What does the thin material that holds the tea leaves represent

It represents a partially permeable membrane

Explanation:

As the water is added to the teabag it causes the tea leaves to move and triggers diffusion of the leaves. ...

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products