Plant Hormones (inc phototropism, geotropism) 4.5.4.1 pt1

positive geoptropism meaning and example

grows towards gravity, roots

negative geotropism def and example

grows opposite gravity, stem

positive phototropism def and example

grows towards light, stem

negative phototropism def and example

grows away from light, roots

why do roots grow in the direction of gravity

to anchor the plant in the soil to enable survival

why do shoots grow towards light

for maximum light absorption for photosynthesis

how does positive phototropism work

auxin diffuses to the shaded side of the stem where it stimulates growth so the shaded cells grow larger and elongate whilst the unshaded cells grow slower. this causes the stem to bend towards the light.

how does negative phototropism work

auxin diffuses to the shaded side of the stem where it inhibits growth so the shaded cells grow slower than the unshaded side. this causes the roots to bend away from the light.

how does positive geotropism work

auxin accumulates at the bottom due to gravity where it inhibits growth, so the bottom side grows slower than the top, which causes the roots to bend downwards.

how does negative geotropism work

auxin accumulates at the bottom due to gravity where it stimulates growth, so the bottom side grows longer and elongates faster than the top, which causes the stem to bend upwards.

where is auxin found in plant originally

tip

what is auxin

a plant growth hormone

What does auxin cause in the roots

Inhibition

What does auxin cause in the shoots

Elongation