Plants also detect and respond to the daily cycle of light and darkness. For example, some plants open their leaves during the day to collect sunlight and then close their leaves at night to prevent water loss. Environmental stimuli that indicate changing seasons trigger other responses. Plants are capable of reacting to a broad range of stimuli, including chemicals, gravity, light, moisture, infections, temperature, oxygen and carbon dioxide concentrations, parasite infestation, disease, physical disruption, sound, and touch.
8. Fig. 39-5b
RESULTS
Light
Tip
removed
Darwin and Darwin: phototropic response
only when tip is illuminated
Tip covered
by opaque
cap
Tip
covered
by trans-
parent
cap
Site of
curvature
covered by
opaque
shield