Slides in this set
· TROPISMS: Directional growth responses of plants
· PHOTOTROPISM: Growth response to light shoots
grow towards the light (+ve phototropism), roots
grow away from the light (-ve phototropism).
· GEOTROPISM: Growth response to gravity roots
grow with gravity (+ve geotropism), shoots grow
against gravity (-ve geotropism).
· CHEMOTROPISM: Growth response to chemicals
pollen grains grow towards ovules.
· THIGMOTROPSIM: Growth response to anything
else e.g.: Ivy twists around plants.…read more
Plant growth regulators
· Other plant growth responses are caused by PLANT
· AUXINS: Promotes cell elongation, inhibits side-
shoot growth & inhibits leaf abscission (fall).
· CYTOKININS: Promote cell division.
· GIBBERELINS: Promote seed germination and
growth of stems.
· ABSCISCIC ACID: Inhibits seed germination and
causes stomata to close.
· ETHENE: Promotes fruit ripening. A gas.…read more
· When you shine light on a shoot it will bend
towards the light this is +ve phototropism.
· Auxin causes cell elongation by transporting
hydrogen ions into the cell walls, lowering the pH,
providing the optimum condition for expansins
(wall-loosening enzymes) which break bonds in the
cellulose, making the cell walls more stretchy, so
that when they take in water by osmosis, the can
expand and grow.…read more
· When light shines directly overhead auxin travels
down both sides of the shoot equally, causing both
sides of the shoot to grow at the same rate.
· When light shines from the side, auxin moves to the
opposite side of the shoot, causing this side to
elongate and grow faster than the other, so the
shoot bends towards the light. Phototropin 1, an
enzyme, is thought to be involved in this.
· The same thing happens in roots, except here auxin
causes cells to elongate less, so the roots bend
away from the light.…read more