Why do some plants lose leaves at once?

Answer: Abscission layer activates

Disease makes leaves fall — Wrong. Healthy deciduous trees intentionally drop leaves through abscission layers, not disease. It's a controlled survival strategy for winter.

Sudden temperature drop — Wrong. Cold weather triggers the process, but leaves don't just fall off—trees actively form abscission layers to seal and cut off leaves.

Abscission layer activates ✓ — Correct! As days shorten (photoperiod change), trees form abscission layers—special cells at leaf bases that cork and disconnect vascular tissue. Trees reabsorb nutrients, chlorophyll breaks down (color change), then the layer weakens. All leaves disconnect around the same time because they respond to the same seasonal signal. Coordinated survival strategy!