Why is it difficult to tear green leaves from the stem, and yellowed leaves fall off even with a slight gust of wind?

In autumn, a special zone is formed in the cutting of a leaf of deciduous plants (in evergreens – all year round on old, worn leaves) a special zone is formed – a leaf disc. In this place, under the influence of special enzymes, destruction and healing occurs. The leaf in this place is torn off, and where it was on the shoot a “leaf trail” remains.