Physiological time is often expressed in units called

Physiological time is often expressed in units called

• A. Degree days
• B. Hours
• C. Weeks
• D. Minutes

Answer: (A)

Physiological time is based on heat accumulation over time, not calendar time. Degree days are the units that capture that heat build-up. They’re calculated by summing, for each day, the amount by which the daily mean temperature exceeds a base temperature required for development. This accumulated heat correlates with how far an organism has progressed through its stages, so a crop or pest reaches a developmental point after a specific total of degree days, regardless of how many actual days pass. For example, if the base temperature is 10°C and a day averages 18°C, that day adds 8 degree days toward development. Other options like hours, weeks, or minutes are just clock time and don’t reflect how temperature drives biological processes, so they don’t represent physiological time.

Physiological time is based on heat accumulation over time, not calendar time. Degree days are the units that capture that heat build-up. They’re calculated by summing, for each day, the amount by which the daily mean temperature exceeds a base temperature required for development. This accumulated heat correlates with how far an organism has progressed through its stages, so a crop or pest reaches a developmental point after a specific total of degree days, regardless of how many actual days pass. For example, if the base temperature is 10°C and a day averages 18°C, that day adds 8 degree days toward development. Other options like hours, weeks, or minutes are just clock time and don’t reflect how temperature drives biological processes, so they don’t represent physiological time.