Plant Processes Section 2 Plant Responses Section 2

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.