It is the best studied biological cycle due to the relative ease of gathering sufficient data over multiple 24-hour periods to be statistically significant. Thus, if a researcher has a one year grant, they can obtain 365 days of observations for their study.
Green plants use light to produce chlorophyll .
The byproduct of plant respiration during the day is oxygen. Some plants open their leaves during the day and close them at night. Certain animals are nocturnal , usually only coming out at night. Bats, raccoons and hedgehogs are good examples. The male nightingale sings his best in the evenings.