Tropisms

change in the environment

• caused by a stimulus - which triggers a change or reaction (effect)

the growth in response to a stimulus

the growth towards a stimulus

the growth away from a stimulus

• negatively phototropic and positively gravitropic • because they grow away from light and towards the ground as they obey gravity • photo = light and negatively = away • gravi = ground and positively = towards • they do this to grow underground.

hormones

elongation and inhibition of cells

• when theres a shaded part of the plant • the auxins go to that shaded side and elongate the cells • this causes the plant to curve and face towards the light so it can receive more sunlight

• at the tip of the shoot - they move to the shaded area form there

• the auxins in roots inhibit elongation • this is because when they go to a shaded area which will be the bottom of the root • you want the root to grow downwards • so it halts the growth of cells at the bottom in order to allow the cells at the top to grow over it and cause the root to droop downward

gravitropism

growth of an organism in response to light

growth of an organism in response to gravity

• when a shoot is growing sideways • gravity produces an unequal distribution of auxin in the tip • with more auxins on the lower side, this causes the lower side to grow faster • which leads to the bending of the shoot upwards

• the root is growing sideways so will have more auxins on its lower side due to gravity acting downwards • but in a root the auxins inhibit cell growth • so they cells on the top elongate faster • and the root bends downwards