Plant Response to Stimuli

negative tropism

When there is growth away from a stimulus like the stem of plant growing in the opposite direction of gravity.

positive tropism

When there is growth toward a stimuli like roots growing toward gravity.

auxin

a plant hormone that increases growth by elongating the cells on the dark side of the stem causing the plant to grow toward light

geotropism

a plant's response to gravity. Stems grow away from gravity while roots grow toward gravity.

photoperiodism

a plant's response to the number of hours of darkness in it's environment.

hydrotropism

a plant's response to water

tropism

a response toward or away from a stimulus

homeostasis

an organisms ability to maintain steady internal conditions when its external environment changes

stimuli

any changes in an organisms environment that cause a response

day- neutral plants

flower when they reach maturity and environmental conditions are right. These plants are not affected by the number of hours of darkness.

cytokinins

hormone produced mostly in the root system and carried by xylem to other plant parts to increase cell division. In some plants this hormone slows the aging process of flowers and fruits.

gibberellins

hormones that increase the rate of cell division and cell elongation which results in a rapid growth of leaves, stems and roots. This growth can be both vertical (elongation) as well as horizontal.

ethylene

plant hormone that helps stimulate ripening of fruit & is released as a gas. May also cause a plant to drop its fruit of leaves.

long-day plants

plants that flower when exposed to fewer than 10-12 hours of darkness; usually produces flowers in the summer when there are more hours of daylight than darkness.

short-day plants

plants that require 12 or more hours of darkness to flower. Flower in late summer or fall when the number of hours of daylight are decreasing and the number of hours of darkness in increasing.

phototropism

A plant's response to light. Leaves and stems grow in the direction of the light to maximize photosynthesis while roots tend to grow toward the soil to anchor the plant.

thigmotropism

A plant's response to touch; like a vine growing up a post.... or the venus flytrap closing to catch an insect