2.83-2.85 plants coordination and response

What is a tropism?

The directional growth of an organism or its parts in response to an external stimulus

What are the different tropisms and their meaning?

Phototropism- light

Gravitropism/Geotropism - gravity/the earth

Do plants show positive/negative phototropism and how?

Positive phototropism - they grow towards the light source

• auxin is a growth hormone and moves to the shaded side of the shoot

• Auxin stimulates cells to grow more

• So the shoot bends towards the light, allowing faster photosynthesis

Do shoots show positive/negative geotropism and how?

Negative geotropism - shoots grow away from the ground/gravity

• If shoot is horizontal : auxin moves to the lower side - stimulates cells to grow more here

• Makes shoot bend and grow away from the ground

Do roots show positive/negative geotropism and how?

Positive geotropism - roots grow down

• if a root is horizontal: auxin moves to lower side

• The cells of the root grow more on the side with more auxin so it stimulates cells to grow on the upper side- making root bend and grow downward

Why is it beneficial that shoots show negative geotropism?

Because light is likely further away from the ground

Why is it beneficial that roots show positive geotropism?

Because there is most likely increased levels of water and nutrients lower down and provides stability for the plant