Fact 1: Plants detect and respond to the daily cycle of light and darkness.

Fact 2: Diurnal cycles Diurnal cycles are the daily cycles of light and darkness.

Given the two facts above, answer the question "Plants detect and respond to what?" with the following options: 
- water cycles
 - Greenhouse gasses
 - plant cycles
 - Electrical energy
 - sleep cycles
 - heat or cold
 - Diurnal cycles
 - Temperature changing


 

       Diurnal cycles  