominance?

Answer 2

Where auxins prevent side buds from growing on stems

Question 3

Why is apical dominance a thing?

Answer 3

• Mostly better for plants to grow up towards light
• Ensures plant has access to more energy for photosynthesis
• Sideways growth is less useful to plants
• Auxin ensures plant grows upwards

Question 4

What happens when tip of plant is removed?

Answer 4

• Source of auxins removed
• So lateral growth of buds occur
• Because there is no longer apical dominance
• In time however shoots grow from these lateral buds and curl up towards light, so plant continues to grow in an upwards direction

Question 5

Experimentally, how can you prove apical dominance exists in plants?

Answer 5

Question 6

How do Auxins Work?

Answer 6

In shoots, a higher concentration of auxins results in greater rate of stem elongation. Auxin molecules move to the more shaded side of the shoot tip, causing the shaded side to grow at a faster rate and towards the light.

Gravity also causes auxins to accumulate on lower side of root, so shoots grow upwards.

In roots, higher concentrations of auxins result in a lower rate of cell elongation, IAA accumulates at lower side of root which inhibits cell elongation. So lower side grows at a slower rate than upper side, so root bends downwards.