According to the Lock and Key model, the enzyme acts as:

Explanation

According to the Lock and Key model, enzymes are likened to a lock that only fits a specific key, which in this case is the substrate. The model highlights the specificity of enzyme action, where the active site of the enzyme has a distinct shape that allows only the correct substrate to bind and form an enzyme-substrate complex. This binding is essential for the catalytic process to occur.Option A is correct because it accurately represents enzymes as locks. Option B is incorrect since it incorrectly suggests that the enzyme acts as the key. Option C is misleading as the Lock and Key model does not support the idea that enzymes can function as both locks and keys. Option D is incorrect because it disregards the fundamental role of enzymes as locks in this model.