biology 25.2

25-2 Plant ResponsesCh. 25: Plant Responses and Adaptations

Tropism

Response of a plant to an external stimulus

Thigmotropism

Response of plants to touch

Short-day plant

Plant that flowers when daylight is short

Long-day plant

Plant that flowers when days are long

Photoperiodism

Response of plants to periods of light and darkness

Phytochrome

Plant pigment responsible for photoperiodism

Dormancy

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

Abscission Layer

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

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.

Key Concept

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

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.