In the lock-and-key model of enzyme action, the enzyme active site is thought of as .

Rigid and non flexible surface

Explanation:

Enzymes are catalyst that speeds up rate of chemical reactions, they bind to a substrate which are known as reactant substrate to speed up rate of chemical reaction and to unlock the key.

The enzyme is said to be rigid and non flexible fitting perfectly to the surface of the substrate where the reaction takes place. Fitting perfectly enable the enzyme to perform its action on the substrate unlocking the key and activating the action in the molecule.

volcanoes (an event in the geosphere) release a large amount of particulate matter into the atmosphere. these particles serve as nuclei for the formation of water droplets (hydrosphere). rainfall (hydrosphere) often increases following an eruption, stimulating plant growth (biosphere).