Tropism movement in response to a stimulus plants can move … 1. toward a stimulus (a positive tropism) OR 2. away from a stimulus (a negative tropism) tropisms are hormone mediated

Tropisms Type of TropismDescription Phototropismgrowth or movement in response to light Geotropism (aka gravitropism) growth in response to gravity positive = roots grow down negative = stems grow up Chemotropismresponse to chemicals in the environment Hydrotropismresponse to water Thigmotropismresponse to touch which causes a permanent change in growth direction

Hormones Hormones are chemical signals. Hormones are produced by cells in one part of the plant and are transported to other parts of the plant where they influence growth or metabolic activity. There are five major types of plant hormones.

Hormones HormoneFunction(s) Auxins  promote cell elongation & increase cell division  stimulates apical bud growth & inhibits lateral bud growth  stimulates growth / ripening of fruit & dropping of fruit & leaves Cytokinins  stimulate cell division & leaf mesophyll growth  found in endosperm & young fruit Gibberellins  promote cell division & elongation in plant shoots  cause stem to elongate before the plant flowers Abscisic acid  inhibitors  promotes closure of stomata inducing seed & bud dormancy & provides resistance to water stress Ethylene  role in fruit ripening  related to colour change & softening of the tissue of ripening fruit

Seeds an ovule after fertilization contains plant embryo can lay dormant for years seeds begin to germinate when temperature & moisture conditions are optimum

Typical Monocot Seed

Typical Dicot Seed