Download Section 2: Energy Flow in Ecosystems

Plant Processes
Section 2: Plant Responses
Section 2
Plant Processes
Section 2
Key Ideas
• Why are hormones important for plant growth and
development?
• How do tropisms affect plants?
• What triggers seasonal change in plants?
• How do nastic movements affect plants?
Plant Processes
Section 2
Plant Hormones
• Plants can sense changes in the environment and
respond to these changes in adaptive ways.
• hormone
– chemical that is produced by an organism that causes a
response
– Can stimulate or inhibit growth
– plant responses to environmental stimuli
• small amounts of hormones may have large effects on
the growth and development of plants.
Plant Processes
Section 2
Plant Hormones, continued
• Auxins stimulate cell elongation.
• Gibberellins stimulate fruit development and seed
germination.
• Cytokinins stimulate cell division.
• Ethylene promotes the ripening of fruit.
• Abscisic acid often slows growth in plants and helps
maintain dormancy in seeds.
Plant Processes
Section 2
Tropisms
• Tropisms, a plant’s responses to environmental
stimuli, are triggered by the hormones that
regulate plant growth.
• A tropism is a response in which a plant grows
toward or away from a stimulus.
Plant Processes
Section 2
Tropisms, continued
• A positive tropism is when a plant grows toward a
stimulus.
• A negative tropism is when a plant grows away from a
stimulus.
• Directional movements in response to light are called
phototropisms.
Plant Processes
Section 2
Tropisms, continued
• Growth responses to touch are called thigmotropisms.
• Responses to gravity are called gravitropisms.
Plant Processes
Visual Concept: Tropism
Section 2
Plant Processes
Section 2
Seasonal Responses
• Many responses to the seasons have evolved in plants.
• The principal way in which plants time seasonal
responses is by sensing changes in night length.
• The response of a plant to the length of days and nights
is called photoperiodism.
Plant Processes
Section 2
Seasonal Responses, continued
• Three types of photoperiodism plants: short-day plants,
long-day plants, or day-neutral plants.
• Controlling the length of days and night in a greenhouse
can force plants to flower at times of year when they
ordinarily would not.
Plant Processes
Section 2
Seasonal Responses, continued
• Temperature affects growth and development in many
plants.
• For example, most tomato plants will not produce fruit if
nighttime temperatures are too high.
• Dormancy is the condition in which a plant or seed
remains inactive, even when conditions are suitable for
growth.
Plant Processes
Section 2
Plant Movements
• Some plant movements respond to an environmental
stimulus but are not influenced by the direction of the
stimulus.
• These movements are called nastic movements. Nastic
movements are usually regulated by changes in the
water content of special cells.
• Examples of nastic movements include the rapid closing
of the leaves of a Venus’ flytrap and the closing of the
leaves of a sensitive plant.