This document defines and describes various plant responses and adaptations, including tropisms like thigmotropism and phototropism, short-day and long-day plants and their response to photoperiodism mediated by the phytochrome pigment, dormancy which allows plant embryos to survive without growing, and the abscission layer which seals off leaves from the vascular system. Key concepts are that tropisms demonstrate how plants respond to external stimuli, photoperiodism times seasonal activities, and deciduous plants prepare for winter by transporting materials and sealing off leaves.

1. 25-2 Plant Responses Ch. 25: Plant Responses and Adaptations

2. Tropism Response of a plant to an external stimulus

3. Thigmotropism Response of plants to touch

4. Short-day plant Plant that flowers when daylight is short

5. Long-day plant Plant that flowers when days are long

6. Photoperiodism Response of plants to periods of light and darkness

7. Phytochrome Plant pigment responsible for photoperiodism

8. Dormancy Period of time during which a plant embryo is alive but not growing

9. Abscission Layer Layer of cells at the petiole that seals off a leaf from the vascular system

10. Key Concept Plant tropisms include gravitropism, phototropism, and thigmotropism. Each of these responses demonstrates the ability of plants to respond effectively to external stimuli, such as gravity, light, and touch.

11. Key Concept Photoperiodism in plants is responsible for the timing of seasonal activities such as flowering and growth

12. Key Concept As cold weather approaches, deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant.