Terms to Know:
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Plant Responses
Stimulus – is any change in an organism’s environment that causes a response.
- Plant’s response to stimuli can be so slow that it is hard to see happen. --
- Light is a stimulus --
- Plants grow towards light
Environmental Stimuli
Plants respond to their environment in a variety of ways.
Growth Responses
Environmental Stimuli include: light, touch, and gravity
Tropism – a response that results in plant growth toward or away from a stimulus.
Positive – when a plant is bending toward light
Negative – when a plant’s stem grows upward against gravity
Light
Phototropism – the growth of a plant toward or away from light.
Roots generally grow away from light
Touch
Thigmotropism – the response of a plant to touch
Tendrils – special structures that respond to touch (Positive Thigmotropism)
Roots (Negative Thigmotropism)
Gravity
Gravitropism – the response of a plant to gravity --
Stems grow away from gravity while roots grow towards gravity
Flowering Responses
Flowering is a response to darkness
Photoperiodism – a plant’s response to the number of hours of darkness in its environment --
Long-Day Plants
Plants that flower when exposed to less than 10-12 hours of darkness
Short-Day Plants
Require 12 or more hours of darkness for flowering to begin
Day-Neutral Plants
Flower when they reach maturity and the environmental conditions are right
Growth Responses
Environmental Stimuli include: light, touch, and gravity
Tropism – a response that results in plant growth toward or away from a stimulus.
Positive – when a plant is bending toward light
Negative – when a plant’s stem grows upward against gravity
Light
Phototropism – the growth of a plant toward or away from light.
Roots generally grow away from light
Touch
Thigmotropism – the response of a plant to touch
Tendrils – special structures that respond to touch (Positive Thigmotropism)
Roots (Negative Thigmotropism)
Gravity
Gravitropism – the response of a plant to gravity --
Stems grow away from gravity while roots grow towards gravity
Flowering Responses
Flowering is a response to darkness
Photoperiodism – a plant’s response to the number of hours of darkness in its environment --
Long-Day Plants
Plants that flower when exposed to less than 10-12 hours of darkness
Short-Day Plants
Require 12 or more hours of darkness for flowering to begin
Day-Neutral Plants
Flower when they reach maturity and the environmental conditions are right
Chemical Stimuli
Plant hormones - substances that act as chemical messengers within plants.
They are called messengers because they are produced in one part of a plant and affect another part of that plant.
Auxins - a plant hormone that causes increased plant growth and is responsible for phototropism
Ethylene - a gas that can be produced by fruits, seeds, flowers, and leaves
Gibberellins - hormones that increase the rate of cell division and cell elongation
Cytokinins - hormones that increase the rate of cell division and in some plants, slow the aging process of flowers and fruits.
Produced in the root tips and carried throughout the plant by Xylem.
They are called messengers because they are produced in one part of a plant and affect another part of that plant.
Auxins - a plant hormone that causes increased plant growth and is responsible for phototropism
Ethylene - a gas that can be produced by fruits, seeds, flowers, and leaves
Gibberellins - hormones that increase the rate of cell division and cell elongation
Cytokinins - hormones that increase the rate of cell division and in some plants, slow the aging process of flowers and fruits.
Produced in the root tips and carried throughout the plant by Xylem.
Human and Plant responses
Humans depend on plants for food, fuel, shelter, and clothing.
Humans make plants more productive using plant hormones.
Humans make plants more productive using plant hormones.
